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libtdevnc/x11vnc/README

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x11vnc README file Date: Sat Jul 15 12:13:51 EDT 2006
The following information is taken from these URLs:
http://www.karlrunge.com/x11vnc/index.html
http://www.karlrunge.com/x11vnc/x11vnc_opts.html
...
they contain the most up to date info.
=======================================================================
http://www.karlrunge.com/x11vnc/index.html:
_________________________________________________________________
x11vnc: a VNC server for real X displays
(to [1]FAQ) (to [2]Downloads) (to [3]Building) (to
[4]Beta Test) (to [5]Donations) [6][PayPal]
x11vnc allows one to view remotely and interact with real X displays
(i.e. a display corresponding to a physical monitor, keyboard, and
mouse) with any VNC viewer. In this way it plays the role for Unix/X11
that WinVNC plays for Windows.
It has built-in [7]SSL encryption and authentication, UNIX [8]account
and password support, server-side [9]scaling, [10]single port HTTPS
and VNC, and TightVNC and UltraVNC [11]file-transfer. It has also been
extended to work with [12]webcams and TV tuner capture devices.
I wrote x11vnc back in 2002 because x0rfbserver was basically
impossible to build on Solaris and had poor performance. The primary
x0rfbserver build problems centered around esoteric C++ toolkits.
x11vnc is written in plain C and uses only standard libraries. I also
added a some enhancements to improve the interactive response, add
many esoteric features, etc.
This page and the [13]FAQ contain a lot of information [14][*] and
solutions to many problems and interesting applications, but
nevertheless please feel free to [15]contact me if you have problems
or questions.
Background:
VNC (Virtual Network Computing) is a very useful network graphics
protocol (applications running on one computer but displaying their
windows on another) in the spirit of X, however, unlike X, the
viewing-end is very simple and maintains no state. It is a remote
framebuffer (RFB) protocol
Some VNC links:
* [16]http://www.realvnc.com
* [17]http://www.tightvnc.com
* [18]http://www.ultravnc.com/
* [19]http://www.redstonesoftware.com/
For Unix, the traditional VNC implementation includes a virtual X11
server Xvnc (usually launched via the vncserver command) that is not
associated with a physical display, but provides a "fake" one X11
clients (xterm, mozilla, etc.) can attach to. A remote user then
connects to Xvnc via the VNC client vncviewer from anywhere on the
network to view and interact with the whole virtual X11 desktop.
The VNC protocol is in most cases better suited for remote connections
with low bandwidth and high latency than is the X11 protocol (the
exception is cached pixmap data on the viewing-end). Also, with no
state maintained the viewing-end can crash, be rebooted, or relocated
and the applications and desktop continue running. Not so with X11.
So the standard Xvnc/vncserver program is very useful, I use it for
things like:
* Desktop conferencing with other users (e.g. codereviews).
* Long running apps/tasks I want to be able to view from many
places.
* Motif, GNOME, and similar applications that would yield very poor
performance over a high latency link.
However, sometimes one wants to connect to a real X11 display (i.e.
one attached to a physical monitor, keyboard, and mouse: a Workstation
or a SunRay session) from far away. Maybe you want to close down an
application cleanly rather than using kill, or want to work a bit in
an already running application, or would like to help a distant
colleague solve a problem with their desktop, or would just like to
work out on your deck for a while. This is where x11vnc is useful.
_________________________________________________________________
How to use x11vnc:
In this basic example let's assume the remote machine with the X
display you wish to view is "far-away.east:0" and the workstation you
are presently working at is "sitting-here.west".
Step 0. Download x11vnc ([20]see below) and have it available to run
on far-away.east. Similarly, have a VNC viewer (e.g. vncviewer) ready
to run on sitting-here.west. We recommend [21]TightVNC Viewers.
Step 1. By some means log in to far-away.east and get a command shell
running there. You can use ssh, rlogin, telnet, or any other method to
do this. The x11vnc process needs to be run on the same machine the X
server process is running on (otherwise things would be extremely
slow).
Step 2. In that far-away.east shell (with command prompt "far-away>"
in this example) run x11vnc directed at the far-away.east X session
display:
far-away> x11vnc -display :0
You could have also set the environment variable DISPLAY=:0 instead of
using -display. This step attaches x11vnc to the far-away.east:0 X
display (i.e. no viewer clients yet).
Common Gotcha: To get X11 permissions right, you may also need to set
the XAUTHORITY environment variable (or use the [22]-auth option) to
point to the correct MIT-MAGIC-COOKIE file (e.g.
/home/joe/.Xauthority). If x11vnc does not have the authority to
connect to the display it exits immediately. More on how to fix this
[23]below.
If you suspect an X11 permissions problem do this simple test: while
sitting at the physical X display open a terminal window
(gnome-terminal, xterm, etc). You should be able to run x11vnc
successfully in that terminal without any need for command line
options. If that works OK then you know X11 permissions are the only
thing preventing it from working when you try to start x11vnc via a
remote shell. Then fix this with the tips [24]below.
When x11vnc starts up there will then be much chatter printed out,
until it finally says something like:
.
.
13/05/2004 14:59:54 Autoprobing selected port 5900
13/05/2004 14:59:54 screen setup finished.
13/05/2004 14:59:54
13/05/2004 14:59:54 The VNC desktop is far-away:0
PORT=5900
which means all is OK, and we are ready for the final step.
Step 3. At the place where you are sitting (sitting-here.west in this
example) you now want to run a VNC viewer program. There are VNC
viewers for Unix, Windows, MacOS, Java-enabled web browsers, and even
for PDA's like the Palm Pilot! You can use any of them to connect to
x11vnc (see the above VNC links under "Background:" on how to obtain a
viewer for your platform or see [25]this FAQ. For Solaris, vncviewer
is available in the [26]Companion CD package SFWvnc).
In this example we'll use the Unix vncviewer program on sitting-here
by typing the following command in a second terminal window:
sitting-here> vncviewer far-away.east:0
That should pop up a viewer window on sitting-here.west showing and
allowing interaction with the far-away.east:0 X11 desktop. Pretty
nifty! When finished, exit the viewer: the remote x11vnc process will
shutdown automatically (or you can use the [27]-forever option to have
it wait for additional viewer connections).
Shortcut: Of course if you left x11vnc running on far-away.east:0 in a
terminal window with the [28]-forever option or as a [29]service,
you'd only have to do Step 3 as you moved around. Be sure to use a VNC
[30]Password or [31]other measures if you do that.
Desktop Sharing: The above more or less assumed nobody was sitting at
the workstation display "far-away.east:0". This is often the case: a
user wants to access her workstation remotely. Another usage pattern
has the user sitting at "far-away.east:0" and invites one or more
other people to view and interact with his desktop. Perhaps the user
gives a demo or presentation this way (using the telephone for vocal
communication). A "Remote Help Desk" mode would be similar: a
technician remotely connects to the user's desktop to interactively
solve a problem the user is having.
For these cases it should be obvious how it is done. The above steps
will work, but more easily the user sitting at far-away.east:0 simply
starts up x11vnc from a terminal window, after which the guests would
start their VNC viewers. For this usage mode the "[32]-connect
host1,host2" option may be of use automatically connect to vncviewers
in "-listen" mode on the list of hosts.
_________________________________________________________________
Tunnelling x11vnc via ssh:
The above example had no security or privacy at all. When logging into
remote machines (certainly when going over the internet) it is best to
use ssh, or use a VPN. For x11vnc one can tunnel the VNC protocol
through the encrypted ssh channel. It would look something like this:
sitting-here> ssh -L 5900:localhost:5900 far-away.east 'x11vnc -localhost -di
splay :0'
(you will likely have to provide passwords/passphrases for the ssh
login) and then in another terminal window on sitting-here run the
command:
sitting-here> vncviewer -encodings "copyrect tight zrle hextile" localhost:0
Note: The -encodings option is very important: vncviewer will often
default to "raw" encoding if it thinks the connection is to the local
machine, and so vncviewer gets tricked this way by the ssh
redirection. "raw" encoding will be extremely slow over a networked
link, so you need to force the issue with -encodings "copyrect tight
...".
Note that "x11vnc -localhost ..." limits incoming vncviewer
connections to only those from the same machine. This is very natural
for ssh tunnelling (the redirection appears to come from the same
machine). Use of a [33]VNC password is also strongly recommended.
Some VNC viewers will do the ssh tunnelling for you automatically, the
TightVNC vncviewer does this when the "-via far-away.east" option is
supplied to it (this requires x11vnc to be already running on
far-away.east or having it started by [34]inetd(8)). See the 3rd
script example [35]below for more info.
If the machine you SSH into is not the same machine with the X display
you wish to view (e.g. your company provides incoming SSH access to a
gateway machine), then you need to change the above to, e.g.: "-L
5900:OtherHOST:5900". Once logged in, you'll need to do a second login
(ssh, rsh, etc.) to the workstation machine 'otherhost' and then start
up x11vnc on it (if it isn't already running). For an automatic way to
use a gateway and have all the network traffic encrypted (including
inside the firewall) see [36]chaining ssh's
_________________________________________________________________
Scripts to automate ssh tunneling: As discussed below, there may be
some problems with port 5900 being available. If that happens, the
above port and display numbers may change a bit (e.g. -> 5901 and :1).
However, if you "know" port 5900 will be free on the local and remote
machines, you can easily automate the above two steps by using the
x11vnc option [37]-bg (forks into background after connection to the
display is set up) or using the -f option of ssh. Some example scripts
are shown below.
_________________________________________________________________
#1. A simple example script, assuming no problems with port 5900 being
taken on the local or remote sides, looks like:
#!/bin/sh
# usage: x11vnc_ssh <host>:<xdisplay>
# e.g.: x11vnc_ssh snoopy.peanuts.com:0
host=`echo $1 | awk -F: '{print $1}'`
disp=`echo $1 | awk -F: '{print $2}'`
if [ "x$disp" = "x" ]; then disp=0; fi
cmd="x11vnc -display :$disp -localhost -rfbauth .vnc/passwd"
enc="copyrect tight zrle hextile zlib corre rre raw"
ssh -f -L 5900:localhost:5900 $host "$cmd"
for i in 1 2 3
do
sleep 2
if vncviewer -encodings "$enc" :0; then break; fi
done
See also rx11vnc.pl below.
_________________________________________________________________
#2. Another method is to start the VNC viewer in listen mode
"vncviewer -listen" and have x11vnc initiate a reverse connection
using the [38]-connect option:
#!/bin/sh
# usage: x11vnc_ssh <host>:<xdisplay>
# e.g.: x11vnc_ssh snoopy.peanuts.com:0
host=`echo $1 | awk -F: '{print $1}'`
disp=`echo $1 | awk -F: '{print $2}'`
if [ "x$disp" = "x" ]; then disp=0; fi
cmd="x11vnc -display :$disp -localhost -connect localhost" # <== note new opt
ion
enc="copyrect tight zrle hextile zlib corre rre raw"
vncviewer -encodings "$enc" -listen &
pid=$!
ssh -R 5500:localhost:5500 $host "$cmd"
kill $pid
Note the use of the ssh option "-R" instead of "-L" to set up a remote
port redirection.
_________________________________________________________________
#3. A third way is specific to the TightVNC vncviewer special option
-via for gateways. The only tricky part is we need to start up x11vnc
and give it some time (5 seconds in this example) to start listening
for connections (so we cannot use the TightVNC default setting for
VNC_VIA_CMD):
#!/bin/sh
# usage: x11vnc_ssh <host>:<xdisplay>
# e.g.: x11vnc_ssh snoopy.peanuts.com:0
host=`echo $1 | awk -F: '{print $1}'`
disp=`echo $1 | awk -F: '{print $2}'`
if [ "x$disp" = "x" ]; then disp=0; fi
VNC_VIA_CMD="ssh -f -L %L:%H:%R %G x11vnc -localhost -rfbport 5900 -display :$d
isp; sleep 5"
export VNC_VIA_CMD
vncviewer -via $host localhost:0 # must be TightVNC vncviewer.
Of course if you already have the x11vnc running waiting for
connections (or have it started out of [39]inetd(8)), you can simply
use the TightVNC "vncviewer -via gateway host:port" in its default
mode to provide secure ssh tunnelling.
_________________________________________________________________
VNC password file: Also note in the #1. example script that the
[40]option "-rfbauth .vnc/passwd" provides additional protection by
requiring a VNC password for every VNC viewer that connects. The
vncpasswd or storepasswd programs, or the x11vnc [41]-storepasswd
option can be used to create the password file. x11vnc also has the
slightly less secure [42]-passwdfile and "-passwd XXXXX" [43]options
to specify passwords.
Very Important: It is up to YOU to tell x11vnc to use password
protection (-rfbauth or -passwdfile), it will NOT do it for you
automatically or force you to (see [44]-usepw if you want to be forced
to). The same goes for encrypting the channel between the viewer and
x11vnc: it is up to you to use ssh, stunnel, [45]-ssl mode, a VPN,
etc. For additional safety, also look into the -allow and -localhost
[46]options and building x11vnc with [47]tcp_wrappers support to limit
host access.
_________________________________________________________________
Tunnelling x11vnc via SSL:
One can also encrypt the VNC traffic using an SSL tunnel such as
[48]stunnel or using the built-in (Mar/2006) [49]-ssl openssl mode. A
SSL-enabled Java applet VNC Viewer is also provided (and https can be
used to download it).
Although not as ubiquitous as ssh, SSL tunnelling still provides a
useful alternative. See [50]this FAQ on -ssl and -stunnel modes for
details and examples.
_________________________________________________________________
Downloading x11vnc:
x11vnc is a contributed program to the [51]LibVNCServer project at
SourceForge.net. I use libvncserver for all of the VNC aspects; I
couldn't have done without it. The full source code may be found and
downloaded (either file-release tarball or CVS tree) from the above
link. As of Jul 2006, the [52]x11vnc-0.8.2.tar.gz source package is
released (recommended download). The [53]x11vnc 0.8.2 release notes.
The x11vnc package is the subset of the libvncserver package needed to
build the x11vnc program. Also, you can get a copy of my latest,
bleeding edge [54]x11vnc-0.8.3.tar.gz tarball to build the most up to
date one.
Precompiled Binaries/Packages: See the [55]FAQ below for information
about where you might obtain a precompiled x11vnc binary from 3rd
parties and some ones I create.
To obtain VNC viewers for the viewing side (Windows, Mac OS, or Unix)
try these links:
* [56]http://www.tightvnc.com/download.html
* [57]http://www.realvnc.com/download-free.html
* [58]http://sourceforge.net/projects/cotvnc/
* [59]http://www.ultravnc.com/
More tools: Here is a rsh/ssh wrapper script rx11vnc that attempts to
automatically do the above Steps 1-3 for you (provided you have
rsh/ssh login permission on the machine x11vnc is to be run on). The
above example would be: "rx11vnc far-away.east:0" typed into a shell
on sitting-here.west. Also included is an experimental script
rx11vnc.pl that attempts to tunnel the vnc traffic through an ssh port
redirection (and does not assume port 5900 is free). Have a look at
them to see what they do and customize as needed:
* [60]rx11vnc wrapper script
* [61]rx11vnc.pl wrapper script to tunnel traffic thru ssh
_________________________________________________________________
Building x11vnc:
If your OS has libjpeg.so and libz.so in standard locations you can
build as follows (example given for the 0.8.2 release of x11vnc:
replace with the version you downloaded):
(un-tar the x11vnc+libvncserver tarball)
# gzip -dc x11vnc-0.8.2.tar.gz | tar -xvf -
(cd to the source directory)
# cd x11vnc-0.8.2
(run configure and then run make)
# ./configure
# make
(if all went OK, copy x11vnc to the desired destination, e.g. $HOME/bin)
# cp ./x11vnc/x11vnc $HOME/bin
Or do make install, it will probably install to /usr/local/bin (run
./configure --help for information on customizing your configuration,
e.g. --prefix=/my/place). You can now run it via typing "x11vnc",
"x11vnc -help | more", "x11vnc -forever -shared -display :0", etc.
Note: Currently gcc is recommended to build libvncserver. In some
cases it will build with non-gcc compilers, but the resulting binary
sometimes fails to run properly. For Solaris pre-built gcc binaries
are at [62]http://www.sunfreeware.com/. Some Solaris pre-built x11vnc
binaries are [63]here.
However, one user reports it does work fine when built with Sun Studio
10, so YMMV. In fact, here is a little build script to do this on
Solaris 10:
#!/bin/sh
PATH=/usr/ccs/bin:/opt/SUNWspro/bin:$PATH; export PATH
CC='cc' \
CFLAGS='-xO4' \
LDFLAGS='-L/usr/sfw/lib -L/usr/X11/lib -R/usr/sfw/lib -R/usr/X11/lib' \
CPPFLAGS='-I /usr/sfw/include -I/usr/X11/include' \
./configure
MAKE="make -e"
AM_CFLAGS=""
export MAKE AM_CFLAGS
$MAKE
In general you can use the "make -e" trick if you don't like
libvncserver's choice of AM_CFLAGS. See the [64]build scripts below
for more ideas.
You can find information on [65]Misc. Build problems here.
_________________________________________________________________
Building on Solaris, FreeBSD, etc: Depending on your version of
Solaris or other Unix OS the jpeg and/or zlib libraries may be in
non-standard places (e.g. /usr/local, /usr/sfw, /opt/sfw, etc).
Note: If configure cannot find these two libraries then TightVNC and
ZRLE encoding support will be disabled, and you don't want that!!! The
TightVNC encoding gives very good compression and performance, it even
makes a noticeable difference over a fast LAN.
Shortcuts: On Solaris 10 you can pick up almost everything just by
insuring that your PATH has /usr/sfw/bin (for gcc) and /usr/ccs/bin
(for other build tools), e.g.:
env PATH=/usr/sfw/bin:/usr/ccs/bin:$PATH sh -c './configure; make'
(The only thing this misses is /usr/X11/lib/libXrandr.so.2, which is
for the little used -xrandr option, see the script below to pick it up
as well).
libjpeg is included in Solaris 9 and later (/usr/sfw/include and
/usr/sfw/lib), and zlib in Solaris 8 and later (/usr/include and
/usr/lib). So on Solaris 9 you can pick up everything with something
like this:
env PATH=/usr/local/bin:/usr/ccs/bin:$PATH sh -c './configure --with-jpeg=/us
r/sfw; make'
assuming your gcc is in /usr/local/bin and x11vnc 0.7.1 or later.
These are getting pretty long, see those assignments split up in the
build script below.
If your system does not have these libraries at all you can get the
source for the libraries to build them: libjpeg is available at
[66]ftp://ftp.uu.net/graphics/jpeg/ and zlib at
[67]http://www.gzip.org/zlib/. See also
[68]http://www.sunfreeware.com/ for Solaris binary packages of these
libraries as well as for gcc. Normally they will install into
/usr/local but you can install them anywhere with the
--prefix=/path/to/anywhere, etc.
Here is a build script that indicates one way to pass the library
locations information to the libvncserver configuration via the
CPPFLAGS and LDFLAGS environment variables.
---8<---8<---8<---8<---8<---8<---8<---8<---8<---8<---8<---8<---8<---8<---8<---8
<---
#!/bin/sh
# Build script for Solaris, etc, with gcc, libjpeg and libz in
# non-standard locations.
# set to get your gcc, etc:
#
PATH=/path/to/gcc/bin:/usr/ccs/bin:/usr/sfw/bin:$PATH
JPEG=/path/to/jpeg # set to maybe "/usr/local", "/usr/sfw", or "/opt/sfw"
ZLIB=/path/to/zlib # set to maybe "/usr/local", "/usr/sfw", or "/opt/sfw"
# Below we assume headers in $JPEG/include and $ZLIB/include and the
# shared libraries are in $JPEG/lib and $ZLIB/lib. If your situation
# is different change the locations in the two lines below.
#
CPPFLAGS="-I $JPEG/include -I $ZLIB/include"
LDFLAGS="-L $JPEG/lib -R $JPEG/lib -L $ZLIB/lib -R $ZLIB/lib"
# These two lines may not be needed on more recent Solaris releases:
#
CPPFLAGS="$CPPFLAGS -I /usr/openwin/include"
LDFLAGS="$LDFLAGS -L /usr/openwin/lib -R /usr/openwin/lib"
# These are for libXrandr.so on Solaris 10:
#
CPPFLAGS="$CPPFLAGS -I /usr/X11/include"
LDFLAGS="$LDFLAGS -L /usr/X11/lib -R /usr/X11/lib"
# Everything needs to built with _REENTRANT for thread safe errno:
#
CPPFLAGS="$CPPFLAGS -D_REENTRANT"
export PATH CPPFLAGS LDFLAGS
./configure
make
ls -l ./x11vnc/x11vnc
---8<---8<---8<---8<---8<---8<---8<---8<---8<---8<---8<---8<---8<---8<---8<---8
<---
Then do make install or copy the x11vnc binary to your desired
destination.
BTW, To run a shell script, just cut-and-paste the above into a file,
say "myscript", then modify the "/path/to/..." items to correspond to
your system/environment, and then type: "sh myscript" to run it.
Note that on Solaris make is /usr/ccs/bin/make, so that is why the
above puts /usr/ccs/bin in PATH. Other important build utilities are
there too: ld, ar, etc. Also, it is probably a bad idea to have
/usr/ucb in your PATH while building.
Starting with the 0.7.1 x11vnc release the "configure --with-jpeg=DIR
--with-zlib=DIR" options are handy if you want to avoid making a
script.
If you need to build on Solaris 2.5.1 or earlier or other older Unix
OS's, see [69]this workaround FAQ.
Building on FreeBSD, OpenBSD, ...: The jpeg libraries seem to be in
/usr/local or /usr/pkg on these OS's. You won't need the openwin stuff
in the above script (but you may need /usr/X11R6/...). Also starting
with the 0.7.1 x11vnc release, this usually works:
./configure --with-jpeg=/usr/local
make
Building on HP-UX: For jpeg and zlib you will need to do the same
sort of thing as described above for Solaris. You set CPPFLAGS and
LDFLAGS to find them (see below for an example). You do not need to do
any of the above /usr/openwin stuff. Also, HP-UX does not seem to
support -R, so get rid of the -R items in LDFLAGS. Because of this, at
runtime you may need to set LD_LIBRARY_PATH or SHLIB_PATH to indicate
the directory paths so the libraries can be found. It is a good idea
to have static archives, e.g. libz.a and libjpeg.a for the nonstandard
libraries so that they get bolted into the x11vnc binary (and so won't
get "lost").
Here is what we recently did to build x11vnc 0.7.2 on HP-UX 11.11
./configure --with-jpeg=$HOME/hpux/jpeg --with-zlib=$HOME/hpux/zlib
make
Where we had static archives (libjpeg.a, libz.a) only and header files
in the $HOME/hpux/... directories as discussed for the build script.
Building on AIX: AIX: one user had to add the "X11.adt" package to
AIX 4.3.3 and 5.2 to get build header files like XShm.h, etc. You may
also want to make sure that /usr/lpp/X11/include, etc is being picked
up by the configure and make.
_________________________________________________________________
Beta Testing:
I don't have any formal beta-testers for the releases of x11vnc, so
I'd appreciate any additional testing very much!
Thanks to those who suggested features and helped beta test x11vnc
0.8.2 released in Jul 2006!
Please help test and debug the 0.8.3 version for release sometime in
Summer/Fall 2006.
The version 0.8.3 beta tarball is kept here:
[70]x11vnc-0.8.3.tar.gz
There are also some Linux, Solaris, and other OS test binaries
[71]here. Please kick the tires and report bugs, performance
regressions, undesired behavior, etc. to [72]me.
Here are some features that appeared in the 0.8.2 release:
* Linux console framebuffer keystroke and mouse insertion is now
supported by the uinput linux device driver. This enables full
interaction with non-X applications on the Linux console (e.g.
Qt-embedded/Qtopia-Core apps). This will be autodetected in:
[73]-rawfb console mode, and can be forced on via: [74]-pipeinput
UINPUT
* The [75]-display WAIT:... option extends the normal [76]-display
option by having x11vnc wait until a VNC viewer connects before
attaching to an X display. A command can also be supplied that
will determine the DISPLAY and XAUTHORITY data. A default one is
built-in for WAIT:cmd=FINDDISPLAY. Coupling this with "-unixpw
-users unixpw=" (available in beta version) provides a way to
allow a user to login with their UNIX password and have their
display connected to [77]automatically.
* The [78]-grabkdb and [79]-grabptr options allow some degree of
grabbing the pointer and keyboard so local users cannot perform
input (e.g. remote helpdesk application).
* More new options:
+ [80]-allowedcmds to fine-tune which external commands may be
run by x11vnc, rather than shutting them all off with
[81]-nocmds,
+ [82]-env VAR=VALUE convenience option to avoid the need of
setting environment variables before starting x11vnc,
+ [83]-allinput option to enable libvncserver
handleEventsEagerly parameter,
+ [84]-rawfb rand fun/testing option using /dev/urandom as a
fb,
+ [85]-license print license, copying, warranty information.
Here are some features that will appear in the 0.8.3 release:
* The [86]-ssl option provides SSL encryption and authentication
natively via the [87]www.openssl.org library. One can use from a
simple self-signed certificate server certificate up to full CA
and client certificate authentication schemes.
* The [88]-stunnel option starts up a SSL tunnel server stunnel
(that must be installed separately on the system:
[89]www.stunnel.org) to allow only encrypted SSL connections from
the network.
* The [90]-sslverify option allows for authenticating VNC clients
via their certificates in either -ssl or -stunnel modes.
* An SSL enabled Java applet VNC Viewer applet is provided in
classes/ssl/VncViewer.jar. It may also be loaded into the web
browser via https (http over SSL) in addition to http. (via the
VNC port or also by the separate [91]-https port option). A
wrapper shell script [92]ssl_vncviewer is also provided that sets
up a stunnel client-side tunnel on Unix systems.
* The [93]-unixpw option supports Unix username and password
authentication (a variant is the [94]-unixpw_nis option that works
in NIS environments). The [95]-ssl or [96]-localhost +
[97]-stunnel options are enforced in this mode to prevent password
sniffing. As a convenience, the -ssl or -stunnel requirements are
lifted if a SSH tunnel can be deduced (but -localhost still
applies). Coupling -unixpw with "-display WAIT:cmd=FINDDISPLAY"
provides a way to allow a user to login with their UNIX password
and have their display connected to [98]automatically.
Here are some [99]previous release notes
_________________________________________________________________
Some Notes:
Both a client and a server: It is sometimes confusing to people that
x11vnc is both a client and a server at the same time. It is an X
client because it connects to the running X server to do the screen
polls. Think of it as a rather efficient "screenshot" program running
continuously. It is a server in the sense that it is a VNC server that
VNC viewers on the network can connect to and view the screen
framebuffer it manages.
When trying to debug problems, remember to think of both roles. E.g.
"how is x11vnc connecting to the X server?", "how is the vncviewer
connecting to x11vnc?", "what permits/restricts the connection?". Both
links may have reachability, permission, and other issues.
Network performance: Whether you are using Xvnc or x11vnc it is
always a good idea to have a solid background color instead of a
pretty background image. Each and every re-exposure of the background
must be resent over the network: better to have that background be a
solid color that compresses very well compared to a photo image. (This
is one place where the X protocol has an advantage over the VNC
protocol.) I suggest using xsetroot, dtstyle or similar utility to set
a solid background while using x11vnc. You can turn the pretty
background image back on when you are using the display directly.
Update: As of Feb/2005 x11vnc has the [100]-solid [color] option that
works on recent GNOME, KDE, and CDE and also on classic X (background
image is on the root window).
I also find the [101]TightVNC encoding gives the best response for my
usage (Unix <-> Unix over cable modem). One needs a tightvnc-aware
vncviewer to take advantage of this encoding.
TCP port issues: Notice the lines
18/07/2003 14:36:31 Autoprobing selected port 5900
PORT=5900
in the output. 5900 is the default VNC listening port (just like 6000
is X11's default listening port). Had port 5900 been taken by some
other application, x11vnc would have next tried 5901. That would mean
the viewer command above should be changed to vncviewer
far-away.east:1. You can force the port with the "[102]-rfbport NNNN"
option where NNNN is the desired port number. If that port is already
taken, x11vnc will exit immediately. (also see the "SunRay Gotcha"
note below)
Options: x11vnc has (far too) many features that may be activated
via its [103]command line options. Useful options are, e.g., -scale to
do server-side scaling, and -rfbauth passwd-file to use VNC password
protection (the vncpasswd or storepasswd programs, or the x11vnc
[104]-storepasswd option can be used to create the password file).
Algorithm: How does x11vnc do it? Rather brute-forcedly: it
continuously polls the X11 framebuffer for changes using
XShmGetImage(). When changes are discovered, it instructs libvncserver
which rectangular regions of the framebuffer have changed, and
libvncserver compresses the changes and sends them off to any
connected VNC viewers. A number of applications do similar things,
such as x0rfbserver, krfb, x0vncserver, vino. x11vnc uses a 32 x 32
pixel tile model (the desktop is decomposed into roughly 1000 such
tiles), where changed tiles are found by pseudo-randomly polling 1
pixel tall horizontal scanlines. This is a surprisingly effective
algorithm for finding changed regions. For keyboard and mouse user
input the XTEST extension is used to pass the input events to the X
server. To detect XBell "beeps" the XKEYBOARD extension is used. If
available, the XFIXES extension is used to retrieve the current mouse
cursor shape. Also, if available the X DAMAGE extension is used to
receive hints from the X server where modified regions on the screen
are. This greatly reduces the system load when not much is changing on
the screen and also improves how quickly the screen is updated.
Barbershop mirrors effect: What if x11vnc is started up, and
vncviewer is then started up on the same machine and displayed on the
same display x11vnc is polling? One might "accidentally" do this when
first testing out the programs. You get an interesting
recursive/feedback effect where vncviewer images keep popping up each
one contained in the previous one and slightly shifted a bit by the
window manager decorations. There will be an [105]even more
interesting effect if -scale is used. Also, if the XKEYBOARD is
supported and the XBell "beeps" once, you get an infinite loop of
beeps going off. Although all of this is mildly exciting it is not
much use: you will normally run and display the viewer on a different
machine!
_________________________________________________________________
Sun Ray Notes:
You can run x11vnc on your (connected or disconnected) [106]SunRay
session. Here are some [107]notes on SunRay usage with x11vnc.
_________________________________________________________________
Limitations:
* Due to the polling nature, some activities (opaque window moves,
scrolling), can be pretty choppy/ragged and others (exposures of
large areas) slow. Experiment with interacting a bit differently
than you normally do to minimize the effects (e.g. do fullpage
paging rather than line-by-line scrolling, and move windows in a
single, quick motion). Recent work has provided the
[108]-scrollcopyrect and [109]-wireframe speedups using the
CopyRect VNC encoding and other things, but they only speed up
certain activities, not all.
* A rate limiting factor for x11vnc performance is that video
hardware is optimized for writing, not reading (x11vnc reads the
video framebuffer for the screen image data). The difference can
be a factor of 10 to 1000, and so it usually takes about 0.5-1 sec
to read in the whole video hardware framebuffer (e.g. 5MB for
1280x1024 at depth 24 with a read rate of 5-10MB/sec). So whenever
activity changes most of the screen (e.g. moving or iconifying a
large window) there is a delay of 0.5-1 sec while x11vnc reads the
changed regions in.
Note: A quick way to get a 2X speedup for x11vnc is to switch from
depth 24 (32bpp) to depth 16 (16bpp). You get a 4X speedup going
to 8bpp, but the lack of color cells is usually unacceptable.
To get a sense of the read and write speeds of your video card,
you can run benchmarks like: x11perf -getimage500, x11perf
-putimage500, x11perf -shmput500 and for XFree86 displays with
direct graphics access the dga command (press "b" to run the
benchmark and then after a few seconds press "q" to quit). Even
this "dd if=/dev/fb0 of=/dev/null" often gives a good estimate. We
have seen a few cases where the hardware fb read speed is greater
than 65 MB/sec: on high end graphics workstations from SGI and
Sun, and also from a Linux user using nvidia proprietary drivers
for his nvidia video card. If you have a card with a fast read
speed please send us the details.
On XFree86/Xorg it is actually possible to increase the
framebuffer read speed considerably (5-100 times) by using the
Shadow Framebuffer (a copy of the framebuffer is kept in main
memory and this can be read much more quickly). To do this one
puts the line Option "ShadowFB" "true" in the Device section of
the /etc/X11/XF86Config or /etc/X11/xorg.conf file. Note that this
disables 2D acceleration at the physical display and so likely
defeats the purpose. Nevertheless this could be handy in some
circumstances, e.g. if the slower speed while sitting at the
physical display was acceptable (this seems to be true for most
video cards these days). Unfortunately it does not seem shadowfb
can be turned on and off dynamically...
Another amusing thing one can do is use Xvfb as the X server, e.g.
"xinit $HOME/.xinitrc -- /usr/X11R6/bin/Xvfb :1 -screen 0
1024x768x16" x11vnc can poll Xvfb efficiently via main memory.
It's not exactly clear why one would want to do this instead of
using vncserver/Xvnc, (perhaps to take advantage of an x11vnc
feature, such as framebuffer scaling), but we mention it because
it may be of use for special purpose applications.
Also, a faster and more accurate way is to use the "dummy"
XFree86/Xorg device driver (or our Xdummy wrapper script). See
[110]this FAQ for details.
* Somewhat surprisingly, the X11 mouse (cursor) shape is write-only
and cannot be queried from the X server. So traditionally in
x11vnc the cursor shape stays fixed at an arrow. (see the "-cursor
X" and "-cursor some" [111]options, however, for a partial hack
for the root window, etc.). However, on Solaris using the SUN_OVL
overlay extension, x11vnc can show the correct mouse cursor when
the [112]-overlay option is also supplied. A similar thing is done
on IRIX as well when -overlay is supplied.
More generally, as of Dec/2004 x11vnc supports the new XFIXES
extension (in Xorg and Solaris 10) to query the X server for the
exact cursor shape, this works pretty well except that cursors
with transparency (alpha channel) need to approximated to solid
RGB values (some cursors look worse than others).
* Audio from applications is of course not redirected (separate
redirectors do exist, e.g. esd [113]the FAQ on this below.) The
XBell() "beeps" will work if the X server supports the XKEYBOARD
extension. (Note that on Solaris XKEYBOARD is disabled by default.
Passing +kb to Xsun enables it).
* The scroll detection algorithm for the [114]-scrollcopyrect option
can give choppy or bunched up transient output and occasionally
painting errors.
* Using -threads can expose some bugs in libvncserver.
Please feel free to [115]contact me if you have any questions,
problems, or comments about x11vnc, etc.
Also, some people ask if they can make a donation, see [116]this link
for that.
_________________________________________________________________
x11vnc FAQ:
[Building and Starting]
[117]Q-1: I can't get x11vnc to start up. It says "XOpenDisplay failed
(null)" or "Xlib: connection to ":0.0" refused by server Xlib: No
protocol specified" and then exits. What do I need to do?
[118]Q-2: I can't get x11vnc and/or libvncserver to compile.
[119]Q-3: I just built x11vnc successfully, but when I use it my
keystrokes and mouse button clicks are ignored (I am able to move the
mouse though).
[120]Q-4: Help, I need to run x11vnc on Solaris 2.5.1 (or other old
Unix/Linux) and it doesn't compile!
[121]Q-5: Where can I get a precompiled x11vnc binary for my Operating
System?
[122]Q-6: Where can I get a VNC Viewer binary (or source code) for the
Operating System I will be viewing from?
[123]Q-7: How can I see all of x11vnc's command line options and
documentation on how to use them?
[124]Q-8: I don't like typing arcane command line options every time I
start x11vnc. What can I do? Is there a config file? Or a GUI?
[125]Q-9: How can I get the GUI to run in the System Tray, or at least
be a smaller, simpler icon?
[126]Q-10: Can I make x11vnc more quiet and also go into the
background after starting up?
[127]Q-11: Sometimes when a VNC viewer dies abruptly, x11vnc also dies
with the error message like: "Broken pipe". I'm using the -forever
mode and I want x11vnc to keep running.
[128]Q-12: Are there any build-time customizations possible, e.g.
change defaults, create a smaller binary, etc?
[Win2VNC Related]
[129]Q-13: I have two separate machine displays in front of me, one
Windows the other X11: can I use x11vnc in combination with Win2VNC in
dual-screen mode to pass the keystrokes and mouse motions to the X11
display?
[130]Q-14: I am running Win2VNC on my Windows machine and "x11vnc
-nofb" on Unix to pass keyboard and mouse to the Unix monitor.
Whenever I start Win2VNC it quickly disconnects and x11vnc says:
rfbProcessClientNormalMessage: read: Connection reset by peer
[Color Issues]
[131]Q-15: The X display I run x11vnc on is only 8 bits per pixel
(bpp) PseudoColor (i.e. only 256 distinct colors). The x11vnc colors
may start out OK, but after a while they are incorrect in certain
windows.
[132]Q-16: Color problems: Why are the colors for some windows
incorrect in x11vnc? BTW, my X display has nice overlay/multi-depth
visuals of different color depths: e.g. there are both depth 8 and 24
visuals available at the same time.
[133]Q-17: How do I figure out the window id to supply to the -id
windowid option?
[134]Q-18: Why don't menus or other transient windows come up when I
am using the -id windowid option to view a single application window?
[135]Q-19: My X display is depth 24 at 24bpp (instead of the normal
depth 24 at 32bpp). I'm having lots of color and visual problems with
x11vnc and/or vncviewer. What's up?
[Xterminals]
[136]Q-20: Can I use x11vnc to view and interact with an Xterminal
(e.g. NCD) that is not running UNIX and so x11vnc cannot be run on it
directly?
[137]Q-21: How do I get my X permissions (MIT-MAGIC-COOKIE file)
correct for a Unix/Linux machine acting as an Xterminal?
[Sun Rays]
[138]Q-22: I'm having trouble using x11vnc with my Sun Ray session.
[Remote Control]
[139]Q-23: How do I stop x11vnc once it is running in the background?
[140]Q-24: Can I change settings in x11vnc without having to restart
it? Can I remote control it?
[Security and Permissions]
[141]Q-25: How do I create a VNC password for use with x11vnc?
[142]Q-26: Can I make it so -storepasswd doesn't show my password on
the screen?
[143]Q-27: Can I have two passwords for VNC viewers, one for full
access and the other for view-only access to the display?
[144]Q-28: Can I have as many full-access and view-only passwords as I
like?
[145]Q-29: Does x11vnc support Unix usernames and passwords? Can I
further limit the set of Unix usernames who can connect to the VNC
desktop?
[146]Q-30: Why does x11vnc exit as soon as the VNC viewer disconnects?
And why doesn't it allow more than one VNC viewer to connect at the
same time?
[147]Q-31: Can I limit which machines incoming VNC clients can connect
from?
[148]Q-32: How do I build x11vnc/libvncserver with libwrap
(tcp_wrappers) support?
[149]Q-33: Can I have x11vnc only listen on one network interface
(e.g. internal LAN) rather than having it listen on all network
interfaces and relying on -allow to filter unwanted connections out?
[150]Q-34: Now that -localhost implies listening only on the loopback
interface, how I can occasionally allow in a non-localhost via the -R
allowonce remote control command?
[151]Q-35: Can I fine tune what types of user input are allowed? E.g.
have some users just be able to move the mouse, but not click or type
anything?
[152]Q-36: Can I prompt the user at the local X display whether the
incoming VNC client should be accepted or not? Can I decide to make
some clients view-only? How about running an arbitrary program to make
the decisions?
[153]Q-37: I start x11vnc as root because it is launched via inetd(8)
or a display manager like gdm(1). Can I have x11vnc later switch to a
different user?
[154]Q-38: I use a screen-lock when I leave my workstation (e.g.
xscreensaver or xlock). When I remotely access my workstation desktop
via x11vnc I can unlock the desktop fine, but I am worried people will
see my activities on the physical monitor. What can I do to prevent
this, or at least make it more difficult?
[155]Q-39: Can I have x11vnc automatically lock the screen when I
disconnect the VNC viewer?
[Encrypted Connections]
[156]Q-40: How can I tunnel my connection to x11vnc via an encrypted
SSH channel between two Unix machines?
[157]Q-41: How can I tunnel my connection to x11vnc via an encrypted
SSH channel from Windows using an SSH client like Putty?
[158]Q-42: How can I tunnel my connection to x11vnc via an encrypted
SSL channel using an external tool like stunnel?
[159]Q-43: Does x11vnc have built-in SSL tunneling?
[160]Q-44: How do I use VNC Viewers with built-in SSL tunneling?
[161]Q-45: How do I use VNC Viewers with built-in SSL tunneling when
going through a Web Proxy?
[162]Q-46: Can Apache web server act as a gateway for users to connect
via SSL from the Internet with a Web browser to x11vnc running on
their workstations behind a firewall?
[163]Q-47: Can I create and use my own SSL Certificate Authority (CA)
with x11vnc?
[Display Managers and Services]
[164]Q-48: How can I run x11vnc as a "service" that is always
available?
[165]Q-49: How can I use x11vnc to connect to an X login screen like
xdm, GNOME gdm, KDE kdm, or CDE dtlogin? (i.e. nobody is logged into
an X session yet).
[166]Q-50: Can I run x11vnc out of inetd(8)? How about xinetd(8)?
[167]Q-51: Can I have x11vnc allow a user to log in with her UNIX
password and then have it find her X display on that machine and
connect to it?
[168]Q-52: Can I have x11vnc restart itself after it terminates?
[169]Q-53: How do I make x11vnc work with the Java VNC viewer applet
in a web browser?
[170]Q-54: Are reverse connections (i.e. the VNC server connecting to
the VNC viewer) using "vncviewer -listen" and vncconnect(1) supported?
[171]Q-55: Can I use x11vnc as a replacement for Xvnc? (i.e. not for a
real display, but for a virtual one I keep around).
[172]Q-56: How can I use x11vnc on "headless" machines? Why might I
want to?
[Resource Usage and Performance]
[173]Q-57: I have lots of memory, but why does x11vnc fail with
shmget: No space left on device or Minor opcode of failed
request: 1 (X_ShmAttach)?
[174]Q-58: How can I make x11vnc use less system resources?
[175]Q-59: How can I make x11vnc use MORE system resources?
[176]Q-60: I use x11vnc over a slow link with high latency (e.g.
dialup modem), is there anything I can do to speed things up?
[177]Q-61: Does x11vnc support the X DAMAGE Xserver extension to find
modified regions of the screen quickly and efficiently?
[178]Q-62: When I drag windows around with the mouse or scroll up and
down things really bog down (unless I do the drag in a single, quick
motion). Is there anything to do to improve things?
[179]Q-63: Why not do something like wireframe animations to avoid the
windows "lurching" when being moved or resized?
[180]Q-64: Can x11vnc try to apply heuristics to detect when a window
is scrolling its contents and use the CopyRect encoding for a speedup?
[Mouse Cursor Shapes]
[181]Q-65: Why isn't the mouse cursor shape (the little icon shape
where the mouse pointer is) correct as I move from window to window?
[182]Q-66: When using XFIXES cursorshape mode, some of the cursors
look really bad with extra black borders around the cursor and other
cruft. How can I improve their appearance?
[183]Q-67: In XFIXES mode, are there any hacks to handle cursor
transparency ("alpha channel") exactly?
[Mouse Pointer]
[184]Q-68: Why does the mouse arrow just stay in one corner in my
vncviewer, whereas my cursor (that does move) is just a dot?
[185]Q-69: Can I take advantage of the TightVNC extension to the VNC
protocol where Cursor Positions Updates are sent back to all connected
clients (i.e. passive viewers can see the mouse cursor being moved
around by another viewer)?
[186]Q-70: Is it possible to swap the mouse buttons (e.g. left-handed
operation), or arbitrarily remap them? How about mapping button clicks
to keystrokes, e.g. to partially emulate Mouse wheel scrolling?
[Keyboard Issues]
[187]Q-71: How can I get my AltGr and Shift modifiers to work between
keyboards for different languages?
[188]Q-72: When I try to type a "<" (i.e. less than) instead I get ">"
(i.e. greater than)! Strangely, typing ">" works OK!!
[189]Q-73: When I try to type a "<" (i.e. less than) instead I get
"<," (i.e. an extra comma).
[190]Q-74: I'm using an "international" keyboard (e.g. German "de", or
Danish "dk") and the -modtweak mode works well if the VNC viewer is
run on a Unix/Linux machine with a similar keyboard. But if I run
the VNC viewer on Unix/Linux with a different keyboard (e.g. "us") or
Windows with any keyboard, I can't type some keys like: "@", "$",
"<", ">", etc. How can I fix this?
[191]Q-75: When typing I sometimes get double, triple, or more of my
keystrokes repeated. I'm sure I only typed them once, what can I do?
[192]Q-76: The x11vnc -norepeat mode is in effect, but I still get
repeated keystrokes!!
[193]Q-77: The machine where I run x11vnc has an AltGr key, but the
local machine where I run the VNC viewer does not. Is there a way I
can map a local unused key to send an AltGr? How about a Compose key
as well?
[194]Q-78: I have a Sun machine I run x11vnc on. Its Sun keyboard has
just one Alt key labelled "Alt" and two Meta keys labelled with little
diamonds. The machine where I run the VNC viewer only has Alt keys.
How can I send a Meta keypress? (e.g. emacs needs this)
[195]Q-79: Can I map a keystroke to a mouse button click on the remote
machine?
[196]Q-80: How can I get Caps_Lock to work between my VNC viewer and
x11vnc?
[Screen Related Issues and Features]
[197]Q-81: The remote display is larger (in number of pixels) than the
local display I am running the vncviewer on. I don't like the
vncviewer scrollbars, what I can do?
[198]Q-82: Does x11vnc support server-side framebuffer scaling? (E.g.
to make the desktop smaller).
[199]Q-83: Does x11vnc work with Xinerama? (i.e. multiple monitors
joined together to form one big, single screen).
[200]Q-84: Can I use x11vnc on a multi-headed display that is not
Xinerama (i.e. separate screens :0.0, :0.1, ... for each monitor)?
[201]Q-85: Can x11vnc show only a portion of the display? (E.g. for a
special purpose rfb application).
[202]Q-86: Does x11vnc support the XRANDR (X Resize, Rotate and
Reflection) extension? Whenever I rotate or resize the screen x11vnc
just seems to crash.
[203]Q-87: Why is the view in my VNC viewer completely black? Or why
is everything flashing around randomly?
[204]Q-88: I use Linux Virtual Consoles (VC's) to implement 'Fast User
Switching' between users' sessions (e.g. Betty is on Ctrl-Alt-F7,
Bobby is on Ctrl-Alt-F8, and Sid is on Ctrl-Alt-F1: they use those
keystrokes to switch between their sessions). How come the view in a
VNC viewer connecting to x11vnc is either completely black or
otherwise all messed up unless the X session x11vnc is attached to is
in the active VC?
[205]Q-89: I am using x11vnc where my local machine has "popup/hidden
taskbars" (e.g. GNOME or MacOS X) and the remote display where x11vnc
runs also has "popup/hidden taskbars" (e.g. GNOME). When I move the
mouse to the edge of the screen where the popups happen, the taskbars
interfere and fight with each other in strange ways. What can I do?
[206]Q-90: Can I use x11vnc to view my VMWare session remotely?
[207]Q-91: Can non-X devices (e.g. a raw framebuffer) be viewed (and
even controlled) via VNC with x11vnc?
[208]Q-92: Can I export via VNC a Webcam or TV tuner framebuffer using
x11vnc?
[209]Q-93: Can I connect via VNC to a Qt-embedded/Qtopia application
running on my handheld or PC using the Linux console framebuffer (i.e.
not X11)?
[210]Q-94: Can I use x11vnc to record a Shock Wave Flash (or other
format) video of my desktop, e.g. to record a tutorial or demo?
[Misc: Clipboard, File Transfer, Sound, Beeps, Thanks, etc.]
[211]Q-95: Does the Clipboard/Selection get transferred between the
vncviewer and the X display?
[212]Q-96: Can I transfer files back and forth with x11vnc?
[213]Q-97: How can I hear the sound (audio) from the remote
applications on the desktop I am viewing via x11vnc?
[214]Q-98: Why don't I hear the "Beeps" in my X session (e.g. when
typing tput bel in an xterm)?
[215]Q-99: Thanks for your program and for your help! Can I make a
donation?
_________________________________________________________________
[Building and Starting]
Q-1: I can't get x11vnc to start up. It says "XOpenDisplay failed
(null)" or "Xlib: connection to ":0.0" refused by server Xlib: No
protocol specified" and then exits. What do I need to do?
For the former error, you need to specify the X display to connect to
(it also needs to be on the same machine the x11vnc process is to run
on). Set your DISPLAY environment variable or use the [216]-display
option to specify it. Nearly always the correct value will be ":0" (in
fact, x11vnc will now assume :0 if given no other information).
For the latter error, you need to set up the X11 permissions
correctly.
To make sure X11 permissions are the problem do this simple test:
while sitting at the physical X display open a terminal window
(gnome-terminal, xterm, etc). You should be able to run x11vnc
successfully without any need for special steps or command line
options in that terminal (i.e. just type "x11vnc"). If that works OK
then you know X11 permissions are the only thing preventing it from
working when you try to start x11vnc via, say, a remote shell.
How to Solve: See the xauth(1), Xsecurity(7), and xhost(1) man pages
for much info on X11 permissions. For example, you may need to set
your XAUTHORITY environment variable or use the [217]-auth option to
point to the correct MIT-MAGIC-COOKIE file (e.g. /home/joe/.Xauthority
or /var/gdm/:0.Xauth or /var/lib/kdm/A:0-crWk72K or /tmp/.gdmzndVlR,
etc.), or simply be sure you run x11vnc as the correct user (i.e. the
user who is logged into the X session you wish to view).
Note: The MIT cookie file contains the secret key that allows x11vnc
to connect to the desired X display.
If, say, sshd has set XAUTHORITY to point to a random file it has
created for X forwarding that will cause problems. (Under some
circumstances even su(1) and telnet(1) can set XAUTHORITY. See also
the gdm parameter NeverPlaceCookiesOnNFS that sets XAUTHORITY to a
random filename in /tmp for the whole X session).
Running x11vnc as root is often not enough: you need to know where the
MIT-MAGIC-COOKIE file for the desired X display is.
Example solution:
x11vnc -display :0 -auth /var/gdm/:0.Xauth
(this is for the display manager gdm and requires root permission to
read the gdm cookie file, see [218]this faq for other display manager
cookie file names). While running x11vnc as root, remember it comes
with no warranty ;-).
Less safe, but to avoid figuring out where the correct XAUTHORITY file
is, if the person sitting at the physical X session types "xhost
+localhost" then one should be able to attach x11vnc to the session
(from the same machine). The person could then type "xhost -localhost"
after x11vnc has connected to go back to the default permissions.
Also, for some situations the "-users lurk=" option may be of use
(please read the documentation on the [219]-users option).
To test out your X11 permissions from a remote shell, set DISPLAY and
possibly XAUTHORITY (see your shell's man page, bash(1), tcsh(1), on
how to set environment variables) and type xdpyinfo in the same place
you will be typing (or otherwise running) x11vnc. If information is
printed out about the X display (screen sizes, supported extensions,
color visuals info) that means the X11 permissions are set up
properly: xdpyinfo successfully connected to DISPLAY! You could also
type xclock and make sure no errors are reported (a clock should
appear on the X display, press Ctrl-C to stop it). If these work, then
typing "x11vnc" in the same environment should also work.
Important: if you cannot get your X11 permissions so that the xdpyinfo
or xclock tests work, x11vnc also will not work (all of these X
clients must be allowed to connect to the X server to function
properly).
Q-2: I can't get x11vnc and/or libvncserver to compile.
Make sure you have all of the required -devel packages installed.
These include X11/XFree86, libjpeg, libz, ...
After running the libvncserver configure, carefully examine the output
and the messages in the config.log file looking for missing
components. For example, if the configure output looks like:
checking how to run the C preprocessor... gcc -E
checking for X... no
checking for XkbSelectEvents in -lX11... no
checking for XineramaQueryScreens in -lXinerama... no
checking for XTestFakeKeyEvent in -lXtst... no
there is quite a bit wrong with the build environment. Hopefully
simply adding -devel packages will fix it.
For Debian the list seems to be:
gcc
make
libc6-dev
libjpeg62-dev
libx11-dev
libxext-dev
libxrandr-dev
libxtst-dev
x-dev
xlibs-static-dev
zlib1g-dev
For Redhat the list seems to be:
gcc
make
glibc-devel
libjpeg-devel
XFree86-devel or xorg-x11-devel
zlib-devel
Q-3: I just built x11vnc successfully, but when I use it my keystrokes
and mouse button clicks are ignored (I am able to move the mouse
though).
This is most likely due to you not having a working build environment
for the XTEST client library libXtst.so. The library is probably
present on your system, but the package installing the development
header file is missing.
If you were watching carefully while configure was running you would
have seen:
checking for XTestFakeKeyEvent in -lXtst... no
The solution is to add the necessary build environment package (and
the library package if that is missing too). On Debian the build
package is libxtst-dev. Other distros/OS's may have it in another
package.
x11vnc will build without support for this library (e.g. perhaps one
wants a view-only x11vnc on a stripped down or embedded system...).
And at runtime it will also continue to run even if the X server it
connects to does not support XTEST. In both cases it cannot inject
keystrokes or button clicks since XTEST is needed for that (it can
still move the mouse pointer using the X API XWarpPointer()).
You will see a warning message something like this at run time:
20/03/2005 22:33:09 WARNING: XTEST extension not available (either missing fr
om
20/03/2005 22:33:09 display or client library libXtst missing at build time
).
20/03/2005 22:33:09 MOST user input (pointer and keyboard) will be DISCARDE
D.
20/03/2005 22:33:09 If display does have XTEST, be sure to build x11vnc wit
h
20/03/2005 22:33:09 a working libXtst build environment (e.g. libxtst-dev,
20/03/2005 22:33:09 or other packages).
20/03/2005 22:33:09 No XTEST extension, switching to -xwarppointer mode for
20/03/2005 22:33:09 pointer motion input.
Q-4: Help, I need to run x11vnc on Solaris 2.5.1 (or other old
Unix/Linux) and it doesn't compile!
We apologize that x11vnc does not build cleanly on older versions of
Solaris, Linux, etc.: very few users are on these old releases.
We have heard that since Dec/2004 a Solaris 2.6 built x11vnc will run
on Solaris Solaris 2.5 and 2.5.1 (since a workaround for XConvertCase
is provided).
In any event, here is a workaround for Solaris 2.5.1 (and perhaps
earlier and perhaps non-Solaris):
First use the environment settings (CPPFLAGS, LDFLAGS, etc.) in the
above [220]Solaris build script to run the configure command. That
should succeed without failure. Then you have to hand edit the
autogenerated rfb/rfbconfig.h file in the source tree, and just before
the last #endif at the bottom of that file insert these workaround
lines:
struct timeval _tmp_usleep_tv;
#define usleep(x) \
_tmp_usleep_tv.tv_sec = (x) / 1000000; \
_tmp_usleep_tv.tv_usec = (x) % 1000000; \
select(0, NULL, NULL, NULL, &_tmp_usleep_tv);
int gethostname(char *name, int namelen);
long random();
int srandom(unsigned int seed);
#undef LIBVNCSERVER_HAVE_LIBPTHREAD
#define SHUT_RDWR 2
typedef unsigned int in_addr_t;
#define snprintf(a, n, args...) sprintf((a), ## args)
Then run make with the Solaris build script environment, everything
should compile without problems, and the resulting x11vnc binary
should work OK. If some non-x11vnc related programs fail (e.g. test
programs) and the x11vnc binary is not created try "make -k" to have
it keep going. Similar sorts of kludges in rfb/rfbconfig.h can be done
on other older OS (Solaris, Linux, ...) releases.
Here are some notes for similar steps that need to be done to build on
[221]SunOS 4.x
Please let us know if you had to use the above workaround (and whether
it worked or not). If there is enough demand we will try to push clean
compilations back to earlier Solaris, Linux, etc, releases.
Q-5: Where can I get a precompiled x11vnc binary for my Operating
System?
Hopefully the [222]build steps above and [223]FAQ provide enough info
for a painless compile for most environments. Please report problems
with the x11vnc configure, make, etc. on your system (if your system
is known to compile other GNU packages successfully).
There are precompiled x11vnc binaries built by other groups that are
available at the following locations:
Debian: (.deb) [224]http://packages.debian.org/x11vnc
Slackware: (.tgz) [225]http://www.linuxpackages.net/ Redhat/Fedora:
(.rpm) [226]http://dag.wieers.com/packages/x11vnc/
[227]http://dries.ulyssis.org/rpm/packages/x11vnc SuSE: (.rpm)
[228]http://linux01.gwdg.de/~pbleser/ Solaris: (pkg)
[229]http://www.sunfreeware.com/ FreeBSD: (.tbz)
[230]http://www.freebsd.org/ [231]http://www.freshports.org/net/x11vnc
OpenBSD: (.tgz) [232]http://www.openbsd.org/ NetBSD: (src)
[233]http://pkgsrc.se/x11/x11vnc Nokia 770 (.deb)
[234]http://mike.saunby.net/770/x11vnc/ Sharp Zaurus
[235]http://www.pdaxrom.org/ and [236]http://www.focv.com/
If the above binaries don't work and building x11vnc on your OS fails
(and all else fails!) you can try one of [237]my collection of
binaries for various OS's and x11vnc releases.
As a general note, the x11vnc program is simple enough you don't
really need to install a package: the binary will in most cases work
as is and from any location (as long as your system libraries are not
too old, etc). So, for Linux distributions that are not one of the
above, the x11vnc binary from the above packages has a good chance of
working. You can "install" it by just copying the x11vnc binary to the
desired directory in your PATH. Tip on extracting files from a Debian
package: extract the archive via a command like: "ar x
x11vnc_0.6-2_i386.deb" and then you can find the binary in the
resulting data.tar.gz tar file. Also, rpm2cpio(1) is useful in
extracting files from rpm packages.
Q-6: Where can I get a VNC Viewer binary (or source code) for the
Operating System I will be viewing from?
To obtain VNC viewers for the viewing side (Windows, Mac OS, or Unix)
try here:
* [238]http://www.tightvnc.com/download.html
* [239]http://www.realvnc.com/download-free.html
* [240]http://sourceforge.net/projects/cotvnc/
* [241]http://www.ultravnc.com/
Q-7: How can I see all of x11vnc's command line options and
documentation on how to use them?
Run: x11vnc -opts to list just the option names or run: x11vnc
-help for long descriptions about each option. The output is listed
[242]here as well. Yes, x11vnc does have a lot of options, doesn't
it...
Q-8: I don't like typing arcane command line options every time I
start x11vnc. What can I do? Is there a config file? Or a GUI?
You could create a shell script that calls x11vnc with your options:
#!/bin/sh
#
# filename: X11vnc (i.e. not "x11vnc")
# It resides in a directory in $PATH. "chmod 755 X11vnc" has been run on it.
#
x11vnc -wait 50 -localhost -rfbauth $HOME/.vnc/passwd -display :0 $*
a similar thing can be done via aliases in your shell (bash, tcsh,
csh, etc..).
Or as of Jun/2004 you can use the simple $HOME/.x11vncrc config file
support. If that file exists, each line is taken as a command line
option. E.g. the above would be:
# this is a comment in my ~/.x11vncrc file
wait 50 # this is a comment to the end of the line.
-localhost # note: the leading "-" is optional.
rfbauth /home/fred/.vnc/passwd
display :0
As of Dec/2004 there is now a simple Tcl/Tk GUI based on the
remote-control functionality ("-R") that was added. The /usr/bin/wish
program is needed for operation. The gui is not particularly
user-friendly, it just provides a point and click mode to set all the
many x11vnc parameters and obtain help on them. It is also very useful
for testing. See the [243]-gui option for more info. Examples: "x11vnc
... -gui" and "x11vnc ... -gui other:0" in the latter case the gui is
displayed on other:0, not the X display x11vnc is polling. There is
also a "[244]-gui tray" system tray mode.
Q-9: How can I get the GUI to run in the System Tray, or at least be a
smaller, simpler icon?
As of Jul/2005 the gui can run in a more friendly small icon mode
"-gui icon" or in the system tray: "-gui tray". It has balloon status,
a simple menu, and a Properities dialog. The full, complicated, gui is
only available under "Advanced". Other improvements were added as
well. Try "Misc -> simple_gui" for a gui with fewer esoteric menu
items.
If the gui fails to embed itself in the system tray, do a retry via
"Window View -> icon" followed by "Window View -> tray" with the popup
menu.
For inexperienced users starting up x11vnc and the GUI while sitting
at the physical X display (not remotely), using something like "x11vnc
-display :0 -gui tray=setpass" might be something for them that they
are accustomed to in a Desktop environment (it prompts for an initial
password, etc). This is a basic "Share My Desktop" usage mode.
Q-10: Can I make x11vnc more quiet and also go into the background
after starting up?
Use the [245]-q and [246]-bg options, respectively. (also: -quiet is
an alias for -q)
Note that under -bg the stderr messages will be lost unless you use
the "[247]-o logfile" option.
Q-11: Sometimes when a VNC viewer dies abruptly, x11vnc also dies with
the error message like: "Broken pipe". I'm using the -forever mode and
I want x11vnc to keep running.
As of Jan/2004 the SIGPIPE signal is ignored. So if a viewer client
terminates abruptly, libvncserver will notice on the next I/O
operation and will close the connection and continue on.
Up until of Apr/2004 the above fix only works for BSD signal systems
(Linux, FreeBSD, ...) For SYSV systems there is a workaround in place
since about Jun/2004.
Q-12: Are there any build-time customizations possible, e.g. change
defaults, create a smaller binary, etc?
There are some options. They are enabled by adding something like
-Dxxxx=1 to the CPPFLAGS environment variable before running configure
(see the [248]build notes for general background).
/*
* Mar/2006
* Build-time customization via CPPFLAGS.
*
* Summary of options to include in CPPFLAGS for custom builds:
*
* -DVNCSHARED to have the vnc display shared by default.
* -DFOREVER to have -forever on by default.
* -DNOREPEAT=0 to have -repeat on by default.
* -DADDKEYSYMS=0 to have -noadd_keysyms the default.
*
* -DREMOTE_DEFAULT=0 to disable remote-control on by default (-yesremote).
* -DREMOTE_CONTROL=0 to disable remote-control mechanism completely.
* -DEXTERNAL_COMMANDS=0 to disable the running of all external commands.
* -DFILEXFER=0 disable filexfer.
*
* -DHARDWIRE_PASSWD=... hardwired passwords, quoting necessary.
* -DHARDWIRE_VIEWPASSWD=...
* -DNOPW=1 make -nopw the default (skip warning)
* -DUSEPW=1 make -usepw the default
* -DPASSWD_REQUIRED=1 exit unless a password is supplied.
* -DPASSWD_UNLESS_NOPW=1 exit unless a password is supplied and no -nopw.
*
* -DWIREFRAME=0 to have -nowireframe as the default.
* -DWIREFRAME_COPYRECT=0 to have -nowirecopyrect as the default.
* -DWIREFRAME_PARMS=... set default -wirecopyrect parameters.
* -DSCROLL_COPYRECT=0 to have -noscrollcopyrect as the default.
* -DSCROLL_COPYRECT_PARMS=... set default -scrollcopyrect parameters.
* -DSCALING_COPYRECT=0
* -DXDAMAGE=0 to have -noxdamage as the default.
* -DSKIPDUPS=0 to have -noskip_dups as the default or vice versa.
*
* -DPOINTER_MODE_DEFAULT={0,1,2,3,4} set default -pointer_mode.
* -DBOLDLY_CLOSE_DISPLAY=0 to not close X DISPLAY under -rawfb.
* -DSMALL_FOOTPRINT=1 for smaller binary size (no help, no gui, etc)
* use 2 or 3 for even smaller footprint.
* -DNOGUI do not include the gui tkx11vnc.
* -DPOLL_8TO24_DELAY=N
* -DDEBUG_XEVENTS=1 enable printout for X events.
*
* Set these in CPPFLAGS before running configure. E.g.:
*
* % env CPPFLAGS="-DFOREVER -DREMOTE_CONTROL=0" ./configure
* % make
*/
If other things (e.g. "-I ...") are needed in CPPFLAGS add them as
well.
On some systems is seems you need to set LC_ALL=C for configure to
work properly...
Be careful the following two variables: HARDWIRE_PASSWD and
HARDWIRE_VIEWPASSWD. If set (remember to include the double quotes
around the string), they will be used as default values for the
-passwd and -viewpasswd options. Of course the strings will exist
unobscured in the x11vnc: the binary better not be readable by
unintendeds. Perhaps this is of use in remote access for an embedded
application, etc...
Let us know if more build-time customizations would be useful.
[Win2VNC Related]
Q-13: I have two separate machine displays in front of me, one Windows
the other X11: can I use x11vnc in combination with Win2VNC in
dual-screen mode to pass the keystrokes and mouse motions to the X11
display?
Yes, for best response start up x11vnc with the "[249]-nofb" option
(disables framebuffer polling, and does other optimizations) on the
secondary display (X11) machine. Then start up Win2VNC on the primary
display (Windows) referring it to the secondary display.
This will also work X11 to X11 using [250]x2vnc, however you would
probably just want to avoid VNC and use x2x for that.
For reference, here are some links to Win2VNC-like programs for
multiple monitor setups:
* [251]Original Win2VNC
* [252]Enhanced Win2VNC and [253]sourceforge link
* [254]x2vnc
* [255]x2x also [256]here
* [257]zvnc (MorphOS)
All of them will work with x11vnc (except x2x where it is not needed).
Q-14: I am running Win2VNC on my Windows machine and "x11vnc -nofb" on
Unix to pass keyboard and mouse to the Unix monitor. Whenever I start
Win2VNC it quickly disconnects and x11vnc says:
rfbProcessClientNormalMessage: read: Connection reset by peer
Is the default visual of the X display you run x11vnc on low color
(e.g. 8 bit per pixel PseudoColor)? (you can run xdpyinfo to check,
look in the "screen" section). There seems to be a bug in Win2VNC in
that it cannot deal correctly with colormaps (PseudoColor is the most
common example of a visual with a colormap).
If so, there are a couple options. 1) Can you set the default visual
on your display to be depth 24 TrueColor? Sun machines often have 8+24
overlay/multi-depth visuals, and you can make the default visual depth
24 TrueColor (see fbconfig(1) and Xsun(1)). 2) As of Feb/2004 x11vnc
has the [258]-visual option to allow you to force the framebuffer
visual to whatever you want (this usually messes up the colors unless
you are very clever). In this case, the option provides a convenient
workaround for the Win2VNC bug:
x11vnc -nofb -visual TrueColor -display :0 ...
So the visual will be set to 8bpp TrueColor and Win2VNC can handle
this. Since Win2VNC does not use the framebuffer data there should be
no problems in doing this.
[Color Issues]
Q-15: The X display I run x11vnc on is only 8 bits per pixel (bpp)
PseudoColor (i.e. only 256 distinct colors). The x11vnc colors may
start out OK, but after a while they are incorrect in certain windows.
Use the [259]-flashcmap option to have x11vnc watch for changes in the
colormap, and propagate those changes back to connected clients. This
can be slow (since the whole screen must be updated over the network
whenever the colormap changes). This flashing colormap behavior often
happens if an application installs its own private colormap when the
mouse is in its window. "netscape -install" is a well-known historical
example of this. Consider reconfiguring the system to 16 bpp or depth
24 TrueColor if at all possible.
Also note the option [260]-8to24 (Jan/2006) can often remove the need
for flashing the colormap. Everything is dynamically transformed to
depth 24 at 32 bpp using the colormaps. There may be painting errors
however (see the following FAQ for tips on reducing and correcting
them).
In some rare cases the [261]-notruecolor option has corrected colors
on 8bpp displays. The red, green, and blue masks were non-zero in 8bpp
PseudoColor on an obscure setup, and this option corrected the
problems.
Q-16: Color problems: Why are the colors for some windows incorrect in
x11vnc? BTW, my X display has nice overlay/multi-depth visuals of
different color depths: e.g. there are both depth 8 and 24 visuals
available at the same time.
You may want to review the [262]previous question regarding 8 bpp
PseudoColor.
On some hardware (Sun/SPARC and SGI), the [263]-overlay option
discussed a couple paragraphs down may solve this for you (you may
want to skip to it directly). On other hardware the less robust
[264]-8to24 option may help (also discussed below).
Run xdpyinfo(1) to see what the default visual is and what the depths
of the other visuals are. Does the default visual have a depth of 8
but there are other visuals of depth 24? If it does, can you possibly
re-configure your X server to make a depth 24 visual the default? If
you can do it, this will save you a lot of grief WRT colors and x11vnc
(and for general usage too!). Here is how I do this on an old
Sparcstation 20 running Solaris 9 with SX graphics
xinit -- -dev /dev/fb defclass TrueColor defdepth 24
and it works nicely (note: to log into console from the dtlogin
window, select "Options -> Command Line Login", then login and enter
the above command). See the -dev section of the Xsun(1) manpage for a
description of the above arguments. If you have root permission, a
more permanent and convenient thing to do is to record the arguments
in a line like:
:0 Local local_uid@console root /usr/openwin/bin/Xsun -dev /dev/fb defclass
TrueColor defdepth 24
in /etc/dt/config/Xservers (copy /usr/dt/config/Xservers). Also look
at the fbconfig(1) and related manpages (e.g. ffbconfig, m64config,
pgxconfig, SUNWjfb_config, etc ...) for hardware framebuffer settings
that may achieve the same effect.
In general for non-Sun machines, look at the "-cc class" and related
options in your X server manpage (perhaps Xserver(1)), it may allow
modifying the default visual (e.g. "-cc 4", see <X11/X.h> for the
visual class numbers). On XFree86 some video card drivers (e.g. Matrox
mga) have settings like Option "Overlay" "24,8" to support multi-depth
overlays. For these, use the "-cc 4" X server command line option to
get a depth 24 default visual.
The -overlay mode: Another option is if the system with overlay
visuals is a Sun system running Solaris or SGI running IRIX you can
use the [265]-overlay x11vnc option (Aug/2004) to have x11vnc use the
Solaris XReadScreen(3X11) function to poll the "true view" of the
whole screen at depth 24 TrueColor. XReadDisplay(3X11) is used on
IRIX. This is useful for Legacy applications (older versions of
Cadence CAD apps are mentioned by x11vnc users) that require the
default depth be 8bpp, or the app will use a 8bpp visual even if depth
24 visuals are available, and so the default depth workaround
described in the previous paragraph is not sufficient for these apps.
It seems that Xorg is working toward supporting XReadDisplay(3X11) as
part of the RENDER extension work. When it does support it and
provides a library API x11vnc will be modified to take advantage of
the feature to support -overlay on Linux, *BSD, etc. Until then see
the -8to24 mode below.
Misc. notes on -overlay mode: An amusing by-product of -overlay mode
is that the mouse cursor shape is correct! (i.e. XFIXES is not
needed). The -overlay mode may be somewhat slower than normal mode due
to the extra framebuffer manipulations that must be performed. Also,
on Solaris there is a bug in that for some popup menus, the windows
they overlap will have painting errors (flashing colors) while the
popup is up (a workaround is to disable SaveUnders by passing -su to
Xsun, e.g. in your /etc/dt/config/Xservers file).
The -8to24 mode: The [266]-8to24 x11vnc option (Jan/2006) is a kludge
to try to dynamically rewrite the pixel values so that the 8bpp part
of the screen is mapped onto depth 24 TrueColor. This is less robust
than the -overlay mode because it is done by x11vnc outside of the X
server. So only use it on OS's that do not support -overlay. The
-8to24 mode will work if the default visual is depth 24 or depth 8. It
scans for any windows within 3 levels of the root window that are 8bpp
(i.e. legacy application), or in general ones that are not using the
default visual. For the windows it finds it uses XGetSubImage() to
retrieve the pixels values and uses the correct indexed colormap to
create a depth 24 TrueColor view of the whole screen. This depth 24,
32bpp view is exported via VNC.
Even on pure 8bpp displays it can be used as an alternative to
[267]-flashcmap to avoid color flashing completely.
This scheme is approximate and can often lead to painting errors. You
can manually correct most painting errors by pressing 3 Alt_L's in a
row, or by using something like: [268]-fixscreen V=3.0 to
automatically refresh the screen every 3 seconds. Also -fixscreen
8=3.0 has been added to just refresh the non-default visual parts of
the screen.
In general the scheme uses many resources and may give rise to
sluggish behavior. If multiple windows are using different 8bpp
indexed colormaps all but one window may need to be iconified for the
colors to be correct. There are a number of tunable parameters to try
to adjust performance and painting accuracy. The option -8to24
nogetimage can give a nice speedup if the default depth 24 X server
supports hiding the 8bpp bits in bits 25-32 of the framebuffer data.
On very slow machines -8to24 poll=0.2,cachewin=5.0 gives an useful
speedup. See the [269]-8to24 help description for information on
tunable parameters, etc.
Colors still not working correctly? Run xwininfo on the application
with the incorrect colors to verify that the depth of its visual is
different from the default visual depth (gotten from xdpyinfo). One
possible workaround in this case is to use the [270]-id option to
point x11vnc at the application window itself. If the application is
complicated (lots of toplevel windows and popup menus) this may not be
acceptable, and may even crash x11vnc (but not the application).
It is theoretically possible to solve this problem in general (see
xwd(1) for example), but it does not seem trivial or sufficiently fast
for x11vnc to be able to do so in real time. The [271]-8to24 method
does this approximately and is somewhat usable. Fortunately the
[272]-overlay option works for Solaris machines with overlay visuals
where most of this problem occurs.
Q-17: How do I figure out the window id to supply to the -id windowid
option?
Run the xwininfo program in a terminal. It will ask you to click on
the desired application window. After clicking, it will print out much
information, including the window id (e.g. 0x6000010). Also, the
visual and depth of the window printed out is often useful in
debugging x11vnc [273]color problems.
Also, as of Dec/2004 you can use "[274]-id pick" to have x11vnc run
xwininfo(1) for you and after you click the window it extracts the
windowid. Besides "pick" there is also "id:root" to allow you to go
back to root window when doing remote-control.
Q-18: Why don't menus or other transient windows come up when I am
using the -id windowid option to view a single application window?
This is related to the behavior of the XGetImage(3X11) and
XShmGetImage() interfaces regarding backingstore, saveunders, etc. The
way the image is retrieved depends on some aspects of how the X server
maintains the display image data and whether other windows are
clipping or obscuring it. See the XGetImage(3X11) man page for more
details. If you disable BackingStore and SaveUnders in the X server
you should be able to see these transient windows.
If things are not working and you still want to do the single window
polling, try the [275]-sid windowid option ("shifted" windowid).
Q-19: My X display is depth 24 at 24bpp (instead of the normal depth
24 at 32bpp). I'm having lots of color and visual problems with x11vnc
and/or vncviewer. What's up?
First off, depth 24 at 24bpp (bpp=bits-per-pixel) is fairly uncommon
and can cause problems in general. It also can be slower than depth 24
at 32bpp. You might want to switch to 32bpp (for XFree86 see the
"-fbbpp 32", DefaultFbBpp, FbBpp and related options). Perhaps you
have 24bpp because the video memory of the machine is low and the
screen wouldn't fit in video RAM at 32bpp. For this case depth 16 at
16bpp might be an acceptable option.
In any event x11vnc should handle depth 24 at 24bpp (although
performance may be slower). There are some caveats involving the
viewer however:
The RealVNC Unix viewer cannot handle 24bpp from the server, it will
say: "main: setPF: not 8, 16 or 32 bpp?" and exit. I have not checked
the RealVNC Windows viewer.
So you need to use the TightVNC Unix viewer. However there are some
problems with that too. It seems libvncserver does not do 24bpp
correctly with the Tight encoding. The colors and screen ultimately
get messed up. So you have to use a different encoding with the
TightVNC vncviewer, try "zlib", "hextile", or one of the other
encodings (e.g. vncviewer -encodings "zlib hextile" ...). I have not
checked the TightVNC or UltraVNC Windows viewers.
It appears the older RealVNC Unix viewers (e.g. 3.3.3 and 3.3.7) can
handle 24bpp from the server, so you may want to use those. They
evidently request 32 bpp and libvncserver obliges.
Update: as of Apr/2006 you can use the [276]-24to32 option to have
x11vnc dynamically transform the 24bpp pixel data to 32bpp. This extra
transformation could slow things down further however.
Now coming the opposite direction if you are running the vncviewer on
the 24bpp display, TightVNC will fail with "Can't cope with 24
bits-per-pixel. Sorry." and RealVNC will fail with "main: Error:
couldn't find suitable pixmap format" so evidently you cannot use
24bpp for the vncviewers to work on that X display.
[Xterminals]
Q-20: Can I use x11vnc to view and interact with an Xterminal (e.g.
NCD) that is not running UNIX and so x11vnc cannot be run on it
directly?
You can, but it will likely be very wasteful of network bandwidth
since you will be polling the X display over the network as opposed to
over the local hardware. To do this, run x11vnc on a UNIX machine as
close as possible network-wise (e.g. same switch) to the Xterminal
machine. Use the [277]-display option to point the display to that of
the Xterminal (you'll of course need basic X11 permission to do that)
and finally supply the [278]-noshm option (this enables the polling
over the network).
The response will likely be sluggish (maybe only one "frame" per
second). This mode is not recommended except for "quick checks" of
hard to get to X servers. Use something like "-wait 150" to cut down
on the polling rate. You may also need [279]-flipbyteorder if the
colors get messed up due to endian byte order differences.
Q-21: How do I get my X permissions (MIT-MAGIC-COOKIE file) correct
for a Unix/Linux machine acting as an Xterminal?
If the X display machine is a traditional Xterminal (where the X
server process runs on the Xterminal box, but all of the X client
applications (mozilla, etc) run on a central server (aka "terminal
server")), you will need to log into the Xterminal machine (i.e. get a
shell running there) and then start the x11vnc program. If the
Xterminal Linux/Unix machine is stripped down (e.g. no users besides
root) that may be difficult.
The next problem is the login Display Manager (e.g. gdm, kdm), and
hence the MIT-MAGIC-COOKIE auth files, are on the central server and
not on the Xterminal box where the X server and x11vnc processes are.
So unless X permissions are completely turned off (e.g. "xhost +"), to
run the x11vnc process on the Xterminal box the MIT-MAGIC-COOKIE auth
file data (XAUTHORITY or $HOME/.Xauthority) must be accessible by or
copied to the Xterminal. If $HOME/.Xauthority is exported via NFS
(this is insecure of course, but has been going on for decades), then
x11vnc can simply pick it up via NFS (you may need to use the
[280]-auth option to point to the correct file). Other options include
copying the auth file using scp, or something like:
central-server> xauth nextract - xterm123:0 | ssh xterm123 xauth nmerge -
and then, say, ssh from central-server to xterm123 to start x11vnc.
Here "xterm123" refers to the computer acting as the Xterminal and
"central-server" is the terminal server. You can use "xauth -f
/path/to/cookie-file list" to examine the contents of the cookie(s) in
a file "/path/to/cookie-file". See the xauth(1) manpage for more
details.
If the display name in the cookie file needs to be changed between the
two hosts, see [281]this note on the "xauth add ..." command.
A less secure option is to run something like "xhost +127.0.0.1" while
sitting at the Xterminal box to allow cookie-free local access for
x11vnc. You can run "xhost -127.0.0.1" after x11vnc connects if you
want to go back to the original permissions.
If the Xterminal is really stripped down and doesn't have any user
accounts, NFS, etc. you'll need to contact your system administrator
to set something up. It can be done!!! Some Xterminal projects have
actually enabled "run locally" facilities for the running of an
occasional app more efficiently locally on the Xterminal box (e.g.
realplayer).
Not recommended, but as a last resort, you could have x11vnc [282]poll
the Xterminal Display over the network. For this you would run a
"x11vnc -noshm ..." process on the central-server (and hope the
network admin doesn't get angry...)
Note: use of Display Manager (gdm, kdm, ...) auth cookie files (i.e.
from /var/..., /tmp/..., or elsewhere) may require modification via
xauth(1) to correctly include the display x11vnc refers to (e.g.
"xauth -f cookie-file add :0 . 45be51ae2ce9dfbacd882ab3ef8e96b1",
where the "45be51..." cookie value was found from an "xauth -f
/path/to/original/cookie-file list") or other reasons. See xauth(1)
manpage for full details on how to transfer an MIT-MAGIC-COOKIE
between machines and displays.
VNCviewer performance on Xterminals: This isn't related to x11vnc on
Xterminals, but we mention it here anyway because of the similar
issues. If you are on an Xterminal and want to use vncviewer to
connect to a VNC server somewhere, then performance would be best if
you ran the viewer on the Xterminal box. Otherwise, (i.e. running the
viewer process on the central-server) all of the vncviewer screen
drawing is done more inefficiently over the network. Something to
consider, especially on a busy network. (BTW, this has all of the
above permission, etc, problems: both vncviewer and x11vnc are X
client apps desired to be run on the Xterminal box).
[Sun Rays]
Q-22: I'm having trouble using x11vnc with my Sun Ray session.
The [283]Sun Ray technology is a bit like "VNC done in hardware" (the
Sun Ray terminal device, DTU, playing the role of the vncviewer).
Completely independent of that, the SunRay user's session is still an
X server that speaks the X11 protocol and so x11vnc simply talks to
the X server part to export the SunRay desktop to any place in the
world (i.e. not only to a Sun Ray terminal device), creating a sort of
"Soft Ray". Please see [284]this discussion of Sun Ray issues for
solutions to problems.
[Remote Control]
Q-23: How do I stop x11vnc once it is running in the background?
As of Dec/2004 there is a remote control feature. It can change a huge
amount of things on the fly: see the [285]-remote and [286]-query
options. To shut down the running x11vnc server just type "x11vnc -R
stop". To disconnect all clients do "x11vnc -R disconnect:all", etc.
If the [287]-forever option has not been supplied, x11vnc will
automatically exit after the first client disconnects. In general if
you cannot use the remote control, then you will have to kill the
x11vnc process This can be done via: "kill NNNNN" (where NNNNN is the
x11vnc process id number found from ps(1)), or "pkill x11vnc", or
"killall x11vnc" (Linux only).
If you have not put x11vnc in the background via the [288]-bg option
or shell & operator, then simply press Ctrl-C in the shell where
x11vnc is running to stop it.
Potential Gotcha: If somehow your Keypress of Ctrl-C went through
x11vnc to the Xserver that then delivered it to x11vnc it is possible
one or both of the Ctrl or C keys will be left stuck in the pressed
down state in the Xserver. Tapping the stuck key (either via a new
x11vnc or at the physical console) will release it from the stuck
state. If the keyboard seems to be acting strangely it is often fixed
by tapping Ctrl, Shift, and Alt. Alternatively, the [289]-clear_mods
option and [290]-clear_keys option can be used to release pressed keys
at startup and exit.
Q-24: Can I change settings in x11vnc without having to restart it?
Can I remote control it?
Look at the [291]-remote (same as -R) and [292]-query (same as -Q)
options added in Dec/2004. They allow nearly everything to be changed
dynamically and settings to be queried. Examples: "x11vnc -R shared",
"x11vnc -R forever", "x11vnc -R scale:3/4", "x11vnc -Q modtweak",
"x11vnc -R stop", "x11vnc -R disconnect:all", etc.. These commands do
not start a x11vnc server, but rather communicate with one that is
already running. The X display (X11VNC_REMOTE property) is used as the
communication channel, so the X permissions and DISPLAY must be set up
correctly for communication to be possible.
There is also a simple Tcl/Tk gui based on this remote control
mechanism. See the [293]-gui option for more info. You will need to
have Tcl/Tk (i.e. /usr/bin/wish) installed for it to work. It can also
run in the system tray: "-gui tray" or as a standalone icon window:
"-gui icon".
[Security and Permissions]
Q-25: How do I create a VNC password for use with x11vnc?
You may already have one in $HOME/.vnc/passwd if you have used, say,
the vncserver program from the regular RealVNC or TightVNC packages
(i.e. launching the Xvnc server). Otherwise, you could use the
vncpasswd(1) program from those packages.
As of Jun/2004 x11vnc supports the -storepasswd "pass" "file"
[294]option, which is the same functionality of storepasswd. Be sure
to quote the "pass" if it contains shell meta characters, spaces, etc.
Example:
x11vnc -storepasswd 'sword*fish' $HOME/myvncpasswd
You then use the password via the x11vnc option: "[295]-rfbauth
$HOME/myvncpasswd"
As of Jan/2006 if you do not supply any arguments:
x11vnc -storepasswd
you will be prompted for a password to save to ~/.vnc/passwd (your
keystrokes when entering the password will not be echoed to the
screen). If you supply one argument, e.g. "x11vnc -storepasswd
~/.mypass", the password you are prompted for will be stored in that
file.
x11vnc also has the [296]-passwdfile and -passwd/-viewpasswd plain
text (i.e. not obscured like the -rfbauth VNC passwords) password
options.
You can use the [297]-usepw option to automatically use any password
file you have in ~/.vnc/passwd or ~/.vnc/passwdfile (the latter is
used with the -passwdfile option).
x11vnc -usepw -display :0 ...
If neither file exists you are prompted to store a password in
~/.vnc/passwd. If a password file cannot be found or created x11vnc
exits immediately. An admin may want to set it up this way for users
who do not know better.
Q-26: Can I make it so -storepasswd doesn't show my password on the
screen?
You can use the vncpasswd program from RealVNC or TightVNC mentioned
above. As of Jan/2006 the -storepasswd option without any arguments
will not echo your password as you type it and save the file to
~/.vnc/passwd:
# x11vnc -storepasswd
Enter VNC password:
Verify password:
Write password to /home/myname/.vnc/passwd? [y]/n
Password written to: /home/myname/.vnc/passwd
You can also give it an alternate filename, e.g. "x11vnc -storepasswd
~/.mypass"
Q-27: Can I have two passwords for VNC viewers, one for full access
and the other for view-only access to the display?
Yes, as of May/2004 there is the [298]-viewpasswd option to supply the
view-only password. Note the full-access password option [299]-passwd
must be supplied at the same time. E.g.: -passwd sword -viewpasswd
fish.
To avoid specifying the passwords on the command line (where they
could be observed via the ps(1) command by any user) you can use the
[300]-passwdfile option to specify a file containing plain text
passwords. Presumably this file is readable only by you, and ideally
it is located on the machine x11vnc is run on (to avoid being snooped
on over the network). The first line of this file is the full-access
password. If there is a second line in the file and it is non-blank,
it is taken as the view-only password. (use "__EMPTY__" to supply an
empty one).
View-only passwords currently do not work for the [301]-rfbauth
password option (standard VNC password storing mechanism). FWIW, note
that although the output (usually placed in $HOME/.vnc/passwd) by the
vncpasswd or storepasswd programs (or from x11vnc -storepasswd) looks
encrypted they are really just obscured to avoid "casual" password
stealing. It takes almost no skill to figure out how to extract the
plain text passwords from $HOME/.vnc/passwd since it is very
straight-forward to work out what to do from the VNC source code.
Q-28: Can I have as many full-access and view-only passwords as I
like?
Yes, as of Jan/2006 in the libvncserver CVS the [302]-passwdfile
option has been extended to handle as many passwords as you like. You
put the view-only passwords after a line __BEGIN_VIEWONLY__.
You can also easily annotate and comment out passwords in the file.
You can have x11vnc re-read the file dynamically when it is modified.
Q-29: Does x11vnc support Unix usernames and passwords? Can I further
limit the set of Unix usernames who can connect to the VNC desktop?
Update: as of Feb/2006 x11vnc has the [303]-unixpw option that does
this outside of the VNC protocol and libvncserver. The standard su(1)
program is used to validate the user's password. A familiar "login:"
and "Password:" dialog is presented to the user on a black screen
inside the vncviewer. The connection is dropped if the user fails to
supply the correct password in 3 tries or does not send one before a
25 second timeout. Existing clients are view-only during this period.
A list of allowed Unix usernames may also be supplied along with
per-user settings.
There is also the [304]-unixpw_nis option for non-shadow-password
(typically NIS environments, hence the name) systems where the
traditional getpwnam() and crypt() functions are used instead of
su(1). The encrypted user passwords must be accessible to the user
running x11vnc in -unixpw_nis mode, otherwise the logins will always
fail even when the correct password is supplied. See ypcat(1) and
shadow(5).
Two settings are enforced in the -unixpw and -unixpw_nis modes to
provide extra security: the 1) [305]-localhost and 2) [306]-stunnel or
[307]-ssl options. Without these one might send the Unix username and
password data in clear text over the network which is a very bad idea.
They can be relaxed if you want to provide encryption other than
stunnel or [308]-ssl (the constraint is automatically relaxed if
SSH_CONNECTION is set and indicates you have ssh-ed in, however the
-localhost requirement is still enforced).
The two -unixpw modes have been tested on Linux, Solaris, Mac OS X,
HP-UX, Tru64, FreeBSD, OpenBSD, and NetBSD. Additional testing is
appreciated. For the last 4 it appears that su(1) will not prompt for
a password if su-ing to oneself. Since x11vnc requires a password
prompt from su, those logins will fail even when the correct password
is supplied. On *BSD it appears this can be corrected by commenting
out the pam_self.so entry in /etc/pam.d/su.
Previous discussion (prior to -unixpw option):
Until the VNC protocol and libvncserver support this things will be
approximate at best.
One approximate method involves starting x11vnc with the
[309]-localhost option. This basically requires the viewer user to log
into the workstation where x11vnc is running via their Unix username
and password, and then somehow set up a port redirection of his
vncviewer connection to make it appear to emanate from the local
machine. As discussed above, ssh is useful for this: "ssh -L
5900:localhost:5900 user@hostname ..." See the ssh wrapper scripts
mentioned [310]elsewhere on this page. [311]stunnel does this as well.
Of course a malicious user could allow other users to get in through
his channel, but that is a problem with every method. Another thing to
watch out for is a malicious user on the viewer side (where ssh is
running) trying to sneak in through the ssh port redirection there.
Regarding limiting the set of Unix usernames who can connect, the
traditional way would be to further require a VNC password to supplied
(-rfbauth, -passwd, etc) and only tell the people allowed in what the
VNC password is. A scheme that avoids a second password involves using
the [312]-accept option that runs a program to examine the connection
information to determine which user is connecting from the local
machine. That may be difficult to do, but, for example, the program
could use the ident service on the local machine (normally ident
should not be trusted over the network, but on the local machine it
should be accurate: otherwise root has been compromised and so there
are more serious problems! Unfortunately recent Linux distros seem to
provide a random string (MD5 hash?) instead of the username). An
example script passed in via -accept scriptname that deduces the Unix
username and limits who can be accepted might look something like
this:
#!/bin/sh
if [ "$RFB_CLIENT_IP" != "127.0.0.1" -o "$RFB_SERVER_IP" != "127.0.0.1" ]; then
exit 1 # something fishy... reject it.
fi
user=`echo "$RFB_CLIENT_PORT, $RFB_SERVER_PORT" | nc -w 1 $RFB_CLIENT_IP 113 \
| grep 'USERID.*UNIX' | head -1 | sed -e 's/[\r ]//g' | awk -F: '{print
$4}'`
for okuser in fred barney wilma betty
do
if [ "X$user" = "X$okuser" ]; then
exit 0 # accept it
fi
done
exit 1 # reject it
For this to work with ssh port redirection, the ssh option
UsePrivilegeSeparation must be enabled otherwise the userid will
always be "root".
Q-30: Why does x11vnc exit as soon as the VNC viewer disconnects? And
why doesn't it allow more than one VNC viewer to connect at the same
time?
These defaults are simple safety measures to avoid someone unknowingly
leaving his X11 desktop exposed (to the internet, say) for long
periods of time. Use the [313]-forever option (aka -many) to have
x11vnc wait for more connections after the first client disconnects.
Use the [314]-shared option to have x11vnc allow multiple clients to
connect simultaneously.
Recommended additional safety measures include using ssh ([315]see
above), stunnel, [316]-ssl, or a VPN to authenticate and encrypt the
viewer connections or to at least use the -rfbauth passwd-file
[317]option to use VNC password protection (or [318]-passwdfile) It is
up to YOU to apply these security measures, they will not be done for
you automatically.
Q-31: Can I limit which machines incoming VNC clients can connect
from?
Yes, look at the [319]-allow and [320]-localhost options to limit
connections by hostname or IP address. E.g.
x11vnc -allow 192.168.0.1,192.168.0.2
for those two hosts or
x11vnc -allow 192.168.0.
for a subnet. For individual hosts you can use the hostname instead of
the IP number, e.g.: "-allow snoopy", and "-allow darkstar,wombat".
Note that -localhost achieves the same thing as "-allow 127.0.0.1"
For more control, build libvncserver with libwrap support
[321](tcp_wrappers) and then use /etc/hosts.allow See hosts_access(5)
for complete details.
Q-32: How do I build x11vnc/libvncserver with libwrap (tcp_wrappers)
support?
Here is one way to pass this information to the configure script:
env CPPFLAGS=-DUSE_LIBWRAP LDFLAGS=-lwrap ./configure
then run make as usual. This requires libwrap and its development
package (tcpd.h) to be installed on the build machine. If additional
CPPFLAGS or LDFLAGS options are needed supply them as well using
quotes.
The resulting x11vnc then uses libwrap/tcp_wrappers for connections.
The service name you will use in /etc/hosts.allow and /etc/hosts.deny
is "vnc", e.g.:
vnc: 192.168.100.3 .example.com
Note that if you run x11vnc out of [322]inetd you do not need to build
x11vnc with libwrap support because the /usr/sbin/tcpd reference in
/etc/inetd.conf handles the tcp_wrappers stuff.
Q-33: Can I have x11vnc only listen on one network interface (e.g.
internal LAN) rather than having it listen on all network interfaces
and relying on -allow to filter unwanted connections out?
As of Mar/2005 there is the "[323]-listen ipaddr" option that enables
this. For ipaddr either supply the desired network interface's IP
address (or use a hostname that resolves to it) or use the string
"localhost". For additional filtering simultaneously use the
"[324]-allow host1,..." option to allow only specific hosts in.
This option is useful if you want to insure that no one can even begin
a dialog with x11vnc from untrusted network interfaces (e.g. ppp0).
The option [325]-localhost now implies "-listen localhost" since that
is what most people expect it to do.
Q-34: Now that -localhost implies listening only on the loopback
interface, how I can occasionally allow in a non-localhost via the -R
allowonce remote control command?
To do this specify "[326]-allow localhost". Unlike [327]-localhost
this will leave x11vnc listening on all interfaces (but of course only
allowing in local connections, e.g. ssh redirs). Then you can later
run "x11vnc -R allowonce:somehost" or use to gui to permit a one-shot
connection from a remote host.
Q-35: Can I fine tune what types of user input are allowed? E.g. have
some users just be able to move the mouse, but not click or type
anything?
As of Feb/2005, the [328]-input option allows you to do this. "K",
"M", "B", and "C" stand for Keystroke, Mouse-motion, Button-clicks,
and Clipboard, respectively. The setting: "-input M" makes attached
viewers only able to move the mouse. "-input KMBC,M" lets normal
clients do everything and enables view-only clients to move the mouse.
These settings can also be applied on a per-viewer basis via the
remote control mechanism or the GUI. E.g. x11vnc -R input:hostname:M
Q-36: Can I prompt the user at the local X display whether the
incoming VNC client should be accepted or not? Can I decide to make
some clients view-only? How about running an arbitrary program to make
the decisions?
Yes, look at the "[329]-accept command" option, it allows you to
specify an external command that is run for each new client. (use
quotes around the command if it contains spaces, etc.). If the
external command returns 0 the client is accepted, otherwise the
client is rejected. See below how to also accept clients view-only.
The external command will have the RFB_CLIENT_IP environment variable
set to the client's numerical IP address, RFB_CLIENT_PORT its port
number. Similarly for RFB_SERVER_IP and RFB_SERVER_PORT to allow
identification of the tcp virtual circuit. DISPLAY will be set to that
of the X11 display being polled. Also, RFB_X11VNC_PID is set to the
x11vnc process id (e.g. in case you decided to kill it), RFB_CLIENT_ID
will be an id number, and RFB_CLIENT_COUNT the number of other clients
currently connected. RFB_MODE will be "accept".
As a special case, "-accept popup" will instruct x11vnc to create its
own simple popup window. To accept the client press "y" or click mouse
on the "Yes" button. To reject the client press "n" or click mouse on
the "No" button. To accept the client View-only, press "v" or click
mouse on the "View" button. If the [330]-viewonly option has been
supplied, the "View" action will not be present: the whole display is
view only in that case.
The popup window times out after 120 seconds, to change this behavior
use "-accept popup:N" where N is the number of seconds (use 0 for no
timeout). More tricks: "-accept popupmouse" will only take mouse click
responses, while "-accept popupkey" will only take keystroke responses
(popup takes both). After any of the 3 popup keywords you can supply a
position of the window: +N+M, (the default is to center the window)
e.g. -accept popupmouse+10+10.
Also as a special case "-accept xmessage" will run the xmessage(1)
program to prompt the user whether the client should be accepted or
not. This requires that you have xmessage installed and available via
PATH. In case it is not already on your system, the xmessage program
is available at [331]ftp://ftp.x.org/
To include view-only decisions for the external commands, prefix the
command something like this: "yes:0,no:*,view:3 mycommand ..." This
associates the three actions: yes(accept), no(reject), and
view(accept-view-only), with the numerical return codes. Use "*"
instead of a number to set the default action (e.g. in case the
external command returns an unexpected return code).
Here is an example -accept script called accept_or_lock. It uses
xmessage and xlock (replace with your screen lock command, maybe it is
"xscreensaver-command -lock", or kdesktop_lock, or "dtaction
LockDisplay"). It will prompt the user at the X display whether to
accept, reject, or accept view-only the client, but if the prompt
times out after 60 seconds the screen is locked and the VNC client is
accepted. This allows the remote access when no one is at the display.
#!/bin/sh
#
# accept_or_lock: prompt user at X display whether to accept an incoming
# VNC connection. If timeout expires, screen is locked
# and the VNC viewer is accepted (allows remote access
# when no one is sitting at the display).
#
# usage: x11vnc ... -forever -accept 'yes:0,no:*,view:4 accept_or_lock'
#
xmessage -buttons yes:2,no:3,view-only:4 -center \
-timeout 60 "x11vnc: accept connection from $RFB_CLIENT_IP?"
rc=$?
if [ $rc = 0 ]; then
xlock &
sleep 5
exit 0
elif [ $rc = 2 ]; then
exit 0
elif [ $rc = 4 ]; then
exit 4
fi
exit 1
Stefan Radman has written a nice dtksh script [332]dtVncPopup for use
in CDE environments to do the same sort of thing. Information on how
to use it is found at the top of the file. He encourages you to
provide feedback to him to help improve the script.
Note that in all cases x11vnc will block while the external command or
popup is being run, so attached clients will not receive screen
updates, etc during this period.
To run a command when a client disconnects, use the "[333]-gone
command" option. This is for the user's convenience only: the return
code of the command is not interpreted by x11vnc. The same environment
variables are set as in "-accept command" (except that RFB_MODE will
be "gone").
As of Jan/2006 the "[334]-afteraccept command" option will run the
command only after the VNC client has been accepted and authenticated.
Like -gone the return code is not interprted. RFB_MODE will be
"afteraccept").
Q-37: I start x11vnc as root because it is launched via inetd(8) or a
display manager like gdm(1). Can I have x11vnc later switch to a
different user?
As of Feb/2005 x11vnc has the [335]-users option that allows things
like this. Please read the documentation on it (also in the x11vnc
-help output) carefully for features and caveats. It's use can often
decrease security unless care is taken.
BTW, a nice use of it is "-users +nobody" that switches to the Unix
user nobody right after connections to the X display are established.
In any event, while running x11vnc as root, remember it comes with no
warranty ;-).
Q-38: I use a screen-lock when I leave my workstation (e.g.
xscreensaver or xlock). When I remotely access my workstation desktop
via x11vnc I can unlock the desktop fine, but I am worried people will
see my activities on the physical monitor. What can I do to prevent
this, or at least make it more difficult?
Probably most work environments would respect your privacy if you
powered off the monitor. Also remember if people have physical access
to your workstation they basically can do anything they want with it
(e.g. install a backdoor for later use, etc).
In any event, as of Jun/2004 there is an experimental utility to make
it more difficult for nosey people to see your x11vnc activities. The
source for it is [336]blockdpy.c The idea behind it is simple (but
obviously not bulletproof): when a VNC client attaches to x11vnc put
the display monitor in the DPMS "off" state, if the DPMS state ever
changes immediately start up the screen-lock program. The x11vnc user
will notice something is happening and think about what to do next
(while the screen is in a locked state).
This works (or at least has a chance of working) because if the
intruder moves the mouse or presses a key on the keyboard, the monitor
wakes up out of the DPMS off state, and this induces the screen lock
program to activate as soon as possible. Of course there are cracks in
this, the eavesdropper could detach your monitor and insert a non-DPMS
one, and there are race conditions. As mentioned above this is not
bulletproof. A really robust solution would likely require X server
and perhaps even video hardware support.
The blockdpy utility is launched by the [337]-accept option and told
to exit via the [338]-gone option (the vnc client user should
obviously re-lock the screen before disconnecting!). Instructions can
be found in the source code for the utility at the above link.
Q-39: Can I have x11vnc automatically lock the screen when I
disconnect the VNC viewer?
Yes, a user mentions he uses the [339]-gone option under CDE to run a
screen lock program:
x11vnc -display :0 -forever -gone 'dtaction LockDisplay'
Other possibilities are:
x11vnc -display :0 -forever -gone 'xscreensaver-command -lock'
x11vnc -display :0 -forever -gone 'kdesktop_lock'
x11vnc -display :0 -forever -gone 'xlock &'
Here is a scheme using the [340]-afteraccept option (in version 0.7.3)
to unlock the screen after the first valid VNC login and to lock the
screen after the last valid VNC login disconnects:
x11vnc -display :0 -forever -shared -afteraccept ./myxlocker -gone ./myxlocke
r
Where the script ./myxlocker is:
#!/bin/sh
#/usr/bin/env | grep RFB_ | sort # for viewing RFB_* settings.
if [ "X$RFB_MODE" = "Xafteraccept" ]; then
if [ "X$RFB_STATE" = "XNORMAL" ]; then # require valid login
if [ "X$RFB_CLIENT_COUNT" = "X1" ]; then
killall xlock # Linux only.
fi
fi
elif [ "X$RFB_MODE" = "Xgone" ]; then
if [ "X$RFB_STATE" = "XNORMAL" ]; then # require valid login
if [ "X$RFB_CLIENT_COUNT" = "X0" ]; then
xlock -mode blank &
fi
fi
fi
[Encrypted Connections]
Q-40: How can I tunnel my connection to x11vnc via an encrypted SSH
channel between two Unix machines?
See the description earlier on this page on [341]how to tunnel VNC via
SSH from Unix to Unix. A number of ways are described along with some
issues you may encounter.
Other secure encrypted methods exists, e.g. stunnel, IPSEC, various
VPNs, etc.
Q-41: How can I tunnel my connection to x11vnc via an encrypted SSH
channel from Windows using an SSH client like Putty?
[342]Above we described how to tunnel VNC via SSH from Unix to Unix,
you may want to review it. To do this from Windows using Putty it
would go something like this:
* In the Putty dialog window under 'Session' enter the hostname or
IP number of the Unix machine with display to be viewed.
* Make sure the SSH protocol is selected and the server port is
correct.
* Under 'Connections/SSH/Tunnels' Add a Local connection with
'Source port: 5900' and 'Destination: localhost:5900'
* Log into the remote machine by pressing 'Open' and supplying
username, password, etc.
* In that SSH shell, start up x11vnc by typing the command: x11vnc
-display :0 plus any other desired options (e.g. -localhost).
* Finally, start up your VNC Viewer in Windows and enter
'localhost:0' as the VNC server.
You can keep all of the settings in a Putty 'Saved Session'. Also,
once everything is working, you can consider putting x11vnc -display
:0 (plus other cmdline options) in the 'Remote command' Putty setting
under 'Connections/SSH'. It is likely possible to script the whole
process in a BAT file including launching the VNC viewer by using the
plink Putty utility. Send us the script if you get that working.
For extra protection feel free to run x11vnc with the [343]-localhost
and [344]-rfbauth/[345]-passwdfile options.
If the machine you SSH into via Putty is not the same machine with the
X display you wish to view (e.g. your company provides incoming SSH
access to a gateway machine), then you need to change the above Putty
dialog setting to: 'Destination: otherhost:5900', Once logged in,
you'll need to do a second login (ssh or rsh) to the workstation
machine 'otherhost' and then start up x11vnc on it. This can also be
automated by [346]chaining ssh's.
As discussed [347]above another option is to first start the VNC
viewer in "listen" mode, and then launch x11vnc with the
"[348]-connect localhost" option to establish the reverse connection.
In this case a Remote port redirection (not Local) is needed for port
5500 instead of 5900 (i.e. 'Source port: 5500' and
'Destination: localhost:5500' for a Remote connection).
Q-42: How can I tunnel my connection to x11vnc via an encrypted SSL
channel using an external tool like stunnel?
It is possible to use a "lighter weight" encryption setup than SSH or
IPSEC. SSL tunnels such as [349]stunnel provide an encrypted channel
without the need for Unix users, passwords, and key passphrases
required for ssh (and at the other extreme SSL can also provide a
complete signed certificate chain of trust). OTOH, since SSH is
usually installed everywhere and firewalls often let its port through,
ssh is frequently the path of least resistance (it also nicely manages
public keys for you).
Update: As of Feb/2006 x11vnc has the options [350]-ssl,
[351]-stunnel, and [352]-sslverify to provide integrated SSL schemes.
They are discussed [353]in the Next FAQ (you may want to skip to it
now).
Here are some basic examples using [354]stunnel but the general idea
for any SSL tunnel utility is the same:
* Start up x11vnc and constrain it to listen on localhost.
* Then start up the SSL tunnel running on the same machine to
forward incoming connections to that x11vnc.
* Set up and run a similar SSL tunnel for the outgoing connection on
the VNC viewer machine pointing it to the SSL/x11vnc server.
* Optionally, set up server (or even client) public/private keys for
use in authenticating one side to the other.
* Finally, start the VNC Viewer and tell it to connect to the local
port (e.g. a vnc display localhost:0) where its outgoing SSL
tunnel is listening.
We'll first use the stunnel version 3 syntax since it is the most
concise and Unixy.
Start up x11vnc listening on port 5900:
x11vnc -display :0 -rfbport 5900 -localhost -bg -passwdfile ~/mypass
Then start stunnel (version 3) with this command:
stunnel -d 5901 -r 5900 -p /path/to/stunnel.pem
The above two commands are run on host "far-away.east". The
stunnel.pem is the self-signed PEM file certificate created when
stunnel is built. One can also create certificates [355]signed by
Certificate Authorities or self-signed if desired using the x11vnc
utilities described there.
Next, on the VNC viewer side we need an SSL tunnel to encrypt the
outgoing connection. The nice thing is any SSL tunnel can be used
because the protocol is a standard. For this example we'll also use
stunnel on the viewer side on Unix. First start up the client-side
stunnel:
stunnel -c -d localhost:5902 -r far-away.east:5901
Then point the viewer to the local tunnel on port 5902:
vncviewer -encodings "copyrect tight zrle hextile" localhost:2
That's it. (note that the [356]ssl_vncviewer script can automate
this.)
Be sure to use a VNC password because unlike ssh by default the
encrypted SSL channel provides no authentication (only privacy). With
some extra configuration one could also set up certificates to provide
authentication of either or both sides as well (and hence avoid
man-in-the-middle attacks). See the stunnel and openssl documentation
and also [357]the key management section for details.
stunnel has also been ported to Windows, and there are likely others
to choose from for that OS. Much info for using it on Windows can be
found at the stunnel site and in this [358]article The article also
shows the detailed steps to set up all the authentication
certificates. (for both server and clients, see also the [359]x11vnc
utilities that do this). The default Windows client setup (no certs)
is simpler and only 4 files are needed in a folder: stunnel.exe,
stunnel.conf, libssl32.dll, libeay32.dll. We used an stunnel.conf
containing:
# stunnel.conf:
client = yes
options = ALL
[myvncssl]
accept = 5902
connect = far-away.east:5901
then double click on the stunnel.exe icon to launch it (followed by
pointing the VNC viewer to localhost:2).
stunnel inetd-like mode:
As an aside, if you don't like the little "gap" of unencrypted TCP
traffic (and a localhost listening socket) on the local machine
between stunnel and x11vnc it can actually be closed by having stunnel
start up x11vnc in [360]-inetd mode:
stunnel -p /path/to/stunnel.pem -P none -d 5900 -l ./x11vnc_sh
Where the script x11vnc_sh starts up x11vnc:
#!/bin/sh
x11vnc -q -inetd -display :0 -passwdfile ~/mypass
Note that this creates a separate x11vnc process for each incoming
connection (as any inetd x11vnc usage would), but for the case of
normally just one viewer at a time it should not be a big problem.
stunnel 4 syntax:
Somewhat sadly, the stunnel version 4 syntax is not so amenable to the
command line or scripts. You need to create a config file with the
parameters. E.g.:
stunnel x11vnc.cfg
Where the file x11vnc.cfg contains:
foreground = yes
pid =
cert = /path/to/stunnel.pem
[x11vnc_stunnel]
accept = 5901
connect = 5900
One nice thing about version 4 is often the PEM file does not need to
be specified because stunnel finds it in its installed area. One other
gotcha the PEM file is usually only readable by root (it has the
private key afterall), so you'll need to relax the permissions or make
a copy that the user running x11vnc/stunnel can read.
SSL VNC Viewers:
Regarding VNC viewers that "natively" do SSL unfortunately there do
not seem to be many. UltraVNC has an encryption plugin, but we have
not tried it (it does not seem to be SSL). Commercial versions of VNC
seem to have some SSL built in, but we haven't tried those either and
they probably wouldn't work since the SSL negotiation is likely
embedded in the VNC protocol unlike our case where it is external.
Note: as of Mar/2006 libvncserver/x11vnc provides a [361]SSL-enabled
Java applet that can be served up via the [362]-httpdir or [363]-http
options when [364]-ssl is enabled. It will also be served via HTTPS
via either the VNC port (e.g. https://host:5900/) or a 2nd port via
the [365]-https option.
In general current SSL VNC solutions are not particularly "seemless".
But it can be done, and with a wrapper script on the viewer side and
the [366]-stunnel or [367]-ssl option on the server side it works well
and is convenient. Here is a simple script [368]ssl_vncviewer that
automates running stunnel on the VNC viewer side on Unix a little more
carefully than the commands printed above. (One could probably do a
similar thing with a .BAT file on Windows in the stunnel folder.)
Q-43: Does x11vnc have built-in SSL tunneling?
You can read about non-built-in methods [369]in the Previous FAQ
SSL tunnels provide an encrypted channel without the need for Unix
users, passwords, and key passphrases required for ssh (and at the
other extreme SSL can also provide a complete signed certificate chain
of trust). OTOH, since SSH is usually installed everywhere and
firewalls often let its port through, ssh is frequently the path of
least resistance.
Built-in SSL x11vnc options:
As of Feb/2006 the x11vnc [370]-ssl and [371]-stunnel options automate
the SSL tunnel creation on the x11vnc server side. An [372]SSL-enabled
Java Viewer applet is also provided that can be served via HTTP or
HTTPS to automate SSL on the client side.
The [373]-ssl mode uses the [374]www.openssl.org library if available
at build time. The [375]-stunnel mode requires the
[376]www.stunnel.org command stunnel(8) to be installed on the system.
Both modes require an SSL certificate and key (i.e. .pem file). These
are usually created via the openssl(1) (in fact in for options "-ssl"
or "-stunnel SAVE" it will run openssl for you automatically). So the
SSL is not completely "built-in" since these external tools need to be
installed, but at least x11vnc runs them for you automatically.
An -stunnel example:
x11vnc -display :0 -stunnel /path/to/stunnel.pem -passwdfile ~/mypass
You'll get output like this:
The VNC desktop is: localhost:50
The SSL VNC desktop is: far-away.east:0
PORT=5950
SSLPORT=5900
That indicates stunnel is listening on port 5900 for incoming
SSL-wrapped VNC connections from viewers. x11vnc is listening for
local connections on port 5950 in this case (remote viewers cannot
connect to it directly). For -stunnel to work the stunnel command must
be installed on the machine and available in PATH (note stunnel is
often installed in sbin directories rather than bin).
An -ssl example:
x11vnc -display :0 -ssl -passwdfile ~/mypass
You'll get output like this:
09/04/2006 19:27:35 Creating a temporary, self-signed PEM certificate...
09/04/2006 19:27:35
...
The SSL VNC desktop is: far-away.east:0
PORT=5900
SSLPORT=5900
In this case openssl(1) was used to create a temporary PEM
automatically.
As seen above, the PEM (privacy enhanced mail) file does not need to
be supplied if the openssl(1) command is available in PATH, in that
case a self-signed, temporary certificate good only for the single
x11vnc session is created (this may take a while on very slow
machines).
In general, the PEM file contains both the Certificate (i.e. public
key) and the Private Key. Because of the latter, the file should be
protected from being read by untrusted users. The best way to do this
is to encrypt the key with a passphrase (note however this requires
supplying the passphrase each time x11vnc is started up).
See the discussion on [377]x11vnc Key Management for some utilities
provided for creating and managing certificates and keys and even for
creating your own Certificate Authority (CA) for signing VNC server
and client certificates. This may be done by importing the certificate
into Web Browser or Java plugin keystores, or pointing stunnel to it.
The wrapper script [378]ssl_vncviewer provides an example on unix
(-verify option).
Here are some notes on the simpler default (non-CA) operation. To have
x11vnc save the generated certificate and key, use the "SAVE" keyword
like this:
x11vnc -ssl SAVE -display :0 ...
x11vnc -stunnel SAVE -display :0 ...
This way it will be saved in the default directory ~/.vnc/certs/ as
server.crt (the certificate only) and server.pem (both certificate and
private key). This opens up the possibility of copying the server.crt
to machines where the VNC Viewer will be run to enable authenticating
the x11vnc SSL VNC server to the clients. When authentication takes
place this way (or via the more sophisticated CA signing described
[379]here), then Man-In-The-Middle-Attacks are prevented. Otherwise,
the SSL encryption only provides protection against passive network
traffic "sniffing". Nowadays, most people seem mostly concerned about
only the latter (and the default x11vnc SSL modes protect against it.)
One can test to some degree that SSL is working after starting x11vnc
with the -stunnel or -ssl option. From another machine one can use the
openssl command something like this:
openssl s_client -debug -msg -showcerts -connect far-away.east:5900
After all of the debugging output and informational messages you'll
see the string "RFB 003.007" that came from x11vnc. Pointing a web
browser connecting to: https://far-away.east:5900/ and then viewing
the SSL certificate information about the connection in the panels
will also work.
Note: If you serve up the SSL enabled Java VNC Viewer via something
like:
x11vnc -ssl -httpdir /usr/local/share/x11vnc/classes/ssl
(or just the -http option), you can test it out completely using that,
including using https to download it into the browser and connect to
x11vnc.
See the [380]next FAQ for SSL enabled VNC Viewers.
Q-44: How do I use VNC Viewers with built-in SSL tunneling?
Notes on the SSL enabled Java VNC Viewer provided in
classes/ssl/VncViewer.jar:
The SSL enabled Java VNC Viewer (VncViewer.jar) in the x11vnc package
supports only SSL based connections by default (set the applet
parameter disableSSL=yes in index.vnc to override). As mentioned above
the [381]-httpdir can be used to specify the path to .../classes/ssl.
A typical location might be /usr/local/share/x11vnc/classes/ssl. Or
[382]-http can be used to try to have it find the directory
automatically.
The Java viewer uses SSL to communicate securely with x11vnc. Note
that the applet can optionally also be downloaded into your web
browser via HTTPS (i.e. HTTP over SSL). This way the HTML page and the
Java applet itself are delivered securely (as opposed to only the VNC
traffic being encrypted).
For this case the output will be something like this:
x11vnc -ssl -http
...
The SSL VNC desktop is: far-away.east:0
Java SSL viewer URL: https://far-away.east:5900/
Java SSL viewer URL: http://far-away.east:5800/
PORT=5900
SSLPORT=5900
Indicating the two URLs (the first one encrypted, the second not) one
could point the web browser at to get the VNC viewer applet.
The https service provided thru the actual VNC port (5900 in the above
example) can occasionally be slow or unreliable (it has to read some
input and try to guess if the connection is VNC or HTTP). If it is
unreliable and you still want to serve the Java applet via https, use
the [383]-https option to get an additional port dedicated to https
(its URL will also be printed in the output).
Another possibility is to add the GET applet parameter:
https://far-away.east:5900/?GET=1
This will have the VNC Viewer send a special HTTP GET string "GET
/request.https.vnc.connection HTTP/1.0 that x11vnc will more quickly
notice is a request for a VNC connection. Otherwise it must wait for a
timeout to expire before it assumes a VNC connection.
You may also use "?GET=somestring" to have /somestring prepended to
/request.https.vnc.connection". Perhaps you are using a web server
[384]proxy scheme to enter a firewall or otherwise have rules applied
to the URL. If you need to have any slashes "/" in "somestring" use
"_2F_" (a deficiency in libvncserver prevents using the more natural
"%2F".)
If you do serve the SSL enabled Java viewer via https be prepared for
quite a number of "are you sure you trust this site?" dialogs:
* First from the Web browser that cannot verify the self-signed
certificate when it downloads index.vnc.
* From the Web browser noting that the common name on the
certificate does not match the hostname of the remote machine.
* Next from the Java VM that cannot verify the self-signed
certificate when it downloads VncViewer.jar.
* And also from the Java VM noting that the common name on the
certificate does not match the hostname of the remote machine.
* Finally from the Java VncViewer applet itself saying it cannot
verify the certificate! (or a popup asking you if you want to see
the certificate.)
Note that sometimes if you pause too long at one of the above dialogs
then x11vnc may exceed a timeout and assume the current socket
connection is VNC instead of the HTTPS it actually is (but since you
have paused too long at the dialog the GET request comes too late).
Often hitting Reload and going through the dialogs more quickly will
let you connect. Use the [385]-https option if you want a dedicated
port for HTTPS connections instead of sharing the VNC port.
Notes on the VNC Viewer ssl_vncviewer wrapper script:
If you want to use a native VNC Viewer with the SSL enabled x11vnc you
will need to run an external SSL tunnel on the Viewer side. There do
not seem to be any native SSL VNC Viewers outside of the x11vnc
package. The basic ideas of doing this were discussed [386]for
external tunnel utilities here.
The [387]ssl_vncviewer script provided with x11vnc can set up the
stunnel tunnel automatically on unix as long as the stunnel command is
installed on the Viewer machine and available in PATH (and vncviewer
too of course). Note that on Debian based system you will need to
install the package stunnel4 not stunnel. You can set the environment
variables STUNNEL and VNCVIEWERCMD to point to the correct programs if
you want to override the defaults.
Here are some examples:
1) ssl_vncviewer far-away.east:0
2) ssl_vncviewer far-away.east:0 -encodings "copyrect tight zrle hextile"
3) ssl_vncviewer -verify ./server.crt far-away.east:0
4) ssl_vncviewer -mycert ./client.pem far-away.east:0
5) ssl_vncviewer -proxy far-away.east:8080 myworkstation:0
The first one is the default mode and accepts the x11vnc certificate
without question. The second one is as the first, but adds the
-encodings options to the vncviewer command line.
The third one requires that the x11vnc server authenticate itself
against the certificate in the file ./server.crt (e.g. one created by
"x11vnc -ssl SAVE" and safely copied to the VNC viewer machine). The
fourth one is for VNC Viewer authentication, it uses ./client.pem to
authenticate itself to x11vnc. One can supply both -verify and -mycert
simultaneously.
The fifth one shows that Web proxies can be used if that is the only
way to get out of the firewall. If the "double proxy" situation arises
separate the two by commas. See [388]this page for more information on
how Web proxies come into play.
If one uses a Certificate Authority (CA) scheme described [389]here,
the wrapper script would use the CA cert instead of the server cert:
3') ssl_vncviewer -verify ./cacert.crt far-away.east:0
Q-45: How do I use VNC Viewers with built-in SSL tunneling when going
through a Web Proxy?
The SSL enabled Java VNC Viewer and firewall Proxies:
SSL/https aside, there is a general problem with Firewall Proxies and
Java Applets that open sockets. The applet is downloaded successfully
(through the browser) using http and the proxy, but when the applet
tries to reconnect to the originating host (the only one allowed by
security) it does not use the proxy channel. So it cannot reconnect to
the server the applet came from!
We have found a convenient workaround: in the directory where
VncViewer.jar resides there is a digitally signed version of the same
applet called SignedVncViewer.jar. Since the applet is digitally
signed, there will be an additional dialog from the Java VM plugin
asking you if you want to trust the applet fully.
You should say "Yes". If you do, the applet will be run in a mode
where it can try to determine the firewall proxy host name and port
(it will ask you for them if it cannot find them). This way it can
connect directly to the Proxy and then request the CONNECT method to
be redirected to the originating host (the x11vnc VNC Server). SSL is
then layered over this socket.
To do this you should use the proxy.vnc HTML file like via this URL in
your browser:
https://yourmachine.com:5900/proxy.vnc
(instead of the unsigned one in https://yourmachine.com:5900/ that
gives the default index.vnc)
Note that the [390]ssl_vncviewer stunnel wrapper script can use Web
proxies as well.
Proxies that limit CONNECT to ports 443 and 563:
Things become trickier if the proxy restricts which CONNECT ports can
be redirected to. For security, some (most?) proxies only allow port
443 (HTTPS) and 563 (SNEWS) by default. In this case, the only thing
to do is run x11vnc on that low port, e.g. "-rfbport 443", (or use a
port redirection on, say, a firewall or router port 443 to the
internal machine).
If you do such a redirection to an internal machine and x11vnc is not
listening on port 443, you will probably need to edit proxy.vnc.
Suppose the SSL x11vnc server was listening on port 5901. You should
change the line in proxy.vnc from:
<param name=PORT value=$PORT>
to:
<param name=PORT value=443>
Since otherwise $PORT will be expanded to 5901 by x11vnc and the
viewer applet will fail to connect to that port.
Another way to acheive the same thing is to use the applet PORT
parameter:
https://yourmachine.com/proxy.vnc?PORT=443
this is cleaner because it avoids editing the file, but requires more
parameters in the URL. To use the GET [391]trick discussed above, do:
https://yourmachine.com/proxy.vnc?PORT=443&GET=1
Q-46: Can Apache web server act as a gateway for users to connect via
SSL from the Internet with a Web browser to x11vnc running on their
workstations behind a firewall?
Yes. You will need to configure apache to forward these connections.
It is discussed [392]here. This provides a clean alternative to the
traditional method where the user uses SSH to log in through the
gateway to create the encrypted port redirection to x11vnc running on
her desktop.
Q-47: Can I create and use my own SSL Certificate Authority (CA) with
x11vnc?
Yes, see [393]this page for how to do this and the utility commands
x11vnc provides to create and manage many types of certificates and
private keys.
[Display Managers and Services]
Q-48: How can I run x11vnc as a "service" that is always available?
There are a number of ways to do this. The primary thing you need to
decide is whether you want x11vnc to connect to the X session on the
machine 1) regardless of who (or if anyone) has the X session, or 2)
only if a certain user has the X session. Because X sessions are
protected by X permissions (MIT-MAGIC-COOKIE files XAUTHORITY and
$HOME/.Xauthority) the automatically started x11vnc will of course
need to have sufficient permissions to connect to the X display.
Here are some ideas:
* Use the description under "Continuously" in the [394]FAQ on x11vnc
and Display Managers
* Use the description in the [395]FAQ on x11vnc and inetd(8)
* Use the description in the [396]FAQ on Unix user logins and
inetd(8)
* Start x11vnc from your $HOME/.xsession (or $HOME/.xinitrc)
* Although less reliable, see the [397]x11vnc_loop rc.local hack
below.
The display manager scheme will not be specific to which user has the
X session unless a test is specifically put into the display startup
script (often named Xsetup). The inetd(8) scheme may or may not be
specific to which user has the X session (and it may not be able to do
all users via the XAUTHORITY permission issues).
The $HOME/.xsession scheme is obviously is specific to a particular
user. If you do not know what a $HOME/.xsession script is or how to
use one, perhaps your desktop has a "session startup commands"
configuration option. The command to be run in the .xsession or
.xinitrc file may look like this:
x11vnc -logfile $HOME/.x11vnc.log -rfbauth $HOME/.vnc/passwd -forever -bg
plus any other options you desire.
Q-49: How can I use x11vnc to connect to an X login screen like xdm,
GNOME gdm, KDE kdm, or CDE dtlogin? (i.e. nobody is logged into an X
session yet).
One time only. If the X login screen is running and you just want to
connect to it once (i.e. a one-shot):
It is usually possible to do this by just adjusting the XAUTHORITY
environment variable to point to the correct MIT-COOKIE auth file
while running x11vnc as root, e.g. for the gnome display manager, gdm:
x11vnc -auth /var/gdm/:0.Xauth -display :0
(the [398]-auth option sets the XAUTHORITY variable for you).
There will be a similar thing for xdm using however a different auth
directory path (perhaps something like
/var/lib/xdm/authdir/authfiles/A:0-XQvaJk for xdm or
/var/lib/kdm/A:0-crWk72 for kdm, where the random characters in
basename will vary a bit). Read your system docs to find out where the
display manager cookie files are kept.
Trick: sometimes ps(1) can reveal the X server process -auth argument
(e.g. "ps wwwwaux | grep auth").
You next connect to x11vnc with a VNC viewer, give your username and
password to the X login prompt to start your session.
Note: gdm seems to have an annoying setting that causes x11vnc (and
any other X clients) to be killed after the user logs in. Setting
KillInitClients=false in the [daemon] section of /etc/X11/gdm/gdm.conf
avoids this. Otherwise, just restart x11vnc and then reconnect your
viewer.
Note: For dtlogin in addition to the above sort of trick (BTW, the
auth file should be in /var/dt), you'll also need to add something
like Dtlogin*grabServer:False to the Xconfig file
(/etc/dt/config/Xconfig or /usr/dt/config/Xconfig on Solaris, see
[399]the example at the end of this FAQ). Then restart dtlogin, e.g.:
/etc/init.d/dtlogin stop; /etc/init.d/dtlogin start or reboot.
Continuously. Have x11vnc reattach each time the X server is
restarted (i.e. after each logout):
To make x11vnc always attached to the X server including the login
screen you will need to add a command to a display manager startup
script.
Please consider the security implications of this! Besides having the
VNC display for the X session always available, there are other
issues: .e.g. if you run the tkx11vnc gui (via say -gui or -gui tray),
then the gui controls (insecure) are available on the physical X
display before anyone has logged in (maybe doing "-gui
tray,geom=+4000+4000" is a good idea...)
The name of the display manager startup script file depends on desktop
used and seem to be:
GNOME /etc/X11/gdm/Init/Default (or Init/:0)
KDE /etc/kde*/kdm/Xsetup
XDM /etc/X11/xdm/Xsetup (or xdm/Xsetup_0)
CDE /etc/dt/config/Xsetup
although the exact location can depend on operating system and
distribution. See the documentation for your display manager: gdm(1),
kdm(1), xdm(1), dtlogin(1) for additional details. There may also be
display number specific scripts: e.g. Xsetup_0 vs. Xsetup, you need to
watch out for.
Note: The above gdm setting of KillInitClients=false in
/etc/X11/gdm/gdm.conf is needed here as well.
Note: The above Dtlogin*grabServer:False step will be needed for
dtlogin here as well.
In any event, the line you will add to the display manager script will
look something like:
/usr/local/bin/x11vnc -rfbauth /path/to/the/vnc/passwd -o /var/log/x11vnc.log
-forever -bg
where you should customize the exact command to your needs.
Happy, happy, joy, joy: Note that we do not need to specify -display
or -auth because happily they are already set for us in the DISPLAY
and XAUTHORITY environment variables for the Xsetup script!!!
You may also want to force the VNC port with something like "-rfbport
5900" to avoid autoselecting one if 5900 is already taken.
_________________________________________________________________
Fedora/gdm: Here is an example of what we did on a vanilla install of
Fedora-C3 (seems to use gdm by default). Add a line like this to
/etc/X11/gdm/Init/:0
/usr/local/bin/x11vnc -rfbauth /etc/x11vnc.passwd -forever -bg -o /var/log/x1
1vnc.log
And then add this line to /etc/X11/gdm/gdm.conf in the [daemon]
section:
KillInitClients=false
Then restart: /usr/sbin/gdm-restart (or reboot). The
KillInitClients=false setting is important: without it x11vnc will be
killed immediately after the user logs in. Here are [400]full details
on how to configure gdm
_________________________________________________________________
Solaris/dtlogin: Here is an example of what we did on a vanilla
install of Solaris:
Make the directory /etc/dt/config:
mkdir -p /etc/dt/config
Copy over the Xconfig file for customization:
cp /usr/dt/config/Xconfig /etc/dt/config/Xconfig
Edit /etc/dt/config/Xconfig and uncomment the line:
Dtlogin*grabServer: False
Next, copy over Xsetup for customization:
cp /usr/dt/config/Xsetup /etc/dt/config/Xsetup
Edit /etc/dt/config/Xsetup and at the bottom put a line like:
/usr/local/bin/x11vnc -forever -o /var/log/x11vnc.log -bg
(tweaked to your local setup and preferences, a password via -rfbauth,
etc. would be a very good idea).
Restart the X server and dtlogin:
/etc/init.d/dtlogin stop
/etc/init.d/dtlogin start
(or reboot or maybe just restart the X session).
_________________________________________________________________
KDM: One user running the kdm display manager reports putting this
line:
x11vnc -forever -rfbauth /home/xyz/.vnc/passwd -bg -o /var/log/x11vnc.log
in /etc/kde/kdm/Xsetup. After rebooting the system it all seemed to
work fine.
_________________________________________________________________
If you do not want to deal with any display manager startup scripts,
here is a kludgey script that can be run manually or out of a boot
file like rc.local: [401]x11vnc_loop It will need some local
customization before running. Because the XAUTHORITY auth file must be
guessed by this script, use of the display manager script method
described above is greatly preferred. There is also the [402]-loop
option that does something similar.
If the machine is a traditional Xterminal you may want to read
[403]this FAQ.
Q-50: Can I run x11vnc out of inetd(8)? How about xinetd(8)?
Yes, perhaps a line something like this in /etc/inetd.conf will do it
for you:
5900 stream tcp nowait root /usr/sbin/tcpd /usr/local/bin/x11vnc_sh
where the shell script /usr/local/bin/x11vnc_sh uses the [404]-inetd
option and looks something like (you'll need to customize to your
settings).
#!/bin/sh
/usr/local/bin/x11vnc -inetd -display :0 -auth /home/fred/.Xauthority \
-rfbauth /home/fred/.vnc/passwd -o /var/log/x11vnc_sh.log
Important: Note that you must redirect the standard error output to a
log file (e.g. -o logfile) or "2>/dev/null" for proper operation via
inetd (otherwise the standard error also goes to the VNC vncviewer,
and that confuses it greatly, causing it to abort). If you do not use
a wrapper script as above but rather call x11vnc directly in
/etc/inetd.conf and do not redirect stderr to a file, then you must
specify the -q (aka [405]-quiet) option: "/usr/local/bin/x11vnc -q
-inetd ...". When you supply both -q and -inet and no "-o logfile"
then stderr will automatically be closed (to prevent, e.g. library
stderr messages leaking out to the viewer). The recommended practice
is to use "-o logfile" to collect the output in a file or wrapper
script with "2>logfile" redirection because the errors and warnings
printed out are very useful in troubleshooting problems.
Note also the need to set XAUTHORITY via [406]-auth to point to the
MIT-COOKIE auth file to get permission to connect to the X display
(setting and exporting the XAUTHORITY variable accomplishes the same
thing). See the x11vnc_loop file in the previous question for more
ideas on what that auth file may be, etc. The scheme described in the
[407]FAQ on Unix user logins and inetd(8) works around the XAUTHORITY
issue nicely.
Note: On Solaris you cannot have the bare number 5900 in
/etc/inetd.conf, you'll need to replace it with a word like x11vnc an
then put something like "x11vnc 5900/tcp" in /etc/services.
Since the process runs as root, it might be a bad idea to have the
logfile in a world-writable area like /tmp if there are untrustworthy
users on the machine. Perhaps /var/log is a better place. Also, while
running x11vnc as root, remember it comes with no warranty ;-).
Be sure to look at your /etc/hosts.allow and /etc/hosts.deny settings
to limit the machines that can connect to this service (your
desktop!). For the above example with /etc/hosts.allow:
x11vnc_sh : 123.45.67.89
A really safe way to do things is to limit the above inetd to
localhost only (via /etc/hosts.allow) and use ssh to tunnel the
incoming connection. Using inetd for this prevents there being a tiny
window of opportunity between x11vnc starting up and your vncviewer
connecting to it. Always use a VNC password to further protect against
unwanted access.
For xinetd(8), one user reports he created the file
/etc/xinetd.d/x11vncservice containing the following:
# default: off
# description:
service x11vncservice
{
flags = REUSE NAMEINARGS
port = 5900
type = UNLISTED
socket_type = stream
protocol = tcp
wait = no
user = root
server = /usr/sbin/tcpd
server_args = /usr/local/bin/x11vnc_sh
disable = no
}
With the contents of /usr/local/bin/x11vnc_sh similar to the example
given above. One user reports this works with avoiding the wrapper
script:
service x11vncservice
{
port = 5900
type = UNLISTED
socket_type = stream
protocol = tcp
wait = no
user = root
server = /usr/local/bin/x11vnc
server_args = -inetd -q -display :0 -auth /var/gdm/:0.Xauth
disable = no
}
(or one can replace the -q with say "-o /var/log/x11vnc.log" to
capture a log)
Q-51: Can I have x11vnc allow a user to log in with her UNIX password
and then have it find her X display on that machine and connect to it?
The easiest way to do this is via [408]inetd(8) using the [409]-unixpw
and [410]-display WAIT options. The reason inetd(8) makes this easier
is that it starts a new x11vnc process for each new user connection.
Otherwise a wrapper would have to listen for connections and spawn new
x11vnc's (see [411]this example).
The [412]-display WAIT option makes x11vnc wait until a VNC viewer is
connected before attaching to the X display. Additionally it can be
used to run an external command that returns the DISPLAY and
XAUTHORITY data. So one could supply "-display
WAIT:cmd=/path/to/find_display" where the script find_display might
look something like:
#!/bin/sh
PATH=$PATH:/bin:/usr/bin:/usr/X11R6/bin:/usr/bin/X11:/usr/openwin/bin
export PATH
if [ "X$user" = "X" ]; then
user=$USER
fi
if [ "X$user" = "X" ]; then
user=$LOGNAME
fi
if [ "X$user" = "X" ]; then
echo ""
exit 1
fi
display=`who | grep "^${user}[ ][ ]*:[0-9]" | head -1 | awk '{print $2}'`
if [ "X$display" = "X" ]; then
display=`who | grep "^${user}[ ]" | awk '{print $NF}' | grep '(:[0-9]'
| sed -e 's/[()]//g' | head -1`
if [ "X$display" = "X" ]; then
echo ""
exit 1
fi
fi
echo "DISPLAY=$display"
xauth extract - "$display" 2>/dev/null
exit 0
A default script similar to the above is used under "-display
WAIT:cmd=FINDDISPLAY" (use "WAIT:cmd=FINDDISPLAY-print" to print it
out). The format for any such script is that it returns DISPLAY=:disp
as the first line and any remaining lines are either XAUTHORITY=file
or raw xauth data (the above example does the latter).
The [413]-unixpw option allows [414]UNIX password logins. Here are a
couple /etc/inetd.conf examples for this:
5900 stream tcp nowait nobody /usr/sbin/tcpd /usr/local/bin/x11vnc -inetd
-unixpw \
-display WAIT:cmd=FINDDISPLAY -o /var/log/x11vnc.log -ssl SAVE -ssldir /u
sr/local/certs
5900 stream tcp nowait root /usr/sbin/tcpd /usr/local/bin/x11vnc -inetd
-unixpw \
-display WAIT:cmd=FINDDISPLAY -o /var/log/x11vnc.log -ssl SAVE -users uni
xpw=
Note the very long lines have been split. An alternative is to use a
wrapper script, e.g. /usr/local/bin/x11vnc.sh that has all of the
options.
In the first one x11vnc is run as user "nobody" and stays user nobody
during the whole session. The permissions of the log files and certs
directory will need to be set up to allow "nobody" to use them.
In the second one x11vnc is run as root and switches to the user that
logs in due to the "[415]-users unixpw=" option.
Note that [416]SSL is required for this mode because otherwise the
unix password would be passed in clear text over the network. In
general -unixpw is not required for this sort of scheme, but it is
convenient because it determines exactly who the user is whose display
should be sought. Otherwise the find_display script would have to use
some method to work out DISPLAY, XAUTHORITY, etc.
Q-52: Can I have x11vnc restart itself after it terminates?
One could do this in a shell script, but now there is an option
[417]-loop that makes it easier. Of course when x11vnc restarts it
needs to have permissions to connect to the (potentially new) X
display. This mode could be useful if the X server restarts often. Use
e.g. "-loop5000" to sleep 5000 ms between restarts. Also "-loop2000,5"
to sleep 2000 ms and only restart 5 times.
Q-53: How do I make x11vnc work with the Java VNC viewer applet in a
web browser?
To have x11vnc serve up a Java VNC viewer applet to any web browsers
that connect to it, run x11vnc with this [418]option:
-httpdir /path/to/the/java/classes/dir
(this directory will contain the files index.vnc and, for example,
VncViewer.jar) Note that libvncserver contains the TightVNC Java
classes jar file for your convenience. (it is the file
classes/VncViewer.jar in the source tree).
You will see output something like this:
14/05/2004 11:13:56 Autoprobing selected port 5900
14/05/2004 11:13:56 Listening for HTTP connections on TCP port 5800
14/05/2004 11:13:56 URL http://walnut:5800
14/05/2004 11:13:56 screen setup finished.
14/05/2004 11:13:56 The VNC desktop is walnut:0
PORT=5900
then you can connect to that URL with any Java enabled browser. Feel
free to customize the default index.vnc file in the classes directory.
As of May/2005 the [419]-http option will try to guess where the Java
classes jar file is by looking in expected locations and ones relative
to the x11vnc binary.
Also note that if you wanted to, you could also start the Java viewer
entirely from the viewer-side by having the jar file there and using
either the java or appletviewer commands to run the program.
java -cp ./VncViewer.jar VncViewer HOST far-away.east PORT 5900
Q-54: Are reverse connections (i.e. the VNC server connecting to the
VNC viewer) using "vncviewer -listen" and vncconnect(1) supported?
As of Mar/2004 x11vnc supports reverse connections. On Unix one starts
the VNC viewer in listen mode: vncviewer -listen (see your
documentation for Windows, etc), and then starts up x11vnc with the
[420]-connect option. To connect immediately at x11vnc startup time
use the "-connect host:port" option (use commas for a list of hosts to
connect to). The ":port" is optional (default is 5500).
If a file is specified instead: -connect /path/to/some/file then that
file is checked periodically (about once a second) for new hosts to
connect to.
The [421]-remote control option (aka -R) can also be used to do this
during an active x11vnc session, e.g.:
x11vnc -display :0 -R connect:hostname.domain
Note that as of Mar/2006 x11vnc requires password authentication for
reverse connections as well as for forward ones (assuming password
auth has been enabled, e.g. via -rfbauth, -passwdfile, etc). Many VNC
servers do not require any password for reverse connections. To regain
the old behavior set: X11VNC_REVERSE_CONNECTION_NO_AUTH=1 before
starting x11vnc.
To use the vncconnect(1) program (from the core VNC package at
www.realvnc.com) specify the [422]-vncconnect option to x11vnc (Note:
as of Dec/2004 -vncconnect is now the default). vncconnect(1) must be
pointed to the same X11 DISPLAY as x11vnc (since it uses X properties
to communicate with x11vnc). If you do not have or do not want to get
the vncconnect(1) program, the following script (named "Vncconnect")
may work if your xprop(1) supports the -set option:
#!/bin/sh
# usage: Vncconnect <host>
# Vncconnect <host:port>
# note: not all xprop(1) support -set.
#
xprop -root -f VNC_CONNECT 8s -set VNC_CONNECT "$1"
Q-55: Can I use x11vnc as a replacement for Xvnc? (i.e. not for a real
display, but for a virtual one I keep around).
You can, but you would not be doing this for performance reasons (for
virtual X sessions via VNC, Xvnc will give the fastest response). You
may want to do this because Xvnc does not support an X server
extension you desire, or you want to take advantage of one of x11vnc's
unending number of options and features.
One way to acheive this is to have a Xvfb(1) virtual framebuffer X
server running in the background and have x11vnc attached to it.
Another method, faster and more accurate is to use the "dummy" Device
Driver in XFree86/Xorg (see below). One could view this desktop both
remotely and also locally using vncviewer. Make sure vncviewer's
"-encodings raw" is in effect for local viewing (compression seems to
slow things down locally). For local viewing you set up a "bare"
window manager that just starts up vncviewer and nothing else.
Here is one way to start up Xvfb:
xinit -- /usr/X11R6/bin/Xvfb :1 -screen 0 1024x768x16
This starts up a 16bpp virtual display. To export it via VNC use
"x11vnc -display :1 ...".
One good thing about Xvfb is that the virtual framebuffer exists in
main memory (rather than in the video hardware), and so x11vnc can
"screen scrape" it efficiently (more than, say, 100X faster than
normal video hardware).
There are some annoyances WRT Xvfb though. The default keyboard
mapping seems to be very poor. One should run x11vnc with
[423]-add_keysyms option to have keysyms added automatically. Also, to
add the Shift_R and Control_R modifiers something like this is needed:
#!/bin/sh
xmodmap -e "keycode any = Shift_R"
xmodmap -e "add Shift = Shift_L Shift_R"
xmodmap -e "keycode any = Control_R"
xmodmap -e "add Control = Control_L Control_R"
Perhaps the Xvfb options -xkbdb or -xkbmap could be used to get a
better default keyboard mapping.
A user points out a faster and more accurate method is to use the
"dummy" Device Driver of XFree86/Xorg instead of Xvfb. He uses this to
create a persistent and resizable desktop accessible from anywhere. In
the Device Section of the config file set Driver "dummy". You may also
need to set VideoRam NNN to be large enough to hold the framebuffer.
The framebuffer is kept in main memory like Xvfb except that the
server code is closely correlated with the real XFree86/Xorg Xserver
unlike Xvfb.
The main drawback to this method (besides requiring extra
configuration and possibly root permission) is that it also does the
Linux Virtual Console/Terminal (VC/VT) [424]switching even though it
does not need to (since it doesn't use a real framebuffer). There are
some "dual headed" (actually multi-headed/multi-user) patches to the X
server that turn off the VT usage in the X server. Update: As of
Jul/2005 we have an LD_PRELOAD script [425]Xdummy that allows you to
use a stock (i.e. unpatched) Xorg or XFree86 server with the "dummy"
driver and not have any VT switching problems! Currently Xdummy needs
to be run as root, but with some luck that may be relaxed in the
future.
The standard way to start the "dummy" driver would be:
startx -- :1 -config /etc/X11/xorg.conf.dummy
where the file /etc/X11/xorg.conf.dummy has its Device Section
modified as described above. To use the LD_PRELOAD wrapper script:
startx -- /path/to/Xdummy :1
An xdm(1) example is also provided.
In general, one can use these sorts of schemes to use x11vnc to export
other virtual X sessions, say Xnest or even Xvnc itself (useful for
testing x11vnc).
Q-56: How can I use x11vnc on "headless" machines? Why might I want
to?
An interesting application of x11vnc is to let it export displays of
"headless" machines. For example, you may have some lab or server
machines with no keyboard, mouse, or monitor, but each one still has a
video card. One can use x11vnc to provide a simple "desktop service"
from these server machines.
An X server can be started on the headless machine (sometimes this
requires configuring the X server to not fail if it cannot detect a
keyboard or mouse, see the next paragraph). Then you can export that X
display via x11vnc (e.g. see [426]this FAQ) and access it from
anywhere on the network via a VNC viewer.
Some tips on getting X servers to start on machines without keyboard
or mouse: For XFree86/Xorg the Option "AllowMouseOpenFail" "true"
"ServerFlags" config file option is useful. On Solaris Xsun the
+nkeyboard and +nmouse options are useful (put them in the server
command line args in /etc/dt/config/Xservers). See Xserver(1) for more
info.
Although this usage may sound strange it can be quite useful for a GUI
(or other) testing or QA setups: the engineers do not need to walk to
lab machines running different hardware, OS's, versions, etc (or have
many different machines in their office). They just connect to the
various test machines over the network via VNC. The advantage to
testing this way instead of using Xvnc or even Xvfb is that the test
is done using the real X server, fonts, video hardware, etc. that will
be used in the field.
One can imagine a single server machine crammed with as many video
cards as it can hold to provide multiple simultaneous access or
testing on different kinds of video hardware.
[Resource Usage and Performance]
Q-57: I have lots of memory, but why does x11vnc fail with shmget:
No space left on device or Minor opcode of failed request: 1
(X_ShmAttach)?
It is not a matter of free memory, but rather free shared memory (shm)
slots, also known as shm segments. This often occurs on a public
Solaris machine using the default of only 100 slots. You (or the owner
or root) can clean them out with ipcrm(1). x11vnc tries hard to
release its slots, but it, and other programs, are not always able to
(e.g. if kill -9'd).
Sometimes x11vnc will notice the problem with shm segments and tries
to get by with fewer, only giving a warning like this:
19/03/2004 10:10:58 shmat(tile_row) failed.
shmat: Too many open files
19/03/2004 10:10:58 error creating tile-row shm for len=4
19/03/2004 10:10:58 reverting to single_copytile mode
Here is a shell script [427]shm_clear to list and prompt for removal
of your unattached shm segments (attached ones are skipped). I use it
while debugging x11vnc (I use "shm_clear -y" to assume "yes" for each
prompt). If x11vnc is regularly not cleaning up its shm segments,
please contact me so we can work to improve the situation.
Longer term, on Solaris you can put something like this in
/etc/system:
set shmsys:shminfo_shmmax = 0x2000000
set shmsys:shminfo_shmmni = 0x1000
to sweep the problem under the rug (4096 slots). On Linux, examine
/proc/sys/kernel/shmmni; you can modify the value by writing to that
file.
Things are even more tight on Solaris 8 and earlier, there is a
default maximum number of shm segments per process of 6. The error is
the X server (not x11vnc) being unable to attach to the segments, and
looks something like this:
30/04/2004 14:04:26 Got connection from client 192.168.1.23
30/04/2004 14:04:26 other clients:
X Error of failed request: BadAccess (attempt to access private resource den
ied)
Major opcode of failed request: 131 (MIT-SHM)
Minor opcode of failed request: 1 (X_ShmAttach)
Serial number of failed request: 14
Current serial number in output stream: 17
This tight limit on Solaris 8 can be increased via:
set shmsys:shminfo_shmseg = 100
in /etc/system. See the next paragraph for more workarounds.
To minimize the number of shm segments used by x11vnc try using the
[428]-onetile option (corresponds to only 3 shm segments used, and
adding -fs 1.0 knocks it down to 2). If you are having much trouble
with shm segments, consider disabling shm completely via the
[429]-noshm option. Performance will be somewhat degraded but when
done over local machine sockets it should be acceptable (see an
[430]earlier question discussing -noshm).
Q-58: How can I make x11vnc use less system resources?
The [431]-nap (now on by default) and "[432]-wait n" (where n is the
sleep between polls in milliseconds, the default is 30 or so) option
are good places to start. Something like "[433]-sb 15" will cause
x11vnc to go into a deep-sleep mode after 15 seconds of no activity
(instead of the default 60).
Reducing the X server bits per pixel depth (e.g. to 16bpp or even
8bpp) will further decrease memory I/O and network I/O. The ShadowFB
will make x11vnc's screen polling less severe. Using the [434]-onetile
option will use less memory and use fewer shared memory slots (add
[435]-fs 1.0 for one less slot).
Q-59: How can I make x11vnc use MORE system resources?
You can try [436]-threads and dial down the wait time (e.g. -wait 1)
and possibly dial down [437]-defer as well. Note that if you try to
increase the "frame rate" too much you can bog down the server end
with the extra work it needs to do compressing the framebuffer data,
etc.
That said, it is possible to "stream" video via x11vnc if the video
window is small enough. E.g. a 256x192 xawtv TV capture window (using
the x11vnc [438]-id option) can be streamed over a LAN or wireless at
a reasonable frame rate.
Q-60: I use x11vnc over a slow link with high latency (e.g. dialup
modem), is there anything I can do to speed things up?
Some things you might want to experiment with (many of which will help
performance on faster links as well):
X server/session parameters:
* Configure the X server bits per pixel to be 16bpp or even 8bpp.
(reduces amount of data needed to be polled, compressed, and sent)
* Use a smaller desktop size (e.g. 1024x768 instead of 1280x1024)
* Make sure the desktop background is a solid color (the background
is resent every time it is re-exposed). Consider using the
[439]-solid [color] option to try to do this automatically.
* Configure your window manager or desktop "theme" to not use fancy
images, shading, and gradients for the window decorations, etc.
Disable window animations, etc. Maybe your desktop has a "low
bandwidth" theme you can easily switch into and out of. Also in
Firefox disable eye-candy, e.g.: Edit -> Preferences -> Advanced
-> Use Smooth Scrolling (deselect it).
* Avoid small scrolls of large windows using the Arrow keys or
scrollbar. Try to use PageUp/PageDown instead. (not so much of a
problem in x11vnc 0.7.2 if [440]-scrollcopyrect is active and
detecting scrolls for the application).
* If the [441]-wireframe option is not available (earlier than
x11vnc 0.7.2 or you have disabled it via -nowireframe) then
Disable Opaque Moves and Resizes in the window manager/desktop.
* However if -wireframe is active (on by default in x11vnc 0.7.2)
then you should Enable Opaque Moves and Resizes in the window
manager! This seems counter-intuitive, but because x11vnc detects
the move/resize events early there is a huge speedup over a slow
link when Opaque Moves and Resizes are enabled. (e.g. CopyRect
encoding will be used).
* Turn off Anti-aliased fonts on your system, web browser, terminal
windows, etc. AA fonts do not compress as well as traditional
fonts (sometimes 10X less).
* On XFree86 turn on the Shadow Framebuffer to speed up reading.
(Option "ShadowFB" "true" in the Device section of
/etc/X11/XF86Config) This disables 2D acceleration on the physical
display and so may not be worth it, but could be of use in some
situations. If the link is very slow, this speedup may not be
noticed.
VNC viewer parameters:
* Use a [442]TightVNC enabled viewer! (Actually, RealVNC 4.x viewer
with ZRLE encoding is not too bad either; some claim it is
faster).
* Make sure the tight (or zrle) encoding is being used (look at
vncviewer and x11vnc outputs)
* Request 8 bits per pixel using -bgr233 (up to 4X speedup over
depth 24 TrueColor (32bpp), but colors will be off)
* RealVNC 4.x viewer has some extremely low color modes (only 64 and
even 8 colors). The colors are poor, but it is usually noticeably
faster than bgr233 (256 colors).
* Try increasing the TightVNC -compresslevel (compresses more on
server side before sending, but uses more CPU)
* Try reducing the TightVNC -quality (increases JPEG compression,
but is lossy with painting artifacts)
* Try other VNC encodings via -encodings (tight may be the fastest,
but you should compare it to zrle and maybe some of the others)
* On the machine where vncviewer is run, make sure Backing Store is
enabled (XFree86/Xorg disables it by default causing re-exposures
of vncviewer to be very slow) Option "backingstore" in config
file.
x11vnc parameters:
* Make sure the [443]-wireframe option is active (it should be on by
default) and you have Opaque Moves/Resizes Enabled in the window
manager.
* Make sure the [444]-scrollcopyrect option is active (it should be
on by default). This detects scrolls in many (but not all)
applications an applies the CopyRect encoding for a big speedup.
* Enforce a solid background when VNC viewers are connected via
[445]-solid
* Specify [446]-speeds modem to force the wireframe and
scrollcopyrect heuristic parameters (and any future ones) to those
of a dialup modem connection (or supply the rd,bw,lat numerical
values that characterize your link).
* If wireframe and scrollcopyrect aren't working, try using the more
drastic [447]-nodragging (no screen updates when dragging mouse,
but sometimes you miss visual feedback)
* Set [448]-fs 1.0 (disables fullscreen updates)
* Try increasing [449]-wait or [450]-defer (reduces the maximum
"frame rate", but won't help much for large screen changes)
* Try the [451]-progressive pixelheight mode with the block
pixelheight 100 or so (delays sending vertical blocks since they
may change while viewer is receiving earlier ones)
* If you just want to watch one (simple) window use [452]-id (cuts
down extraneous polling and updates, but can be buggy or
insufficient)
* Set [453]-nosel (disables all clipboard selection exchange)
* Use [454]-nocursor and [455]-nocursorpos (repainting the remote
cursor position and shape takes resources and round trips)
* On very slow links (e.g. <= 28.8) you may need to increase the
[456]-readtimeout n setting if it sometimes takes more than 20sec
to paint the full screen, etc.
* Do not use [457]-fixscreen to automatically refresh the whole
screen, tap three Alt_L's then the screen has painting errors
(rare problem).
Q-61: Does x11vnc support the X DAMAGE Xserver extension to find
modified regions of the screen quickly and efficiently?
Yes, as of Mar/2005 x11vnc will use the X DAMAGE extension by default
if it is available on the display. This requires libXdamage to be
available in the build environment as well (recent Linux distros and
Solaris 10 have it).
The DAMAGE extension enables the X server to report changed regions of
the screen back to x11vnc. So x11vnc doesn't have to guess where the
changes are (by polling every pixel of the entire screen every 2-4
seconds). The use of X DAMAGE dramatically reduces the load when the
screen is not changing very much (i.e. most of the time). It also
noticeably improves updates, especially for very small changed areas
(e.g. clock ticking, cursor flashing, typing, etc).
Note that the DAMAGE extension does not speed up the actual reading of
pixels from the video card framebuffer memory, by, say, mirroring them
in main memory. So reading the fb is still painfully [458]slow (e.g.
5MB/sec), and so even using X DAMAGE when large changes occur on the
screen the bulk of the time is still spent retrieving them. Not ideal,
but use of the ShadowFB XFree86/Xorg option speeds up the reading
considerably (at the cost of h/w acceleration).
Unfortunately the current Xorg DAMAGE extension implementation can at
times be overly conservative and report very large rectangles as
"damaged" even though only a small portion of the pixels have actually
been modified. This behavior is often the fault of the window manager
(e.g. it redraws the entire, unseen, frame window underneath the
application window when it gains focus), or the application itself
(e.g. does large, unnecessary repaints).
To work around this deficiency, x11vnc currently only trusts small
DAMAGE rectangles to contain real damage. The larger rectangles are
only used as hints to focus the traditional scanline polling (i.e. if
a scanline doesn't intersect a recent DAMAGE rectangle, the scan is
skipped). You can use the "[459]-xd_area A" option to adjust the size
of the trusted DAMAGE rectangles. The default is 20000 pixels (e.g. a
140x140 square, etc). Use "-xd_area 0" to disable the cutoff and trust
all DAMAGE rectangles.
The option "[460]-xd_mem f" may also be of use in tuning the
algorithm. To disable using DAMAGE entirely use "[461]-noxdamage".
Q-62: When I drag windows around with the mouse or scroll up and down
things really bog down (unless I do the drag in a single, quick
motion). Is there anything to do to improve things?
This problem is primarily due to [462]slow hardware read rates from
video cards: as you scroll or move a large window around the screen
changes are much too rapid for x11vnc to keep up them (it can usually
only read the video card at about 5-10 MB/sec, so it can take a good
fraction of a second to read the changes induce from moving a large
window, if this to be done a number of times in succession the window
or scroll appears to "lurch" forward). See the description in the
[463]-pointer_mode option for more info. The next bottleneck is
compressing all of these changes and sending them out to connected
viewers, however the VNC protocol is pretty much self-adapting with
respect to that (updates are only packaged and sent when viewers ask
for them).
As of Jan/2004 there are some improvements to libvncserver. The
default should now be much better than before and dragging small
windows around should no longer be a huge pain. If for some reason
these changes make matters worse, you can go back to the old way via
the "[464]-pointer_mode 1" option.
Also added was the [465]-nodragging option that disables all screen
updates while dragging with the mouse (i.e. mouse motion with a button
held down). This gives the snappiest response, but might be undesired
in some circumstances when you want to see the visual feedback while
dragging (e.g. menu traversal or text selection).
As of Dec/2004 the [466]-pointer_mode n option was introduced. n=1 is
the original mode, n=2 an improvement, etc.. See the -pointer_mode n
help for more info.
Also, in some circumstances the [467]-threads option can improve
response considerably. Be forewarned that if more than one vncviewer
is connected at the same time then libvncserver may not be thread safe
(try to get the viewers to use different VNC encodings, e.g. tight and
ZRLE).
As of Apr/2005 two new options (see the [468]wireframe FAQ and
[469]scrollcopyrect FAQ below) provide schemes to sweep this problem
under the rug for window moves or resizes and for some (but not all)
window scrolls. These are the preferred way of avoiding the "lurching"
problem, contact me if they are not working. (Note on SuSE the RECORD
X extension used by scrollcopyrect is not enabled by default, turn it
on in xorg.conf)
Q-63: Why not do something like wireframe animations to avoid the
windows "lurching" when being moved or resized?
Nice idea for a hack! As of Apr/2005 x11vnc by default will apply
heuristics to try to guess if a window is being (opaquely) moved or
resized. If such a change is detected framebuffer polling and updates
will be suspended and only an animated "wireframe" (a rectangle
outline drawn where the moved/resized window would be) is shown. When
the window move/resize stops, it returns to normal processing: you
should only see the window appear in the new position. This spares you
from interacting with a "lurching" window between all of the
intermediate steps. BTW the lurching is due to [470]slow video card
read rates (see [471]here too). A displacement, even a small one, of a
large window requires a non-negligible amount of time, a good fraction
of a second, to read in from the hardware framebuffer.
Note that Opaque Moves/Resizes must be Enabled by your window manager
for -wireframe to do any good.
The mode is currently on by default because most people are afflicted
with the problem. It can be disabled with the [472]-nowireframe option
(aka -nowf). Why might one want to turn off the wireframing? Since
x11vnc is merely guessing when windows are being moved/resized, it may
guess poorly for your window-manager or desktop, or even for the way
you move the pointer. If your window-manager or desktop already does
its own wireframing then this mode is a waste of time and could do the
wrong thing occasionally. There may be other reasons the new mode
feels unnatural. If you have very expensive video hardware (SGI) or
are using an in-RAM video framebuffer (SunRay, ShadowFB, Xvfb), the
read rate from that framebuffer may be very fast (100's of MB/sec) and
so you don't really see much lurching: opaque moves look smooth in
x11vnc. Note: ShadowFB is often turned on when you are using the
vesafb or fbdev XFree86 video driver instead of a native one so you
might be using it already and not know.
The heuristics used to guess window motion or resizing are simple, but
are not fool proof: x11vnc is sometimes tricked and so you'll
occasionally see the lurching opaque move and rarely something even
worse.
First it assumes that the move/resize will occur with a mouse button
pressed, held down and dragged (of course this is only mostly true).
Next it will only consider a window for wireframing if the mouse
pointer is initially "close enough" to the edges of the window frame,
e.g. you have grabbed the title bar or a resizer edge (this
requirement can be disabled and it also not applied if a modifier key,
e.g. Alt, is pressed). If these are true, it will wait an amount of
time to see if the window starts moving or resizing. If it does, it
starts drawing the wireframe "outline" of where the window would be.
When the mouse button is released, or a timeout occurs, it goes back
to the standard mode to allow the actual framebuffer changes to
propagate to the viewers.
These parameters can be tweaked:
* Color/Shade of the wireframe.
* Linewidth of the outline frame.
* Cutoff size of windows to not apply wireframing to.
* Cutoffs for closeness to Top, Bottom, Left, and Right edges of
window.
* Modifier keys to enable interior window grabbing.
* Maximum time to wait for dragging pointer events.
* Maximum time to wait for the window to start moving/resizing.
* Maximum time to show a wireframe animation.
* Minimum time between sending wireframe outlines.
See the [473]"-wireframe tweaks" option for more details. On a slow
link, e.g. dialup modem, the parameters may be automatically adjusted
for better response.
CopyRect encoding: In addition to the above there is the
[474]"-wirecopyrect mode" option. It is also on by default. This
instructs x11vnc to not only show the wireframe animation, but to also
instruct all connected VNC viewers to locally translate the window
image data from the original position to the new position on the
screen when the animation is done. This speedup is the VNC CopyRect
encoding: the framebuffer update doesn't need to send the actual new
image data. This is nice in general, and very convenient over a slow
link, but since it is based on heuristics you may need to disable it
with the -nowirecopyrect option (aka -nowcr) if it works incorrectly
or unnaturally for you.
The -wirecopyrect modes are: "never" (same as -nowirecopyrect); "top",
only apply the CopyRect if the window is appears to be on the top of
the window stack and is not obstructed by other windows; and "always"
to always try to apply the CopyRect (obstructed regions are usually
clipped off and not translated).
Note that some desktops (KDE and xfce) appear to mess with the window
stacking in ways that are not yet clear. In these cases x11vnc works
around the problem by applying the CopyRect even if obscuring windows'
data is translated! Use -nowirecopyrect if this yields undesirable
effects for your desktop.
Also, the CopyRect encoding may give incorrect results under -scale
(depending on the scale factor the CopyRect operation is often only
approximate: the correctly scaled framebuffer will be slightly
different from the translated one). x11vnc will try to push a
"cleanup" update after the CopyRect if -scale is in effect. Use
-nowirecopyrect if this or other painting errors are unacceptable.
Q-64: Can x11vnc try to apply heuristics to detect when a window is
scrolling its contents and use the CopyRect encoding for a speedup?
Another nice idea for a hack! As of May/2005 x11vnc will by default
apply heuristics to try to detect if the window that has the input
focus is scrolling its contents (but only when x11vnc is feeding user
input, keystroke or pointer, to the X server). So, when detected,
scrolls induced by dragging on a scrollbar or by typing (e.g. Up or
Down arrows, hitting Return in a terminal window, etc), will show up
much more quickly than via the standard x11vnc screen polling update
mechanism.
There will be a speedup for both slow and fast links to viewers. For
slow links the speedup is mostly due to the CopyRect encoding not
requiring the image data to be transmitted over the network. For fast
links the speedup is primarily due to x11vnc not having to read the
scrolled framebuffer data from the X server (recall that reading from
the hardware framebuffer is [475]slow).
To do this x11vnc uses the RECORD X extension to snoop the X11
protocol between the X client with the focus window and the X server.
This extension is usually present on most X servers (but SuSE disables
it for some reason). On XFree86/Xorg it can be enabled via Load
"record" in the Module section of the config file if it isn't already.
Currently the RECORD extension is used as little as possible so as to
not slow down regular use. Only simple heuristics are applied to
detect XCopyArea and XConfigureWindow calls from the application.
These catch a lot of scrolls, e.g. in mozilla/firefox and in terminal
windows like gnome-terminal and xterm. Unfortunately the toolkits KDE
applications use make scroll detection less effective (only rarely are
they detected: i.e. Konqueror and Konsole don't work). An interesting
project, that may be the direction x11vnc takes, is to record all of
the X11 protocol from all clients and try to "tee" the stream into a
modified Xvfb watching for CopyRect and other VNC speedups. A
potential issue is the RECORD stream is delayed from actual view on
the X server display: if one falls too far behind it could become a
mess...
The initial implementation of [476]-scrollcopyrect option is useful in
that it detects many scrolls and thus gives a much nicer working
environment (especially when combined with the [477]-wireframe
[478]-wirecopyrect [479]options, which are also on by default; and if
you are willing to enable the ShadowFB things are very fast). The fact
that there aren't long delays or lurches during scrolling is the
primary improvement.
But there are some drawbacks:
* Not all scrolls are detected. Some apps scroll windows in ways
that cannot currently be detected, and other times x11vnc "misses"
the scroll due to timeouts, etc. Sometimes it is more distracting
that a speedup occasionally doesn't work as opposed to being
consistently slow!
* For rapid scrolling (i.e. sequence of many scrolls over a short
period) there can be painting errors (tearing, bunching up, etc.)
during the scroll. These will repair themselves after the scroll
is over, but when they are severe it can be distracting. Try to
think of the approximate window contents as a quicker and more
useful "animation" compared to the slower polling scheme...
* Scrolling inside shells in terminal windows (gnome-terminal,
xterm), can lead to odd painting errors. This is because x11vnc
did not have time to detect a screen change just before the scroll
(most common is the terminal undraws the block cursor before
scrolling the text up: in the viewer you temporarily see multiple
block cursors). Another issue is with things like more(1): scroll
detection for 5-6 lines happens nicely, but then it can't keep up
and so there is a long pause for the standard polling method to
deliver the remaining updates.
* More rarely sometimes painting errors are not repaired after the
scroll is over. This may be a bug in x11vnc or libvncserver, or it
may be an inescapable fact of the CopyRect encoding and the delay
between RECORD callbacks and what is actually on the X display.
One can tap the Alt_L key (Left "Alt" key) 3 times in a row to
signal x11vnc to refresh the screen to all viewers. Your
VNC-viewer may have its own screen refresh hot-key or button. See
also: [480]-fixscreen
* Some applications, notably OpenOffice, do XCopyArea scrolls in
weird ways that assume ancestor window clipping is taking place.
See the [481]-scr_skip option for ways to tweak this on a
per-application basis.
* Selecting text while dragging the mouse may be slower, especially
if the Button-down event happens near the window's edge. This is
because the scrollcopyrect scheme is watching for scrolls via
RECORD and has to wait for a timeout to occur before it does the
update.
* For reasons not yet understood the RECORD extension can stop
responding (and hence scrolls are missed). As a workaround x11vnc
attempts to reset the RECORD connection every 60 seconds or so.
Another workaround is to type 4 Super_L (Left Super/Windows-Flag
key) in a row to reset RECORD. Work is in progress to try to fix
this bug.
* Sometimes you need to "retrain" x11vnc for a certain window
because it fails to detect scrolls in it. Sometimes clicking
inside the application window or selecting some text in it to
force the focus helps.
* When using the [482]-scale option there will be a quick CopyRect
scroll, but it needs to be followed by a slower "cleanup" update.
This is because for a fixed finite screen resolution (e.g. 75 dpi)
scaling and copyrect-ing are not exactly independent. Scaling
involves a blending of nearby pixels and if you translate a pixel
the neighbor pixel weighting may be different. So you have to wait
a bit for the cleanup update to finish. On slow links x11vnc may
automatically decide to not detect scrolls when -scale is in
effect. In general it will also try to defer the cleanup update if
possible.
If you find the -scrollcopyrect behavior too approximate or
distracting you can go back to the standard polling-only update method
with the [483]-noscrollcopyrect (or -noscr for short). If you find
some extremely bad and repeatable behavior for -scrollcopyrect please
report a bug.
Alternatively, as with -wireframe, there are many tuning parameters to
try to improve the situation. You can also access these parameters
inside the gui under "Tuning". These parameters can be tweaked:
* The minimum pixel area of a rectangle to be watched for scrolls.
* A list if application names to skip scroll detection.
* Which keystrokes should trigger scroll detection.
* Which applications should have a "terminal" tweak applied to them.
* When repeating keys (e.g. Up arrow) should be discarded to
preserve a scroll.
* Cutoffs for closeness to Top, Bottom, Left, and Right edges of
window for mouse induced scrolls.
* Set timeout parameters for keystroke induced scrolls.
* Set timeout parameters for mouse pointer induced scrolls.
* Have the full screen be periodically refreshed to fix painting
errors.
[Mouse Cursor Shapes]
Q-65: Why isn't the mouse cursor shape (the little icon shape where
the mouse pointer is) correct as I move from window to window?
On X servers supporting XFIXES or Solaris/IRIX Overlay extensions it
is possible for x11vnc to do this correctly. See a few paragraphs down
for the answer.
Historically, the X11 mouse cursor shape (i.e. little picture: an
arrow, X, I-beam, resizer, etc) is one of the few WRITE-only objects
in X11. That is, an application can tell the X server what the cursor
shape should be when the pointer is in a given window, but a program
(like x11vnc) unfortunately cannot read this information. I believe
this is because the cursor shape is often downloaded to the graphics
hardware (video card), but I could be mistaken.
A simple kludge is provided by the "[484]-cursor X" option that
changes the cursor when the mouse is on the root background (or any
window has the same cursor as the root background). Note that desktops
like GNOME or KDE often cover up the root background, so this won't
work for those cases. Also see the "[485]-cursor some" option for
additional kludges.
Note that as of Aug/2004 on Solaris using the SUN_OVL overlay
extension and IRIX, x11vnc can show the correct mouse cursor when the
[486]-overlay option is supplied. See [487]this FAQ for more info.
Also as of Dec/2004 XFIXES X extension support has been added to allow
exact extraction of the mouse cursor shape. XFIXES fixes the problem
of the cursor-shape being write-only: x11vnc can now query the X
server for the current shape and send it back to the connected
viewers. XFIXES is available on recent Linux Xorg based distros and
[488]Solaris 10.
The only XFIXES issue is the handling of alpha channel transparency in
cursors. If a cursor has any translucency then in general it must be
approximated to opaque RGB values for use in VNC. There are some
situations where the cursor transparency can also handled exactly:
when the VNC Viewer requires the cursor shape be drawn into the VNC
framebuffer or if you apply a patch to your VNC Viewer to extract
hidden alpha channel data under 32bpp. [489]Details can be found here.
Q-66: When using XFIXES cursorshape mode, some of the cursors look
really bad with extra black borders around the cursor and other cruft.
How can I improve their appearance?
This happens for cursors with transparency ("alpha channel"); regular
X cursors (bitmaps) should be correct. Unfortunately x11vnc 0.7 was
released with a very poor algorithm for approximating the
transparency, which led to the ugly black borders.
The problem is as follows: XFIXES allows x11vnc to retrieve the
current X server cursor shape, including the alpha channel for
transparency. For traditional bitmap cursors the alpha value will be 0
for completely transparent pixels and 255 for completely opaque
pixels; whereas for modern, eye-candy cursors an alpha value between 0
and 255 means to blend in the background colors to that degree with
the cursor colors. The pixel color blending formula is something like
this: Red = Red_cursor * a + Red_background * (1 - a), (where here 0
=< a =< 1), with similar for Green and Blue. The VNC protocol does not
currently support an alpha channel in cursors: it only supports
regular X bitmap cursors and Rich Cursors that have RGB (Red, Green,
Blue) color data, but no "A" = alpha data. So in general x11vnc has to
approximate a cursor with transparency to create a Rich Cursor. This
is easier said than done: some cursor themes have cursors with
complicated drop shadows and other forms of translucency.
Anyway, for the x11vnc 0.7.1 release the algorithm for approximating
transparency is much improved and hopefully gives decent cursor shapes
for most cursor themes and you don't have to worry about it.
In case it still looks bad for your cursor theme, there are (of
course!) some tunable parameters. The "[490]-alphacut n" option lets
you set the threshold "n" (between 0 and 255): cursor pixels with
alpha values below n will be considered completely transparent while
values equal to or above n will be completely opaque. The default is
240. The "[491]-alphafrac f" option tries to correct individual
cursors that did not fare well with the default -alphacut value: if a
cursor has less than fraction f (between 0.0 and 1.0) of its pixels
selected by the default -alphacut, the threshold is lowered until f of
its pixels are selected. The default fraction is 0.33.
Finally, there is an option [492]-alpharemove that is useful for
themes where many cursors are light colored (e.g. "whiteglass").
XFIXES returns the cursor data with the RGB values pre-multiplied by
the alpha value. If the white cursors look too grey, specify
-alpharemove to brighten them by having x11vnc divide out the alpha
value.
One user played with these parameters and reported back:
Of the cursor themes present on my system:
gentoo and gentoo-blue: alphacut:192 - noalpharemove
gentoo-silver: alphacut:127 and alpharemove
whiteglass and redglass (presumably also handhelds, which is based
heavily on redglass) look fine with the apparent default of alphacut:255.
Q-67: In XFIXES mode, are there any hacks to handle cursor
transparency ("alpha channel") exactly?
As of Jan/2005 libvncserver has been modified to allow an alpha
channel (i.e. RGBA data) for Rich Cursors. So x11vnc can now send the
alpha channel data to libvncserver. However, this data will only be
used for VNC clients that do not support the CursorShapeUpdates VNC
extension (or have disabled it). It can be disabled for all clients
with the [493]-nocursorshape x11vnc option. In this case the cursor is
drawn, correctly blended with the background, into the VNC framebuffer
before being sent out to the client. So the alpha blending is done on
the x11vnc side. Use the [494]-noalphablend option to disable this
behavior (always approximate transparent cursors with opaque RGB
values).
The CursorShapeUpdates VNC extension complicates matters because the
cursor shape is sent to the VNC viewers supporting it, and the viewers
draw the cursor locally. This improves response over slow links. Alpha
channel data for these locally drawn cursors is not supported by the
VNC protocol.
However, in the libvncserver CVS there is a patch to the TightVNC
viewer to make this work for CursorShapeUpdates under some
circumstances. This hack is outside of the VNC protocol. It requires
the screens on both sides to be depth 24 at 32bpp (it uses the extra 8
bits to secretly hide the cursor alpha channel data). Not only does it
require depth 24 at 32bpp, but it also currently requires the client
and server to be of the same endianness (otherwise the hidden alpha
data gets reset to zero by a libvncserver translation function; we can
fix this at some point if there is interest). The patch is for the
TightVNC 1.3dev5 Unix vncviewer and it enables the TightVNC viewer to
do the cursor alpha blending locally. The patch code should give an
example on how to change the Windows TightVNC viewer to achieve the
same thing (send me the patch if you get that working).
[Mouse Pointer]
Q-68: Why does the mouse arrow just stay in one corner in my
vncviewer, whereas my cursor (that does move) is just a dot?
This default takes advantage of a [495]tightvnc extension
(CursorShapeUpdates) that allows specifying a cursor image shape for
the local VNC viewer. You may disable it with the [496]-nocursor
option to x11vnc if your viewer does not have this extension.
Note: as of Aug/2004 this should be fixed: the default for
non-tightvnc viewers (or ones that do not support CursorShapeUpdates)
will be to draw the moving cursor into the x11vnc framebuffer. This
can also be disabled via -nocursor.
Q-69: Can I take advantage of the TightVNC extension to the VNC
protocol where Cursor Positions Updates are sent back to all connected
clients (i.e. passive viewers can see the mouse cursor being moved
around by another viewer)?
Use the [497]-cursorpos option when starting x11vnc. A VNC viewer must
support the Cursor Positions Updates for the user to see the mouse
motions (the TightVNC viewers support this). As of Aug/2004 -cursorpos
is the default. See also [498]-nocursorpos and [499]-nocursorshape.
Q-70: Is it possible to swap the mouse buttons (e.g. left-handed
operation), or arbitrarily remap them? How about mapping button clicks
to keystrokes, e.g. to partially emulate Mouse wheel scrolling?
You can remap the mouse buttons via something like: [500]-buttonmap
13-31 (or perhaps 12-21). Also, note that xmodmap(1) lets you directly
adjust the X server's button mappings, but in some circumstances it
might be more desirable to have x11vnc do it.
One user had an X server with only one mouse button(!) and was able to
map all of the VNC client mouse buttons to it via: -buttonmap 123-111.
Note that the [501]-debug_pointer option prints out much info for
every mouse/pointer event and is handy in solving problems.
To map mouse button clicks to keystrokes you can use the alternate
format where the keystrokes are enclosed between colons like this
:<KeySym>: in place of the mouse button digit. For a sequence of
keysyms separate them with "+" signs. Look in the include file
<X11/keysymdef.h>, or use xev(1), or -debug_keyboard to fine the
keysym names. Button clicks can also be included in the sequence via
the fake keysyms Button1, etc.
As an example, suppose the VNC viewer machine has a mouse wheel (these
generate button 4 and 5 events), but the machine that x11vnc is run on
only has the 3 regular buttons. In normal operation x11vnc will
discard the button 4 and 5 events. However, either of the following
button maps could possibly be of use emulating the mouse wheel events
in this case:
-buttonmap 12345-123:Prior::Next:
-buttonmap 12345-123:Up+Up+Up::Down+Down+Down:
Exactly what keystroke "scrolling" events they should be bound to
depends on one's taste. If this method is too approximate, one could
consider not using [502]-buttonmap but rather configuring the X server
to think it has a mouse with 5 buttons even though the physical mouse
does not. (e.g. 'Option "ZAxisMapping" "4 5"').
Note that when a keysym-mapped mouse button is clicked down this
immediately generates the key-press and key-release events (for each
keysym in turn if the mapping has a sequence of keysyms). When the
mouse button goes back up nothing is generated.
If you include modifier keys like Shift_L instead of key-press
immediately followed by key-release the state of the modifier key is
toggled (however the initial state of the modifier key is ignored). So
to map the right button to type my name 'Karl Runge' I could use this:
-buttonmap 3-:Shift_L+k+Shift_L+a+r+l+space+Shift_L+r+Shift_L+u+n+g+e:
(yes, this is getting a little silly).
BTW, Coming the other way around, if the machine you are sitting at
does not have a mouse wheel, but the remote machine does (or at least
has 5 buttons configured), this key remapping can be useful:
-remap Super_R-Button4,Menu-Button5
you just tap those two keys to get the mouse wheel scrolls (this is
more useful than the Up and Down arrow keys because a mouse wheel
"click" usually gives a multi-line scroll).
[Keyboard Issues]
Q-71: How can I get my AltGr and Shift modifiers to work between
keyboards for different languages?
The option [503]-modtweak should help here. It is a mode that monitors
the state of the Shift and AltGr Modifiers and tries to deduce the
correct keycode to send, possibly by sending fake modifier key presses
and releases in addition to the actual keystroke.
Update: As of Jul/2004 -modtweak is now the default (use -nomodtweak
to get the old behavior). This was done because it was noticed on
newer XFree86 setups even on bland "us" keyboards like "pc104 us"
XFree86 included a "ghost" key with both "<" and ">" it. This key does
not exist on the keyboard (see [504]this FAQ for more info). Without
-modtweak there was then an ambiguity in the reverse map keysym =>
keycode, making it so the "<" symbol could not be typed.
Also see the [505]FAQ about the -xkb option for a more powerful method
of modifier tweaking for use on X servers with the XKEYBOARD
extension.
When trying to resolve keyboard mapping problems, note that the
[506]-debug_keyboard option prints out much info for every keystroke
and so can be useful debugging things.
Q-72: When I try to type a "<" (i.e. less than) instead I get ">"
(i.e. greater than)! Strangely, typing ">" works OK!!
Does your keyboard have a single key with both "<" and ">" on it? Even
if it doesn't, your X server may think your keyboard has such a key
(e.g. pc105 in the XF86Config file when it should be something else,
say pc104).
Short Cut: Try the [507]-xkb or [508]-sloppy_keys options and see if
that helps the situation. The discussion below is a bit outdated (e.g.
[509]-modtweak is now the default) but it is useful reference for
various tricks and so is kept.
The problem here is that on the Xserver where x11vnc is run there are
two keycodes that correspond to the "<" keysym. Run something like
this to see:
xmodmap -pk | egrep -i 'KeyCode|less|greater'
There are 4 KeySyms per KeyCode; KeyCodes range from 8 to 255.
KeyCode Keysym (Keysym) ...
59 0x002c (comma) 0x003c (less)
60 0x002e (period) 0x003e (greater)
94 0x003c (less) 0x003e (greater)
That keycode 94 is the special key with both "<" and ">". When x11vnc
receives the "<" keysym over the wire from the remote VNC client, it
unfortunately maps it to keycode 94 instead of 59, and sends 94 to the
X server. Since Shift is down (i.e. you are Shifting the comma key),
the X server interprets this as Shifted-94, which is ">".
A workaround in the X server configuration is to "deaden" that special
key:
xmodmap -e "keycode 94 = "
However, one user said he had to do this:
xmodmap -e "keycode 94 = 0x002c 0x003c"
(If the numerical values are different for your setup, substitute the
ones that correspond to your display. The above xmodmap scheme can
often be used to work around other ambiguous keysym to keycode
mappings).
Alternatively, here are some x11vnc options to try to work around the
problem:
-modtweak
and
-remap less-comma
These are convenient in that they do not modify the actual X server
settings. The former ([510]-modtweak) is a mode that monitors the
state of the Shift and AltGr modifiers and tries to deduce the correct
keycode sequence to send. Since Jul/2004 -modtweak is now the default.
The latter ([511]-remap less-comma) is an immediate remapping of the
keysym less to the keysym comma when it comes in from a client (so
when Shift is down the comma press will yield "<").
See also the [512]FAQ about the -xkb option as a possible workaround
using the XKEYBOARD extension.
Note that the [513]-debug_keyboard option prints out much info for
every keystroke to aid debugging keyboard problems.
Q-73: When I try to type a "<" (i.e. less than) instead I get "<,"
(i.e. an extra comma).
This is likely because you press "Shift" then "<" but then released
the Shift key before releasing the "<". Because of a [514]keymapping
ambiguity the last event "< up" is interpreted as "," because that key
unshifted is the comma.
This should not happen in [515]-xkb mode, because it works hard to
resolve the ambiguities. If you do not want to use -xkb, try the
option [516]-sloppy_keys to attempt a similar type of algorithm.
Q-74: I'm using an "international" keyboard (e.g. German "de", or
Danish "dk") and the -modtweak mode works well if the VNC viewer is
run on a Unix/Linux machine with a similar keyboard. But if I run
the VNC viewer on Unix/Linux with a different keyboard (e.g. "us") or
Windows with any keyboard, I can't type some keys like: "@", "$",
"<", ">", etc. How can I fix this?
The problem with Windows is it does not seem to handle AltGr well. It
seems to fake it up by sending Control_L+Alt_R to applications. The
Windows VNC viewer sends those two down keystrokes out on the wire to
the VNC server, but when the user types the next key to get, e.g., "@"
the Windows VNC viewer sends events bringing the up the
Control_L+Alt_R keys, and then sends the "@" keysym by itself.
The Unix/Linux VNC viewer on a "us" keyboard does a similar thing
since "@" is the Shift of the "2" key. The keysyms Shift and "@" are
sent to the VNC server.
In both cases no AltGr is sent to the VNC server, but we know AltGr is
needed on the physical international keyboard to type a "@".
This all worked fine with x11vnc running with the [517]-modtweak
option (it figures out how to adjust the Modifier keys (Shift or
AltGr) to get the "@"). However it fails under recent versions of
XFree86 (and the X.org fork). These run the XKEYBOARD extension by
default and make heavy use of it to handle international keyboards.
To make a long story short, on these newer XFree86 setups the
traditional X keymap lookup x11vnc uses is no longer accurate. x11vnc
can't find the keysym "@" anywhere in the keymapping! (even though it
is in the XKEYBOARD extended keymapping).
How to Solve: As of Jul/2004 x11vnc has two changes:
* -modtweak (tweak Modifier keys) is now the default (use
-nomodtweak to go back to the old way)
* there is a new option -xkb to use the XKEYBOARD extension API to
do the Modifier key tweaking.
The [518]-xkb option seems to fix all of the missing keys: "@", "<",
">", etc.: it is recommended that you try it if you have this sort of
problem. Let us know if there are any remaining problems (see the next
paragraph for some known problems). If you specify the -debug_keyboard
(aka -dk) option twice you will get a huge amount of keystroke
debugging output (send it along with any problems you report).
Update: as of Jun/2005 x11vnc will try to automatically enable
[519]-xkb if it appears that would be beneficial (e.g. if it sees any
of "@", "<", ">", "[" and similar keys are mapped in a way that needs
the -xkb to access them). To disable this automatic check use -noxkb.
Known problems:
* One user had to disable a "ghost" Mode_switch key that was causing
problems under -xkb. His physical AltGr key was bound to
ISO_Level3_Shift (which seems to be the XKEYBOARD way of doing
things), while there was a ghost key Mode_switch (which seems to
be obsolete) in the mapping as well. Both of these keysyms were
bound to Mod5 and x11vnc was unfortunately choosing Mode_switch.
From the x11vnc -xkb -dk -dk output it was noted that Mode_switch
was attached to keycode 93 (no physical key generates this
keycode) while ISO_Level3_Shift was attached to keycode 113. The
keycode skipping option was used to disable the ghost key:
[520]-skip_keycodes 93
* In implementing -xkb we noticed that some characters were still
not getting through, e.g. "~" and "^". This is not really an
XKEYBOARD problem. What was happening was the VNC viewer was
sending the keysyms asciitilde and asciicircum to x11vnc, but on
the X server with the international keyboard those keysyms were
not mapped to any keys. So x11vnc had to skip them (Note: as of
May/2005 they are added by default see -add_keysyms below).
The way these characters are typically entered on international
keyboards is by "dead" (aka "mute") keys. E.g. to enter "~" at the
physical display the keysym dead_tilde is pressed and released
(this usually involves holding AltGr down while another key is
pressed) and then space is pressed. (this can also be used get
characters with the "~" symbol on top, e.g. "<22>" by typing "a"
instead of space).
What to do? In general the VNC protocol has not really solved this
problem: what should be done if the VNC viewer sends a keysym not
recognized by the VNC server side? Workarounds can possibly be
created using the [521]-remap x11vnc option:
-remap asciitilde-dead_tilde,asciicircum-dead_circumflex
etc. Use -remap filename if the list is long. Please send us your
workarounds for this problem on your keyboard. Perhaps we can have
x11vnc adjust automatically at some point. Also see the
[522]-add_keysyms option in the next paragraph.
Update: for convenience "[523]-remap DEAD" does many of these
mappings at once.
* To complement the above workaround using the [524]-remap, an
option [525]-add_keysyms was added. This option instructs x11vnc
to bind any unknown Keysyms coming in from VNC viewers to unused
Keycodes in the X server. This modifies the global state of the X
server. When x11vnc exits it removes the extra keymappings it
created. Note that the -remap mappings are applied first, right
when the Keysym is received from a VNC viewer, and only after that
would -add_keysyms, or anything else, come into play.
Update: -add_keysyms is now on by default. Use -noadd_keysyms to
disable.
Q-75: When typing I sometimes get double, triple, or more of my
keystrokes repeated. I'm sure I only typed them once, what can I do?
This may be due to an interplay between your X server's key autorepeat
delay and the extra time delays caused by x11vnc processing.
Short answer: disable key autorepeating by running the command "xset r
off" on the Xserver where x11vnc is run (restore via "xset r on") or
use the new (Jul/2004) [526]-norepeat x11vnc option. You will still
have autorepeating because that is taken care of on your VNC viewer
side.
Update: as of Dec/2004 -norepeat is now the default. Use -repeat to
disable it.
Details: suppose you press a key DOWN and it generates changes in
large regions of the screen. The CPU and I/O work x11vnc does for the
large screen change could be longer than your X server's key
autorepeat delay. x11vnc may not get to processing the key UP event
until after the screen work is completed. The X server believes the
key has been held down all this time, and applies its autorepeat
rules.
Even without inducing changes in large regions of the screen, this
problem could arise when accessing x11vnc via a dialup modem or
otherwise high latency link (e.g. > 250 ms latency).
Look at the output of "xset q" for the "auto repeat delay" setting. Is
it low (e.g. < 300 ms)? If you turn off autorepeat completely: "xset r
off", does the problem go away?
The workaround is to manually apply "xset r off" and "xset r on" as
needed, or to use the [527]-norepeat (which has since Dec/2004 been
made the default). Note that with X server autorepeat turned off the
VNC viewer side of the connection will (nearly always) do its own
autorepeating so there is no big loss here, unless someone is also
working at the physical display and misses his autorepeating.
Q-76: The x11vnc -norepeat mode is in effect, but I still get repeated
keystrokes!!
Are you using x11vnc to log in to an X session via display manager?
(as described in [528]this FAQ) If so, x11vnc is starting before your
session and it disables autorepeat when you connect, but then after
you log in your session startup (GNOME, KDE, ...) could be resetting
the autorepeat to be on. Or it could be something inside your desktop
trying to be helpful that decides to turn it back on.
x11vnc in -norepeat mode will by default reset autorepeat to off 2
times (to help get thru the session startup problem), but it will not
continue to battle with things turning autorepeat back on. It will
also turn autorepeat off whenever it goes from a state of zero clients
to one client. You can adjust the number of resets via "-norepeat N",
or use "-norepeat -1" to have it keep resetting it whenever autorepeat
gets turned back on when clients are connected.
In general you can manually turn autorepeating off by typing "xset r
off", or a using desktop utility/menu, or "x11vnc -R norepeat". If
something in your desktop is automatically turning it back on you
should figure out how to disable that somehow.
Q-77: The machine where I run x11vnc has an AltGr key, but the local
machine where I run the VNC viewer does not. Is there a way I can map
a local unused key to send an AltGr? How about a Compose key as well?
Something like "[529]-remap Super_R-Mode_switch" x11vnc option may
work. Note that Super_R is the "Right Windoze(tm) Flaggie" key; you
may want to choose another. The -debug_keyboard option comes in handy
in finding keysym names (so does xev(1)).
For Compose how about "-remap Menu-Multi_key" (note that Multi_key is
the official name for Compose). To do both at the same time: "-remap
Super_R-Mode_switch,Menu-Multi_key" or use "-remap filename" to
specify remappings from a file.
Q-78: I have a Sun machine I run x11vnc on. Its Sun keyboard has just
one Alt key labelled "Alt" and two Meta keys labelled with little
diamonds. The machine where I run the VNC viewer only has Alt keys.
How can I send a Meta keypress? (e.g. emacs needs this)
Here are a couple ideas. The first one is to simply use xmodmap(1) to
adjust the Sun X server. Perhaps xmodmap -e "keysym Alt_L = Meta_L
Alt_L" will do the trick. (there are other ways to do it, one user
used: xmodmap -e "keycode 26 = Meta_L" for his setup).
Since xmodmap(1) modifies the X server mappings you may not want to do
this (because it affects local work on that machine). Something like
the [530]-remap Alt_L-Meta_L to x11vnc may be sufficient for ones
needs, and does not modify the X server environment. Note that you
cannot send Alt_L in this case, maybe -remap Super_L-Meta_L would be a
better choice if the Super_L key is typically unused in Unix.
Q-79: Can I map a keystroke to a mouse button click on the remote
machine?
This can be done directly in some X servers using AccessX and
Pointer_EnableKeys, but is a bit awkward. It may be more convenient to
have x11vnc do the remapping. This can be done via the [531]-remap
option using the fake "keysyms" Button1, Button2, etc. as the "to"
keys (i.e. the ones after the "-")
As an example, consider a laptop where the VNC viewer is run that has
a touchpad with only two buttons. It is difficult to do a middle
button "paste" because (using XFree86/Xorg Emulate3Buttons) you have
to click both buttons on the touch pad at the same time. This
remapping:
[532]-remap Super_R-Button2
maps the Super_R "flag" key press to the Button2 click, thereby making
X pasting a bit easier.
Note that once the key goes down, the button down and button up events
are generated immediately on the x11vnc side. When the key is released
(i.e. goes up) no events are generated.
Q-80: How can I get Caps_Lock to work between my VNC viewer and
x11vnc?
This is a little tricky because it is possible to get the Caps_Lock
state out of sync between your viewer-side machine and the x11vnc-side
X server. For best results, we recommend not ever letting the
Caps_Lock keypresses be processed by x11vnc. That way when you press
Caps_Lock in the viewer your local machine goes into the Caps_Lock on
state and sends keysym "A" say when you press "a". x11vnc will then
fake things up so that Shift is held down to generate "A". The
[533]-skip_lockkeys option should help to accomplish this. For finer
grain control use something like: "[534]-remap Caps_Lock-None".
Also try the [535]-nomodtweak and [536]-capslock options.
[Screen Related Issues and Features]
Q-81: The remote display is larger (in number of pixels) than the
local display I am running the vncviewer on. I don't like the
vncviewer scrollbars, what I can do?
vncviewer has a option (usually accessible via F8 key or -fullscreen
option) for vncviewer to run in full screen, where it will
automatically scroll when the mouse is near the edge of the current
view. For quick scrolling, also make sure Backing Store is enabled on
the machine vncviewer is run on. (XFree86/Xorg disables it by default
for some reason, add Option "backingstore" to XF86Config on the
vncviewer side).
BTW, contact me if you are having problems with vncviewer in
fullscreen mode with your window manager (i.e. no keyboard response).
I have a workaround for vncviewer using XGrabServer().
There may also be scaling viewers out there (e.g. TightVNC or UltraVNC
on Windows) that automatically shrink or expand the remote framebuffer
to fit the local display. Especially for hand-held devices. See also
[537]this FAQ on x11vnc scaling.
Q-82: Does x11vnc support server-side framebuffer scaling? (E.g. to
make the desktop smaller).
As of Jun/2004 x11vnc provides basic server-side scaling. It is a
global scaling of the desktop, not a per-client setting. To enable it
use the "[538]-scale fraction" option. "fraction" can either be a
floating point number (e.g. -scale 0.5) or the alternative m/n
fraction notation (e.g. -scale 3/4). Note that if fraction is greater
than one the display is magnified.
Extra resources (CPU, memory I/O, and memory) are required to do the
scaling. If the machine is slow where x11vnc is run with scaling
enabled, the interactive response can be unacceptable. OTOH, if run
with scaling on a fast machine the performance degradation is usually
not a big issue or even noticeable.
Also, if you just want a quick, rough "thumbnail" of the display you
can append ":nb" to the fraction to turn on "no blending" mode. E.g.:
"-scale 1/3:nb" Fonts will be difficult to read, but the larger
features will be recognizable. BTW, "no blending" mode is forced on
when scaling 8bpp PseudoColor displays (because blending an indexed
colormap is a bad idea and leads to random colors, use :fb to force it
on).
One can also use the ":nb" with an integer scale factor (say "-scale
2:nb") to use x11vnc as a screen magnifier for vision impaired
[539]applications. Since with integer scale factors the framebuffers
become huge and scaling operations time consuming, be sure to use
":nb" for the fastest response.
In general for a scaled display if you are using a TightVNC viewer you
may want to turn off jpeg encoding (e.g. vncviewer -nojpeg host:0).
There appears to be a noise enhancement effect, especially for regions
containing font/text: the scaling can introduce some pixel artifacts
that evidently causes the tight encoding algorithm to incorrectly
detect the regions as image data and thereby introduce additional
pixel artifacts due to the lossiness of the jpeg compression
algorithm. Experiment to see if -nojpeg vncviewer option improves the
readability of text when using -scale to shrink the display size. Also
note that scaling may actually slow down the transfer of text regions
because after being scaled they do not compress as well. (this can
often be a significant slowdown, e.g. 10X).
Another issue is that it appears VNC viewers require the screen width
to be a multiple of 4. When scaling x11vnc will round the width to the
nearest multiple of 4. To disable this use the ":n4" sub option (like
":nb" in the previous paragraph; to specify both use a comma:
":nb,n4", etc.)
If one desires per-client scaling for something like 1:1 from a
workstation and 1:2 from a smaller device (e.g. handheld), currently
the only option is to run two (or more) x11vnc processes with
different scalings listening on separate ports ([540]-rfbport option,
etc.).
Update: As of May/2006 x11vnc also supports the UltraVNC server-side
scaling. This is a per-client scaling by factors 1/2, 1/3, ... and so
may be useful for PDA's ("-scale 1/2", etc. will give similar results
except that it applies to all clients). You may need to supply
"-rfbversion 3.6" for this to be recognized by UltraVNC viewers.
BTW, whenever you run two or more x11vnc's on the same X display and
use the [541]GUI, then to avoid all of the x11vnc's simultaneously
answering the gui you will need to use something like [542]"-connect
file1 -gui ..." with different connect files for each x11vnc you want
to control via the gui (or remote-control). The "-connect file1" usage
gives separate communication channels between a x11vnc proces and the
gui process. Otherwise they all share the same X property channels:
VNC_CONNECT and X11VNC_REMOTE.
Update: As of Mar/2005 x11vnc now scales the mouse cursor with the
same scale factor as the screen. If you don't want that, use the
[543]"-scale_cursor frac" option to set the cursor scaling to a
different factor (e.g. use "-scale_cursor 1" to keep the cursor at its
natural unscaled size).
Q-83: Does x11vnc work with Xinerama? (i.e. multiple monitors joined
together to form one big, single screen).
Yes, it should generally work because it simply polls the big
effective screen.
If the viewing-end monitor is not as big as the remote Xinerama
display, then the vncviewer scrollbars, etc, will have to be used to
pan across the large area. However one user started two x11vnc's, one
with "-clip 1280x1024+0+0" and the other with "-clip 1280x1024+1280+0"
to split the big screen into two and used two VNC viewers to access
them.
There are a couple potential issues with Xinerama however. If the
screen is not rectangular (e.g. 1280x1024 and 1024x768 monitors joined
together), then there will be "non-existent" areas on the screen. The
X server will return "garbage" image data for these areas and so they
may be distracting to the viewer. The [544]-blackout x11vnc option
allows you to blacken-out rectangles by manually specifying their
WxH+X+Y geometries. If your system has the libXinerama library, the
[545]-xinerama x11vnc option can be used to have it automatically
determine the rectangles to be blackened out. (Note on 8bpp
PseudoColor displays the fill color may not be black). Update:
[546]-xinerama is now on by default.
Some users have reported that the mouse does not behave properly for
their Xinerama display: i.e. the mouse cannot be moved to all regions
of the large display. If this happens try using the [547]-xwarppointer
option. This instructs x11vnc to fake mouse pointer motions using the
XWarpPointer function instead of the XTestFakeMotionEvent XTEST
function. (This may be due to a bug in the X server for XTEST when
Xinerama is enabled).
Q-84: Can I use x11vnc on a multi-headed display that is not Xinerama
(i.e. separate screens :0.0, :0.1, ... for each monitor)?
You can, but it is a little bit awkward: you must start separate
x11vnc processes for each screen, and on the viewing end start up
separate VNC viewer processes connecting to them. e.g. on the remote
end:
x11vnc -display :0.0 -bg -q -rfbport 5900
x11vnc -display :0.1 -bg -q -rfbport 5901
(this could be automated in the display manager Xsetup for example)
and then on the local machine where you are sitting:
vncviewer somehost:0 &
vncviewer somehost:1 &
Note: if you are running on Solaris 8 or earlier you can easily hit up
against the maximum of 6 shm segments per process (for Xsun in this
case) from running multiple x11vnc processes. You should modify
/etc/system as mentioned in another [548]FAQ to increase the limit. It
is probably also a good idea to run with the [549]-onetile option in
this case (to limit each x11vnc to 3 shm segments), or even
[550]-noshm to use no shm segments.
Q-85: Can x11vnc show only a portion of the display? (E.g. for a
special purpose rfb application).
As of Mar/2005 x11vnc has the "[551]-clip WxH+X+Y" option to select a
rectangle of width W, height H and offset (X, Y). Thus the VNC screen
will be the clipped sub-region of the display and be only WxH in size.
One user used -clip to split up a large [552]Xinerama screen into two
more managable smaller screens.
This also works to view a sub-region of a single application window if
the [553]-id or [554]-sid options are used. The offset is measured
from the upper left corner of the selected window.
Q-86: Does x11vnc support the XRANDR (X Resize, Rotate and Reflection)
extension? Whenever I rotate or resize the screen x11vnc just seems to
crash.
As of Dec/2004 x11vnc supports XRANDR. You enable it with the
[555]-xrandr option to make x11vnc monitor XRANDR events and also trap
X server errors if the screen change occurred in the middle of an X
call like XGetImage. Once it traps the screen change it will create a
new framebuffer using the new screen.
If the connected vnc viewers support the NewFBSize VNC extension
(Windows TightVNC viewer and RealVNC 4.0 windows and Unix viewers do)
then the viewer will automatically resize. Otherwise, the new
framebuffer is fit as best as possible into the original viewer size
(portions of the screen may be clipped, unused, etc). For these
viewers you can try the [556]-padgeom option to make the region big
enough to hold all resizes and rotations.
If you specify "-xrandr newfbsize" then vnc viewers that do not
support NewFBSize will be disconnected before the resize. If you
specify "-xrandr exit" then all will be disconnected and x11vnc will
terminate.
Q-87: Why is the view in my VNC viewer completely black? Or why is
everything flashing around randomly?
See the next FAQ for a possible explanation.
Q-88: I use Linux Virtual Consoles (VC's) to implement 'Fast User
Switching' between users' sessions (e.g. Betty is on Ctrl-Alt-F7,
Bobby is on Ctrl-Alt-F8, and Sid is on Ctrl-Alt-F1: they use those
keystrokes to switch between their sessions). How come the view in a
VNC viewer connecting to x11vnc is either completely black or
otherwise all messed up unless the X session x11vnc is attached to is
in the active VC?
This seems to have to do with how applications (the X server processes
in this case) must "play nicely" if they are not on the active VC
(sometimes called VT for virtual terminal). That is, they should not
read from the keyboard or mouse or manage the video display unless
they have the active VC. Given that it appears the XGetImage() call
must ultimately retrieve the framebuffer data from the video hardware
itself, it would make sense x11vnc's polling wouldn't work unless the
X session had active control of the VC.
There does not seem to be an easy way to work around this. Even xwd(1)
doesn't work in this case (try it). Something would need to be done at
a lower level, say in the XFree86 X server. Also, using the XFree86
Shadow Framebuffer (a copy of the video framebuffer is kept in main
memory) does not appear to fix the problem.
If no one is sitting at the workstation and you just want to remotely
switch the VC over to the one associated with your X session (so
x11vnc can poll it correctly), one can use the chvt(1) command, e.g.
"chvt 7" for VC #7.
Q-89: I am using x11vnc where my local machine has "popup/hidden
taskbars" (e.g. GNOME or MacOS X) and the remote display where x11vnc
runs also has "popup/hidden taskbars" (e.g. GNOME). When I move the
mouse to the edge of the screen where the popups happen, the taskbars
interfere and fight with each other in strange ways. What can I do?
Is there a way to temporarily disable one or both of these magic
desktop taskbars?
One x11vnc user suggests: it should be straightforward to right mouse
click on the task bar panel, and uncheck "enable auto-hide" from the
panel properties dialog box. This will make the panel always visible.
Q-90: Can I use x11vnc to view my VMWare session remotely?
Yes, since VMWare usually runs as an X application you can view it via
x11vnc in the normal way.
Note that VMWare has several viewing modes:
* Normal X application window (with window manager frame)
* Quick-Switch mode (with no window manager frame)
* Fullscreen mode
The way VMWare does Fullscreen mode on Linux is to display the Guest
desktop in a separate Virtual Console (e.g. VC 8) (see [557]this FAQ
on VC's for background). Unfortunately, this Fullscreen VC is not an X
server. So x11vnc cannot access it (however, [558]see this discussion
of -rawfb for a possible workaround). x11vnc works fine with "Normal X
application window" and "Quick-Switch mode" because these use X.
Update: It appears the in VMWare 5.x the Fullscreen mode is X, so
x11vnc access does work.
One user reports he left his machine with VMWare in the Fullscreen
mode, and even though his X session wasn't in the active VC, he could
still connect x11vnc to the X session and pass the keystrokes Ctrl-Alt
(typing "blind") to the VMWare X app. This induced VMWare to switch
out of Fullscreen into Normal X mode and he could continue working in
the Guest desktop remotely.
Aside: Sometimes it is convenient (for performance, etc.) to start
VMWare in its own X session using startx(1). This can be used to have
a minimal window manger (e.g. twm or even no window manager), to
improve response. One can also cut the display depth (e.g. to 16bpp)
in this 2nd X session to improve video performance. This 2nd X session
emulates Fullscreen mode to some degree and can be viewed via x11vnc
as long as the VMWare X session [559]is in the active VC.
Also note that with a little bit of playing with "xwininfo -all
-children" output one can extract the (non-toplevel) windowid of the
of the Guest desktop only when VMWare is running as a normal X
application. Then one can export just the guest desktop (i.e. without
the VMWare menu buttons) by use of the [560]-id windowid option. The
caveats are the X session VMWare is in must be in the active VC and
the window must be fully visible, so this mode is not terribly
convenient, but could be useful in some circumstances (e.g. running
VMWare on a very powerful server machine in a server room that happens
to have a video card, (but need not have a monitor, Keyboard or
mouse)).
Q-91: Can non-X devices (e.g. a raw framebuffer) be viewed (and even
controlled) via VNC with x11vnc?
As of Apr/2005 there is support for this. Two options were added:
"[561]-rawfb string" (to indicate the raw framembuffer device, file,
etc. and its parameters) and "[562]-pipeinput command" (to provide an
external program that will inject or otherwise process mouse and
keystroke input). Some useful [563]-pipeinput schemes, VID, CONSOLE,
and UINPUT, have since been built into x11vnc for convenience.
This non-X mode for x11vnc is somewhat experimental because it is so
removed in scope from the intended usage of the tool. Incomplete
attempt is made to make all of the other options consistent with non-X
framebuffer polling. So all of the X-related options (e.g.
-add_keysyms, -xkb) are just ignored or may cause an error if used. Be
careful applying such an option via remote control.
The format for the -rawfb string is:
-rawfb <type>:<object>@<W>x<H>x<bpp>[:<R>/<G>/<B>][+<offset>]
There are also some useful aliases (e.g. "console"). Some examples:
-rawfb shm:210337933@800x600x32:ff/ff00/ff0000
-rawfb map:/dev/fb0@1024x768x16
-rawfb map:/tmp/Xvfb_screen0@640x480x8+3232
-rawfb file:/tmp/my.pnm@250x200x24+37
-rawfb file:/dev/urandom@128x128x8
-rawfb snap:/dev/video0@320x240x24 -24to32
-rawfb console
-rawfb video
-rawfb setup:mycmd.sh
So the type can be "shm" for shared memory objects, and "map" or
"file" for file objects. "map" uses mmap(2) to map the file into
memory and is preferred over "file" (that uses the slower lseek(2)
access method). Only use file if map isn't working. BTW, "mmap" is an
alias for "map" and if you do not supply a type and the file exists,
map is assumed (see the -help output and below for some exceptions to
this). The "snap:" setting applies the [564]-snapfb option with
"file:" type reading (this is useful for exporting webcams or TV tuner
video; see [565]the next FAQ for more info).
Also, if the string is of the form "setup:cmd" then cmd is run and the
first line of its output retrieved and used as the rawfb string. This
allows initializing the device, determining WxHxB, etc.
The object will be the numerical shared memory id for the case of shm.
The idea here is some other program has created this shared memory
segment and periodically updates it with new framebuffer data. x11vnc
polls the area for changes. See shmat(2) and ipcs(8) for more info.
The ipcs command will list current shared memory segments on the
system. Sometimes you can snoop on a program's framebuffer it did not
expect you would be polling!
The object will be the path to the regular or character special file
for the cases of map and file. The idea here is that in the case of a
regular file some other program is writing/updating framebuffer image
data to it. In the case of a character special (e.g. /dev/fb0) it is
the kernel that is "updating" the framebuffer data.
In most cases x11vnc needs to be told the width, height, and number of
bits per pixel (bpp) of the framebuffer. This is the @WxHxB field. For
the case of the Linux framebuffer device, /dev/fb0, the fbset(8) may
be of use (but may not always be accurate for what is currently
viewable). In general some guessing may be required, especially for
the bpp. Update: in "-rawfb console" mode x11vnc will use the linuxfb
API to try to guess (it is still not always accurate).
Based on the bpp x11vnc will try to guess the red, green, and blue
masks (these indicate which bits correspond to each color). It if gets
it wrong you can specify them manually via the optional ":R/G/B"
field. E.g. ":0xff0000/0x00ff00/0x0000ff" (this is the default for
32bpp).
Finally, the framebuffer may not begin at the beginning of the memory
object, so use the optional "+offset" parameter to indicate where the
framebuffer information starts. So as an example, the Xvfb virtual
framebuffer has options -shmem and -fbdir for exporting its virtual
screen to either shm or a mapped file. The format of these is XWD and
so the initial header should be skipped. BTW, since XWD is not
strictly RGB the view will only be approximate, but usable. Of course
for the case of Xvfb x11vnc can poll it much better via the [566]X
API, but you get the idea.
By default in -rawfb mode x11vnc will actually close any X display it
happened to open. This is basically to shake out bugs (e.g it will
crash rather than mysteriously interacting with the X display). If you
want x11vnc to keep the X display open while polling the raw
framebuffer prefix a "+" sign at the beginning of the string (e.g.
+file:/dev/urandom@64x64x8) This could be convenient for keeping the
remote control channel active (it uses X properties). The "-connect
/path/to/file" mechanism could also be used for remote control to
avoid the X property channel. Rare usage, but if you also supply
-noviewonly in this "+" mode then the mouse and keyboard input are
still sent to the X display, presumably for doing something amusing
with /dev/fb...
Interesting Devices:. Here are some interesting device files that can
be polled via -rawfb:
-rawfb console /dev/fb0 Linux Console
-rawfb video /dev/video0 Video4Linux Capture device
-rawfb rand /dev/urandom Random Bytes
-rawfb null /dev/zero Zero Bytes (black screen)
The Linux console, /dev/fb0, etc needs to have its driver enable in
the kernel. Some of the drivers are video card specific and
accelerated. The console is either the Text consoles (usually
tty1-tty6), or X graphical display (usually starting at tty7). In
addition to text console may be other graphical ones may be viewed and
interacted with, e.g. SVGAlib apps, VMWare non-X fullscreen, or
[567]Qt-embedded apps (PDAs/Handhelds). By default the pipeinput
mechanisms UINPUT and CONSOLE (keystrokes only) are automatically
attempted in this mode under "-rawfb console".
The Video4Linux Capture device, /dev/video0, etc is either a Webcam or
a TV capture device and needs to have its driver enable in the kernel.
See [568]this FAQ for details. If specified via "-rawfb Video" then
the pipeinput method "VID" is applied (it lets you change video
parameters dynamically via keystrokes).
The last two, /dev/urandom and /dev/zero are just for fun, but are
also useful in testing.
All of the above [569]-rawfb options are just for viewing the raw
framebuffer (although some of the aliases do imply keystroke and mouse
pipeinput methods). That may be enough for certain applications of
this feature (e.g. suppose a [570]video camera mapped its framebuffer
into memory and you just wanted to look at it via VNC).
To handle the pointer and keyboard input from the viewer users the
"-pipeinput cmd" option was added to indicate a helper program to
process the user input. The input is streamed to it and looks
something like this:
Pointer 1 205 257 0 None
Pointer 1 198 253 0 None
Pointer 1 198 253 1 ButtonPress-1
Pointer 1 198 253 0 ButtonRelease-1
Pointer 1 198 252 0 None
Keysym 1 1 119 w KeyPress
Keysym 1 0 119 w KeyRelease
Keysym 1 1 65288 BackSpace KeyPress
Keysym 1 0 65288 BackSpace KeyRelease
Keysym 1 1 112 p KeyPress
Keysym 1 0 112 p KeyRelease
Run "-pipeinput tee:/bin/cat" to get a description of the format. Note
that the -pipeinput option is independent of -rawfb mode and so may
have some other interesting uses. The "tee:" prefix means x11vnc will
both process the user input and pipe it to the command. The default is
to just pipe it to the -pipeinput command.
Note the -pipeinput helper program could actually control the raw
framebuffer. In the libvncserver CVS a simple example program
x11vnc/misc/slide.pl is provided that demonstrates a simple jpeg
"slideshow" application. Also the builtin "-pipeinput VID" mode does
this for webcams and TV capture devices (/dev/video0).
The -pipeinput program is run with these environment variables set:
X11VNC_PID, X11VNC_PROG, X11VNC_CMDLINE, X11VNC_RAWFB_STR to aid its
knowing what is up.
Another example provided in libvncserver CVS is a script to inject
keystrokes into the Linux console (e.g. the virtual consoles:
/dev/tty1, /dev/tty2, etc) in x11vnc/misc/vcinject.pl. It is based on
the vncterm/LinuxVNC.c program also in the libvncserver CVS. So to
view and interact with VC #2 (assuming it is the [571]active VC) one
can run something like:
x11vnc -rawfb map:/dev/fb0@1024x768x16 -pipeinput './vcinject.pl 2'
This assumes your Linux framebuffer device (/dev/fb0) is properly
configured. See fbset(8) and other documentation. Try
"file:/dev/fb0@WxHxB" as a last resort. Starting with x11vnc 0.8.1,
the above vc injection is built in, as well as WxHxB determination.
Just use something like:
x11vnc -rawfb console
this will try to guess the active virtual console (via /dev/tty0) and
also the /dev/fb0 WxHxB and rgb masks automatically. Use, e.g.,
"-rawfb console3" to force the VT number. This input method can be
used generally via "-pipeinput CONSOLE". Also starting with x11vnc
0.8.2 the "-pipeinput UINPUT" mode is tried first (it does both
keyboard and mouse input) and then falls back to CONSOLE mode if it is
not available. Here is the -help output for this mode:
If the rawfb string begins with "console" the framebuffer device
/dev/fb0 is opened (this requires the appropriate kernel modules to
be installed) and so is /dev/tty0. The latter is used to inject
keystrokes (not all are supported, but the basic ones are). You
will need to be root to inject keystrokes. /dev/tty0 refers to the
active VT, to indicate one explicitly, use "console2", etc. using
the VT number.
If the Linux version seems to be 2.6 or later and the "uinput"
module appears to be present, then the uinput method will be used
instead of /dev/ttyN. uinput allows insertion of BOTH keystrokes
and mouse input and so it preferred when accessing graphical (e.g.
Qt-embedded) linux console apps. See -pipeinput UINPUT below for
more information on this mode (you may want to also use the
-nodragging and -cursor none options). Use "console0", etc or
-pipeinput CONSOLE to force the /dev/ttyN method.
Note you can change VT remotely using the chvt(1) command.
Sometimes switching out and back corrects the framebuffer state.
To skip input injecting entirely use "consolex".
The string "/dev/fb0" (1, etc) can be used instead of "console".
This can be used to specify a different framebuffer device, e.g.
/dev/fb1. As a shortcut the "/dev/" can be dropped. If the name is
something nonstandard, use "console:/dev/foofb"
If you do not want x11vnc to guess the framebuffer's WxHxB and
masks automatically (sometimes the kernel given inaccurate
information), specify them with a @WxHxB at the end of the string.
The above is just an example of what can be done. Note that if you
really want to view and interact with the Linux Text console it is
better to use the more accurate and faster LinuxVNC program. The
advantage x11vnc -rawfb might have is that it can allow interaction
with a non-text application, e.g. one based on SVGAlib or
[572]Qt-embedded Also, for example the [573]VMWare Fullscreen mode is
actually viewable under -rawfb and can be interacted with if uinput is
enabled.
If the Linux uinput driver is available then full keystroke and mouse
input into the Linux console can be performed. You may be able to
enable uinput via commands like these:
modprobe uinput
mknod /dev/input/uinput c 10 223
The -rawfb and -pipeinput features are intended to help one creatively
"get out of a jam" (say on a legacy or embedded device) where X is
absent or doesn't work properly. Feedback and bug reports are welcome.
For more control and less overhead use libvncserver in your own C
program that passes the framebuffer to libvncserver.
Q-92: Can I export via VNC a Webcam or TV tuner framebuffer using
x11vnc?
Yes, this is possible to some degree with the [574]-rawfb option.
There is no X11 involved: snapshots from the video capture device are
used for the screen image data. See the [575]previous FAQ on -rawfb
for background. For best results, use x11vnc version 0.8.1 or later.
Roughly, one would do something like this:
x11vnc -rawfb snap:/dev/video@320x240x32
This requires that the system allows simple read(2) access to the
video device. This is true for video4Linux on Linux kernel 2.6 and
later (it won't work for 2.4, you'll need a separate program to
snapshot to a file that you point -rawfb to; ask me if it is not clear
what to do).
The "snap:" enforces [576]-snapfb mode which appears to be necessary.
The read pointer for video capture devices cannot be repositioned
(which would be needed for scanline polling), but you can read a full
frame of data from the device.
On Linux, if the Video4Linux API is present or the v4l-info(1) program
(related to xawtv) exists in in PATH, then x11vnc can be instructed to
try it to determine the -rawfb WxHxB parameters for you automatically.
In this case one would just type:
x11vnc -rawfb video
or "-rawfb video1" for the 2nd video device, etc.
x11vnc has also been extended to use the Video4Linux API over v4l-info
if it is available at build time. This enables setting parameters
(e.g. size and brightness) via x11vnc. See the description below.
Without Video4Linux you will need to initialize the settings of the
video device using something like xawtv or spcaview (and then hope the
settings persist until x11vnc reopens the device).
Many video4linux drivers tend to set the framebuffer to be 24bpp (as
opposed to 32bpp). Since this can cause problems with VNC viewers,
etc, the [577]-24to32 option will be automatically imposed when in
24bpp.
Note that by its very nature, video capture involves rapid change in
the framebuffer. This is especially true for cameras where slight
wavering in brightness is always happening. This can lead to much
network bandwidth consumption for the VNC traffic and also local CPU
and I/O resource usage. You may want to experiment with "dialing down"
the framerate via the [578]-wait, [579]-slow_fb, or [580]-defer
options. Decreasing the window size and bpp also helps.
Setting Camera/Tuner parameters via x11vnc:
There is also some support for setting parameters of the capture
device. This is done via "-rawfb video:<settings>". This could be
useful for unattended startup at boottime, etc. Here is the -help
description:
A more sophisticated video device scheme allows initializing the
device's settings using:
-rawfb video:<settings>
The prefix could also be, as above, e.g. "video1:" to specify the
device file. The v4l API must be available for this to work.
Otherwise, you will need to try to initialize the device with an
external program, e.g. xawtv, spcaview, and hope they persist when
x11vnc re-opens the device.
<settings> is a comma separated list of key=value pairs. The
device's brightness, color, contrast, and hue can be set to
percentages, e.g. br=80,co=50,cn=44,hu=60.
The device filename can be set too if needed (if it does not start
with "video"), e.g. fn=/dev/qcam.
The width, height and bpp of the framebuffer can be set via, e.g.,
w=160,h=120,bpp=16.
Related to the bpp above, the pixel format can be set via the
fmt=XXX, where XXX can be one of: GREY, HI240, RGB555, RGB565,
RGB24, and RGB32 (with bpp 8, 8, 16, 16, 24, and 32 respectively).
See http://www.linuxtv.org for more info (V4L api).
For TV/rf tuner cards one can set the tuning mode via tun=XXX where
XXX can be one of PAL, NTSC, SECAM, or AUTO.
One can switch the input channel by the inp=XXX setting, where XXX
is the name of the input channel (Television, Composite1, S-Video,
etc). Use the name that is in the information about the device that
is printed at startup.
For input channels with tuners (e.g. Television) one can change
which station is selected by the sta=XXX setting. XXX is the
station number. Currently only the ntsc-cable-us (US cable)
channels are built into x11vnc. See the -freqtab option below to
supply one from xawtv. If XXX is greater than 500, then it is
interpreted as a raw frequency in KHz.
Example:
-rawfb video:br=80,w=320,h=240,fmt=RGB32,tun=NTSC,sta=47
one might need to add inp=Television too for the input channel to
be TV if the card doesn't come up by default in that one.
Note that not all video capture devices will support all of the
above settings.
See the -pipeinput VID option below for a way to control the
settings through the VNC Viewer via keystrokes.
As above, if you specify a "@WxHxB..." after the <settings> string
they are used verbatim: the device is not queried for the current
values. Otherwise the device will be queried.
Also, if you supply the "-pipeinput VID" (or use "-rawfb Video")
option you can control the settings to some degree via keystroke
mappings, e.g. B to increase the brightness or Up arrow to change the
TV station:
For "-pipeinput VID" and you are using the -rawfb for a video
capture device, then an internal list of keyboard mappings is used
to set parameters of the video. The mappings are:
"B" and "b" adjust the brightness up and down.
"H" and "h" adjust the hue.
"C" and "c" adjust the colour.
"N" and "n" adjust the contrast.
"S" and "s" adjust the size of the capture screen.
"I" and "i" cycle through input channels.
Up and Down arrows adjust the station (if a tuner)
F1, F2, ..., F6 will switch the video capture pixel
format to HI240, RGB565, RGB24, RGB32, RGB555, and
GREY respectively. See -rawfb video for details.
See also the [581]-freqtab option to supply your own xawtv channel to
frequency mappings for your country (only ntsc-cable-us is built into
x11vnc).
Q-93: Can I connect via VNC to a Qt-embedded/Qtopia application
running on my handheld or PC using the Linux console framebuffer (i.e.
not X11)?
Yes, the basic method for this is the [582]-rawfb scheme where the
Linux console framebuffer (usually /dev/fb0) is polled and the uinput
driver is used to inject keystrokes and mouse input. Often you will
just have to type:
x11vnc -rawfb console
(you may need to enable the uinput driver on the system via "modprobe
uinput; mknod /dev/input/uinput c 10 223") If this does not find the
correct frame buffer properties figure them out or guess them and use
something like:
x11vnc -rawfb /dev/fb0@640x480x16
Also, to force usage of the uinput injection method use "-pipeinput
UINPUT". See the [583]-pipeinput description for tunable parameters,
etc.
One problem with the x11vnc uinput scheme is that it cannot guess the
mouse motion "acceleration" used by the windowing application (e.g.
QWS or X11). For X11 and Qt-embedded the acceleration is usually 2
(i.e. a dx of 1 from the mouse yields a 2 pixel displacement of the
mouse cursor). The default x11vnc uses is 2, since that is often used.
However for one Qt-embedded system we needed to do:
x11vnc -rawfb console -pipeinput UINPUT:accel=4.0
to get reasonable positioning of the mouse.
Even with the correct acceleration setting there is stil some drift
(probably because of the mouse threshold where the acceleration kicks
in) and so x11vnc needs to reposition the cursor from 0,0 about 5
times a second. See the [584]-pipeinput UINPUT option for tuning
parameters that can be set (there are some experimental thresh=N
tuning parameters as well)
Currently, one can expect mouse input to be a little flakey. All in
all, the Linux framebuffer input mechanism for Qt-embedded framebuffer
apps is not perfect, but it is usable.
If you need to create a smaller x11vnc binary for a handheld
environment be sure to run strip(1) on it and also consider
configuring with, e.g. "env CPPFLAGS='-DSMALL_FOOTPRINT=1' ./configure
..." to remove rarely used features and large texts (use 2 or 3
instead of 1 to remove more). Currently (Jul/2006) this can lower the
size of the x11vnc from 1.1MB to 0.6-0.7MB.
The x11vnc uinput method applies to nearly anything on the Linux
framebuffer console, not just Qt-embedded/Qtopia. DirectFB, SDL using
fbcon driver, SVGAlib applications can also be viewed and interacted
with. Even a Linux X session can be viewed and interacted with without
using X11 (and x11vnc does not have to terminate when the X server
restarts!). The Linux Text consoles (F1-F6) also work.
Note that Qt-embedded supplies its own VNC graphics driver, but it
cannot do both the Linux console framebuffer and VNC at the same time,
which is often what is desired from VNC.
Q-94: Can I use x11vnc to record a Shock Wave Flash (or other format)
video of my desktop, e.g. to record a tutorial or demo?
Yes, it is possible with a number of tools that record VNC and
transform it to swf format or others. One such popular tool is
[585]pyvnc2swf. There are a number of [586]tutorials on how to do
this. Another option is to use the vnc2mpg that comes in the
LibVNCServer package.
An important thing to remember when doing this is that tuning
parameters should be applied to x11vnc to speed up its polling for
this sort of application, e.g. "-wait 10 -defer 10".
[Misc: Clipboard, File Transfer, Sound, Beeps, Thanks, etc.]
Q-95: Does the Clipboard/Selection get transferred between the
vncviewer and the X display?
As of Jan/2004 x11vnc supports the "CutText" part of the rfb protocol.
Furthermore, x11vnc is able to hold the PRIMARY and CLIPBOARD
selection (Xvnc does not seem to do this). If you don't want the
Clipboard/Selection exchanged use the [587]-nosel option. If you don't
want the PRIMARY selection to be polled for changes use the
[588]-noprimary option. (with a similar thing for CLIPBOARD). You can
also fine-tune it a bit with the [589]-seldir dir option and also
[590]-input.
You may need to watch out for desktop utilities such as KDE's
"Klipper" that do odd things with the selection, clipboard, and
cutbuffers.
Q-96: Can I transfer files back and forth with x11vnc?
As of Oct/2005 and May/2006 x11vnc enables, respectively, the TightVNC
and UltraVNC file transfer implementations that were added to
libvncserver. This currently works with TightVNC and UltraVNC viewers
(and Windows viewers only support filetransfer it appears).
TightVNC file transfer is on by default, if you want to disable it use
the [591]-nofilexfer option. UltraVNC file transfer is currently off
by default, to enable it use something like "-rfbversion 3.6
-permitfiletransfer"
options (UltraVNC incorrectly uses the RFB protocol version to
determine if its features are available, so x11vnc has to pretend to
be version 3.6).
Q-97: How can I hear the sound (audio) from the remote applications on
the desktop I am viewing via x11vnc?
You will have to use an external network audio mechanism for this.
Audio is not part of the VNC protocol.
We show a simple unix to unix esd example here (artsd should be
possible too, and perhaps even one or both of these have been ported
to Windows so you can redirect the sound there).
First you will need a tunnel to redirect the audio from the remote
machine to the one you sitting at. We use an ssh tunnel:
sitting-here> ssh -C -R 16001:localhost:16001 far-away.east
Or one could combine this with the VNC tunnel at the same time, e.g.:
sitting-here> ssh -C -R 16001:localhost:16001 -L 5900:localhost:5900 far-away
.east 'x11vnc -localhost -display :0'
Port 16001 is the default ESD uses. So when an application on the
remote desktop makes a sound it will connect to this tunnel and be
redirected to port 16001 on the local machine (sitting-here in this
example). The -C option is an attempt to compress the audio a little
bit.
So we next need a local (sitting-here) esd daemon running that will
receive those requests and play them on the local sound device:
sitting-here> esd -promiscuous -port 16001 -tcp
See the esd(1) man page for the meaning of the options (the above are
not very secure).
To test this sound tunnel, we use the esdplay program to play a simple
.wav file:
far-away> esdplay -s localhost:16001 im_so_happy.wav
If you hear the sound (Captain Kirk in this example), that means you
are in great shape.
To run individual audio applications you can use the esddsp(1)
command:
far-away> esddsp -s localhost:16001 xmms
Then you could try playing some sounds inside xmms. You could also set
the environment variable ESPEAKER=localhost:16001 to not need to
supply the -s option all the time. (for reasons not clear, sometimes
esddsp can figure it out on its own). All the script esddsp does is to
set ESPEAKER and LD_PRELOAD for you so that when the application opens
the sound device (usually /dev/dsp) its interactions with the device
will be intercepted and sent to the esd daemon running on sitting-here
(that in turn writes them to the real, local /dev/dsp.
Redirecting All sound:
It does not seem to be possible to switch all of the sound of the
remote machine from its sound device to the above esd+ssh tunnel
without some preparation. But it can be done reasonably well if you
prepare (i.e. restart) the desktop with this in mind.
Here is one way to redirect all sound. The idea is we run the entire
desktop with sound directed to localhost:16001. When we are sitting at
far-away.east we run "esd -promiscuous -port 16001 -tcp" on
far-away.east (to be able to hear the sound). However, when we are
sitting at sitting-here.west we kill that esd process and run that
same esd command on sitting-here.west and start up the above ssh
tunnel. This is a little awkward, but with some scripts one would
probably kill and restart the esd processes automatically when x11vnc
is used.
So next we have to run the whole desktop pointing toward our esd. Here
is a simple way to test. Log in to the machine via the "FailSafe"
desktop. Then in the lone terminal type something like:
esddsp -s localhost:16001 gnome-session
or:
esddsp -s localhost:16001 startkde
where the last part is whatever command starts your desktop (even
fvwm2). This causes the environment variables ESPEAKER and LD_PRELOAD
to be set appropriately and every application (processes with the
desktop as an ancestor) will use them. If this scheme works well you
can make it less klunky by adding the command to your ~/.xsession,
etc. file that starts your default desktop. Or you may be able to
configure your desktop to use localhost:16001, or whatever is needed,
via a gui configuration panel. Some Notes:
* Not all audio applications are compatible with the esd and artsd
mechanisms, but many are.
* The audio is not compressed so you probably need a broadband or
faster connection. Listening to music may not be very pleasant...
(Although we found streaming music from across the US over cable
modem worked OK, but took 200 KB/sec, to use less bandwidth
consider something like "ssh far-away.east 'cat favorite.mp3' |
mpg123 -b 4000 -")
* Linux does not seem to have the concept of LD_PRELOAD_64 so if you
run on a mixed 64- and 32-bit ABI system (e.g. AMD x86_64) some of
the applications will fail to run because LD_PRELOAD will point to
libraries of the wrong wordsize.
Q-98: Why don't I hear the "Beeps" in my X session (e.g. when typing
tput bel in an xterm)?
As of Dec/2003 "Beep" XBell events are tracked by default. The X
server must support the XKEYBOARD extension (this is not on by default
in Solaris, see Xserver(1) for how to turn it on via +kb), and so you
won't hear them if the extension is not present.
If you don't want to hear the beeps use the [592]-nobell option. If
you want to hear the audio from the remote applications, consider
trying a [593]redirector such as esd.
Contributions:
Q-99: Thanks for your program and for your help! Can I make a
donation?
Please do (any amount is appreciated) and thank you for your support!
Click on the PayPal button below for more info.
[PayPal]
References
1. http://www.karlrunge.com/x11vnc/index.html#faq
2. http://www.karlrunge.com/x11vnc/index.html#downloading
3. http://www.karlrunge.com/x11vnc/index.html#building
4. http://www.karlrunge.com/x11vnc/index.html#beta-test
5. http://www.karlrunge.com/x11vnc/index.html#faq-thanks
6. http://www.karlrunge.com/x11vnc/index.html#faq-thanks
7. http://www.karlrunge.com/x11vnc/index.html#faq-ssl-tunnel-int
8. http://www.karlrunge.com/x11vnc/index.html#faq-userlogin
9. http://www.karlrunge.com/x11vnc/index.html#faq-scaling
10. http://www.karlrunge.com/x11vnc/index.html#faq-ssl-tunnel-viewers
11. http://www.karlrunge.com/x11vnc/index.html#faq-filexfer
12. http://www.karlrunge.com/x11vnc/index.html#faq-video
13. http://www.karlrunge.com/x11vnc/index.html#faq
14. http://www.karlrunge.com/x11vnc/disclaimer.html
15. http://www.karlrunge.com/x11vnc/index.html#contact
16. http://www.realvnc.com/
17. http://www.tightvnc.com/
18. http://www.ultravnc.com/
19. http://www.redstonesoftware.com/vnc.html
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21. http://www.tightvnc.com/download.html
22. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-auth
23. http://www.karlrunge.com/x11vnc/index.html#faq-xperms
24. http://www.karlrunge.com/x11vnc/index.html#faq-xperms
25. http://www.karlrunge.com/x11vnc/index.html#faq-viewer-download
26. http://www.sun.com/software/solaris/freeware/
27. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-forever
28. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-forever
29. http://www.karlrunge.com/x11vnc/index.html#faq-service
30. http://www.karlrunge.com/x11vnc/index.html#faq-passwd
31. http://www.karlrunge.com/x11vnc/index.html#vnc_password_file
32. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-connect
33. http://www.karlrunge.com/x11vnc/index.html#vnc_password_file
34. http://www.karlrunge.com/x11vnc/index.html#faq-inetd
35. http://www.karlrunge.com/x11vnc/index.html#tightvnc_via
36. http://www.karlrunge.com/x11vnc/chainingssh.html
37. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-bg
38. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-connect
39. http://www.karlrunge.com/x11vnc/index.html#faq-inetd
40. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-rfbauth
41. http://www.karlrunge.com/x11vnc/index.html#faq-passwd
42. http://www.karlrunge.com/x11vnc/index.html#faq-passwdfile
43. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-passwdfile
44. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-usepw
45. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-ssl
46. http://www.karlrunge.com/x11vnc/index.html#faq-allow-opt
47. http://www.karlrunge.com/x11vnc/index.html#faq-tcp_wrappers
48. http://www.stunnel.org/
49. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-ssl
50. http://www.karlrunge.com/x11vnc/index.html#faq-ssl-tunnel-int
51. http://sourceforge.net/projects/libvncserver/
52. http://sourceforge.net/project/showfiles.php?group_id=32584&package_id=119006&release_id=431725
53. http://sourceforge.net/project/shownotes.php?release_id=431725&group_id=32584
54. http://www.karlrunge.com/x11vnc/x11vnc-0.8.3.tar.gz
55. http://www.karlrunge.com/x11vnc/index.html#faq-binaries
56. http://www.tightvnc.com/download.html
57. http://www.realvnc.com/download-free.html
58. http://sourceforge.net/projects/cotvnc/
59. http://www.ultravnc.com/
60. http://www.karlrunge.com/x11vnc/rx11vnc
61. http://www.karlrunge.com/x11vnc/rx11vnc.pl
62. http://www.sunfreeware.com/
63. http://www.karlrunge.com/x11vnc/bins
64. http://www.karlrunge.com/x11vnc/index.html#solarisbuilding
65. http://www.karlrunge.com/x11vnc/miscbuild.html
66. ftp://ftp.uu.net/graphics/jpeg/
67. http://www.gzip.org/zlib/
68. http://www.sunfreeware.com/
69. http://www.karlrunge.com/x11vnc/index.html#faq-solaris251build
70. http://www.karlrunge.com/x11vnc/x11vnc-0.8.3.tar.gz
71. http://www.karlrunge.com/x11vnc/bins
72. mailto:x11vnc-beta@karlrunge.com
73. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-rawfb
74. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-pipeinput
75. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-display_WAIT
76. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-display
77. http://www.karlrunge.com/x11vnc/index.html#faq-userlogin
78. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-grabkdb
79. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-grabptr
80. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-allowedcmds
81. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-nocmds
82. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-env
83. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-allinput
84. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-rawfb
85. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-license
86. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-ssl
87. http://www.openssl.org/
88. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-stunnel
89. http://www.stunnel.org/
90. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-sslverify
91. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-https
92. http://www.karlrunge.com/x11vnc/index.html#ssl_vncviewer
93. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-unixpw
94. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-unixpw_nis
95. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-ssl
96. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-localhost
97. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-stunnel
98. http://www.karlrunge.com/x11vnc/index.html#faq-userlogin
99. http://www.karlrunge.com/x11vnc/prevrels.html
100. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-solid
101. http://www.tightvnc.com/
102. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-rfbport
103. http://www.karlrunge.com/x11vnc/x11vnc_opts.html
104. http://www.karlrunge.com/x11vnc/index.html#faq-passwd
105. http://www.karlrunge.com/x11vnc/recurse_x11vnc.jpg
106. http://wwws.sun.com/sunray/index.html
107. http://www.karlrunge.com/x11vnc/sunray.html
108. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-scrollcopyrect
109. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-wireframe
110. http://www.karlrunge.com/x11vnc/index.html#faq-xvfb
111. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-cursor
112. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-overlay
113. http://www.karlrunge.com/x11vnc/index.html#faq-sound
114. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-scrollcopyrect
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116. http://www.karlrunge.com/x11vnc/index.html#faq-thanks
117. http://www.karlrunge.com/x11vnc/index.html#faq-xperms
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119. http://www.karlrunge.com/x11vnc/index.html#faq-missing-xtest
120. http://www.karlrunge.com/x11vnc/index.html#faq-solaris251build
121. http://www.karlrunge.com/x11vnc/index.html#faq-binaries
122. http://www.karlrunge.com/x11vnc/index.html#faq-viewer-download
123. http://www.karlrunge.com/x11vnc/index.html#faq-cmdline-opts
124. http://www.karlrunge.com/x11vnc/index.html#faq-config-file
125. http://www.karlrunge.com/x11vnc/index.html#faq-gui-tray
126. http://www.karlrunge.com/x11vnc/index.html#faq-quiet-bg
127. http://www.karlrunge.com/x11vnc/index.html#faq-sigpipe
128. http://www.karlrunge.com/x11vnc/index.html#faq-build-customizations
129. http://www.karlrunge.com/x11vnc/index.html#faq-win2vnc
130. http://www.karlrunge.com/x11vnc/index.html#faq-win2vnc-8bpp
131. http://www.karlrunge.com/x11vnc/index.html#faq-8bpp
132. http://www.karlrunge.com/x11vnc/index.html#faq-overlays
133. http://www.karlrunge.com/x11vnc/index.html#faq-windowid
134. http://www.karlrunge.com/x11vnc/index.html#faq-transients-id
135. http://www.karlrunge.com/x11vnc/index.html#faq-24bpp
136. http://www.karlrunge.com/x11vnc/index.html#faq-noshm
137. http://www.karlrunge.com/x11vnc/index.html#faq-xterminal-xauth
138. http://www.karlrunge.com/x11vnc/index.html#faq-sunrays
139. http://www.karlrunge.com/x11vnc/index.html#faq-stop-bg
140. http://www.karlrunge.com/x11vnc/index.html#faq-remote_control
141. http://www.karlrunge.com/x11vnc/index.html#faq-passwd
142. http://www.karlrunge.com/x11vnc/index.html#faq-passwd-noecho
143. http://www.karlrunge.com/x11vnc/index.html#faq-passwdfile
144. http://www.karlrunge.com/x11vnc/index.html#faq-multipasswd
145. http://www.karlrunge.com/x11vnc/index.html#faq-unix-passwords
146. http://www.karlrunge.com/x11vnc/index.html#faq-forever-shared
147. http://www.karlrunge.com/x11vnc/index.html#faq-allow-opt
148. http://www.karlrunge.com/x11vnc/index.html#faq-tcp_wrappers
149. http://www.karlrunge.com/x11vnc/index.html#faq-listen-interface
150. http://www.karlrunge.com/x11vnc/index.html#faq-listen-localhost
151. http://www.karlrunge.com/x11vnc/index.html#faq-input-opt
152. http://www.karlrunge.com/x11vnc/index.html#faq-accept-opt
153. http://www.karlrunge.com/x11vnc/index.html#faq-users-opt
154. http://www.karlrunge.com/x11vnc/index.html#faq-blockdpy
155. http://www.karlrunge.com/x11vnc/index.html#faq-gone-lock
156. http://www.karlrunge.com/x11vnc/index.html#faq-ssh-unix
157. http://www.karlrunge.com/x11vnc/index.html#faq-ssh-putty
158. http://www.karlrunge.com/x11vnc/index.html#faq-ssl-tunnel-ext
159. http://www.karlrunge.com/x11vnc/index.html#faq-ssl-tunnel-int
160. http://www.karlrunge.com/x11vnc/index.html#faq-ssl-tunnel-viewers
161. http://www.karlrunge.com/x11vnc/index.html#faq-ssl-java-viewer-proxy
162. http://www.karlrunge.com/x11vnc/index.html#faq-ssl-portal
163. http://www.karlrunge.com/x11vnc/index.html#faq-ssl-ca
164. http://www.karlrunge.com/x11vnc/index.html#faq-service
165. http://www.karlrunge.com/x11vnc/index.html#faq-display-manager
166. http://www.karlrunge.com/x11vnc/index.html#faq-inetd
167. http://www.karlrunge.com/x11vnc/index.html#faq-userlogin
168. http://www.karlrunge.com/x11vnc/index.html#faq-loop
169. http://www.karlrunge.com/x11vnc/index.html#faq-java-http
170. http://www.karlrunge.com/x11vnc/index.html#faq-reverse-connect
171. http://www.karlrunge.com/x11vnc/index.html#faq-xvfb
172. http://www.karlrunge.com/x11vnc/index.html#faq-headless
173. http://www.karlrunge.com/x11vnc/index.html#faq-solshm
174. http://www.karlrunge.com/x11vnc/index.html#faq-less-resource
175. http://www.karlrunge.com/x11vnc/index.html#faq-more-resource
176. http://www.karlrunge.com/x11vnc/index.html#faq-slow-link
177. http://www.karlrunge.com/x11vnc/index.html#faq-xdamage
178. http://www.karlrunge.com/x11vnc/index.html#faq-pointer-mode
179. http://www.karlrunge.com/x11vnc/index.html#faq-wireframe
180. http://www.karlrunge.com/x11vnc/index.html#faq-scrollcopyrect
181. http://www.karlrunge.com/x11vnc/index.html#faq-cursor-shape
182. http://www.karlrunge.com/x11vnc/index.html#faq-xfixes-alpha
183. http://www.karlrunge.com/x11vnc/index.html#faq-xfixes-alpha-hacks
184. http://www.karlrunge.com/x11vnc/index.html#faq-cursor-arrow
185. http://www.karlrunge.com/x11vnc/index.html#faq-cursor-positions
186. http://www.karlrunge.com/x11vnc/index.html#faq-buttonmap-opt
187. http://www.karlrunge.com/x11vnc/index.html#faq-altgr
188. http://www.karlrunge.com/x11vnc/index.html#faq-greaterless
189. http://www.karlrunge.com/x11vnc/index.html#faq-greaterless-sloppy
190. http://www.karlrunge.com/x11vnc/index.html#faq-xkbmodtweak
191. http://www.karlrunge.com/x11vnc/index.html#faq-repeated-keys
192. http://www.karlrunge.com/x11vnc/index.html#faq-repeated-keys-still
193. http://www.karlrunge.com/x11vnc/index.html#faq-remap-opt
194. http://www.karlrunge.com/x11vnc/index.html#faq-sun-alt-meta
195. http://www.karlrunge.com/x11vnc/index.html#faq-remap-button-click
196. http://www.karlrunge.com/x11vnc/index.html#faq-remap-capslock
197. http://www.karlrunge.com/x11vnc/index.html#faq-scrollbars
198. http://www.karlrunge.com/x11vnc/index.html#faq-scaling
199. http://www.karlrunge.com/x11vnc/index.html#faq-xinerama
200. http://www.karlrunge.com/x11vnc/index.html#faq-multi-screen
201. http://www.karlrunge.com/x11vnc/index.html#faq-clip-screen
202. http://www.karlrunge.com/x11vnc/index.html#faq-xrandr
203. http://www.karlrunge.com/x11vnc/index.html#faq-black-screen
204. http://www.karlrunge.com/x11vnc/index.html#faq-linuxvc
205. http://www.karlrunge.com/x11vnc/index.html#faq-hidden-taskbars
206. http://www.karlrunge.com/x11vnc/index.html#faq-vmware
207. http://www.karlrunge.com/x11vnc/index.html#faq-rawfb
208. http://www.karlrunge.com/x11vnc/index.html#faq-video
209. http://www.karlrunge.com/x11vnc/index.html#faq-qt-embedded
210. http://www.karlrunge.com/x11vnc/index.html#faq-record-swf
211. http://www.karlrunge.com/x11vnc/index.html#faq-clipboard
212. http://www.karlrunge.com/x11vnc/index.html#faq-filexfer
213. http://www.karlrunge.com/x11vnc/index.html#faq-sound
214. http://www.karlrunge.com/x11vnc/index.html#faq-beeps
215. http://www.karlrunge.com/x11vnc/index.html#faq-thanks
216. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-display
217. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-auth
218. http://www.karlrunge.com/x11vnc/index.html#faq-display-manager
219. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-users
220. http://www.karlrunge.com/x11vnc/index.html#solarisbuilding
221. http://www.karlrunge.com/x11vnc/x11vnc_sunos4.html
222. http://www.karlrunge.com/x11vnc/index.html#building
223. http://www.karlrunge.com/x11vnc/index.html#faq-build
224. http://packages.debian.org/x11vnc
225. http://www.linuxpackages.net/search_view.php?by=name&name=x11vnc
226. http://dag.wieers.com/packages/x11vnc/
227. http://dries.ulyssis.org/rpm/packages/x11vnc/info.html
228. http://linux01.gwdg.de/~pbleser/rpm-navigation.php?cat=Network/x11vnc/
229. http://www.sunfreeware.com/
230. http://www.freebsd.org/cgi/ports.cgi?query=x11vnc&stype=all
231. http://www.freshports.org/net/x11vnc
232. http://www.openbsd.org/3.9_packages/i386/x11vnc-0.6.2.tgz-long.html
233. http://pkgsrc.se/x11/x11vnc
234. http://mike.saunby.net/770/x11vnc/
235. http://www.pdaxrom.org/ipk_feed.php?menuid=11&showfeed=unstable#x11vnc
236. http://www.focv.com/ipkg/
237. http://www.karlrunge.com/x11vnc/bins
238. http://www.tightvnc.com/download.html
239. http://www.realvnc.com/download-free.html
240. http://sourceforge.net/projects/cotvnc/
241. http://www.ultravnc.com/
242. http://www.karlrunge.com/x11vnc/x11vnc_opts.html
243. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-gui
244. http://www.karlrunge.com/x11vnc/index.html#faq-gui-tray
245. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-q
246. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-bg
247. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-o
248. http://www.karlrunge.com/x11vnc/index.html#solarisbuilding
249. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-nofb
250. http://fredrik.hubbe.net/x2vnc.html
251. http://www.hubbe.net/~hubbe/win2vnc.html
252. http://www.deboer.gmxhome.de/
253. http://sourceforge.net/projects/win2vnc/
254. http://fredrik.hubbe.net/x2vnc.html
255. http://freshmeat.net/projects/x2x/
256. http://ftp.digital.com/pub/Digital/SRC/x2x/
257. http://zapek.com/software/zvnc/
258. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-visual
259. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-flashcmap
260. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-8to24
261. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-notruecolor
262. http://www.karlrunge.com/x11vnc/index.html#faq-8bpp
263. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-overlay
264. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-8to24
265. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-overlay
266. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-8to24
267. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-flashcmap
268. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-fixscreen
269. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-8to24
270. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-id
271. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-8to24
272. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-overlay
273. http://www.karlrunge.com/x11vnc/index.html#faq-overlays
274. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-id
275. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-sid
276. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-24to32
277. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-display
278. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-noshm
279. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-flipbyteorder
280. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-auth
281. http://www.karlrunge.com/x11vnc/index.html#xauth_pain
282. http://www.karlrunge.com/x11vnc/index.html#faq-noshm
283. http://wwws.sun.com/sunray/index.html
284. http://www.karlrunge.com/x11vnc/sunray.html
285. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-remote
286. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-query
287. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-forever
288. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-bg
289. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-clear_mods
290. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-clear_keys
291. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-remote
292. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-query
293. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-gui
294. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-storepasswd
295. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-rfbauth
296. http://www.karlrunge.com/x11vnc/index.html#faq-passwdfile
297. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-usepw
298. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-viewpasswd
299. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-passwd
300. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-passwdfile
301. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-rfbauth
302. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-passwdfile
303. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-unixpw
304. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-unixpw_nis
305. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-localhost
306. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-stunnel
307. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-ssl
308. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-ssl
309. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-localhost
310. http://www.karlrunge.com/x11vnc/index.html#tunnelling
311. http://www.karlrunge.com/x11vnc/index.html#faq-ssl-tunnel
312. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-accept
313. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-forever
314. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-shared
315. http://www.karlrunge.com/x11vnc/index.html#tunnelling
316. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-ssl
317. http://www.karlrunge.com/x11vnc/index.html#faq-passwd
318. http://www.karlrunge.com/x11vnc/index.html#faq-passwdfile
319. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-allow
320. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-localhost
321. http://www.karlrunge.com/x11vnc/index.html#faq-tcp_wrappers
322. http://www.karlrunge.com/x11vnc/index.html#faq-inetd
323. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-listen
324. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-allow
325. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-localhost
326. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-allow
327. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-localhost
328. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-input
329. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-accept
330. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-viewonly
331. ftp://ftp.x.org/
332. http://www.karlrunge.com/x11vnc/dtVncPopup
333. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-gone
334. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-afteraccept
335. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-users
336. http://www.karlrunge.com/x11vnc/blockdpy.c
337. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-accept
338. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-gone
339. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-gone
340. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-afteraccept
341. http://www.karlrunge.com/x11vnc/index.html#tunnelling
342. http://www.karlrunge.com/x11vnc/index.html#tunnelling
343. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-localhost
344. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-rfbauth
345. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-passwdfile
346. http://www.karlrunge.com/x11vnc/index.html#gateway_double_ssh
347. http://www.karlrunge.com/x11vnc/index.html#tunnelling
348. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-connect
349. http://www.stunnel.org/
350. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-ssl
351. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-stunnel
352. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-sslverify
353. http://www.karlrunge.com/x11vnc/index.html#faq-ssl-tunnel-int
354. http://www.stunnel.org/
355. http://www.karlrunge.com/x11vnc/ssl.html
356. http://www.karlrunge.com/x11vnc/index.html#ssl_vncviewer
357. http://www.karlrunge.com/x11vnc/ssl.html
358. http://www.securityfocus.com/infocus/1677
359. http://www.karlrunge.com/x11vnc/ssl.html
360. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-inetd
361. http://www.karlrunge.com/x11vnc/index.html#faq-ssl-tunnel-viewers
362. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-httpdir
363. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-http
364. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-ssl
365. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-https
366. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-stunnel
367. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-ssl
368. http://www.karlrunge.com/x11vnc/index.html#ssl_vncviewer
369. http://www.karlrunge.com/x11vnc/index.html#faq-ssl-tunnel-ext
370. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-ssl
371. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-stunnel
372. http://www.karlrunge.com/x11vnc/index.html#faq-ssl-tunnel-viewers
373. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-ssl
374. http://www.openssl.org/
375. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-stunnel
376. http://www.stunnel.org/
377. http://www.karlrunge.com/x11vnc/ssl.html
378. http://www.karlrunge.com/x11vnc/index.html#ssl_vncviewer
379. http://www.karlrunge.com/x11vnc/ssl.html
380. http://www.karlrunge.com/x11vnc/index.html#faq-ssl-tunnel-viewers
381. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-httpdir
382. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-http
383. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-https
384. http://www.karlrunge.com/x11vnc/index.html#faq-ssl-portal
385. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-https
386. http://www.karlrunge.com/x11vnc/index.html#faq-ssl-tunnel-ext
387. http://www.karlrunge.com/x11vnc/ssl_vncviewer
388. http://www.karlrunge.com/x11vnc/ssl-portal.html
389. http://www.karlrunge.com/x11vnc/ssl.html
390. http://www.karlrunge.com/x11vnc/index.html#ssl_vncviewer
391. http://www.karlrunge.com/x11vnc/index.html#faq-ssl-tunnel-viewers
392. http://www.karlrunge.com/x11vnc/ssl-portal.html
393. http://www.karlrunge.com/x11vnc/ssl.html
394. http://www.karlrunge.com/x11vnc/index.html#display-manager-continuously
395. http://www.karlrunge.com/x11vnc/index.html#faq-inetd
396. http://www.karlrunge.com/x11vnc/index.html#faq-userlogin
397. http://www.karlrunge.com/x11vnc/index.html#x11vnc_loop
398. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-auth
399. http://www.karlrunge.com/x11vnc/index.html#dtlogin_solaris
400. http://www.jirka.org/gdm-documentation/x241.html
401. http://www.karlrunge.com/x11vnc/x11vnc_loop
402. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-loop
403. http://www.karlrunge.com/x11vnc/index.html#faq-xterminal-xauth
404. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-inetd
405. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-q
406. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-auth
407. http://www.karlrunge.com/x11vnc/index.html#faq-userlogin
408. http://www.karlrunge.com/x11vnc/index.html#faq-inetd
409. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-unixpw
410. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-display_WAIT
411. http://www.karlrunge.com/x11vnc/index.html#stunnel-inetd
412. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-display_WAIT
413. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-unixpw
414. http://www.karlrunge.com/x11vnc/index.html#faq-unix-passwords
415. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-users
416. http://www.karlrunge.com/x11vnc/index.html#faq-ssl-tunnel-int
417. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-loop
418. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-httpdir
419. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-http
420. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-connect
421. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-remote
422. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-vncconnect
423. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-add_keysyms
424. http://www.karlrunge.com/x11vnc/index.html#faq-linuxvc
425. http://www.karlrunge.com/x11vnc/Xdummy
426. http://www.karlrunge.com/x11vnc/index.html#display-manager-continuously
427. http://www.karlrunge.com/x11vnc/shm_clear
428. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-onetile
429. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-noshm
430. http://www.karlrunge.com/x11vnc/index.html#faq-noshm
431. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-nap
432. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-wait
433. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-sb
434. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-onetile
435. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-fs
436. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-threads
437. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-defer
438. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-id
439. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-solid
440. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-scrollcopyrect
441. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-wireframe
442. http://www.tightvnc.com/
443. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-wireframe
444. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-scrollcopyrect
445. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-solid
446. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-speeds
447. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-nodragging
448. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-fs
449. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-wait
450. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-defer
451. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-progressive
452. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-id
453. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-nosel
454. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-nocursor
455. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-nocursorpos
456. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-readtimeout
457. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-fixscreen
458. http://www.karlrunge.com/x11vnc/index.html#fb_read_slow
459. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-xd_area
460. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-xd_mem
461. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-noxdamage
462. http://www.karlrunge.com/x11vnc/index.html#fb_read_slow
463. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-pointer_mode
464. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-pointer_mode
465. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-nodragging
466. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-pointer_mode
467. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-threads
468. http://www.karlrunge.com/x11vnc/index.html#faq-wireframe
469. http://www.karlrunge.com/x11vnc/index.html#faq-scrollcopyrect
470. http://www.karlrunge.com/x11vnc/index.html#faq-pointer-mode
471. http://www.karlrunge.com/x11vnc/index.html#fb_read_slow
472. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-wireframe
473. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-wireframe
474. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-wireframe
475. http://www.karlrunge.com/x11vnc/index.html#fb_read_slow
476. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-scrollcopyrect
477. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-wireframe
478. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-wirecopyrect
479. http://www.karlrunge.com/x11vnc/index.html#faq-wireframe
480. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-fixscreen
481. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-scr_skip
482. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-scale
483. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-scrollcopyrect
484. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-cursor
485. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-cursor
486. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-overlay
487. http://www.karlrunge.com/x11vnc/index.html#the-overlay-mode
488. http://www.karlrunge.com/x11vnc/index.html#solaris10-build
489. http://www.karlrunge.com/x11vnc/index.html#faq-xfixes-alpha-hacks
490. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-alphacut
491. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-alphafrac
492. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-alpharemove
493. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-nocursorshape
494. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-noalphablend
495. http://www.tightvnc.com/
496. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-nocursor
497. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-cursorpos
498. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-nocursorpos
499. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-nocursorshape
500. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-buttonmap
501. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-debug_pointer
502. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-buttonmap
503. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-modtweak
504. http://www.karlrunge.com/x11vnc/index.html#faq-greaterless
505. http://www.karlrunge.com/x11vnc/index.html#faq-xkbmodtweak
506. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-debug_keyboard
507. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-xkb
508. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-sloppy_keys
509. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-modtweak
510. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-modtweak
511. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-remap
512. http://www.karlrunge.com/x11vnc/index.html#faq-xkbmodtweak
513. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-debug_keyboard
514. http://www.karlrunge.com/x11vnc/index.html#faq-greaterless
515. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-xkb
516. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-sloppy_keys
517. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-modtweak
518. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-xkb
519. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-xkb
520. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-skip_keycodes
521. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-remap
522. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-add_keysyms
523. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-remap
524. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-remap
525. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-add_keysyms
526. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-norepeat
527. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-norepeat
528. http://www.karlrunge.com/x11vnc/index.html#faq-display-manager
529. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-remap
530. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-remap
531. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-remap
532. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-remap
533. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-skip_lockkeys
534. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-remap
535. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-nomodtweak
536. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-capslock
537. http://www.karlrunge.com/x11vnc/index.html#faq-scaling
538. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-scale
539. http://www.cus.cam.ac.uk/~ssb22/source/vnc-magnification.html
540. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-rfbport
541. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-gui
542. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-connect
543. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-scale_cursor
544. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-blackout
545. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-xinerama
546. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-xinerama
547. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-xwarppointer
548. http://www.karlrunge.com/x11vnc/index.html#faq-solshm
549. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-onetile
550. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-noshm
551. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-clip
552. http://www.karlrunge.com/x11vnc/index.html#faq-xinerama
553. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-id
554. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-id
555. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-xrandr
556. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-padgeom
557. http://www.karlrunge.com/x11vnc/index.html#faq-linuxvc
558. http://www.karlrunge.com/x11vnc/index.html#faq-rawfb
559. http://www.karlrunge.com/x11vnc/index.html#faq-linuxvc
560. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-id
561. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-rawfb
562. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-pipeinput
563. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-pipeinput
564. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-snapfb
565. http://www.karlrunge.com/x11vnc/index.html#faq-video
566. http://www.karlrunge.com/x11vnc/index.html#faq-xvfb
567. http://www.karlrunge.com/x11vnc/index.html#faq-qt-embedded
568. http://www.karlrunge.com/x11vnc/index.html#faq-video
569. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-rawfb
570. http://www.karlrunge.com/x11vnc/index.html#faq-video
571. http://www.karlrunge.com/x11vnc/index.html#faq-linuxvc
572. http://www.karlrunge.com/x11vnc/index.html#faq-qt-embedded
573. http://www.karlrunge.com/x11vnc/index.html#faq-vmware
574. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-rawfb
575. http://www.karlrunge.com/x11vnc/index.html#faq-rawfb
576. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-snapfb
577. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-24to32
578. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-wait
579. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-slow_fb
580. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-defer
581. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-freqtab
582. http://www.karlrunge.com/x11vnc/index.html#faq-rawfb
583. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-pipeinput
584. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-pipeinput
585. http://www.unixuser.org/~euske/vnc2swf/
586. http://wolphination.com/linux/2006/06/30/how-to-record-videos-of-your-desktop/
587. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-nosel
588. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-noprimary
589. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-seldir
590. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-input
591. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-nofilexfer
592. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-nobell
593. http://www.karlrunge.com/x11vnc/index.html#faq-sound
=======================================================================
http://www.karlrunge.com/x11vnc/chainingssh.html:
_________________________________________________________________
Chaining ssh's: Note that for use of a ssh gateway and -L redirection
to an internal host (e.g. "-L 5900:otherhost:5900") the VNC traffic
inside the firewall is not encrypted and you have to manually log into
otherhost to start x11vnc. Kyle Amon shows a method where you chain
two ssh's together that encrypts all network traffic and also
automatically starts up x11vnc on the internal workstation:
#!/bin/sh
#
gateway="example.com" # or "user@example.com"
host="labyrinth" # or "user@hostname"
user="kyle"
# Need to sleep long enough for all of the passwords and x11vnc to start up.
# The </dev/null below makes the vncviewer prompt for passwd via popup window.
#
(sleep 10; vncviewer -encodings "copyrect tight zrle zlib hextile" \
localhost:0 </dev/null >/dev/null) &
# Chain the vnc connection thru 2 ssh's, and connect x11vnc to user's display:
#
exec /usr/bin/ssh -t -L 5900:localhost:5900 $gateway \
/usr/bin/ssh -t -L 5900:localhost:5900 $host \
sudo /usr/bin/x11vnc -localhost -auth /home/$user/.Xauthority \
-rfbauth .vnc/passwd -display :0
Also note the use of sudo(1) to switch to root so that the different
user's .Xauthority file can be accessed. See the visudo(8) manpage for
details on how to set this up (remove the sudo if you do not want to
do this). One can also chain together ssh's for reverse connections
with vncviewers using the -listen option. For this case -R would
replace the -L (and 5500 the 5900, see the #2 example script above).
If the gateway machine's sshd is configured with GatewayPorts=no (the
default) then the double chaining of "ssh -R ..." will be required for
reverse connections to work.
=======================================================================
http://www.karlrunge.com/x11vnc/miscbuild.html:
_________________________________________________________________
Misc. Build problems: We collect here rare build problems some users
have reported and the corresponding workarounds. See also the [1]FAQ's
on building.
One user had a problem where the build script below was failing
because his work environment had the ENV variable set to a script that
was resetting his PATH so that gcc could no longer be found. Make sure
you do not have any ENV or BASH_ENV in your environment doing things
like that. Typing "unset ENV", etc. before configuring and building
should clear it.
One user had his bash shell compiled with --enable-xpg-echo-default
that causes some strange behavior with things like echo "\\1 ..." the
configure script executes. In particular instead of getting "\1" the
non-printable character "^A" is produced, and causes failures at
compile time like:
../rfb/rfbconfig.h:9:22: warning: extra tokens at end of #ifndef directive
The workaround is to configure like this:
env CONFIG_SHELL=/bin/sh /bin/sh ./configure
i.e. avoid using the bash with the misbehavior. A bug has been filed
against autoconf to guard against this.
AIX: one user had to add the "X11.adt" package to AIX to get build
header files like XShm.h, etc.
References
1. http://www.karlrunge.com/x11vnc/miscbuild.html#faq-build
=======================================================================
http://www.karlrunge.com/x11vnc/sunray.html:
Sun Ray Notes:
You can run x11vnc on your (connected or disconnected) [1]SunRay
session (Please remember to use settings like [2]-wait 200, [3]-sb 15,
and not running a screensaver animation (blank instead) to avoid being
a resource hog! x11vnc does induce a lot of memory I/O from polling
the X server. It also helps to have a solid background color, e.g.
[4]-solid).
You have to know the name of the machine your SunRay session X server
is running on (so you can ssh into it and start x11vnc). You also need
to know the X11 DISPLAY number for the session: on a SunRay it could
be a large number, e.g. :137, since there are many people with X
sessions (Xsun processes) on the same machine. If you don't know it,
you can get it by running who(1) in a shell on the SunRay server and
looking for the dtlocal entry with your username (and if you don't
even know which server machine has your session, you could login to
all possible ones looking at the who output for your username...).
I put some code in my ~/.dtprofile script that stores $DISPLAY in my
~/.sunray_current file at session startup and deletes it when the
session ends to make it easy to get at the hostname and X11 display
number info for my current X sessions.
SunRay Gotcha #1: Note that even though your SunRay X11 DISPLAY is
something like :137, x11vnc still tries for port 5900 as its listening
port if it can get it, in which case the VNC display (i.e. the
information you supply to the VNC viewer) is something like
sunray-server:0 (note the :0 corresponding to port 5900, it is not
:137). If it cannot get 5900, it tries for 5901, and so on. You can
also try to force the port (and thereby the VNC display) using the
[5]-rfbport NNNN option.
Especially on a busy Sun Ray server it is often difficult to find free
ports for both VNC and the HTTP Java applet server to listen on. This
script, [6]vnc_findports may be of use for doing this automatically.
It suggests x11vnc command line options based on netstat output that
lists the occupied ports. It is even more difficult to start
vncserver/Xvnc on a busy Sun Ray because then 3 ports (HTTP, VNC, and
X11), all separated by 100 are needed! This script, [7]findvncports
may be helpful as well. Both scripts start at VNC display :10 and work
their way up.
SunRay Gotcha #2: If you get an error like:
shmget(tile) failed.
shmget: No space left on device
when starting up x11vnc that most likely means all the shared memory
(shm) slots are filled up on your machine. The Solaris default is only
100, and that can get filled up in a week or so on a SunRay server
with lots of users. If the shm slot is orphaned (e.g. creator process
dies) the slot is not reclaimed. You can view the shm slots with the
"ipcs -mA" command. If there are about 100 then you've probably hit
this problem. They can be cleaned out (by the owner or by root) using
the ipcrm command. I wrote a script [8]shm_clear that finds the
orphans and lists or removes them. Longer term, have your SunRay
sysadmin add something like this to /etc/system:
set shmsys:shminfo_shmmax = 0x2000000
set shmsys:shminfo_shmmni = 0x1000
SunRay Gotcha #3: Some SunRay installations have implemented
suspending certain applications when a SunRay session is in a
disconnected state (e.g. Java Badge pulled out, utdetach, etc). This
is a good thing because it limits hoggy or runaway apps from wasting
the shared CPU resource. Think how much CPU and memory I/O is wasted
by a bunch of Firefox windows running worthless Flash animations while
your session is disconnected!
So some sites have implemented scripts to suspend (e.g. kill -STOP)
certain apps when your badge is removed from the SunRay terminal. When
you reattach, it kill -CONT them. This causes problems for viewing the
detached SunRay session via x11vnc: those suspended apps will not
respond (their windows will be blank or otherwise inactive).
What to do? Well, since you are going to be using the application you
might as well unfreeze it rather than starting up a 2nd instance. Here
is one way to do it using the kill -CONT mechanism:
kill -CONT `ps -ealf | grep ' T ' | grep $LOGNAME | awk '{print $4}'`
If you want to be a good citizen and re-freeze them before you exit
x11vnc this script could be of use:
#!/bin/sh
#
# kill -STOP/-CONT script for x11vnc (or other) SunRay usage ("freezes"
# certain apps from hogging resources when disconnected).
#
# Put here a pattern that matches the apps that are frozen:
#
appmatch="java_vm|jre|netscape-bin|firefox-bin|realplay|acroread|mozilla-bin"
if [ "X$1" = "Xfreeze" ]; then
pkill -STOP -U $LOGNAME "$appmatch"
elif [ "X$1" = "Xthaw" ]; then
pkill -CONT -U $LOGNAME "$appmatch"
elif [ "$RFB_MODE" = "afteraccept" -a "$RFB_STATE" = "NORMAL" ]; then
# a valid x11vnc login.
if [ "$RFB_CLIENT_COUNT" = "1" ]; then
# only one client present.
pkill -CONT -U $LOGNAME "$appmatch"
fi
elif [ "$RFB_MODE" = "gone" -a "$RFB_STATE" = "NORMAL" ]; then
# a valid x11vnc login.
if [ "$RFB_CLIENT_COUNT" = "0" ]; then
# last client present has just left.
pkill -STOP -U $LOGNAME "$appmatch"
fi
fi
exit 0
If you called the script "goodcitizen" you could type "goodcitizen
thaw" to unfreeze them, and then "goodcitizen freeze" to refreeze
them. One could also use these x11vnc options "-afteraccept
goodcitizen -gone goodcitizen" to do it automatically.
SunRay Gotcha #4: Recent versions of the Sun Ray Server Software
SRSS (seems to be version 3.0 or 3.1) have a "misfeature" that when
the session is disconnected (i.e. badge/smartcard out) the screen
locker (xscreensaver) will freeze the X server just when the "Enter
Password" dialog box appears. So you cannot unlock the screen remotely
via x11vnc!
Here "freeze" means "stop other X clients from inserting keyboard and
mouse input and from viewing the current contents of the screen". Or
something like that; the upshot is x11vnc can't do its normal thing.
There are several workarounds for this.
1) The easiest one by far is to put these lines in your
$HOME/.dtprofile file:
SUN_SUNRAY_UTXLOCK_PREF="/usr/openwin/bin/xlock -mode blank"
export SUN_SUNRAY_UTXLOCK_PREF
One might argue that xlock isn't particularly "pretty". (Just IMHO,
but if something like this not being pretty actually gets in the way
of your work I think some introspection may be in order. :-)
2) The problem has been traced to the pam_sunray.so PAM module.
Evidently xscreensaver invokes this pam module and it communicates
with utsessiond who in turn instructs the Xsun server to not process
any synthetic mouse/keyboard input or to update the screen
framebuffer. It is not clear if this is by design (security?) or
something else.
In any event, the problem can be avoided by commenting out the
corresponding line in /etc/pam.conf:
#xscreensaver auth sufficient /opt/SUNWut/lib/pam_sunray.so syncondisplay
Leave the other xscreensaver pam authentication lines unchanged. The
dtsession-SunRay line may also need to be commented out to avoid the
problem for CDE sessions. N.B. it is possible the application of a
SSRS patch, etc, may re-enable that /etc/pam.conf line.
3) A more drastic way is to kill the xscreensaver process from a shell
prompt whenever you connect via x11vnc and the screen is in a locked
state:
pkill -U $LOGNAME '^xscreensaver$'
And then after you are in be sure to restart it by typing something
like:
xscreensaver &
You may want to avoid restarting it until you are about to disconnect
your VNC viewer (since if it locks the screen while you are working
you'll be stuck again).
3') The above idea can be done a bit more cleanly by having x11vnc do
it. Suppose we called the following script xss_killer:
#!/bin/sh
#
# xss_killer: kill xscreensaver after a valid x11vnc client logs in.
# Restart xscreensaver and lock it when the last client
# disconnects.
PATH=/usr/openwin/bin:/usr/bin:$PATH
export PATH
if [ "$RFB_MODE" = "afteraccept" -a "$RFB_STATE" = "NORMAL" ]; then
# a valid x11vnc login.
if [ "$RFB_CLIENT_COUNT" = "1" ]; then
# only one client present.
pkill -U $LOGNAME '^xscreensaver$'
pkill -KILL -U $LOGNAME -f xscreensaver/hacks
fi
elif [ "$RFB_MODE" = "gone" -a "$RFB_STATE" = "NORMAL" ]; then
# a valid x11vnc login.
if [ "$RFB_CLIENT_COUNT" = "0" ]; then
# last client present has just left.
xscreensaver -nosplash &
sleep 1
xscreensaver-command -lock &
fi
fi
Then we would run x11vnc with these options: "-afteraccept xss_killer
-gone xss_killer". The [9]-afteraccept option (introduced in version
0.8) is used to run a command after a vncviewer has successfully
logged in (note that this is a VNC login, not a Unix login, so you may
not want to do this if you are really paranoid...)
Note if you use the above script and also plan to Ctrl-C (SIGINT)
x11vnc you have to run the xscreensaver in a new process group to
avoid killing it as well. One way to do this is via this kludge:
perl -e 'setpgrp(0,0); exec "xscreensaver -nosplash &"'
in the above script.
4) There appears to be a bug in pam_sunray.so in that it doesn't seem
to honor the convention that, say, DISPLAY=unix:3 means to use Unix
sockets to connect to display 3 on the local machine (this is a bit
faster than TCP sockets). Rather, it thinks the display is a non-local
one to a machine named "unix" (that usually does not resolve to an IP
address).
Amusingly, this can be used to bypass the pam_sunray.so blocking of
Xsun that prevents one from unlocking the screen remotely via x11vnc.
One could put something like this in $HOME/.dtprofile to kill any
existing xscreensavers and then start up a fresh xscreensaver using
DISPLAY=unix:N
# stop/kill any running xscreensavers (probably not running yet, but to be sure
)
xscreensaver-command -exit
pkill -U $LOGNAME '^xscreensaver$'
env DISPLAY=`echo $DISPLAY | sed -e 's/^.*:/unix:/'` xscreensaver &
Note that all of the above workarounds side-step the pam_sunray.so PAM
module in one way or another. You'll need to see if that is
appropriate for your site's SunRay / smartcard usage. Also, these
hacks may break other things and so you may want to test various
scenarios carefully. E.g. check corner cases like XDMCP/dtremote,
NSCM, etc.
References
1. http://wwws.sun.com/sunray/index.html
2. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-wait
3. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-sb
4. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-solid
5. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-rfbport
6. http://www.karlrunge.com/x11vnc/vnc_findports
7. http://www.karlrunge.com/x11vnc/findvncports
8. http://www.karlrunge.com/x11vnc/shm_clear
9. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-afteraccept
=======================================================================
http://www.karlrunge.com/x11vnc/ssl.html:
Notes on x11vnc SSL Certificates and Key Management:
The simplest scheme ("x11vnc -ssl") is where x11vnc generates a
temporary, self-signed certificate each time (automatically using
openssl(1)) and the VNC viewer client accepts the certificate without
question (e.g. user clicks "Yes" in a dialog box. Perhaps the dialog
allows them to view the certificate too). Also note stunnel's default
is to quietly accept all certificates.
The encryption this provides protects against all passive sniffing of
the VNC traffic and passwords on the network and so it is quite good,
but it does not prevent a Man-In-The-Middle attack: e.g. an attacker
intercepts the VNC client stream and sends it his own Public key for
SSL negotiation (pretending to be the server). Then it makes a
connection to SSL x11vnc itself and forwards the data back and forth.
He can see all the traffic and modify it as well.
Most people don't seem to worry about Man-In-The-Middle attacks these
days; they are more concerned about passive sniffing. Perhaps someday
that will change if attack tools are created that make it simpler to
perform the attack.
If you are not worried about Man-In-The-Middle attacks you do not have
to read the techniques described in the rest of this section.
To prevent Man-In-The-Middle attacks, certificates must somehow be
verified. This requires the VNC client side have some piece of
information that can be used to verify the SSL x11vnc server.
Alternatively, although rarely done, x11vnc could verify VNC Clients'
certificates, see the [1]-sslverify option that is discussed briefly
below.
There are a number of ways to have the client authenticate x11vnc. The
quickest way perhaps would be to copy (safely) the certificate x11vnc
prints out:
26/03/2006 21:12:00 Creating a temporary, self-signed PEM certificate...
...
-----BEGIN CERTIFICATE-----
MIIC4TCCAkqgAwIBAgIJAMnwCaOjvEKaMA0GCSqGSIb3DQEBBAUAMIGmMQswCQYD
VQQGEwJBVTEOMAwGA1UEBxMFTGludXgxITAfBgNVBAsTGGFuZ2VsYS0xMTQzNDI1
NTIwLjQxMTE2OTEPMA0GA1UEChMGeDExdm5jMS4wLAYDVQQDEyV4MTF2bmMtU0VM
(more lines) ...
-----END CERTIFICATE-----
to the client machine(s) and have the client's SSL machinery (e.g.
stunnel, Web Browser, or Java plugin) import the certificate. That way
when the connection to x11vnc is made the client can verify that is it
the desired server on the other side of the SSL connection.
So, for example suppose the user is using the SSL enabled Java VNC
Viewer and has incorporated the x11vnc certificate into his Web
browser on the viewing side. If he gets a dialog that the certificate
is not verified he knows something is wrong. It may be a
Man-In-The-Middle attack, but more likely x11vnc certificate has
changed or expired or his browser was reinstalled and lost the
certificate, etc, etc.
As another example, if the user was using [2]stunnel with his VNC
viewer (this is mentioned [3]in this FAQ), e.g. STUNNEL.EXE on
Windows, then he would have to set the "CAfile = path-to-the-cert" and
"verify = 2" options in the stunnel.conf file before starting up the
tunnel. If a x11vnc certificate cannot be verified, stunnel will drop
the connection (and print a failure message in its log file).
A third example, using the VNC viewer on Unix with stunnel the wrapper
script can be used this way: "[4]ssl_vncviewer -verify ./x11vnc.crt
far-away.east:0" where ./x11vnc.crt is the copied certificate x11vnc
printed out.
Note that in principle the copying of the certificate to the client
machine(s) itself could be altered in a Man-In-The-Middle attack! You
can't win. It is unlikely the attacker could predict how you were
going to send it unless you had, say, done it many times before the
same way. SSH is a very good way to send it (but of course it too
depends on public keys being sent unaltered between the two
machines!). If you are really paranoid, I'm sure you'll figure out a
really good way to transport the certificates. See the Certificate
Authority scheme below for a way to make this easier (you just have to
do it once).
Saving SSL certificates and keys:
Now, it would be very inconvenient to copy the new temporary
certificate every time x11vnc is run in SSL mode. So for convenience
there is the "SAVE" keyword to instruct x11vnc to save the certificate
it creates:
x11vnc -ssl SAVE -display :0 ...
This way it will save the certificate and private key in these files:
~/.vnc/certs/server.crt
~/.vnc/certs/server.pem
The ".crt" file contains only the certificate and should be copied to
the VNC Viewer machine(s) that will be authenticating the x11vnc
server. The ".pem" file contains both the certificate and the private
key and should be kept secret. (If you don't like the default location
~/.vnc/certs, e.g. it is on an NFS share and you are worried about
local network sniffing, use the [5]-ssldir dir option to point to a
different directory.)
So the next time you run "x11vnc -ssl SAVE ..." it will read the
server.pem file directly instead of creating a new one.
You can manage multiple SSL x11vnc server keys in this simple way by
using:
x11vnc -ssl SAVE-key2 -display :0 ...
etc, where you put whatever name you choose for the key after "SAVE-".
E.g. "-ssl SAVE-fred".
Also, if you want to be prompted to possibly change the made up names,
etc. that x11vnc creates (e.g. "x11vnc-SELF-SIGNED-CERT-7762" for the
CommonName) for the certificates distinguished name (DN), then use
"x11vnc -ssl SAVE_PROMPT ...", "x11vnc -ssl SAVE_PROMPT-fred ..." etc.
when you create the key the first time.
Tip: when prompting, if you choose the CommonName entry to be the full
internet hostname of the machine the clients will be connecting to
then that will avoid an annoying dialog box in their Web browsers that
warn that the CommonName doesn't match the hostname.
Passphrases for server keys:
Well, since now with the "SAVE" keyword the certificate and key will
be longer lived, one can next worry about somebody stealing the
private key and pretending to be the x11vnc server! How to guard
against this?
The first is that the file is created with perms 600 (i.e. -rw-------)
to make it harder for an untrusted user to copy the file. A better way
is to also encrypt the private key with a passphrase. You are prompted
whether you want to do this or not when the key is first created under
"-ssl SAVE" mode ("Protect key with a passphrase? [y]/n"). It is
suggested that you use a passphrase. The inconvenience is every time
you run "x11vnc -ssl SAVE ..." you will need to supply the passphrase
to access the private key:
06/04/2006 11:39:11 using PEM /home/runge/.vnc/certs/server.pem 0.000s
A passphrase is needed to unlock an OpenSSL private key (PEM file).
Enter passphrase>
before x11vnc can continue.
Being your own Certificate Authority:
A very sophisticated way that scales well if the number of users is
large is to use a Certificate Authority (CA) whose public certificate
is available to all of the VNC clients and whose private key has been
used to digitally sign the x11vnc server certificate(s).
The idea is as follows:
* A special CA cert and key is generated.
* Its private key is always protected by a good passphrase since it
is only used for signing.
* The CA cert is (safely) distributed to all machines where VNC
clients will run.
* One or more x11vnc server certs and keys are generated.
* The x11vnc server cert is signed with the CA private key.
* x11vnc is run using the server key. (e.g. "[6]-ssl SAVE")
* VNC clients (viewers) can now authenticate the x11vnc server
because they have the CA certificate.
The advantage is the CA cert only needs to be distributed once to the
various machines, that can be done even before x11vnc server certs are
generated.
As above, it is important the CA private key and the x11vnc server key
are kept secret, otherwise someone could steal them and pretend to be
the CA or the x11vnc server if they copied the key. It is recommended
that the x11vnc server keys are also protected via a passphrase (see
the previous section).
Optionally, VNC viewer certs and keys could also be generated to
enable the x11vnc server to authenticate each client. This is not
normally done (usually a simple viewer password scheme is used), but
this can be useful in some situations. These optional steps go like
this:
* One or more VNC client certs and keys are generated.
* These VNC client certs are signed with the CA private key.
* The VNC client certs+keys are safely distributed to the
corresponding client machines.
* x11vnc is told to verify clients by using the CA cert. (e.g.
"[7]-sslverify CA")
* When VNC clients (viewers) connect, they must authenticate
themselves to x11vnc by using their client key.
Again, it is a good idea if the client private keys are protected with
a passphrase, otherwise if stolen they could be used to gain access to
the x11vnc server. Once distributed to the client machines, there is
no need to keep the client key on the CA machine that generated and
signed it. You can keep the client certs if you like because they are
public, and they could also be used let in only a subset of all the
clients. (see [8]-sslverify)
How to do the above CA steps with x11vnc:
Some utility commands are provided to ease the cert+key creation,
signing, and management: [9]-sslGenCA, [10]-sslGenCert,
[11]-sslDelCert, [12]-sslEncKey, [13]-sslCertInfo. They basically run
the openssl(1) command for you to manage the certs/keys. It is
required that openssl(1) is installed on the machine and available in
PATH. All commands can be pointed to an alternate toplevel certificate
directory via the [14]-ssldir option if you don't want to use the
default ~/.vnc/certs.
1) To generate your Certificate Authority (CA) cert and key run this:
x11vnc -sslGenCA
Follow the prompts, you can modify any information strings you care
to. You will also be required to encrypt the CA private key with a
passphrase. This generates these files:
~/.vnc/certs/CA/cacert.pem (the CA public certificate)
~/.vnc/certs/CA/private/cakey.pem (the CA private key)
If you want to use a different directory use [15]-ssldir It must
supplied with all subsequent SSL utility options to point them to the
correct directory.
2) To generate a signed x11vnc server cert and key run this:
x11vnc -sslGenCert server
As with the CA generation, follow the prompts and you can modify any
information strings you care to. This will create the files:
~/.vnc/certs/server.crt (the server public certificate)
~/.vnc/certs/server.pem (the server private key + public cert)
It is recommended to protect the server private key with a passphrase
(you will be prompted whether you want to). You will need to provide
it whenever you start x11vnc using this key.
3) Start up x11vnc using this server key:
x11vnc -ssl SAVE -display :0 ...
(SAVE corresponds to server.pem, see [16]-sslGenCert server somename
info on creating additional server keys, server-somename.crt ...)
4) Next, safely copy the CA certificate to the VNC viewer (client)
machine(s). Perhaps:
scp ~/.vnc/CA/cacert.pem clientmachine:.
5) Then the tricky part, make it so the SSL VNC Viewer uses this
certificate. There are a number of ways this might be done, it depends
on what your client and/or SSL tunnel is. Some examples:
For the SSL Java VNC viewer supplied with x11vnc in
classes/ssl/VncViewer.jar or classes/ssl/SignedVncViewer.jar:
* Import the cacert.pem cert into your Web Browser (e.g. Edit ->
Preferences -> Privacy & Security -> Manage Certificates ->
WebSites -> Import)
* Or Import the cacert.pem cert into your Java Plugin (e.g. run
ControlPanel, then Security -> Certificates -> Secure Site ->
Import)
When importing, one would give the browser/java-plugin the path to the
copied cacert.pem file in some dialog. Note that the Web browser or
Java plugin is used for the server authentication. If the user gets a
"Site not verified" message while connecting he should investigate
further.
For the use of stunnel (e.g. on Windows) one would add this to the
stunnel.conf:
# stunnel.conf:
client = yes
options = ALL
CAfile = /path/to/cacert.pem # or maybe C:\path\to\cacert.pem
[myvncssl]
accept = 5901
connect = far-away.east:5900
(then point the VNC viewer to localhost:1).
Here is an example for the Unix stunnel wrapper script
[17]ssl_vncviewer:
ssl_vncviewer -verify ./cacert.pem far-away.east:0
Tricks for server keys:
To create additional x11vnc server keys do something like this:
x11vnc -sslGenCert server myotherkey
and use it this way:
x11vnc -ssl SAVE-myotherkey ...
The files will be ~/.vnc/certs/server-myotherkey.{crt,pem}
You can also create a self-signed server key:
x11vnc -sslGenCert server self:third_key
and use it this way:
x11vnc -ssl SAVE-self:third_key ...
This key is not signed by your CA. This can be handy to have a key set
separate from your CA when you do not want to create a 2nd CA
cert+key.
Using external CA's:
You don't have to use your own CA cert+key you can use a third
party's. Perhaps you have a company-wide CA or you can even have your
x11vnc certificate signed by a professional CA (e.g. www.thawte.com or
www.verisign.com).
The advantage to doing this is that the VNC client machines will
already have the CA certificates installed and you don't have to
install it on each machine.
To generate an x11vnc server cert+key this way you should generate a
"request" for a certicate signing something like this:
x11vnc -sslGenCert server req:external
This will create the request file:
~/.vnc/certs/server-req:external.req
Which you should send to the external CA. When you get the signed
certificate back from them, save it in the file:
~/.vnc/certs/server-req:external.crt
and create the .pem this way:
mv ~/.vnc/certs/server-req:external.key ~/.vnc/certs/server-req:external.
pem
chmod 600 ~/.vnc/certs/server-req:external.pem
cat ~/.vnc/certs/server-req:external.crt >> ~/.vnc/certs/server-req:external.
pem
You also rename the two files (.crt and .pem) to have a shorter
basename if you like.
Using Client Keys for Authentication:
You can optionally create certs+keys for your VNC client machines as
well. After distributing them to the client machines you can have
x11vnc verify the clients using SSL. Here is how to do this:
x11vnc -sslGenCert client dilbert
x11vnc -sslGenCert client wally
x11vnc -sslGenCert client alice
...
As usual, follow the prompts if you want to change any of the info
field values. As always, it is a good idea to protect the private keys
with a passphrase. These files are created:
~/.vnc/certs/clients/dilbert.crt
~/.vnc/certs/clients/dilbert.pem
...
Note that these are kept in a clients subdirectory.
Next, safely copy the .pem files to each corresponding client machine
and incorporate them into the VNC viewer / SSL software (see the ideas
mentioned above for the CA and server keys). The only difference is
these certificates might be referred to as "My Certificates" or
"Client Certificates". They are used for client authentication (which
is relatively rare for SSL).
After copying them you can delete the clients/*.pem files for extra
safety because the private keys are not needed by the x11vnc server.
You don't really need the clients/*.crt files either (because they
have been signed by the CA). But they could come in handy if you
wanted to let in just one client.
Now start up x11vnc and instruct it to verify connecting clients via
SSL and the CA cert:
x11vnc -ssl SAVE -sslverify CA
Finally, connect with your VNC viewer using the key. For the Java
Applet viewer (TBD...). Here is an example for the Unix stunnel
wrapper script [18]ssl_vncviewer: using client authentication (and the
standard server authentication with the CA cert):
ssl_vncviewer -mycert ./dilbert.pem -verify ./cacert.pem far-away.east:0
It is also possible to use [19]-sslverify on a per-client key basis,
and also using self-signed client keys (x11vnc -sslGenCert client
self:dilbert)
Additional utlities:
You can get information about your keys via [20]-sslCertInfo. These
lists all your keys:
x11vnc -sslCertInfo list
x11vnc -sslCertInfo ll
(the latter is long format).
These print long output, including the public certificate, for
individual keys:
x11vnc -sslCertInfo server
x11vnc -sslCertInfo dilbert
x11vnc -sslCertInfo all (every key, very long)
If you want to add a protecting passphrase to a key originally created
without one:
x11vnc -sslEncKey SAVE
x11vnc -sslEncKey SAVE-fred
To delete a cert+key:
x11vnc -sslDelCert SAVE
x11vnc -sslDelCert SAVE-fred
x11vnc -sslDelCert wally
(but rm(1) will be just as effective).
More info:
See also this [21]article for some some general info and examples
using stunnel and openssl on Windows with VNC.
References
1. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-sslverify
2. http://www.stunnel.org/
3. http://www.karlrunge.com/x11vnc/index.html#faq-ssl-tunnel-ext
4. http://www.karlrunge.com/x11vnc/ssl_vncviewer
5. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-ssldir
6. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-ssl
7. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-sslverify
8. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-sslverify
9. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-sslGenCA
10. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-sslGenCert
11. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-sslDelCert
12. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-sslEncKey
13. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-sslCertInfo
14. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-ssldir
15. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-ssldir
16. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-ssldir
17. http://www.karlrunge.com/x11vnc/ssl_vncviewer
18. http://www.karlrunge.com/x11vnc/ssl_vncviewer
19. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-sslverify
20. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-sslCertInfo
21. http://www.securityfocus.com/infocus/1677
=======================================================================
http://www.karlrunge.com/x11vnc/ssl-portal.html:
Using Apache as an SSL Gateway to x11vnc servers inside a firewall:
Background:
The standard way to allow access to x11vnc running on workstations
inside a firewall is via SSH. The user somewhere out on the Internet
logs in to the SSH gateway machine and uses port forwarding (e.g. ssh
-L 5900:myworkstation:5900 user@gateway) to set up the encrypted
channel that VNC is then tunneled through. Next he starts up the VNC
viewer on the machine where he is sitting directed to the local tunnel
port.
The SSH scheme is nice because it is a common and well tested login
technique for users connecting to machines inside their company or
home firewall. It is a bit awkward, however, because SSH needs to be
installed on the Viewer machine and the user usually has to rig up his
own port redirection plumbing.
With the SSL support in x11vnc and the SSL enabled Java VNC viewer
applet, a convenient and secure alternative exists that uses the
Apache webserver. The idea is that the company or home internet
connection is already running apache as a web server (either SSL or
non-SSL) and we add to it the ability to act as a gateway for SSL VNC
connections. The only thing needed on the Viewer side is a Java
enabled Web Browser. The stunnel VNC viewer wrapper script provided
(ssl_vncviewer) can also take advantage of the method described here.
The apache solution may be overkill for you (e.g. home system) see
[1]below for some simpler setups.
There are numerous ways to do this. We present the simplest one here.
Important: these schemes allow incoming connections from anywhere on
the Internet to specific ports on machines inside the firewall. Care
must be taken to implement and test thoroughly. If one is paranoid one
can (and should) add extra layers of protection. (e.g. extra
passwords, packet filtering, SSL certificate verification, etc).
The scheme described here sets up apache on the firewall/gateway as a
regular Web proxy into the intranet and allows connections to a fixed
port on a limited set of machines.
Example:
In this example suppose the gateway machine running apache is named
"www.gateway.east" (e.g. it may also provide normal web service). We
also choose the Internet-facing port for this VNC service to be port
563. One could choose any port, including the default HTTP port 80.
We choose 563 because it is the rarely used SNEWS port that is usually
allowed by Web proxies for the CONNECT method. The idea is the user
may be coming out of another firewall using a proxy (not the one we
describe here, that is, the case when two proxies are involved; the
"double proxy" problem) and using port 563 simplifies things because
CONNECT's to it are usually allowed by default.
We also assume all of the x11vnc servers on the internal machines are
all listening on port 5915 ("-rfbport 5915") instead of the default
5900. This is to limit any unintended proxy redirections to a lesser
used port, and also to stay out of the way of normal VNC servers on
the same machines. One could obviously implement a scheme that handles
different ports, but we just discuss this simplest setup here.
So we assume x11vnc has been started this way on all of the
workstations to be granted VNC access:
x11vnc -ssl -http -display :0 -forever -rfbauth ~/.vnc/passwd -rfbport 5915
i.e. we force SSL VNC connections, port 5915, serve the Java VNC
viewer applet, and require a VNC password (another option would be
[2]-unixpw). The above command could also be run out of [3]inetd(8),
that can also be used to autodetect the user's display and Xauthority
data.
These sections are added to the httpd.conf apache configuration file
on www.gateway.east:
Listen 563
<VirtualHost localhost:563>
# this is a "bounce" failure from the ProxyRemoteMatch below.
ProxyRequests Off
</VirtualHost>
<VirtualHost *:563>
# for convenience, a rewrite to avoid having ...?CONNECT=..&PORT=... in the
URL.
RewriteEngine On
RewriteRule /vnc/([^/]*)$ /vnc/$1/index.vnc?CONNECT=$1+5915&PORT=
563 [R,NE]
RewriteRule /vnc/proxy/([^/]*)$ /vnc/$1/proxy.vnc?CONNECT=$1+5915&PORT=
563 [R,NE]
# allow incoming proxy CONNECT requests to port 5915 *only*
ProxyRequests On
AllowCONNECT 5915
# this will fetch the jar file from port 5815 via http (not https)
# (list all allowed x11vnc servers here)
ProxyPass /vnc/mach1/ http://mach1:5815/
ProxyPass /vnc/mach2/ http://mach2:5815/
ProxyPass /vnc/mach3/ http://mach3:5815/
ProxyPass /vnc/mach4/ http://mach4:5815/
# ...
# force a reject for any CONNECT not to the known list of x11vnc servers:
# (list all allowed x11vnc servers here)
ProxyRemoteMatch ^(?!(http://|mach1:|mach2:|mach3:|mach4:)) http://localhos
t:563/
</VirtualHost>
Note that the listing of allowed internal workstations (mach1, mach2,
...) is done in two places. The above setup requires mod_rewrite
(optional) and mod_proxy (required) be enabled in the apache web
server.
The user at the Java enabled Web browser would simply enter this URL
into the browser:
http://www.gateway.east:563/vnc/mach2
to connect to internal workstation mach2, etc. There will be a number
of SSL certificate, etc, dialogs he will have to respond to in
addition to any passwords he is required to provide (this depends on
how you set up user authentication for x11vnc).
If a second Web proxy is involved (i.e. the user's browser is inside
another firewall that requires proxying) then use this URL:
http://www.gateway.east:563/vnc/proxy/mach2
See [4]this FAQ for more info on how this works.
Let's go through the httpd.conf additions in detail.
The VirtualHost localhost:563 section is used as a bounce if anyone
tries to connect to a workstation machine not listed in httpd.conf.
See ProxyRemoteMatch below.
The RewriteRule's are for convenience only so that the URL entered
into the Web browser does not need the various extra parameters, e.g.:
http://www.gateway.east:563/vnc/mach2/index.vnc?CONNECT=mach2+5915&PORT=563
(or otherwise make direct edits to index.vnc to set these parameters).
Next, the "ProxyRequests On" and "AllowCONNECT 5915" enable the web
server to forward proxy requests to port 5915 (and only this port)
INSIDE the firewall. Test this carefully.
The "ProxyPass /vnc/mach1/ ..." lines forward the initial page (e.g.
index.vnc) and Java applet JAR file (e.g. VncViewer.jar) requests to
port 5815 on the x11vnc server machines.
Note that these index.vnc and VncViewer.jar downloads are not
encrypted via SSL. The subsequent VNC connections are encrypted
however. See below for how to have these initial downloads encrypted
as well (if the apache web server has SSL, i.e. https, enabled and
configured).
Finally, the ProxyRemoteMatch redirects any request that is not a
http: URL or a CONNECT to a valid machine (mach1, ... etc) to
localhost:563 which has proxying disabled ("ProxyRequests Off") and so
effectively drops the connection.
Some Ideas for adding extra authentication, etc. for the paranoid:
* VNC passwords: [5]-rfbauth, [6]-passwdfile, or [7]-usepw. Even
adding a company-wide VNC password helps block unwanted access.
* Unix passwords: [8]-unixpw
* SSL Client certificates: [9]-sslverify
* Apache AuthUserFile directive: .htaccess, etc.
* Add proxy password authentication (requires Viewer changes?)
* Run a separate instance of Apache that provides this VNC service
so it can be brought up and down independently of the normal web
server.
Using non-Java viewers with this scheme:
The [10]ssl_vncviewer stunnel wrapper script for VNC viewers has the
-proxy option that can take advantage of this method. For the case of
the "double proxy" situation (see below) supply both separated by a
comma.
ssl_vncviewer -proxy www.gateway.east:563 mach1:15
ssl_vncviewer -proxy proxy1.foobar.com:8080,www.gateway.east:563 mach1:15
Downloading the Java applet via HTTPS:
To have the Java applet downloaded to the user's Web Browswer via an
encrypted (and evidently safer) SSL connection the Apache webserver
should be configured for SSL via [11]mod_ssl (this is probably not
absolutely necessary; show us how you did it).
It is actually possible to use the x11vnc [12]Key Management utility
"[13]-sslGenCert" to generate your Apache/SSL .crt and .key files. (In
brief, run something like "x11vnc -sslGenCert server self:apache" then
copy the resulting self:apache.crt file to conf/ssl.crt/server.crt and
extract the private key part from self:apache.pem and paste it into
conf/ssl.key/server.key). Or you can use the standard methods
described in the Apache mod_ssl documentation.
In addition to the above sections in httpd.conf one should add the
following to ssl.conf:
SSLProxyEngine On
# for convenience, a rewrite to avoid having ...?CONNECT=... in URL.
RewriteEngine On
RewriteRule /vnc/([^/]*)$ /vnc/$1/index.vnc?CONNECT=$1+5915&PORT=
563 [R,NE]
RewriteRule /vnc/proxy/([^/]*)$ /vnc/$1/proxy.vnc?CONNECT=$1+5915&PORT=
563 [R,NE]
# these "vncs" are for https applet downloading:
RewriteRule /vncs/([^/]*)$ /vncs/$1/index.vnc?CONNECT=$1+5915&PORT=
563 [R,NE]
RewriteRule /vncs/proxy/([^/]*)$ /vncs/$1/proxy.vnc?CONNECT=$1+5915&PORT=
563 [R,NE]
# fetch the jar file from port 5815 via http or port 5915 via https
# inside the firewall
# (list all allowed x11vnc servers here)
ProxyPass /vnc/mach1/ http://mach1:5815/
ProxyPass /vnc/mach2/ http://mach2:5815/
ProxyPass /vnc/mach3/ http://mach3:5815/
ProxyPass /vnc/mach4/ http://mach4:5815/
ProxyPass /vncs/mach1/ https://mach1:5915/
ProxyPass /vncs/mach2/ https://mach2:5915/
ProxyPass /vncs/mach3/ https://mach3:5915/
ProxyPass /vncs/mach4/ https://mach4:5915/
This is all in the "<VirtualHost _default_:443>" section of ssl.conf.
The user could then point the Web Browser to:
https://www.gateway.east/vnc/mach2
or
https://www.gateway.east/vnc/proxy/mach2
for the "double proxy" case.
Note that inside the firewall the Java applet download traffic is not
encrypted (only over the Internet is SSL used) for these cases:
https://www.gateway.east/vnc/mach2
https://www.gateway.east/vnc/proxy/mach2
However for the special "vncs" rules above:
https://www.gateway.east/vncs/mach2
the Java applet download is encrypted via SSL for both legs. Note that
the two legs are two separate SSL sessions. So the data is uncrypted
inside an apache process and reencrypted for the 2nd SSL session
inside the same apache process (a very small gap one might overlook).
In all of the above cases the VNC traffic from Viewer to x11vnc is
encrypted end-to-end in a single SSL session, even for the "double
proxy" case. This is the important part to have encrypted.
Note that the Certificate dialogs the user has in his web browser will
be for the Apache Certificate, while for the Java applet it will be
the x11vnc certificate.
Note also that you can have Apache serve up the Jar file VncViewer.jar
instead of each x11vnc if you want to.
INETD automation:
The "single-port" (i.e. 5915) HTTPS applet download and VNC connection
aspect shown here is convenient and also enables having x11vnc run out
of inetd. That way x11vnc is run on demand instead of being run all
the time (the user does not have to remember to start it). The first
connections to inetd download index.vnc and the Jar file (via https)
and the the last connection to inetd establishes the SSL VNC
connection. Since x11vnc is restarted for each connection, this will
be a bit slower than the normal process.
For example, the /etc/inetd.conf line could be:
5915 stream tcp nowait root /usr/sbin/tcpd /usr/local/bin/x11vnc_ssl.sh
where the script x11vnc_ssl.sh looks something like this:
#!/bin/sh
/usr/local/bin/x11vnc -inetd -oa /var/log/x11vnc-15.log \
-ssl SAVE -http -unixpw -localhost \
-display :0 -auth /home/THE_USER/.Xauthority
where, as usual, the inetd launching needs to know which user is
typically using the display on that machine. One could imagine giving
different users different ports, 5915, 5916, etc. to distinguish (then
the script would need to be passed the username). mod_rewrite could be
used to automatically map username in the URL to his port number.
A better way is to use the "-display WAIT:cmd=FINDDISPLAY" feature to
autodetect the user and Xauthority data:
#!/bin/sh
/usr/local/bin/x11vnc -inetd -oa /var/log/x11vnc-15.log \
-ssl SAVE -http -unixpw -localhost -users unixpw= \
-display WAIT:cmd=FINDDISPLAY
this way the user must supply his Unix username and password and then
his display and Xauthority data on that machine will be located and
returned to x11vnc to allow it to attach. If he doesn't have a display
running on that machine or he fails to log in correctly, the
connection will be dropped.
To enable inetd operation for the non-HTTPS Java viewer download (port
5815 in the above httpd.conf example) you will need to run x11vnc in
HTTPONCE mode on port 5815: For example, the /etc/inetd.conf line
could be:
5815 stream tcp nowait root /usr/sbin/tcpd /usr/local/bin/x11vnc \
-inetd -oa /var/log/x11vnc-15.log -http_ssl -display WAIT:cmd=HTTPONCE
where the long inetd.conf line has been split. Note how the
[14]-http_ssl tries to automatically find the .../classes/ssl
subdirectory.
Also note the use of "-ssl SAVE" above. This way a saved server.pem is
used for each inetd invocation (rather generating a new one each
time). Note that it cannot have a protecting passphrase because inetd
will not be able to supply it.
Other Ideas:
- The above schemes work, but they are a bit complicated with all of
the rigging. There should be better ways to configure Apache to do
these, but we have not found them (please let us know if you discover
something nice). However, once this scheme has been set up and is
working it is easy to maintain and add workstations, etc.
- In general Apache is not required, but it makes things convenient.
The firewall itself could do the port redirection via its firewall
rules. Evidently different Internet-facing ports would be required for
each workstation. This could be set up using iptables rules for
example. If there were just one or two machines this would be the
easiest method. For example:
iptables -t nat -A PREROUTING -p tcp -d 24.35.46.57 --dport 5901 -j DNAT --to
-destination 192.168.1.2:5915
iptables -t nat -A PREROUTING -p tcp -d 24.35.46.57 --dport 5902 -j DNAT --to
-destination 192.168.1.3:5915
Where 24.35.46.57 is the internet IP address of the gateway. In this
example 24.35.46.57:5901 is redirected to the internal machine
192.168.1.2:5915 and 24.35.46.57:5902 is redirected to another
internal machine 192.168.1.3:5915, both running x11vnc -ssl ... in SSL
mode. For this example, the user would point the web browser to, e.g.:
https://24.35.46.57:5901/?PORT=5901
or using the stunnel wrapper script:
ssl_vncviewer 24.35.46.57:1
One can acheive similar things with dedicated firewall/routers (e.g.
Linksys) using the device's web or other interface to configure the
firewall.
If the user may be coming out of a firewall using a proxy it may be
better to redirect ports 443 and 563 (instead of 5901 and 5902) to the
internal machines so that the user's proxy will allow CONNECTing to
them.
- The redirection could also be done at the application level using a
TCP redirect program (e.g. ip_relay or fancier ones). Evidently more
careful internal hostname checking, etc., could be performed by the
special purpose application to add security.
- One might imagine the ProxyPass could be done for the VNC traffic as
well (for the ssl.conf case) to avoid the CONNECT proxying completely
(which would be nice to avoid). Unfortunately we were not able to get
this to work. Since HTTP is a request-response protocol (as opposed to
a full bidirectional link required by VNC) this makes it difficult to
do. It may be possible, but we haven't found out how yet.
References
1. http://www.karlrunge.com/x11vnc/ssl-portal.html#no-apache
2. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-unixpw
3. http://www.karlrunge.com/x11vnc/ssl-portal.html#inetd
4. http://www.karlrunge.com/x11vnc/index.html#faq-ssl-java-viewer-proxy
5. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-rfbauth
6. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-passwdfile
7. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-usepw
8. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-unixpw
9. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-sslverify
10. http://www.karlrunge.com/x11vnc/index.html#ssl_vncviewer
11. http://httpd.apache.org/docs/2.0/mod/mod_ssl.html
12. http://www.karlrunge.com/x11vnc/ssl.html
13. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-sslGenCert
14. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-http_ssl
=======================================================================
http://www.karlrunge.com/x11vnc/x11vnc_opts.html:
_________________________________________________________________
x11vnc: a VNC server for real X displays
Here are all of x11vnc command line options:
% x11vnc -opts (see below for -help long descriptions)
x11vnc: allow VNC connections to real X11 displays. 0.8.3 lastmod: 2006-07-15
x11vnc options:
-display disp -auth file -id windowid
-sid windowid -clip WxH+X+Y -flashcmap
-shiftcmap n -notruecolor -visual n
-overlay -overlay_nocursor -8to24 [opts]
-24to32 -scale fraction -scale_cursor frac
-viewonly -shared -once
-forever -loop -timeout n
-inetd -nofilexfer -http
-http_ssl -connect string -vncconnect
-novncconnect -allow host1[,host2..] -localhost
-nolookup -input string -grabkbd
-grabptr -viewpasswd string -passwdfile filename
-unixpw [list] -unixpw_nis [list] -display WAIT:...
-ssl [pem] -ssldir [dir] -sslverify [path]
-sslGenCA [dir] -sslGenCert type name -sslEncKey [pem]
-sslCertInfo [pem] -sslDelCert [pem] -stunnel [pem]
-stunnel3 [pem] -https [port] -usepw
-storepasswd pass file -nopw -accept string
-afteraccept string -gone string -users list
-noshm -flipbyteorder -onetile
-solid [color] -blackout string -xinerama
-noxinerama -xtrap -xrandr [mode]
-padgeom WxH -o logfile -flag file
-rc filename -norc -env VAR=VALUE
-h, -help -?, -opts -V, -version
-license -dbg -q
-bg -modtweak -nomodtweak
-xkb -noxkb -capslock
-skip_lockkeys -skip_keycodes string -sloppy_keys
-skip_dups -noskip_dups -add_keysyms
-noadd_keysyms -clear_mods -clear_keys
-remap string -norepeat -repeat
-nofb -nobell -nosel
-noprimary -nosetprimary -noclipboard
-nosetclipboard -seldir string -cursor [mode]
-nocursor -arrow n -noxfixes
-alphacut n -alphafrac fraction -alpharemove
-noalphablend -nocursorshape -cursorpos
-nocursorpos -xwarppointer -buttonmap string
-nodragging -wireframe [str] -nowireframe
-wirecopyrect mode -nowirecopyrect -debug_wireframe
-scrollcopyrect mode -noscrollcopyrect -scr_area n
-scr_skip list -scr_inc list -scr_keys list
-scr_term list -scr_keyrepeat lo-hi -scr_parms string
-fixscreen string -debug_scroll -noxrecord
-grab_buster -nograb_buster -debug_grabs
-debug_sel -pointer_mode n -input_skip n
-allinput -speeds rd,bw,lat -wmdt string
-debug_pointer -debug_keyboard -defer time
-wait time -wait_ui factor -nowait_bog
-slow_fb time -readtimeout n -nap
-nonap -sb time -nofbpm
-fbpm -noxdamage -xd_area A
-xd_mem f -sigpipe string -threads
-nothreads -fs f -gaps n
-grow n -fuzz n -debug_tiles
-snapfb -rawfb string -freqtab file
-pipeinput cmd -gui [gui-opts] -remote command
-query variable -QD variable -sync
-noremote -yesremote -unsafe
-safer -privremote -nocmds
-allowedcmds list -deny_all
libvncserver options:
-rfbport port TCP port for RFB protocol
-rfbwait time max time in ms to wait for RFB client
-rfbauth passwd-file use authentication on RFB protocol
(use 'storepasswd' to create a password file)
-rfbversion 3.x Set the version of the RFB we choose to advertise
-permitfiletransfer permit file transfer support
-passwd plain-password use authentication
(use plain-password as password, USE AT YOUR RISK)
-deferupdate time time in ms to defer updates (default 40)
-deferptrupdate time time in ms to defer pointer updates (default none)
-desktop name VNC desktop name (default "LibVNCServer")
-alwaysshared always treat new clients as shared
-nevershared never treat new clients as shared
-dontdisconnect don't disconnect existing clients when a new non-shared
connection comes in (refuse new connection instead)
-httpdir dir-path enable http server using dir-path home
-httpport portnum use portnum for http connection
-enablehttpproxy enable http proxy support
-progressive height enable progressive updating for slow links
-listen ipaddr listen for connections only on network interface with
addr ipaddr. '-listen localhost' and hostname work too.
libvncserver-tight-extension options:
-disablefiletransfer disable file transfer
-ftproot string set ftp root
% x11vnc -help
x11vnc: allow VNC connections to real X11 displays. 0.8.3 lastmod: 2006-07-15
(type "x11vnc -opts" to just list the options.)
Typical usage is:
Run this command in a shell on the remote machine "far-host"
with X session you wish to view:
x11vnc -display :0
Then run this in another window on the machine you are sitting at:
vncviewer far-host:0
Once x11vnc establishes connections with the X11 server and starts listening
as a VNC server it will print out a string: PORT=XXXX where XXXX is typically
5900 (the default VNC server port). One would next run something like
this on the local machine: "vncviewer hostname:N" where "hostname" is
the name of the machine running x11vnc and N is XXXX - 5900, i.e. usually
"vncviewer hostname:0".
By default x11vnc will not allow the screen to be shared and it will exit
as soon as the client disconnects. See -shared and -forever below to override
these protections. See the FAQ for details how to tunnel the VNC connection
through an encrypted channel such as ssh(1). In brief:
ssh -L 5900:localhost:5900 far-host 'x11vnc -localhost -display :0'
vncviewer -encodings 'copyrect tight zrle hextile' localhost:0
Also, use of a VNC password (-rfbauth or -passwdfile) is strongly recommended.
For additional info see: http://www.karlrunge.com/x11vnc/
and http://www.karlrunge.com/x11vnc/#faq
Rudimentary config file support: if the file $HOME/.x11vncrc exists then each
line in it is treated as a single command line option. Disable with -norc.
For each option name, the leading character "-" is not required. E.g. a
line that is either "forever" or "-forever" may be used and are equivalent.
Likewise "wait 100" or "-wait 100" are acceptable and equivalent lines.
The "#" character comments out to the end of the line in the usual way
(backslash it for a literal). Leading and trailing whitespace is trimmed off.
Lines may be continued with a "\" as the last character of a line (it
becomes a space character).
Options:
-display disp X11 server display to connect to, usually :0. The X
server process must be running on same machine and
support MIT-SHM. Equivalent to setting the DISPLAY
environment variable to "disp". See the description
below of the "-display WAIT:..." extensions.
-auth file Set the X authority file to be "file", equivalent to
setting the XAUTHORITY environment variable to "file"
before startup. Same as -xauth file. See Xsecurity(7),
xauth(1) man pages for more info.
-id windowid Show the window corresponding to "windowid" not
the entire display. New windows like popup menus,
transient toplevels, etc, may not be seen or may be
clipped. Disabling SaveUnders or BackingStore in the
X server may help show them. x11vnc may crash if the
window is initially partially obscured, changes size,
is iconified, etc. Some steps are taken to avoid this
and the -xrandr mechanism is used to track resizes. Use
xwininfo(1) to get the window id, or use "-id pick"
to have x11vnc run xwininfo(1) for you and extract
the id. The -id option is useful for exporting very
simple applications (e.g. the current view on a webcam).
-sid windowid As -id, but instead of using the window directly it
shifts a root view to it: this shows SaveUnders menus,
etc, although they will be clipped if they extend beyond
the window.
-clip WxH+X+Y Only show the sub-region of the full display that
corresponds to the rectangle with size WxH and offset
+X+Y. The VNC display has size WxH (i.e. smaller than
the full display). This also works for -id/-sid mode
where the offset is relative to the upper left corner
of the selected window.
-flashcmap In 8bpp indexed color, let the installed colormap flash
as the pointer moves from window to window (slow).
Also try the -8to24 option to avoid flash altogether.
-shiftcmap n Rare problem, but some 8bpp displays use less than 256
colorcells (e.g. 16-color grayscale, perhaps the other
bits are used for double buffering) *and* also need to
shift the pixels values away from 0, .., ncells. "n"
indicates the shift to be applied to the pixel values.
To see the pixel values set DEBUG_CMAP=1 to print out
a colormap histogram. Example: -shiftcmap 240
-notruecolor For 8bpp displays, force indexed color (i.e. a colormap)
even if it looks like 8bpp TrueColor (rare problem).
-visual n Experimental option: probably does not do what you
think. It simply *forces* the visual used for the
framebuffer; this may be a bad thing... (e.g. messes
up colors or cause a crash). It is useful for testing
and for some workarounds. n may be a decimal number,
or 0x hex. Run xdpyinfo(1) for the values. One may
also use "TrueColor", etc. see <X11/X.h> for a list.
If the string ends in ":m" then for better or for
worse the visual depth is forced to be m.
-overlay Handle multiple depth visuals on one screen, e.g. 8+24
and 24+8 overlay visuals (the 32 bits per pixel are
packed with 8 for PseudoColor and 24 for TrueColor).
Currently -overlay only works on Solaris via
XReadScreen(3X11) and IRIX using XReadDisplay(3).
On Solaris there is a problem with image "bleeding"
around transient popup menus (but not for the menu
itself): a workaround is to disable SaveUnders
by passing the "-su" argument to Xsun (in
/etc/dt/config/Xservers).
Use -overlay as a workaround for situations like these:
Some legacy applications require the default visual to
be 8bpp (8+24), or they will use 8bpp PseudoColor even
when the default visual is depth 24 TrueColor (24+8).
In these cases colors in some windows will be incorrect
in x11vnc unless -overlay is used. Another use of
-overlay is to enable showing the exact mouse cursor
shape (details below).
Under -overlay, performance will be somewhat slower
due to the extra image transformations required.
For optimal performance do not use -overlay, but rather
configure the X server so that the default visual is
depth 24 TrueColor and try to have all apps use that
visual (e.g. some apps have -use24 or -visual options).
-overlay_nocursor Sets -overlay, but does not try to draw the exact mouse
cursor shape using the overlay mechanism.
-8to24 [opts] Try this option if -overlay is not supported on your
OS, and you have a legacy 8bpp app that you want to
view on a multi-depth display with default depth 24
(and is 32 bpp) OR have a default depth 8 display with
depth 24 overlay windows for some apps. This option
may not work on all X servers and hardware (tested
on XFree86/Xorg mga driver and Xsun). The "opts"
string is not required and is described below.
This mode enables a hack where x11vnc monitors windows
within 3 levels from the root window. If it finds
any that are 8bpp it extracts the indexed color
pixel values using XGetImage() and then applies a
transformation using the colormap(s) to create TrueColor
RGB values that it in turn inserts into bits 1-24 of
the framebuffer. This creates a depth 24 "view"
of the display that is then exported via VNC.
Conversely, for default depth 8 displays, the depth
24 regions are read by XGetImage() and everything is
transformed and inserted into a depth 24 TrueColor
framebuffer.
Note that even if there are *no* depth 24 visuals or
windows (i.e. pure 8bpp), this mode is potentially
an improvement over -flashcmap because it avoids the
flashing and shows each window in the correct color.
This method appear to work, but may still have bugs
and it does hog resources. If there are multiple 8bpp
windows using different colormaps, one may have to
iconify all but one for the colors to be correct.
There may be painting errors for clipping and switching
between windows of depths 8 and 24. Heuristics are
applied to try to minimize the painting errors. One can
also press 3 Alt_L's in a row to refresh the screen
if the error does not repair itself. Also the option
-fixscreen 8=3.0 or -fixscreen V=3.0 may be used to
periodically refresh the screen at the cost of bandwidth
(every 3 sec for this example).
The [opts] string can contain the following settings.
Multiple settings are separated by commas.
For for some X servers with default depth 24 a
speedup may be achieved via the option "nogetimage".
This enables a scheme were XGetImage() is not used
to retrieve the 8bpp data. Instead, it assumes that
the 8bpp data is in bits 25-32 of the 32bit X pixels.
There is no requirement that the X server should put
the data there for our poll requests, but some do and
so the extra steps to retrieve it can be skipped.
Tested with mga driver with XFree86/Xorg. For the
default depth 8 case this option is ignored.
To adjust how often XGetImage() is used to poll the
non-default visual regions for changes, use the option
"poll=t" where "t" is a floating point time.
(default: 0.05)
Setting the option "level2" will limit the search
for non-default visual windows to two levels from the
root window. Do this on slow machines where you know
the window manager only imposes one extra window between
the app window and the root window.
Also for very slow machines use "cachewin=t"
where t is a floating point amount of time to cache
XGetWindowAttributes results. E.g. cachewin=5.0.
This may lead to the windows being unnoticed for this
amount of time when deiconifying, painting errors, etc.
While testing on a very old SS20 these options gave
tolerable response: -8to24 poll=0.2,cachewin=5.0. For
this machine -overlay is supported and gives better
response.
Debugging for this mode can be enabled by setting
"dbg=1", "dbg=2", or "dbg=3".
-24to32 Very rare problem: if the framebuffer (X display
or -rawfb) is 24bpp instead of the usual 32bpp, then
dynamically transform the pixels to 32bpp. This will be
slower, but can be used to work around problems where
VNC viewers cannot handle 24bpp (e.g. "main: setPF:
not 8, 16 or 32 bpp?"). See the FAQ for more info.
In the case of -rawfb mode, the pixels are directly
modified by inserting a 0 byte to pad them out to 32bpp.
For X displays, a kludge is done that is equivalent to
"-noshm -visual TrueColor:32". (If better performance
is needed for the latter, feel free to ask).
-scale fraction Scale the framebuffer by factor "fraction". Values
less than 1 shrink the fb, larger ones expand it. Note:
image may not be sharp and response may be slower.
If "fraction" contains a decimal point "." it
is taken as a floating point number, alternatively
the notation "m/n" may be used to denote fractions
exactly, e.g. -scale 2/3
Scaling Options: can be added after "fraction" via
":", to supply multiple ":" options use commas.
If you just want a quick, rough scaling without
blending, append ":nb" to "fraction" (e.g. -scale
1/3:nb). No blending is the default for 8bpp indexed
color, to force blending for this case use ":fb".
To disable -scrollcopyrect and -wirecopyrect under
-scale use ":nocr". If you need to to enable them use
":cr" or specify them explicitly on the command line.
If a slow link is detected, ":nocr" may be applied
automatically. Default: :cr
More esoteric options: for compatibility with vncviewers
the scaled width is adjusted to be a multiple of 4:
to disable this use ":n4". ":in" use interpolation
scheme even when shrinking, ":pad" pad scaled width
and height to be multiples of scaling denominator
(e.g. 3 for 2/3).
-scale_cursor frac By default if -scale is supplied the cursor shape is
scaled by the same factor. Depending on your usage,
you may want to scale the cursor independently of the
screen or not at all. If you specify -scale_cursor
the cursor will be scaled by that factor. When using
-scale mode to keep the cursor at its "natural" size
use "-scale_cursor 1". Most of the ":" scaling
options apply here as well.
-viewonly All VNC clients can only watch (default off).
-shared VNC display is shared, i.e. more than one viewer can
connect at the same time (default off).
-once Exit after the first successfully connected viewer
disconnects, opposite of -forever. This is the Default.
-forever Keep listening for more connections rather than exiting
as soon as the first client(s) disconnect. Same as -many
-loop Create an outer loop restarting the x11vnc process
whenever it terminates. -bg and -inetd are ignored in
this mode. Useful for continuing even if the X server
terminates and restarts (you will need permission to
reconnect of course). Use, e.g., -loop100 to sleep
100 millisecs between restarts, etc. Default is 2000ms
(i.e. 2 secs) Use, e.g. -loop300,5 to sleep 300 ms
and only loop 5 times.
-timeout n Exit unless a client connects within the first n seconds
after startup.
-inetd Launched by inetd(8): stdio instead of listening socket.
Note: if you are not redirecting stderr to a log file
(via shell 2> or -o option) you MUST also specify the -q
option, otherwise the stderr goes to the viewer which
will cause it to abort. Specifying both -inetd and -q
and no -o will automatically close the stderr.
-nofilexfer Disable the TightVNC file transfer extension. (same as
-disablefiletransfer). Note that when the -viewonly
option is supplied all file transfers are disabled.
Also clients that log in viewonly cannot transfer files.
However, if the remote control mechanism is used to
change the global or per-client viewonly state the
filetransfer permissions will NOT change.
Note, to *enable* UltraVNC filetransfer (currently
disabled by default, this may change...) and to get it
to work you probably need to supply these libvncserver
options: "-rfbversion 3.6 -permitfiletransfer"
-http Instead of using -httpdir (see below) to specify
where the Java vncviewer applet is, have x11vnc try
to *guess* where the directory is by looking relative
to the program location and in standard locations
(/usr/local/share/x11vnc/classes, etc). Under -ssl or
-stunnel the ssl classes subdirectory is sought.
-http_ssl As -http, but force lookup for ssl classes subdir.
-connect string For use with "vncviewer -listen" reverse connections.
If "string" has the form "host" or "host:port"
the connection is made once at startup. Use commas
for a list of host's and host:port's.
Note that unlike most vnc servers, x11vnc will require a
password for reverse as well as for forward connections.
(provided password auth has been enabled, -rfbauth, etc)
If you do not want to require a password for reverse
connections set X11VNC_REVERSE_CONNECTION_NO_AUTH=1 in
your environment before starting x11vnc.
If "string" contains "/" it is instead interpreted
as a file to periodically check for new hosts.
The first line is read and then the file is truncated.
Be careful for this usage mode if x11vnc is running as
root (e.g. via gdm(1), etc).
-vncconnect Monitor the VNC_CONNECT X property set by the standard
-novncconnect VNC program vncconnect(1). When the property is
set to "host" or "host:port" establish a reverse
connection. Using xprop(1) instead of vncconnect may
work (see the FAQ). The -remote control mechanism uses
X11VNC_REMOTE channel, and this option disables/enables
it as well. Default: -vncconnect
-allow host1[,host2..] Only allow client connections from hosts matching
the comma separated list of hostnames or IP addresses.
Can also be a numerical IP prefix, e.g. "192.168.100."
to match a simple subnet, for more control build
libvncserver with libwrap support (See the FAQ). If the
list contains a "/" it instead is a interpreted as a
file containing addresses or prefixes that is re-read
each time a new client connects. Lines can be commented
out with the "#" character in the usual way.
-localhost Basically the same as "-allow 127.0.0.1".
Note: if you want to restrict which network interface
x11vnc listens on, see the -listen option below.
E.g. "-listen localhost" or "-listen 192.168.3.21".
As a special case, the option "-localhost" implies
"-listen localhost".
A rare case, but for non-localhost -listen usage, if
you use the remote control mechanism (-R) to change
the -listen interface you may need to manually adjust
the -allow list (and vice versa) to avoid situations
where no connections (or too many) are allowed.
-nolookup Do not use gethostbyname() or gethostbyaddr() to look up
host names or IP numbers. Use this if name resolution
is incorrectly set up and leads to long pauses as name
lookups time out, etc.
-input string Fine tuning of allowed user input. If "string" does
not contain a comma "," the tuning applies only to
normal clients. Otherwise the part before "," is for
normal clients and the part after for view-only clients.
"K" is for Keystroke input, "M" for Mouse-motion
input, "B" for Button-click input, and "C" is for
Clipboard input. Their presence in the string enables
that type of input. E.g. "-input M" means normal
users can only move the mouse and "-input KMBC,M"
lets normal users do anything and enables view-only
users to move the mouse. This option is ignored when
a global -viewonly is in effect (all input is discarded
in that case).
-grabkbd When VNC viewers are connected, attempt to the grab
the keyboard so a (non-malicious) user sitting at the
physical display is not able to enter keystrokes.
This method uses XGrabKeyboard(3X11) and so it is
not secure and does not rule out the person at the
physical display injecting keystrokes by flooding the
server with them, grabbing the keyboard himself, etc.
Some degree of cooperation from the person at the
display is assumed. This is intended for remote
help-desk or educational usage modes.
-grabptr As -grabkbd, but for the mouse pointer using
XGrabPointer(3X11). Unfortunately due to the way the X
server works, the mouse can still be moved around by the
user at the physical display, but he will not be able to
change window focus with it. Also some window managers
that call XGrabServer(3X11) for resizes, etc, will
act on the local user's input. Again, some degree of
cooperation from the person at the display is assumed.
-viewpasswd string Supply a 2nd password for view-only logins. The -passwd
(full-access) password must also be supplied.
-passwdfile filename Specify the libvncserver password via the first line
of the file "filename" (instead of via -passwd on
the command line where others might see it via ps(1)).
See below for how to supply multiple passwords.
If the filename is prefixed with "rm:" it will be
removed after being read. Perhaps this is useful in
limiting the readability of the file. In general,
the password file should not be readable by untrusted
users (BTW: neither should the VNC -rfbauth file:
it is NOT encrypted, only obscured).
If the filename is prefixed with "read:" it will
periodically be checked for changes and reread.
Note that only the first 8 characters of a password
are used.
If multiple non-blank lines exist in the file they are
all taken as valid passwords. Blank lines are ignored.
Password lines may be "commented out" (ignored) if
they begin with the charactor "#" or the line contains
the string "__SKIP__". Lines may be annotated by use
of the "__COMM__" string: from it to the end of the
line is ignored. An empty password may be specified
via the "__EMPTY__" string on a line by itself (note
your viewer might not accept empty passwords).
If the string "__BEGIN_VIEWONLY__" appears on a
line by itself, the remaining passwords are used for
viewonly access. For compatibility, as a special case
if the file contains only two password lines the 2nd
one is automatically taken as the viewonly password.
Otherwise the "__BEGIN_VIEWONLY__" token must be
used to have viewonly passwords. (tip: make the 3rd
and last line be "__BEGIN_VIEWONLY__" to have 2
full-access passwords)
-unixpw [list] Use Unix username and password authentication. x11vnc
uses the su(1) program to verify the user's password.
[list] is an optional comma separated list of allowed
Unix usernames. See below for per-user options that
can be applied.
A familiar "login:" and "Password:" dialog is
presented to the user on a black screen inside the
vncviewer. The connection is dropped if the user fails
to supply the correct password in 3 tries or does not
send one before a 25 second timeout. Existing clients
are view-only during this period.
Since the detailed behavior of su(1) can vary from
OS to OS and for local configurations, test the mode
carefully on your systems before using it in production.
Test different combinations of valid/invalid usernames
and valid/invalid passwords to see if it behaves as
expected. x11vnc will attempt to be conservative and
reject a login if anything abnormal occurs.
On FreeBSD and the other BSD's by default it is
impossible for the user running x11vnc to validate
his *own* password via su(1) (evidently commenting out
the pam_self.so entry in /etc/pam.d/su eliminates this
problem). So the x11vnc login will always *fail* for
this case (even when the correct password is supplied).
A possible workaround for this would be to start
x11vnc as root with the "-users +nobody" option to
immediately switch to user nobody. Another source of
problems are PAM modules that prompt for extra info,
e.g. password aging modules. These logins will fail
as well even when the correct password is supplied.
**IMPORTANT**: to prevent the Unix password being sent
in *clear text* over the network, one of two schemes
will be enforced: 1) the -ssl builtin SSL mode, or 2)
require both -localhost and -stunnel be enabled.
Method 1) ensures the traffic is encrypted between
viewer and server. A PEM file will be required, see the
discussion under -ssl below (under some circumstances
a temporary one can be automatically generated).
Method 2) requires the viewer connection to appear
to come from the same machine x11vnc is running on
(e.g. from a ssh -L port redirection). And that the
-stunnel SSL mode be used for encryption over the
network.(see the description of -stunnel below).
Note: as a convenience, if you ssh(1) in and start
x11vnc it will check if the environment variable
SSH_CONNECTION is set and appears reasonable. If it
does, then the -ssl or -stunnel requirement will be
dropped since it is assumed you are using ssh for the
encrypted tunnelling. -localhost is still enforced.
Use -ssl or -stunnel to force SSL usage even if
SSH_CONNECTION is set.
To override the above restrictions you can set
environment variables before starting x11vnc:
Set UNIXPW_DISABLE_SSL=1 to disable requiring either
-ssl or -stunnel. Evidently you will be using a
different method to encrypt the data between the
vncviewer and x11vnc: perhaps ssh(1) or an IPSEC VPN.
Note that use of -localhost with ssh(1) is roughly
the same as requiring a Unix user login (since a Unix
password or the user's public key authentication is
used by sshd on the machine where x11vnc runs and only
local connections from that machine are accepted)
Set UNIXPW_DISABLE_LOCALHOST=1 to disable the -localhost
requirement in Method 2). One should never do this
(i.e. allow the Unix passwords to be sniffed on the
network).
Regarding reverse connections (e.g. -R connect:host
and -connect host), when the -localhost constraint is
in effect then reverse connections can only be used
to connect to the same machine x11vnc is running on
(default port 5500). Please use a ssh or stunnel port
redirection to the viewer machine to tunnel the reverse
connection over an encrypted channel. Note that in -ssl
mode reverse connection are disabled (see below).
In -inetd mode the Method 1) will be enforced (not
Method 2). With -ssl in effect reverse connections
are disabled. If you override this via env. var, be
sure to also use encryption from the viewer to inetd.
Tip: you can also have your own stunnel spawn x11vnc
in -inetd mode (thereby bypassing inetd). See the FAQ
for details.
The user names in the comma separated [list] can have
per-user options after a ":", e.g. "fred:opts"
where "opts" is a "+" separated list of
"viewonly", "fullaccess", "input=XXXX", or
"deny", e.g. "karl,wally:viewonly,boss:input=M".
For "input=" it is the K,M,B,C described under -input.
If a user in the list is "*" that means those
options apply to all users. It also means all users
are allowed to log in after supplying a valid password.
Use "deny" to explicitly deny some users if you use
"*" to set a global option.
There are also some utilities for testing password
if [list] starts with the "%" character. See the
quick_pw() function in the source for details.
-unixpw_nis [list] As -unixpw above, however do not use su(1) but rather
use the traditional getpwnam(3) + crypt(3) method to
verify passwords instead. This requires that the
encrypted passwords be readable. Passwords stored
in /etc/shadow will be inaccessible unless x11vnc
is run as root.
This is called "NIS" mode simply because in most
NIS setups the user encrypted passwords are accessible
(e.g. "ypcat passwd"). NIS is not required for this
mode to work (only that getpwnam(3) return the encrypted
password is required), but it is unlikely it will work
for any other modern environment unless x11vnc is run
as root (which, btw, is often done when running x11vnc
from inetd and xdm/gdm/kdm). All of the -unixpw options
and contraints apply.
-display_WAIT :... A special usage mode for the normal -display option.
Useful with -unixpw, but can be used independently
of it. If the display string begins with WAIT: then
x11vnc waits until a VNC client connects before opening
the X display (or -rawfb device).
This could be useful for delaying opening the display
for certain usage modes (say if x11vnc is started at
boot time and no X server is running or users logged
in yet).
If the string is, e.g. WAIT:0.0 or WAIT:1, i.e. "WAIT"
in front of a normal X display, then that indicated
display is used. A more interesting case is like this:
WAIT:cmd=/usr/local/bin/find_display
in which case the command after "cmd=" is run to
dynamically work out the DISPLAY and optionally the
XAUTHORITY data. The first line of the command output
must be of the form DISPLAY=<xdisplay>. Any remaining
output is taken as XAUTHORITY data. It can be either
of the form XAUTHORITY=<file> or raw xauthority data for
the display (e.g. "xauth extract - $DISPLAY" output).
In the case of -unixpw (but not -unixpw_nis), then the
above command is run as the user who just authenticated
via the login and password prompt.
Also in the case of -unixpw, the user logging in
can place a colon at the end of his username and
supply a few options: scale=, scale_cursor= (or sc=),
solid (or so), id=, clear_mods (or cm), clear_keys
(or ck), repeat, speeds= (or sp=), or readtimeout=
(or rd=) separated by commas if there is more than one.
After the user logs in successfully, these options will
be applied to the VNC screen. For example,
login: fred:scale=3/4,sc=1,repeat
Password: ...
login: runge:sp=modem,rd=120,solid=root:
for convenience m/n implies scale= e.g. fred:3/4
To disable this set the environment variable
X11VNC_NO_UNIXPW_OPTS=1. To set any other options,
the user can use the gui (x11vnc -gui connect) or the
remote control method (x11vnc -R opt:val) during his
VNC session.
So the combination of -display WAIT:cmd=... and
-unixpw allows automatic pairing of an unix
authenticated VNC user with his desktop. This could
be very useful on SunRays and also any system where
multiple users share a given machine. The user does
not need to remember special ports or passwords set up
for his desktop and VNC.
A nice way to use WAIT:cmd=... is out of inetd(8)
(it automatically forks a new x11vnc for each user).
You can have the x11vnc inetd spawned process run as,
say, root or nobody. When run as root (for either inetd
or display manager), you can also supply the option
"-users unixpw=" to have the x11vnc process switch to
the user as well. Note: there will be a 2nd SSL helper
process that will not switch, but it is only encoding
and decoding the encrypted stream at that point.
As a special case, WAIT:cmd=FINDDISPLAY will run a
script that works on most Unixes to determine a user's
DISPLAY variable and xauthority data (see who(1)).
To have this default script printed to stdout (e.g. for
customization) run with WAIT:cmd=FINDDISPLAY-print
As another special case, WAIT:cmd=HTTPONCE will allow
x11vnc to service one http request and then exit.
This is usually done in -inetd mode to run on, say,
port 5800 and allow the Java vncviewer to be downloaded
by client web browsers. For example:
5815 stream tcp nowait root /usr/sbin/tcpd .../x11vnc \
-inetd -q -http_ssl -display WAIT:cmd=HTTPONCE
It is used in the Apache SSL-portal example (see FAQ).
Finally, one can insert a geometry between colons,
e.g. WAIT:1280x1024:... to set the size of the display
the VNC client first attaches to since some VNC viewers
will not automatically adjust to a new framebuffer size.
-ssl [pem] Use the openssl library (www.openssl.org) to provide a
built-in encrypted SSL tunnel between VNC viewers and
x11vnc. This requires libssl support to be compiled
into x11vnc at build time. If x11vnc is not built
with libssl support it will exit immediately when -ssl
is prescribed.
[pem] is optional, use "-ssl /path/to/mycert.pem"
to specify a PEM certificate file to use to identify
and provide a key for this server. See openssl(1) for
more info about PEMs and the -sslGenCert option below.
The connecting VNC viewer SSL tunnel can optionally
authenticate this server if they have the public
key part of the certificate (or a common certificate
authority, CA, is a more sophisicated way to verify
this server's cert, see -sslGenCA below). This is
used to prevent man-in-the-middle attacks. Otherwise,
if the VNC viewer accepts this server's key without
verification, at least the traffic is protected
from passive sniffing on the network (but NOT from
man-in-the-middle attacks).
If [pem] is not supplied and the openssl(1) utility
command exists in PATH, then a temporary, self-signed
certificate will be generated for this session (this
may take 5-30 seconds on slow machines). If openssl(1)
cannot be used to generate a temporary certificate
x11vnc exits immediately.
If successful in using openssl(1) to generate a
temporary certificate, the public part of it will be
displayed to stderr (e.g. one could copy it to the
client-side to provide authentication of the server to
VNC viewers.) See following paragraphs for how to save
keys to reuse when x11vnc is restarted.
Set the env. var. X11VNC_SHOW_TMP_PEM=1 to have x11vnc
print out the entire certificate, including the PRIVATE
KEY part, to stderr. One could reuse this cert if saved
in a [pem] file. Similarly, set X11VNC_KEEP_TMP_PEM=1
to not delete the temporary PEM file: the file name
will be printed to stderr (so one could move it to
a safe place for reuse). You will be prompted for a
passphrase for the private key.
If [pem] is "SAVE" then the certificate will be saved
to the file ~/.vnc/certs/server.pem, or if that file
exists it will be used directly. Similarly, if [pem]
is "SAVE_PROMPT" the server.pem certificate will be
made based on your answers to its prompts for info such
as OrganizationalName, CommonName, etc.
Use "SAVE-<string>" and "SAVE_PROMPT-<string>"
to refer to the file ~/.vnc/certs/server-<string>.pem
instead. E.g. "SAVE-charlie" will store to the file
~/.vnc/certs/server-charlie.pem
See -ssldir below to use a directory besides the
default ~/.vnc/certs
Example: x11vnc -ssl SAVE -display :0 ...
Reverse connections are disabled in -ssl mode because
there is no way to ensure that data channel will
be encrypted. Set X11VNC_SSL_ALLOW_REVERSE=1 to
override this.
Your VNC viewer will also need to be able to connect
via SSL. See the discussion below under -stunnel and
the FAQ (ssl_vncviewer script) for how this might be
achieved. E.g. on Unix it is easy to write a shell
script that starts up stunnel and then vncviewer.
Also in the x11vnc source a SSL enabled Java VNC Viewer
applet is provided in the classes/ssl directory.
-ssldir [dir] Use [dir] as an alternate ssl certificate and key
management toplevel directory. The default is
~/.vnc/certs
This directory is used to store server and other
certificates and keys and also other materials. E.g. in
the simplest case, "-ssl SAVE" will store the x11vnc
server cert in [dir]/server.pem
Use of alternate directories via -ssldir allows you to
manage multiple VNC Certificate Authority (CA) keys.
Another use is if ~/.vnc/cert is on an NFS share you
might want your certificates and keys to be on a local
filesystem to prevent network snooping (for example
-ssldir /var/lib/x11vnc-certs).
-ssldir affects nearly all of the other -ssl* options,
e.g. -ssl SAVE, -sslGenCert, etc..
-sslverify [path] For either of the -ssl or -stunnel modes, use [path]
to provide certificates to authenticate incoming VNC
*Client* connections (normally only the server is
authenticated in SSL.) This can be used as a method
to replace standard password authentication of clients.
If [path] is a directory it contains the client (or CA)
certificates in separate files. If [path] is a file,
it contains multiple certificates. See special tokens
below. These correspond to the "CApath = dir" and
"CAfile = file" stunnel options. See the stunnel(8)
manpage for details.
Examples:
x11vnc -ssl -sslverify ~/my.pem
x11vnc -ssl -sslverify ~/my_pem_dir/
Note that if [path] is a directory, it must contain
the certs in separate files named like <HASH>.0, where
the value of <HASH> is found by running the command
"openssl x509 -hash -noout -in file.crt". Evidently
one uses <HASH>.1 if there is a collision...
The the key-management utility "-sslCertInfo HASHON"
and "-sslCertInfo HASHOFF" will create/delete these
hashes for you automatically (via symlink) in the HASH
subdirs it manages. Then you can point -sslverify to
the HASH subdir.
Special tokens: in -ssl mode, if [path] is not a file or
a directory, it is taken as a comma separated list of
tokens that are interpreted as follows:
If a token is "CA" that means load the CA/cacert.pem
file from the ssl directory. If a token is "clients"
then all the files clients/*.crt in the ssl directory
are loaded. Otherwise the file clients/token.crt
is attempted to be loaded. As a kludge, use a token
like ../server-foo to load a server cert if you find
that necessary.
Use -ssldir to use a directory different from the
~/.vnc/certs default.
Note that if the "CA" cert is loaded you do not need
to load any of the certs that have been signed by it.
You will need to load any additional self-signed certs
however.
Examples:
x11vnc -ssl -sslverify CA
x11vnc -ssl -sslverify self:fred,self:jim
x11vnc -ssl -sslverify CA,clients
Usually "-sslverify CA" is the most effective.
See the -sslGenCA and -sslGenCert options below for
how to set up and manage the CA framework.
NOTE: the following utilities, -sslGenCA, -sslGenCert,
-sslEncKey, and -sslCertInfo are provided for
completeness, but for casual usage they are overkill.
They provide VNC Certificate Authority (CA) key creation
and server / client key generation and signing. So they
provide a basic Public Key management framework for
VNC-ing with x11vnc. (note that they require openssl(1)
be installed on the system)
However, the simplest usage mode (where x11vnc
automatically generates its own, self-signed, temporary
key and the VNC viewers always accept it, e.g. accepting
via a dialog box) is probably safe enough for most
scenarios. CA management is not needed.
To protect against Man-In-The-Middle attacks the
simplest mode can be improved by using "-ssl SAVE"
to have x11vnc create a longer term self-signed
certificate, and then (safely) copy the corresponding
public key cert to the desired client machines (care
must be taken the private key part is not stolen;
you will be prompted for a passphrase).
So keep in mind no CA key creation or management
(-sslGenCA and -sslGenCert) is needed for either of
the above two common usage modes.
One might want to use -sslGenCA and -sslGenCert
if you had a large number of VNC client and server
workstations. That way the administrator could generate
a single CA key with -sslGenCA and distribute its
certificate part to all of the workstations.
Next, he could create signed VNC server keys
(-sslGenCert server ...) for each workstation or user
that then x11vnc would use to authenticate itself to
any VNC client that has the CA cert.
Optionally, the admin could also make it so the
VNC clients themselves are authenticated to x11vnc
(-sslGenCert client ...) For this -sslverify would be
pointed to the CA cert (and/or self-signed certs).
x11vnc will be able to use all of these cert and
key files. On the VNC client side, they will need to
be "imported" somehow. Web browsers have "Manage
Certificates" actions as does the Java applet plugin
Control Panel. stunnel can also use these files (see
the ssl_vncviewer example script in the FAQ.)
-sslGenCA [dir] Generate your own Certificate Authority private key,
certificate, and other files in directory [dir].
If [dir] is not supplied, a -ssldir setting is used,
or otherwise ~/.vnc/certs is used.
This command also creates directories where server and
client certs and keys will be stored. The openssl(1)
program must be installed on the system and available
in PATH.
After the CA files and directories are created the
command exits; the VNC server is not run.
You will be prompted for information to put into the CA
certificate. The info does not have to be accurate just
as long as clients accept the cert for VNC connections.
You will also need to supply a passphrase of at least
4 characters for the CA private key.
Once you have generated the CA you can distribute
its certificate part, [dir]/CA/cacert.pem, to other
workstations where VNC viewers will be run. One will
need to "import" this certicate in the applications,
e.g. Web browser, Java applet plugin, stunnel, etc.
Next, you can create and sign keys using the CA with
the -sslGenCert option below.
Examples:
x11vnc -sslGenCA
x11vnc -sslGenCA ~/myCAdir
x11vnc -ssldir ~/myCAdir -sslGenCA
(the last two lines are equivalent)
-sslGenCert type name Generate a VNC server or client certificate and private
key pair signed by the CA created previously with
-sslGenCA. The openssl(1) program must be installed
on the system and available in PATH.
After the Certificate is generated the command exits;
the VNC server is not run.
The type of key to be generated is the string "type".
It is either "server" (i.e. for use by x11vnc) or
"client" (for a VNC viewer). Note that typically
only "server" is used: the VNC clients authenticate
themselves by a non-public-key method (e.g. VNC or
unix password). "type" is required.
An arbitrary default name you want to associate with
the key is supplied by the "name" string. You can
change it at the various prompts when creating the key.
"name" is optional.
If name is left blank for clients keys then "nobody"
is used. If left blank for server keys, then the
primary server key: "server.pem" is created (this
is the saved one referenced by "-ssl SAVE" when the
server is started)
If "name" begins with the string "self:" then
a self-signed certificate is created instead of one
signed by your CA key.
If "name" begins with the string "req:" then only a
key (.key) and a certificate signing *request* (.req)
are generated. You can then send the .req file to
an external CA (even a professional one, e.g. Thawte)
and then combine the .key and the received cert into
the .pem file with the same basename.
The distinction between "server" and "client" is
simply the choice of output filenames and sub-directory.
This makes it so the -ssl SAVE-name option can easily
pick up the x11vnc PEM file this option generates.
And similarly makes it easy for the -sslverify option
to pick up your client certs.
There is nothing special about the filename or directory
location of either the "server" and "client" certs.
You can rename the files or move them to wherever
you like.
Precede this option with -ssldir [dir] to use a
directory other than the default ~/.vnc/certs You will
need to run -sslGenCA on that directory first before
doing any -sslGenCert key creation.
Note you cannot recreate a cert with exactly the same
distiguished name (DN) as an existing one. To do so,
you will need to edit the [dir]/CA/index.txt file to
delete the line.
Similar to -sslGenCA, you will be prompted to fill
in some information that will be recorded in the
certificate when it is created. Tip: if you know
the fully-quailified hostname other people will be
connecting to you can use that as the CommonName "CN"
to avoid some applications (e.g. web browsers and java
plugin) complaining it does not match the hostname.
You will also need to supply the CA private key
passphrase to unlock the private key created from
-sslGenCA. This private key is used to sign the server
or client certicate.
The "server" certs can be used by x11vnc directly by
pointing to them via the -ssl [pem] option. The default
file will be ~/.vnc/certs/server.pem. This one would
be used by simply typing -ssl SAVE. The pem file
contains both the certificate and the private key.
server.crt file contains the cert only.
The "client" cert + private key file will need
to be copied and imported into the VNC viewer
side applications (Web browser, Java plugin,
stunnel, etc.) Once that is done you can delete the
"client" private key file on this machine since
it is only needed on the VNC viewer side. The,
e.g. ~/.vnc/certs/clients/<name>.pem contains both
the cert and private key. The <name>.crt contains the
certificate only.
NOTE: It is very important to know one should always
generate new keys with a passphrase. Otherwise if an
untrusted user steals the key file he could use it to
masquerade as the x11vnc server (or VNC viewer client).
You will be prompted whether to encrypt the key with
a passphrase or not. It is recommended that you do.
One inconvenience to a passphrase is that it must
be suppled every time x11vnc or the client app is
started up.
Examples:
x11vnc -sslGenCert server
x11vnc -ssl SAVE -display :0 ...
and then on viewer using ssl_vncviewer stunnel wrapper
(see the FAQ):
ssl_vncviewer -verify ./cacert.crt hostname:0
(this assumes the cacert.crt cert from -sslGenCA
was safely copied to the VNC viewer machine where
ssl_vncviewer is run)
Example using a name:
x11vnc -sslGenCert server charlie
x11vnc -ssl SAVE-charlie -display :0 ...
Example for a client certificate (rarely used):
x11vnc -sslGenCert client roger
scp ~/.vnc/certs/clients/roger.pem somehost:.
rm ~/.vnc/certs/clients/roger.pem
x11vnc is then started with the the option -sslverify
~/.vnc/certs/clients/roger.crt (or simply -sslverify
roger), and on the viewer user on somehost could do
for example:
ssl_vncviewer -mycert ./roger.pem hostname:0
-sslEncKey [pem] Utility to encrypt an existing PEM file with a
passphrase you supply when prompted. For that key to be
used (e.g. by x11vnc) the passphrase must be supplied
each time.
The "SAVE" notation described under -ssl applies as
well. (precede this option with -ssldir [dir] to refer
a directory besides the default ~/.vnc/certs)
The openssl(1) program must be installed on the system
and available in PATH. After the Key file is encrypted
the command exits; the VNC server is not run.
Examples:
x11vnc -sslEncKey /path/to/foo.pem
x11vnc -sslEncKey SAVE
x11vnc -sslEncKey SAVE-charlie
-sslCertInfo [pem] Prints out information about an existing PEM file.
In addition the public certificate is also printed.
The openssl(1) program must be in PATH. Basically the
command "openssl x509 -text" is run on the pem.
The "SAVE" notation described under -ssl applies
as well.
Using "LIST" will give a list of all certs being
managed (in the ~/.vnc/certs dir, use -ssldir to refer
to another dir). "ALL" will print out the info for
every managed key (this can be very long). Giving a
client or server cert shortname will also try a lookup
(e.g. -sslCertInfo charlie). Use "LISTL" or "LL"
for a long (ls -l style) listing.
Using "HASHON" will create subdirs [dir]/HASH and
[dir]/HASH with OpenSSL hash filenames (e.g. 0d5fbbf1.0)
symlinks pointing up to the corresponding *.crt file.
([dir] is ~/.vnc/certs or one given by -ssldir.)
This is a useful way for other OpenSSL applications
(e.g. stunnel) to access all of the certs without
having to concatenate them. x11vnc will not use them
unless you specifically reference them. "HASHOFF"
removes these HASH subdirs.
The LIST, LISTL, LL, ALL, HASHON, HASHOFF words can
also be lowercase, e.g. "list".
-sslDelCert [pem] Prompts you to delete all .crt .pem .key .req files
associated with [pem]. "SAVE" and lookups as in
-sslCertInfo apply as well.
-stunnel [pem] Use the stunnel(8) (www.stunnel.org) to provide an
encrypted SSL tunnel between viewers and x11vnc.
This external tunnel method was implemented prior to the
integrated -ssl encryption described above. It still
works well. This requires stunnel to be installed
on the system and available via PATH (n.b. stunnel is
often installed in sbin directories). Version 4.x of
stunnel is assumed (but see -stunnel3 below.)
[pem] is optional, use "-stunnel /path/to/stunnel.pem"
to specify a PEM certificate file to pass to stunnel.
Whether one is needed or not depends on your stunnel
configuration. stunnel often generates one at install
time. See the stunnel documentation for details.
stunnel is started up as a child process of x11vnc and
any SSL connections stunnel receives are decrypted and
sent to x11vnc over a local socket. The strings
"The SSL VNC desktop is ..." and "SSLPORT=..."
are printed out at startup to indicate this.
The -localhost option is enforced by default
to avoid people routing around the SSL channel.
Set STUNNEL_DISABLE_LOCALHOST=1 before starting x11vnc
to disable the requirement.
Your VNC viewer will also need to be able to connect via
SSL. Unfortunately not too many do this. UltraVNC has
an encryption plugin but it does not seem to be SSL.
Also, in the x11vnc distribution, a patched TightVNC
Java applet is provided in classes/ssl that does SSL
connections (only).
It is also not too difficult to set up an stunnel or
other SSL tunnel on the viewer side. A simple example
on Unix using stunnel 3.x is:
% stunnel -c -d localhost:5901 -r remotehost:5900
% vncviewer localhost:1
For Windows, stunnel has been ported to it and there
are probably other such tools available. See the FAQ
for more examples.
-stunnel3 [pem] Use version 3.x stunnel command line syntax instead of
version 4.x
-https [port] Choose a separate HTTPS port (-ssl mode only).
In -ssl mode, it turns out you can use the
single VNC port (e.g. 5900) for both VNC and HTTPS
connections. (HTTPS is used to retrieve a SSL-aware
VncViewer.jar applet that is provided with x11vnc).
Since both use SSL the implementation was extended to
detect if HTTP traffic (i.e. GET) is taking place and
handle it accordingly. The URL would be, e.g.:
https://mymachine.org:5900/
This is convenient for firewalls, etc, because only one
port needs to be allowed in. However, this heuristic
adds a few seconds delay to each connection and can be
unreliable (especially if the user takes much time to
ponder the Certificate dialogs in his browser, Java VM,
or VNC Viewer applet. That's right 3 separate "Are
you sure you want to connect" dialogs!)
So use the -https option to provide a separate, more
reliable HTTPS port that x11vnc will listen on. If
[port] is not provided (or is 0), one is autoselected.
The URL to use is printed out at startup.
The SSL Java applet directory is specified via the
-httpdir option. If not supplied it will try to guess
the directory as though the -http option was supplied.
-usepw If no other password method was supplied on the command
line, first look for ~/.vnc/passwd and if found use it
with -rfbauth; next, look for ~/.vnc/passwdfile and
use it with -passwdfile; otherwise, prompt the user
for a password to create ~/.vnc/passwd and use it with
the -rfbauth option. If none of these succeed x11vnc
exits immediately.
-storepasswd pass file Store password "pass" as the VNC password in the
file "file". Once the password is stored the
program exits. Use the password via "-rfbauth file"
If called with no arguments, "x11vnc -storepasswd",
the user is prompted for a password and it is stored
in the file ~/.vnc/passwd. Called with one argument,
that will be the file to store the prompted password in.
-nopw Disable the big warning message when you use x11vnc
without some sort of password.
-accept string Run a command (possibly to prompt the user at the
X11 display) to decide whether an incoming client
should be allowed to connect or not. "string" is
an external command run via system(3) or some special
cases described below. Be sure to quote "string"
if it contains spaces, shell characters, etc. If the
external command returns 0 the client is accepted,
otherwise the client is rejected. See below for an
extension to accept a client view-only.
If x11vnc is running as root (say from inetd(8) or from
display managers xdm(1), gdm(1), etc), think about the
security implications carefully before supplying this
option (likewise for the -gone option).
Environment: The RFB_CLIENT_IP environment variable will
be set to the incoming client IP number and the port
in RFB_CLIENT_PORT (or -1 if unavailable). Similarly,
RFB_SERVER_IP and RFB_SERVER_PORT (the x11vnc side
of the connection), are set to allow identification
of the tcp virtual circuit. The x11vnc process
id will be in RFB_X11VNC_PID, a client id number in
RFB_CLIENT_ID, and the number of other connected clients
in RFB_CLIENT_COUNT. RFB_MODE will be "accept".
RFB_STATE will be PROTOCOL_VERSION, SECURITY_TYPE,
AUTHENTICATION, INITIALISATION, NORMAL, or UNKNOWN
indicating up to which state the client has acheived.
RFB_LOGIN_VIEWONLY will be 0, 1, or -1 (unknown).
RFB_USERNAME, RFB_LOGIN_TIME, and RFB_CURRENT_TIME may
also be set.
If "string" is "popup" then a builtin popup window
is used. The popup will time out after 120 seconds,
use "popup:N" to modify the timeout to N seconds
(use 0 for no timeout).
In the case of "popup" and when the -unixpw option
is specified, then a *second* window will be popped
up after the user successfully logs in via his UNIX
password. This time the user will be identified as
UNIX:username@hostname, the "UNIX:" prefix indicates
which user the viewer logged as via -unixpw. The first
popup is only for whether to allow him to even *try*
to login via unix password.
If "string" is "xmessage" then an xmessage(1)
invocation is used for the command. xmessage must be
installed on the machine for this to work.
Both "popup" and "xmessage" will present an option
for accepting the client "View-Only" (the client
can only watch). This option will not be presented if
-viewonly has been specified, in which case the entire
display is view only.
If the user supplied command is prefixed with something
like "yes:0,no:*,view:3 mycommand ..." then this
associates the numerical command return code with
the actions: accept, reject, and accept-view-only,
respectively. Use "*" instead of a number to indicate
the default action (in case the command returns an
unexpected value). E.g. "no:*" is a good choice.
Note that x11vnc blocks while the external command
or popup is running (other clients may see no updates
during this period). So a person sitting a the physical
display is needed to respond to an popup prompt. (use
a 2nd x11vnc if you lock yourself out).
More -accept tricks: use "popupmouse" to only allow
mouse clicks in the builtin popup to be recognized.
Similarly use "popupkey" to only recognize
keystroke responses. These are to help avoid the
user accidentally accepting a client by typing or
clicking. All 3 of the popup keywords can be followed
by +N+M to supply a position for the popup window.
The default is to center the popup window.
-afteraccept string As -accept, except to run a user supplied command after
a client has been accepted and authenticated. RFB_MODE
will be set to "afteraccept" and the other RFB_*
variables are as in -accept. Unlike -accept, the
command return code is not interpreted by x11vnc.
Example: -afteraccept 'killall xlock &'
-gone string As -accept, except to run a user supplied command when
a client goes away (disconnects). RFB_MODE will be
set to "gone" and the other RFB_* variables are as
in -accept. The "popup" actions apply as well.
Unlike -accept, the command return code is not
interpreted by x11vnc. Example: -gone 'xlock &'
-users list If x11vnc is started as root (say from inetd(8) or from
display managers xdm(1), gdm(1), etc), then as soon
as possible after connections to the X display are
established try to switch to one of the users in the
comma separated "list". If x11vnc is not running as
root this option is ignored.
Why use this option? In general it is not needed since
x11vnc is already connected to the X display and can
perform its primary functions. The option was added
to make some of the *external* utility commands x11vnc
occasionally runs work properly. In particular under
GNOME and KDE to implement the "-solid color" feature
external commands (gconftool-2 and dcop) unfortunately
must be run as the user owning the desktop session.
Since this option switches userid it also affects the
userid used to run the processes for the -accept and
-gone options. It also affects the ability to read
files for options such as -connect, -allow, and -remap.
Note that the -connect file is also sometimes written
to.
So be careful with this option since in some situations
its use can decrease security.
In general the switch to a user will only take place
if the display can still be successfully opened as that
user (this is primarily to try to guess the actual owner
of the session). Example: "-users fred,wilma,betty".
Note that a malicious user "barney" by quickly using
"xhost +" when logging in may possibly get the x11vnc
process to switch to user "fred". What happens next?
Under display managers it may be a long time before
the switch succeeds (i.e. a user logs in). To instead
make it switch immediately regardless if the display
can be reopened prefix the username with the "+"
character. E.g. "-users +bob" or "-users +nobody".
The latter (i.e. switching immediately to user
"nobody") is probably the only use of this option
that increases security.
In -unixpw mode, if "-users unixpw=" is supplied
then after a user authenticates himself via the
-unixpw mechanism, x11vnc will try to switch to that
user as though "-users +username" had been supplied.
If you want to limit which users this will be done for,
provide them as a comma separated list after "unixpw="
To immediately switch to a user *before* connections
to the X display are made or any files opened use the
"=" character: "-users =bob". That user needs to
be able to open the X display and any files of course.
The special user "guess=" means to examine the utmpx
database (see who(1)) looking for a user attached to
the display number (from DISPLAY or -display option)
and try him/her. To limit the list of guesses, use:
"-users guess=bob,betty".
Even more sinister is the special user "lurk="
that means to try to guess the DISPLAY from the utmpx
login database as well. So it "lurks" waiting for
anyone to log into an X session and then connects to it.
Specify a list of users after the = to limit which users
will be tried. To enable a different searching mode, if
the first user in the list is something like ":0" or
":0-2" that indicates a range of DISPLAY numbers that
will be tried (regardless of whether they are in the
utmpx database) for all users that are logged in. Also
see the "-display WAIT:..." functionality. Examples:
"-users lurk=" and also "-users lurk=:0-1,bob,mary"
Be especially careful using the "guess=" and "lurk="
modes. They are not recommended for use on machines
with untrustworthy local users.
-noshm Do not use the MIT-SHM extension for the polling.
Remote displays can be polled this way: be careful this
can use large amounts of network bandwidth. This is
also of use if the local machine has a limited number
of shm segments and -onetile is not sufficient.
-flipbyteorder Sometimes needed if remotely polled host has different
endianness. Ignored unless -noshm is set.
-onetile Do not use the new copy_tiles() framebuffer mechanism,
just use 1 shm tile for polling. Limits shm segments
used to 3.
-solid [color] To improve performance, when VNC clients are connected
try to change the desktop background to a solid color.
The [color] is optional: the default color is "cyan4".
For a different one specify the X color (rgb.txt name,
e.g. "darkblue" or numerical "#RRGGBB").
Currently this option only works on GNOME, KDE, CDE,
and classic X (i.e. with the background image on the
root window). The "gconftool-2" and "dcop" external
commands are run for GNOME and KDE respectively.
Other desktops won't work, e.g. Xfce (send us the
corresponding commands if you find them). If x11vnc is
running as root (inetd(8) or gdm(1)), the -users option
may be needed for GNOME and KDE. If x11vnc guesses
your desktop incorrectly, you can force it by prefixing
color with "gnome:", "kde:", "cde:" or "root:".
-blackout string Black out rectangles on the screen. "string" is a
comma separated list of WxH+X+Y type geometries for
each rectangle. If one of the items on the list is the
string "noptr" the mouse pointer will not be allowed
to go into a blacked out region.
-xinerama If your screen is composed of multiple monitors
-noxinerama glued together via XINERAMA, and that screen is
not a rectangle this option will try to guess the
areas to black out (if your system has libXinerama).
default: -xinerama
In general, we have noticed on XINERAMA displays you
may need to use the "-xwarppointer" option if the mouse
pointer misbehaves.
-xtrap Use the DEC-XTRAP extension for keystroke and mouse
input insertion. For use on legacy systems, e.g. X11R5,
running an incomplete or missing XTEST extension.
By default DEC-XTRAP will be used if XTEST server grab
control is missing, use -xtrap to do the keystroke and
mouse insertion via DEC-XTRAP as well.
-xrandr [mode] If the display supports the XRANDR (X Resize, Rotate
and Reflection) extension, and you expect XRANDR events
to occur to the display while x11vnc is running, this
options indicates x11vnc should try to respond to
them (as opposed to simply crashing by assuming the
old screen size). See the xrandr(1) manpage and run
'xrandr -q' for more info. [mode] is optional and
described below.
Since watching for XRANDR events and trapping errors
increases polling overhead, only use this option if
XRANDR changes are expected. For example on a rotatable
screen PDA or laptop, or using a XRANDR-aware Desktop
where you resize often. It is best to be viewing with a
vncviewer that supports the NewFBSize encoding, since it
knows how to react to screen size changes. Otherwise,
libvncserver tries to do so something reasonable for
viewers that cannot do this (portions of the screen
may be clipped, unused, etc).
"mode" defaults to "resize", which means create a
new, resized, framebuffer and hope all viewers can cope
with the change. "newfbsize" means first disconnect
all viewers that do not support the NewFBSize VNC
encoding, and then resize the framebuffer. "exit"
means disconnect all viewer clients, and then terminate
x11vnc.
-padgeom WxH Whenever a new vncviewer connects, the framebuffer is
replaced with a fake, solid black one of geometry WxH.
Shortly afterwards the framebuffer is replaced with the
real one. This is intended for use with vncviewers
that do not support NewFBSize and one wants to make
sure the initial viewer geometry will be big enough
to handle all subsequent resizes (e.g. under -xrandr,
-remote id:windowid, rescaling, etc.)
-o logfile Write stderr messages to file "logfile" instead of
to the terminal. Same as "-logfile file". To append
to the file use "-oa file" or "-logappend file".
-flag file Write the "PORT=NNNN" (e.g. PORT=5900) string to
"file" in addition to stdout. This option could be
useful by wrapper script to detect when x11vnc is ready.
-rc filename Use "filename" instead of $HOME/.x11vncrc for rc file.
-norc Do not process any .x11vncrc file for options.
-env VAR=VALUE Set the environment variable 'VAR' to value 'VALUE'
at x11vnc startup. This is a convenience utility to
avoid shell script wrappers, etc. to set the env. var.
You may specify as many of these as needed on the
command line.
-h, -help Print this help text.
-?, -opts Only list the x11vnc options.
-V, -version Print program version and last modification date.
-license Print out license information. Same as -copying and
-warranty.
-dbg Instead of exiting after cleaning up, run a simple
"debug crash shell" when fatal errors are trapped.
-q Be quiet by printing less informational output to
stderr. Same as -quiet.
-bg Go into the background after screen setup. Messages to
stderr are lost unless -o logfile is used. Something
like this could be useful in a script:
port=`ssh $host "x11vnc -display :0 -bg" | grep PORT`
port=`echo "$port" | sed -e 's/PORT=//'`
port=`expr $port - 5900`
vncviewer $host:$port
-modtweak Option -modtweak automatically tries to adjust the AltGr
-nomodtweak and Shift modifiers for differing language keyboards
between client and host. Otherwise, only a single key
press/release of a Keycode is simulated (i.e. ignoring
the state of the modifiers: this usually works for
identical keyboards). Also useful in resolving cases
where a Keysym is bound to multiple keys (e.g. "<" + ">"
and "," + "<" keys). Default: -modtweak
-xkb When in modtweak mode, use the XKEYBOARD extension (if
-noxkb the X display supports it) to do the modifier tweaking.
This is powerful and should be tried if there are still
keymapping problems when using -modtweak by itself.
The default is to check whether some common keysyms,
e.g. !, @, [, are only accessible via -xkb mode and if
so then automatically enable the mode. To disable this
automatic detection use -noxkb.
-capslock When in -modtweak (the default) or -xkb mode,
if a keysym in the range A-Z comes in check the X
server to see if the Caps_Lock is set. If it is do
not artificially press Shift to generate the keysym.
This will enable the CapsLock key to behave correctly
in some circumstances: namely *both* the VNC viewer
machine and the x11vnc X server are in the CapsLock
on state. If one side has CapsLock on and the other
off and the keyboard is not behaving as you think it
should you should correct the CapsLock states (hint:
pressing CapsLock inside and outside of the viewer can
help toggle them both to the correct state). However,
for best results do not use this option, but rather
*only* enable CapsLock on the VNC viewer side (i.e. by
pressing CapsLock outside of the viewer window, also
-skip_lockkeys below). Also try -nomodtweak for a
possible workaround.
-skip_lockkeys Have x11vnc ignore all Caps_Lock, Shift_Lock, Num_Lock,
Scroll_Lock keysyms received from viewers. The idea is
you press Caps_Lock on the VNC Viewer side but that does
not change the lock state in the x11vnc-side X server.
Nevertheless your capitalized letters come in over
the wire and are applied correctly to the x11vnc-side
X server. Note this mode probably won't do what you
want in -nomodtweak mode. Also, a kludge for KP_n
digits is always done it this mode: they are mapped to
regular digit keysyms. See also -capslock above.
-skip_keycodes string Ignore the comma separated list of decimal keycodes.
Perhaps these are keycodes not on your keyboard but
your X server thinks exist. Currently only applies
to -xkb mode. Use this option to help x11vnc in the
reverse problem it tries to solve: Keysym -> Keycode(s)
when ambiguities exist (more than one Keycode per
Keysym). Run 'xmodmap -pk' to see your keymapping.
Example: "-skip_keycodes 94,114"
-sloppy_keys Experimental option that tries to correct some
"sloppy" key behavior. E.g. if at the viewer you
press Shift+Key but then release the Shift before
Key that could give rise to extra unwanted characters
(usually only between keyboards of different languages).
Only use this option if you observe problems with
some keystrokes.
-skip_dups Some VNC viewers send impossible repeated key events,
-noskip_dups e.g. key-down, key-down, key-up, key-up all for the same
key, or 20 downs in a row for the same modifier key!
Setting -skip_dups means to skip these duplicates and
just process the first event. Note: some VNC viewers
assume they can send down's without the corresponding
up's and so you should not set this option for
these viewers (symptom: some keys do not autorepeat)
Default: -noskip_dups
-add_keysyms If a Keysym is received from a VNC viewer and that
-noadd_keysyms Keysym does not exist in the X server, then add the
Keysym to the X server's keyboard mapping on an unused
key. Added Keysyms will be removed periodically and
also when x11vnc exits. Default: -add_keysyms
-clear_mods At startup and exit clear the modifier keys by sending
KeyRelease for each one. The Lock modifiers are skipped.
Used to clear the state if the display was accidentally
left with any pressed down.
-clear_keys As -clear_mods, except try to release any pressed key.
Note that this option and -clear_mods can interfere
with a person typing at the physical keyboard.
-remap string Read Keysym remappings from file named "string".
Format is one pair of Keysyms per line (can be name
or hex value) separated by a space. If no file named
"string" exists, it is instead interpreted as this
form: key1-key2,key3-key4,... See <X11/keysymdef.h>
header file for a list of Keysym names, or use xev(1).
To map a key to a button click, use the fake Keysyms
"Button1", ..., etc. E.g: "-remap Super_R-Button2"
(useful for pasting on a laptop)
To disable a keysym (i.e. make it so it will not be
injected), remap it to "NoSymbol" or "None".
Dead keys: "dead" (or silent, mute) keys are keys that
do not produce a character but must be followed by a 2nd
keystroke. This is often used for accenting characters,
e.g. to put "`" on top of "a" by pressing the dead
key and then "a". Note that this interpretation
is not part of core X11, it is up to the toolkit or
application to decide how to react to the sequence.
The X11 names for these keysyms are "dead_grave",
"dead_acute", etc. However some VNC viewers send the
keysyms "grave", "acute" instead thereby disabling
the accenting. To work around this -remap can be used.
For example "-remap grave-dead_grave,acute-dead_acute"
As a convenience, "-remap DEAD" applies these remaps:
g grave-dead_grave
a acute-dead_acute
c asciicircum-dead_circumflex
t asciitilde-dead_tilde
m macron-dead_macron
b breve-dead_breve
D abovedot-dead_abovedot
d diaeresis-dead_diaeresis
o degree-dead_abovering
A doubleacute-dead_doubleacute
r caron-dead_caron
e cedilla-dead_cedilla
If you just want a subset use the first letter
label, e.g. "-remap DEAD=ga" to get the first two.
Additional remaps may also be supplied via commas,
e.g. "-remap DEAD=ga,Super_R-Button2". Finally,
"DEAD=missing" means to apply all of the above as
long as the left hand member is not already in the
X11 keymap.
-norepeat Option -norepeat disables X server key auto repeat when
-repeat VNC clients are connected and VNC keyboard input is
not idle for more than 5 minutes. This works around a
repeating keystrokes bug (triggered by long processing
delays between key down and key up client events: either
from large screen changes or high latency).
Default: -norepeat
Note: your VNC viewer side will likely do autorepeating,
so this is no loss unless someone is simultaneously at
the real X display.
Use "-norepeat N" to set how many times norepeat will
be reset if something else (e.g. X session manager)
undoes it. The default is 2. Use a negative value
for unlimited resets.
-nofb Ignore video framebuffer: only process keyboard and
pointer. Intended for use with Win2VNC and x2vnc
dual-monitor setups.
-nobell Do not watch for XBell events. (no beeps will be heard)
Note: XBell monitoring requires the XKEYBOARD extension.
-nosel Do not manage exchange of X selection/cutbuffer between
VNC viewers and the X server at all.
-noprimary Do not poll the PRIMARY selection for changes to send
back to clients. (PRIMARY is still set on received
changes, however).
-nosetprimary Do not set the PRIMARY selection for changes received
from VNC clients.
-noclipboard Do not poll the CLIPBOARD selection for changes to send
back to clients. (CLIPBOARD is still set on received
changes, however).
-nosetclipboard Do not set the CLIPBOARD selection for changes
received from VNC clients.
-seldir string If direction string is "send", only send the selection
to viewers, and if it is "recv" only receive it from
viewers. To work around apps setting the selection
too frequently and messing up the other end. You can
actually supply a comma separated list of directions,
including "debug" to turn on debugging output.
-cursor [mode] Sets how the pointer cursor shape (little icon at the
-nocursor mouse pointer) should be handled. The "mode" string
is optional and is described below. The default
is to show some sort of cursor shape(s). How this
is done depends on the VNC viewer and the X server.
Use -nocursor to disable cursor shapes completely.
Some VNC viewers support the TightVNC CursorPosUpdates
and CursorShapeUpdates extensions (cuts down on
network traffic by not having to send the cursor image
every time the pointer is moved), in which case these
extensions are used (see -nocursorshape and -nocursorpos
below to disable). For other viewers the cursor shape
is written directly to the framebuffer every time the
pointer is moved or changed and gets sent along with
the other framebuffer updates. In this case, there
will be some lag between the vnc viewer pointer and
the remote cursor position.
If the X display supports retrieving the cursor shape
information from the X server, then the default is
to use that mode. On Solaris this can be done with
the SUN_OVL extension using -overlay (see also the
-overlay_nocursor option). A similar overlay scheme
is used on IRIX. Xorg (e.g. Linux) and recent Solaris
Xsun servers support the XFIXES extension to retrieve
the exact cursor shape from the X server. If XFIXES
is present it is preferred over Overlay and is used by
default (see -noxfixes below). This can be disabled
with -nocursor, and also some values of the "mode"
option below.
Note that under XFIXES cursors with transparency (alpha
channel) will usually not be exactly represented and one
may find Overlay preferable. See also the -alphacut
and -alphafrac options below as fudge factors to try
to improve the situation for cursors with transparency
for a given theme.
The "mode" string can be used to fine-tune the
displaying of cursor shapes. It can be used the
following ways:
"-cursor arrow" - just show the standard arrow
nothing more or nothing less.
"-cursor none" - same as "-nocursor"
"-cursor X" - when the cursor appears to be on the
root window, draw the familiar X shape. Some desktops
such as GNOME cover up the root window completely,
and so this will not work, try "X1", etc, to try to
shift the tree depth. On high latency links or slow
machines there will be a time lag between expected and
the actual cursor shape.
"-cursor some" - like "X" but use additional
heuristics to try to guess if the window should have
a windowmanager-like resizer cursor or a text input
I-beam cursor. This is a complete hack, but may be
useful in some situations because it provides a little
more feedback about the cursor shape.
"-cursor most" - try to show as many cursors as
possible. Often this will only be the same as "some"
unless the display has overlay visuals or XFIXES
extensions available. On Solaris and IRIX if XFIXES
is not available, -overlay mode will be attempted.
-arrow n Choose an alternate "arrow" cursor from a set of
some common ones. n can be 1 to 6. Default is: 1
Ignored when in XFIXES cursor-grabbing mode.
-noxfixes Do not use the XFIXES extension to draw the exact cursor
shape even if it is available.
-alphacut n When using the XFIXES extension for the cursor shape,
cursors with transparency will not usually be displayed
exactly (but opaque ones will). This option sets n as
a cutoff for cursors that have transparency ("alpha
channel" with values ranging from 0 to 255) Any cursor
pixel with alpha value less than n becomes completely
transparent. Otherwise the pixel is completely opaque.
Default 240
-alphafrac fraction With the threshold in -alphacut some cursors will become
almost completely transparent because their alpha values
are not high enough. For those cursors adjust the
alpha threshold until fraction of the non-zero alpha
channel pixels become opaque. Default 0.33
-alpharemove By default, XFIXES cursors pixels with transparency have
the alpha factor multiplied into the RGB color values
(i.e. that corresponding to blending the cursor with a
black background). Specify this option to remove the
alpha factor. (useful for light colored semi-transparent
cursors).
-noalphablend In XFIXES mode do not send cursor alpha channel data
to libvncserver. The default is to send it. The
alphablend effect will only be visible in -nocursorshape
mode or for clients with cursorshapeupdates turned
off. (However there is a hack for 32bpp with depth 24,
it uses the extra 8 bits to store cursor transparency
for use with a hacked vncviewer that applies the
transparency locally. See the FAQ for more info).
-nocursorshape Do not use the TightVNC CursorShapeUpdates extension
even if clients support it. See -cursor above.
-cursorpos Option -cursorpos enables sending the X cursor position
-nocursorpos back to all vnc clients that support the TightVNC
CursorPosUpdates extension. Other clients will be able
to see the pointer motions. Default: -cursorpos
-xwarppointer Move the pointer with XWarpPointer(3X) instead of
the XTEST extension. Use this as a workaround
if the pointer motion behaves incorrectly, e.g.
on touchscreens or other non-standard setups.
Also sometimes needed on XINERAMA displays.
-buttonmap string String to remap mouse buttons. Format: IJK-LMN, this
maps buttons I -> L, etc., e.g. -buttonmap 13-31
Button presses can also be mapped to keystrokes: replace
a button digit on the right of the dash with :<sym>:
or :<sym1>+<sym2>: etc. for multiple keys. For example,
if the viewing machine has a mouse-wheel (buttons 4 5)
but the x11vnc side does not, these will do scrolls:
-buttonmap 12345-123:Prior::Next:
-buttonmap 12345-123:Up+Up+Up::Down+Down+Down:
See <X11/keysymdef.h> header file for a list of Keysyms,
or use the xev(1) program. Note: mapping of button
clicks to Keysyms may not work if -modtweak or -xkb is
needed for the Keysym.
If you include a modifier like "Shift_L" the
modifier's up/down state is toggled, e.g. to send
"The" use :Shift_L+t+Shift_L+h+e: (the 1st one is
shift down and the 2nd one is shift up). (note: the
initial state of the modifier is ignored and not reset)
To include button events use "Button1", ... etc.
-nodragging Do not update the display during mouse dragging events
(mouse button held down). Greatly improves response on
slow setups, but you lose all visual feedback for drags,
text selection, and some menu traversals. It overrides
any -pointer_mode setting.
-wireframe [str] Try to detect window moves or resizes when a mouse
-nowireframe button is held down and show a wireframe instead of
the full opaque window. This is based completely on
heuristics and may not always work: it depends on your
window manager and even how you move things around.
See -pointer_mode below for discussion of the "bogging
down" problem this tries to avoid.
Default: -wireframe
Shorter aliases: -wf [str] and -nowf
The value "str" is optional and, of course, is
packed with many tunable parameters for this scheme:
Format: shade,linewidth,percent,T+B+L+R,mod,t1+t2+t3+t4
Default: 0xff,3,0,32+8+8+8,all,0.15+0.30+5.0+0.125
If you leave nothing between commas: ",," the default
value is used. If you don't specify enough commas,
the trailing parameters are set to their defaults.
"shade" indicate the "color" for the wireframe,
usually a greyscale: 0-255, however for 16 and 32bpp you
can specify an rgb.txt X color (e.g. "dodgerblue") or
a value > 255 is treated as RGB (e.g. red is 0xff0000).
"linewidth" sets the width of the wireframe in pixels.
"percent" indicates to not apply the wireframe scheme
to windows with area less than this percent of the
full screen.
"T+B+L+R" indicates four integers for how close in
pixels the pointer has to be from the Top, Bottom, Left,
or Right edges of the window to consider wireframing.
This is a speedup to quickly exclude a window from being
wireframed: set them all to zero to not try the speedup
(scrolling and selecting text will likely be slower).
"mod" specifies if a button down event in the
interior of the window with a modifier key (Alt, Shift,
etc.) down should indicate a wireframe opportunity.
It can be "0" or "none" to skip it, "1" or "all"
to apply it to any modifier, or "Shift", "Alt",
"Control", "Meta", "Super", or "Hyper" to only
apply for that type of modifier key.
"t1+t2+t3+t4" specify four floating point times in
seconds: t1 is how long to wait for the pointer to move,
t2 is how long to wait for the window to start moving
or being resized (for some window managers this can be
rather long), t3 is how long to keep a wireframe moving
before repainting the window. t4 is the minimum time
between sending wireframe "animations". If a slow
link is detected, these values may be automatically
changed to something better for a slow link.
-wirecopyrect mode Since the -wireframe mechanism evidently tracks moving
-nowirecopyrect windows accurately, a speedup can be obtained by
telling the VNC viewers to locally copy the translated
window region. This is the VNC CopyRect encoding:
the framebuffer update doesn't need to send the actual
new image data.
Shorter aliases: -wcr [mode] and -nowcr
"mode" can be "never" (same as -nowirecopyrect)
to never try the copyrect, "top" means only do it if
the window was not covered by any other windows, and
"always" means to translate the orginally unobscured
region (this may look odd as the remaining pieces come
in, but helps on a slow link). Default: "always"
Note: there can be painting errors or slow response
when using -scale so you may want to disable CopyRect
in this case "-wirecopyrect never" on the command
line or by remote-control. Or you can also use the
"-scale xxx:nocr" scale option.
-debug_wireframe Turn on debugging info printout for the wireframe
heuristics. "-dwf" is an alias. Specify multiple
times for more output.
-scrollcopyrect mode Like -wirecopyrect, but use heuristics to try to guess
-noscrollcopyrect if a window has scrolled its contents (either vertically
or horizontally). This requires the RECORD X extension
to "snoop" on X applications (currently for certain
XCopyArea and XConfigureWindow X protocol requests).
Examples: Hitting <Return> in a terminal window when the
cursor was at the bottom, the text scrolls up one line.
Hitting <Down> arrow in a web browser window, the web
page scrolls up a small amount. Or scrolling with a
scrollbar or mouse wheel.
Shorter aliases: -scr [mode] and -noscr
This scheme will not always detect scrolls, but when
it does there is a nice speedup from using the VNC
CopyRect encoding (see -wirecopyrect). The speedup
is both in reduced network traffic and reduced X
framebuffer polling/copying. On the other hand, it may
induce undesired transients (e.g. a terminal cursor
being scrolled up when it should not be) or other
painting errors (window tearing, bunching-up, etc).
These are automatically repaired in a short period
of time. If this is unacceptable disable the feature
with -noscrollcopyrect.
Screen clearing kludges: for testing at least, there
are some "magic key sequences" (must be done in less
than 1 second) to aid repairing painting errors that
may be seen when using this mode:
3 Alt_L's in a row: resend whole screen,
4 Alt_L's in a row: reread and resend whole screen,
3 Super_L's in a row: mark whole screen for polling,
4 Super_L's in a row: reset RECORD context,
5 Super_L's in a row: try to push a black screen
note: Alt_L is the Left "Alt" key (a single key)
Super_L is the Left "Super" key (Windows flag).
Both of these are modifier keys, and so should not
generate characters when pressed by themselves. Also,
your VNC viewer may have its own refresh hot-key
or button.
"mode" can be "never" (same as -noscrollcopyrect)
to never try the copyrect, "keys" means to try it
in response to keystrokes only, "mouse" means to
try it in response to mouse events only, "always"
means to do both. Default: "always"
Note: there can be painting errors or slow response
when using -scale so you may want to disable CopyRect
in this case "-scrollcopyrect never" on the command
line or by remote-control. Or you can also use the
"-scale xxx:nocr" scale option.
-scr_area n Set the minimum area in pixels for a rectangle
to be considered for the -scrollcopyrect detection
scheme. This is to avoid wasting the effort on small
rectangles that would be quickly updated the normal way.
E.g. suppose an app updated the position of its skinny
scrollbar first and then shifted the large panel
it controlled. We want to be sure to skip the small
scrollbar and get the large panel. Default: 60000
-scr_skip list Skip scroll detection for applications matching
the comma separated list of strings in "list".
Some applications implement their scrolling in
strange ways where the XCopyArea, etc, also applies
to invisible portions of the window: if we CopyRect
those areas it looks awful during the scroll and
there may be painting errors left after the scroll.
Soffice.bin is the worst known offender.
Use "##" to denote the start of the application class
(e.g. "##XTerm") and "++" to denote the start
of the application instance name (e.g. "++xterm").
The string your list is matched against is of the form
"^^WM_NAME##Class++Instance<same-for-any-subwindows>"
The "xlsclients -la" command will provide this info.
If a pattern is prefixed with "KEY:" it only applies
to Keystroke generated scrolls (e.g. Up arrow). If it
is prefixed with "MOUSE:" it only applies to Mouse
induced scrolls (e.g. dragging on a scrollbar).
Default: ##Soffice.bin,##StarOffice
-scr_inc list Opposite of -scr_skip: this list is consulted first
and if there is a match the window will be monitored
via RECORD for scrolls irrespective of -scr_skip.
Use -scr_skip '*' to skip anything that does not match
your -scr_inc. Use -scr_inc '*' to include everything.
-scr_keys list For keystroke scroll detection, only apply the RECORD
heuristics to the comma separated list of keysyms in
"list". You may find the RECORD overhead for every
one of your keystrokes disrupts typing too much, but you
don't want to turn it off completely with "-scr mouse"
and -scr_parms does not work or is too confusing.
The listed keysyms can be numeric or the keysym
names in the <X11/keysymdef.h> header file or from the
xev(1) program. Example: "-scr_keys Up,Down,Return".
One probably wants to have application specific lists
(e.g. for terminals, etc) but that is too icky to think
about for now...
If "list" begins with the "-" character the list
is taken as an exclude list: all keysyms except those
list will be considered. The special string "builtin"
expands to an internal list of keysyms that are likely
to cause scrolls. BTW, by default modifier keys,
Shift_L, Control_R, etc, are skipped since they almost
never induce scrolling by themselves.
-scr_term list Yet another cosmetic kludge. Apply shell/terminal
heuristics to applications matching comma separated
list (same as for -scr_skip/-scr_inc). For example an
annoying transient under scroll detection is if you
hit Enter in a terminal shell with full text window,
the solid text cursor block will be scrolled up.
So for a short time there are two (or more) block
cursors on the screen. There are similar scenarios,
(e.g. an output line is duplicated).
These transients are induced by the approximation of
scroll detection (e.g. it detects the scroll, but not
the fact that the block cursor was cleared just before
the scroll). In nearly all cases these transient errors
are repaired when the true X framebuffer is consulted
by the normal polling. But they are distracting, so
what this option provides is extra "padding" near the
bottom of the terminal window: a few extra lines near
the bottom will not be scrolled, but rather updated
from the actual X framebuffer. This usually reduces
the annoying artifacts. Use "none" to disable.
Default: "term"
-scr_keyrepeat lo-hi If a key is held down (or otherwise repeats rapidly) and
this induces a rapid sequence of scrolls (e.g. holding
down an Arrow key) the "scrollcopyrect" detection
and overhead may not be able to keep up. A time per
single scroll estimate is performed and if that estimate
predicts a sustainable scrollrate of keys per second
between "lo" and "hi" then repeated keys will be
DISCARDED to maintain the scrollrate. For example your
key autorepeat may be 25 keys/sec, but for a large
window or slow link only 8 scrolls per second can be
sustained, then roughly 2 out of every 3 repeated keys
will be discarded during this period. Default: "4-20"
-scr_parms string Set various parameters for the scrollcopyrect mode.
The format is similar to that for -wireframe and packed
with lots of parameters:
Format: T+B+L+R,t1+t2+t3,s1+s2+s3+s4+s5
Default: 0+64+32+32,0.02+0.10+0.9,0.03+0.06+0.5+0.1+5.0
If you leave nothing between commas: ",," the default
value is used. If you don't specify enough commas,
the trailing parameters are set to their defaults.
"T+B+L+R" indicates four integers for how close in
pixels the pointer has to be from the Top, Bottom, Left,
or Right edges of the window to consider scrollcopyrect.
If -wireframe overlaps it takes precedence. This is a
speedup to quickly exclude a window from being watched
for scrollcopyrect: set them all to zero to not try
the speedup (things like selecting text will likely
be slower).
"t1+t2+t3" specify three floating point times in
seconds that apply to scrollcopyrect detection with
*Keystroke* input: t1 is how long to wait after a key
is pressed for the first scroll, t2 is how long to keep
looking after a Keystroke scroll for more scrolls.
t3 is how frequently to try to update surrounding
scrollbars outside of the scrolling area (0.0 to
disable)
"s1+s2+s3+s4+s5" specify five floating point times
in seconds that apply to scrollcopyrect detection with
*Mouse* input: s1 is how long to wait after a mouse
button is pressed for the first scroll, s2 is how long
to keep waiting for additional scrolls after the first
Mouse scroll was detected. s3 is how frequently to
try to update surrounding scrollbars outside of the
scrolling area (0.0 to disable). s4 is how long to
buffer pointer motion (to try to get fewer, bigger
mouse scrolls). s5 is the maximum time to spend just
updating the scroll window without updating the rest
of the screen.
-fixscreen string Periodically "repair" the screen based on settings
in "string". Hopefully you won't need this option,
it is intended for cases when the -scrollcopyrect or
-wirecopyrect features leave too many painting errors,
but it can be used for any scenario. This option
periodically performs costly operations and so
interactive response may be reduced when it is on.
You can use 3 Alt_L's (the Left "Alt" key) taps in
a row (as described under -scrollcopyrect) instead to
manually request a screen repaint when it is needed.
"string" is a comma separated list of one or more of
the following: "V=t", "C=t", "X=t", and "8=t".
In these "t" stands for a time in seconds (it is
a floating point even though one should usually use
values > 2 to avoid wasting resources). V sets how
frequently the entire screen should be sent to viewers
(it is like the 3 Alt_L's). C sets how long to wait
after a CopyRect to repaint the full screen. X sets
how frequently to reread the full X11 framebuffer from
the X server and push it out to connected viewers.
Use of X should be rare, please report a bug if you
find you need it. 8= applies only for -8to24 mode: it
sets how often the non-default visual regions of the
screen (e.g. 8bpp windows) are refreshed. Examples:
-fixscreen V=10 -fixscreen C=10
-debug_scroll Turn on debugging info printout for the scroll
heuristics. "-ds" is an alias. Specify it multiple
times for more output.
-noxrecord Disable any use of the RECORD extension. This is
currently used by the -scrollcopyrect scheme and to
monitor X server grabs.
-grab_buster Some of the use of the RECORD extension can leave a
-nograb_buster tiny window for XGrabServer deadlock. This is only if
the whole-server grabbing application expects mouse or
keyboard input before releasing the grab. It is usually
a window manager that does this. x11vnc takes care to
avoid the the problem, but if caught x11vnc will freeze.
Without -grab_buster, the only solution is to go the
physical display and give it some input to satisfy the
grabbing app. Or manually kill and restart the window
manager if that is feasible. With -grab_buster, x11vnc
will fork a helper thread and if x11vnc appears to be
stuck in a grab after a period of time (20-30 sec) then
it will inject some user input: button clicks, Escape,
mouse motion, etc to try to break the grab. If you
experience a lot of grab deadlock, please report a bug.
-debug_grabs Turn on debugging info printout with respect to
XGrabServer() deadlock for -scrollcopyrect mode.
-debug_sel Turn on debugging info printout with respect to
PRIMARY, CLIPBOARD, and CUTBUFFER0 selections.
-pointer_mode n Various pointer motion update schemes. "-pm" is
an alias. The problem is pointer motion can cause
rapid changes on the screen: consider the rapid
changes when you drag a large window around opaquely.
Neither x11vnc's screen polling and vnc compression
routines nor the bandwidth to the vncviewers can keep
up these rapid screen changes: everything will bog down
when dragging or scrolling. So a scheme has to be used
to "eat" much of that pointer input before re-polling
the screen and sending out framebuffer updates. The
mode number "n" can be 0 to 4 and selects one of
the schemes desribed below.
Note that the -wireframe and -scrollcopyrect modes
complement -pointer_mode by detecting (and improving)
certain periods of "rapid screen change".
n=0: does the same as -nodragging. (all screen polling
is suspended if a mouse button is pressed.)
n=1: was the original scheme used to about Jan 2004:
it basically just skips -input_skip keyboard or pointer
events before repolling the screen.
n=2 is an improved scheme: by watching the current rate
of input events it tries to detect if it should try to
"eat" additional pointer events before continuing.
n=3 is basically a dynamic -nodragging mode: it detects
when the mouse motion has paused and then refreshes
the display.
n=4 attempts to measures network rates and latency,
the video card read rate, and how many tiles have been
changed on the screen. From this, it aggressively tries
to push screen "frames" when it decides it has enough
resources to do so. NOT FINISHED.
The default n is 2. Note that modes 2, 3, 4 will skip
-input_skip keyboard events (but it will not count
pointer events). Also note that these modes are not
available in -threads mode which has its own pointer
event handling mechanism.
To try out the different pointer modes to see which
one gives the best response for your usage, it is
convenient to use the remote control function, for
example "x11vnc -R pm:4" or the tcl/tk gui (Tuning ->
pointer_mode -> n).
-input_skip n For the pointer handling when non-threaded: try to
read n user input events before scanning display. n < 0
means to act as though there is always user input.
Default: 10
-allinput Have x11vnc read and process all available client input
before proceeding.
-speeds rd,bw,lat x11vnc tries to estimate some speed parameters that
are used to optimize scheduling (e.g. -pointer_mode
4, -wireframe, -scrollcopyrect) and other things.
Use the -speeds option to set these manually.
The triple "rd,bw,lat" corresponds to video h/w
read rate in MB/sec, network bandwidth to clients in
KB/sec, and network latency to clients in milliseconds,
respectively. If a value is left blank, e.g. "-speeds
,100,15", then the internal scheme is used to estimate
the empty value(s).
Typical PC video cards have read rates of 5-10 MB/sec.
If the framebuffer is in main memory instead of video
h/w (e.g. SunRay, shadowfb, dummy driver, Xvfb), the
read rate may be much faster. "x11perf -getimage500"
can be used to get a lower bound (remember to factor
in the bytes per pixel). It is up to you to estimate
the network bandwith and latency to clients. For the
latency the ping(1) command can be used.
For convenience there are some aliases provided,
e.g. "-speeds modem". The aliases are: "modem" for
6,4,200; "dsl" for 6,100,50; and "lan" for 6,5000,1
-wmdt string For some features, e.g. -wireframe and -scrollcopyrect,
x11vnc has to work around issues for certain window
managers or desktops (currently kde and xfce).
By default it tries to guess which one, but it can
guess incorrectly. Use this option to indicate which
wm/dt. "string" can be "gnome", "kde", "cde",
"xfce", or "root" (classic X wm). Anything else
is interpreted as "root".
-debug_pointer Print debugging output for every pointer event.
-debug_keyboard Print debugging output for every keyboard event.
Same as -dp and -dk, respectively. Use multiple
times for more output.
-defer time Time in ms to wait for updates before sending to client
(deferUpdateTime) Default: 30
-wait time Time in ms to pause between screen polls. Used to cut
down on load. Default: 30
-wait_ui factor Factor by which to cut the -wait time if there
has been recent user input (pointer or keyboard).
Improves response, but increases the load whenever you
are moving the mouse or typing. Default: 2.00
-nowait_bog Do not detect if the screen polling is "bogging down"
and sleep more. Some activities with no user input can
slow things down a lot: consider a large terminal window
with a long build running in it continously streaming
text output. By default x11vnc will try to detect this
(3 screen polls in a row each longer than 0.25 sec with
no user input), and sleep up to 1.5 secs to let things
"catch up". Use this option to disable that detection.
-slow_fb time Floating point time in seconds delay all screen polling.
For special purpose usage where a low frame rate is
acceptable and desirable, but you want the user input
processed at the normal rate so you cannot use -wait.
-readtimeout n Set libvncserver rfbMaxClientWait to n seconds. On
slow links that take a long time to paint the first
screen libvncserver may hit the timeout and drop the
connection. Default: 20 seconds.
-nap Monitor activity and if it is low take longer naps
-nonap between screen polls to really cut down load when idle.
Default: take naps
-sb time Time in seconds after NO activity (e.g. screen blank)
to really throttle down the screen polls (i.e. sleep
for about 1.5 secs). Use 0 to disable. Default: 60
-nofbpm If the system supports the FBPM (Frame Buffer Power
-fbpm Management) extension (i.e. some Sun systems), then
prevent the video h/w from going into a reduced power
state when VNC clients are connected.
FBPM capable video h/w save energy when the workstation
is idle by going into low power states (similar to DPMS
for monitors). This interferes with x11vnc's polling
of the framebuffer data.
"-nofbpm" means prevent FBPM low power states whenever
VNC clients are connected, while "-fbpm" means to not
monitor the FBPM state at all. See the xset(1) manpage
for details. -nofbpm is basically the same as running
"xset fbpm force on" periodically. Default: -fbpm
-noxdamage Do not use the X DAMAGE extension to detect framebuffer
changes even if it is available. Use -xdamage if your
default is to have it off.
x11vnc's use of the DAMAGE extension: 1) significantly
reduces the load when the screen is not changing much,
and 2) detects changed areas (small ones by default)
more quickly.
Currently the DAMAGE extension is overly conservative
and often reports large areas (e.g. a whole terminal
or browser window) as damaged even though the actual
changed region is much smaller (sometimes just a few
pixels). So heuristics were introduced to skip large
areas and use the damage rectangles only as "hints"
for the traditional scanline polling. The following
tuning parameters are introduced to adjust this
behavior:
-xd_area A Set the largest DAMAGE rectangle area "A" (in
pixels: width * height) to trust as truly damaged:
the rectangle will be copied from the framebuffer
(slow) no matter what. Set to zero to trust *all*
rectangles. Default: 20000
-xd_mem f Set how long DAMAGE rectangles should be "remembered",
"f" is a floating point number and is in units of the
scanline repeat cycle time (32 iterations). The default
(1.0) should give no painting problems. Increase it if
there are problems or decrease it to live on the edge
(perhaps useful on a slow machine).
-sigpipe string Broken pipe (SIGPIPE) handling. "string" can be
"ignore" or "exit". For "ignore" libvncserver
will handle the abrupt loss of a client and continue,
for "exit" x11vnc will cleanup and exit at the 1st
broken connection. Default: "ignore". This option
is obsolete.
-threads Whether or not to use the threaded libvncserver
-nothreads algorithm [rfbRunEventLoop] if libpthread is available
Default: -nothreads
-fs f If the fraction of changed tiles in a poll is greater
than f, the whole screen is updated. Default: 0.75
-gaps n Heuristic to fill in gaps in rows or cols of n or
less tiles. Used to improve text paging. Default: 4
-grow n Heuristic to grow islands of changed tiles n or wider
by checking the tile near the boundary. Default: 3
-fuzz n Tolerance in pixels to mark a tiles edges as changed.
Default: 2
-debug_tiles Print debugging output for tiles, fb updates, etc.
-snapfb Instead of polling the X display framebuffer (fb) for
changes, periodically copy all of X display fb into main
memory and examine that copy for changes. Under some
circumstances this will improve interactive response,
or at least make things look smoother, but in others
(most!) it will make the response worse. If the video
h/w fb is such that reading small tiles is very slow
this mode could help. To keep the "framerate" up
the screen size x bpp cannot be too large. Note that
this mode is very wasteful of memory I/O resources
(it makes full screen copies even if nothing changes).
It may be of use in video capture-like applications,
or where window tearing is a problem.
-rawfb string Experimental option, instead of polling X, poll the
memory object specified in "string".
For shared memory segments string is of the
form: "shm:N@WxHxB" which specifies a shmid
N and framebuffer Width, Height, and Bits
per pixel.
For file polling to memory map mmap(2) a file use:
"map:/path/to/a/file@WxHxB", with WxHxB as above.
"mmap:..." is the same. If there is trouble with mmap,
use "file:/..." for slower lseek(2) based reading.
Use "snap:..." to imply -snapfb mode and the "file:"
access (this is for devices that only provide the fb
all at once).
If you do not supply a type "map" is assumed if
the file exists (see the next paragraphs for some
exceptions to this.)
If string is "setup:cmd", then the command "cmd"
is run and the first line from it is read and used
as "string". This allows initializing the device,
determining WxHxB, etc. These are often done as root
so take care.
If the string begins with "video", see the VIDEO4LINUX
discusion below where the device may be queried for
(and possibly set) the framebuffer parameters.
If the string begins with "console", "/dev/fb", or
"fb", see the LINUX CONSOLE discussion below where
the framebuffer device is opened and keystrokes (and
possibly mouse events) are inserted into the console.
Optional suffixes are ":R/G/B" and "+O" to specify
red, green, and blue masks and an offset into the
memory object. If the masks are not provided x11vnc
guesses them based on the bpp.
Examples:
-rawfb shm:210337933@800x600x32:ff/ff00/ff0000
-rawfb map:/dev/fb0@1024x768x32
-rawfb map:/tmp/Xvfb_screen0@640x480x8+3232
-rawfb file:/tmp/my.pnm@250x200x24+37
-rawfb file:/dev/urandom@128x128x8
-rawfb snap:/dev/video0@320x240x24 -24to32
-rawfb video0
-rawfb video -pipeinput VID
-rawfb console
(see ipcs(1) and fbset(1) for the first two examples)
In general all user input is discarded by default (see
the -pipeinput option for how to use a helper program
to insert). Most of the X11 (screen, keyboard, mouse)
options do not make sense and many will cause this
mode to crash, so please think twice before setting or
changing them in a running x11vnc.
If you DO NOT want x11vnc to close the X DISPLAY in
rawfb mode, prepend a "+" e.g. +file:/dev/fb0...
Keeping the display open enables the default
remote-control channel, which could be useful.
Alternatively, if you specify -noviewonly, then the
mouse and keyboard input are STILL sent to the X
display, this usage should be very rare, i.e. doing
something strange with /dev/fb0.
If the device is not "seekable" try reading it all
at once in full snaps via the "snap:" mode (note:
this is a resource hog). If you are using file: or
map: and the device needs to be reopened for *every*
snapfb snapshot, set the environment variable:
SNAPFB_RAWFB_RESET=1 as well.
If you want x11vnc to dynamically transform a 24bpp
rawfb to 32bpp (note that this will be slower) also
supply the -24to32 option. This would be useful for,
say, a video camera that delivers the pixel data as
24bpp packed RGB. This is the default under "video"
mode if the bpp is 24.
VIDEO4LINUX: on Linux some attempt is made to handle
video devices (webcams or TV tuners) automatically.
The idea is the WxHxB will be extracted from the
device itself. So if you do not supply "@WxHxB...
parameters x11vnc will try to determine them. It first
tries the v4l API if that support has been compiled in.
Otherwise it will run the v4l-info(1) external program
if it is available.
The simplest examples are "-rawfb video" and "-rawfb
video1" which imply the device file /dev/video and
/dev/video1, respectively. You can also supply the
/dev if you like, e.g. "-rawfb /dev/video0"
Since the video capture device framebuffer usually
changes continuously (e.g. brightness fluctuations),
you may want to use the -wait, -slow_fb, or -defer
options to lower the "framerate" to cut down on
network VNC traffic.
A more sophisticated video device scheme allows
initializing the device's settings using:
-rawfb video:<settings>
The prefix could also be, as above, e.g. "video1:" to
specify the device file. The v4l API must be available
for this to work. Otherwise, you will need to try
to initialize the device with an external program,
e.g. xawtv, spcaview, and hope they persist when x11vnc
re-opens the device.
<settings> is a comma separated list of key=value pairs.
The device's brightness, color, contrast, and hue can
be set to percentages, e.g. br=80,co=50,cn=44,hu=60.
The device filename can be set too if needed (if it
does not start with "video"), e.g. fn=/dev/qcam.
The width, height and bpp of the framebuffer can be
set via, e.g., w=160,h=120,bpp=16.
Related to the bpp above, the pixel format can be set
via the fmt=XXX, where XXX can be one of: GREY, HI240,
RGB555, RGB565, RGB24, and RGB32 (with bpp 8, 8, 16, 16,
24, and 32 respectively). See http://www.linuxtv.org
for more info (V4L api).
For TV/rf tuner cards one can set the tuning mode
via tun=XXX where XXX can be one of PAL, NTSC, SECAM,
or AUTO.
One can switch the input channel by the inp=XXX setting,
where XXX is the name of the input channel (Television,
Composite1, S-Video, etc). Use the name that is in the
information about the device that is printed at startup.
For input channels with tuners (e.g. Television) one
can change which station is selected by the sta=XXX
setting. XXX is the station number. Currently only
the ntsc-cable-us (US cable) channels are built into
x11vnc. See the -freqtab option below to supply one
from xawtv. If XXX is greater than 500, then it is
interpreted as a raw frequency in KHz.
Example:
-rawfb video:br=80,w=320,h=240,fmt=RGB32,tun=NTSC,sta=47
one might need to add inp=Television too for the input
channel to be TV if the card doesn't come up by default
in that one.
Note that not all video capture devices will support
all of the above settings.
See the -pipeinput VID option below for a way to control
the settings through the VNC Viewer via keystrokes.
As a shortcut, if the string begins "Video.." instead
of "video.." then -pipeinput VID is implied.
As above, if you specify a "@WxHxB..." after the
<settings> string they are used verbatim: the device
is not queried for the current values. Otherwise the
device will be queried.
LINUX CONSOLE: If the libvncserver LinuxVNC program
is on your system you may want to use that instead of
the following method because it will be faster and more
accurate for Linux text console.
If the rawfb string begins with "console" the
framebuffer device /dev/fb0 is opened (this requires
the appropriate kernel modules to be installed) and so
is /dev/tty0. The latter is used to inject keystrokes
(not all are supported, but the basic ones are).
You will need to be root to inject keystrokes.
/dev/tty0 refers to the active VT, to indicate one
explicitly, use "console2", etc. using the VT number.
If the Linux version seems to be 2.6 or later and the
"uinput" module appears to be present, then the uinput
method will be used instead of /dev/ttyN. uinput allows
insertion of BOTH keystrokes and mouse input and so it
preferred when accessing graphical (e.g. QT-embedded)
linux console apps. See -pipeinput UINPUT below for
more information on this mode; you will have to use
-pipeinput if you want to tweak any UINPUT parameters.
You may also want to also use the -nodragging and
-cursor none options. Use "console0", etc or
-pipeinput CONSOLE to force the /dev/ttyN method.
Note you can change VT remotely using the chvt(1)
command. Sometimes switching out and back corrects
the framebuffer state.
To skip input injecting entirely use "consolex".
The string "/dev/fb0" (1, etc.) can be used instead
of "console". This can be used to specify a different
framebuffer device, e.g. /dev/fb1. As a shortcut the
"/dev/" can be dropped. If the name is something
nonstandard, use "console:/dev/foofb"
If you do not want x11vnc to guess the framebuffer's
WxHxB and masks automatically (sometimes the kernel
given inaccurate information), specify them with a
@WxHxB at the end of the string.
Examples:
-rawfb console (same as -rawfb console)
-rawfb /dev/fb0 (same)
-rawfb console3 (force /dev/tty3)
-rawfb consolex (no keystrokes or mouse)
-rawfb console:/dev/nonstd
-rawfb console -pipeinput UINPUT:accel=4.0
-freqtab file For use with "-rawfb video" for TV tuner devices to
specify station frequencies. Instead of using the built
in ntsc-cable-us mapping of station number to frequency,
use the data in file. For stations that are not
numeric, e.g. SE20, they are placed above the highest
numbered station in the order they are found. Example:
"-freqtab /usr/X11R6/share/xawtv/europe-west.list"
You can make your own freqtab by copying the xawtv
format.
-pipeinput cmd Another experimental option: it lets you supply an
external command in "cmd" that x11vnc will pipe
all of the user input events to in a simple format.
In -pipeinput mode by default x11vnc will not process
any of the user input events. If you prefix "cmd"
with "tee:" it will both send them to the pipe
command and process them. For a description of the
format run "-pipeinput tee:/bin/cat". Another prefix
is "reopen" which means to reopen pipe if it exits.
Separate multiple prefixes with commas.
In combination with -rawfb one might be able to
do amusing things (e.g. control non-X devices).
To facilitate this, if -rawfb is in effect then the
value is stored in X11VNC_RAWFB_STR for the pipe command
to use if it wants. Do 'env | grep X11VNC' for more.
Built-in pipeinput modes (no external program required):
If cmd is "VID" and you are using the -rawfb for a
video capture device, then an internal list of keyboard
mappings is used to set parameters of the video.
The mappings are:
"B" and "b" adjust the brightness up and down.
"H" and "h" adjust the hue.
"C" and "c" adjust the colour.
"N" and "n" adjust the contrast.
"S" and "s" adjust the size of the capture screen.
"I" and "i" cycle through input channels.
Up and Down arrows adjust the station (if a tuner)
F1, F2, ..., F6 will switch the video capture pixel
format to HI240, RGB565, RGB24, RGB32, RGB555, and
GREY respectively. See -rawfb video for details.
If cmd is "CONSOLE" or "CONSOLEn" where n
is a Linux console number, then the linux console
keystroke insertion to /dev/ttyN (see -rawfb console)
is performed.
If cmd begins with "UINPUT" then the Linux uinput
module is used to insert both keystroke and mouse events
to the Linux console (see -rawfb above). This usually
is the /dev/input/uinput device file (you may need to
create it with "mknod /dev/input/uinput c 10 223"
and insert the module with "modprobe uinput".
The UINPUT mode currently only does US keyboards (a
scan code option may be added), and not all keysyms
are supported.
You may want to use the options -cursor none and
-nodragging in this mode.
Additional tuning options may be supplied via:
UINPUT:opt1,opt2,... (a comma separated list). If an
option begins with "/" it is taken as the uinput
device file.
Which uinput is injected can be controlled by an option
string made of the characters "K", "M", and "B"
(see the -input option), e.g. "KM" allows keystroke
and motion but not button clicks.
A UINPUT option of the form: accel=f, or accel=fx+fy
sets the mouse motion "acceleration". This is used
to correct raw mouse relative motion into how much the
application cursor moves (x11vnc has no control over,
or knowledge of how the windowing application interprets
the raw mouse motions). Typically the acceleration
for an X display is 2 (see xset "m" option). "f"
is a floating point number, e.g. 3.0. Use "fx+fy"
if you need to supply different corrections for x and y.
Note: the default acceleration is 2.0 since it seems
both X and qt-embedded often (but not always) use
this value.
Even with a correct accel setting the mouse position
will get out of sync (probably due to a mouse
"threshold" setting where the acceleration doe not
apply, set xset(1)). The option reset=N sets the
number of ms (default 150) after which the cursor is
attempted to be reset (by forcing the mouse to (0,
0) via small increments and then back out to (x, y)
in 1 jump), This correction seems to be needed but can
cause jerkiness or unexpected behavior with menus, etc.
Use reset=0 to disable.
If you set the env. var X11VNC_UINPUT_THRESHOLDS then
the thresh=n mode will be enabled. It it currently
not working well. If |dx| <= thresh and |dy| < thresh
no acceleration is applied. Use "thresh=+n" |dx| +
|dy| < thresh to be used instead (X11?)
Example:
-pipeinput UINPUT:accel=4.0 -cursor none
You can also set the env. var X11VNC_UINPUT_DEBUG=1 or
higher to get debugging output for UINPUT mode.
-gui [gui-opts] Start up a simple tcl/tk gui based on the the remote
control options -remote/-query described below.
Requires the "wish" program to be installed on the
machine. "gui-opts" is not required: the default
is to start up both the full gui and x11vnc with the
gui showing up on the X display in the environment
variable DISPLAY.
"gui-opts" can be a comma separated list of items.
Currently there are these types of items: 1) a gui
mode, a 2) gui "simplicity", 3) the X display the
gui should display on, 4) a "tray" or "icon" mode,
and 5) a gui geometry.
1) The gui mode can be "start", "conn", or "wait"
"start" is the default mode above and is not required.
"conn" means do not automatically start up x11vnc,
but instead just try to connect to an existing x11vnc
process. "wait" means just start the gui and nothing
else (you will later instruct the gui to start x11vnc
or connect to an existing one.)
2) The gui simplicity is off by default (a power-user
gui with all options is presented) To start with
something less daunting supply the string "simple"
("ez" is an alias for this). Once the gui is
started you can toggle between the two with "Misc ->
simple_gui".
3) Note the possible confusion regarding the potentially
two different X displays: x11vnc polls one, but you
may want the gui to appear on another. For example, if
you ssh in and x11vnc is not running yet you may want
the gui to come back to you via your ssh redirected X
display (e.g. localhost:10).
If you do not specify a gui X display in "gui-opts"
then the DISPLAY environment variable and -display
option are tried (in that order). Regarding the x11vnc
X display the gui will try to communication with, it
first tries -display and then DISPLAY. For example,
"x11vnc -display :0 -gui otherhost:0", will remote
control an x11vnc polling :0 and display the gui on
otherhost:0 The "tray/icon" mode below reverses this
preference, preferring to display on the x11vnc display.
4) When "tray" or "icon" is specified, the gui
presents itself as a small icon with behavior typical
of a "system tray" or "dock applet". The color
of the icon indicates status (connected clients) and
there is also a balloon status. Clicking on the icon
gives a menu from which properties, etc, can be set and
the full gui is available under "Advanced". To be
fully functional, the gui mode should be "start"
(the default).
For "icon" the gui just a small standalone window.
For "tray" it will attempt to embed itself in the
"system tray" if possible. If "=setpass" is appended the
n
at startup the X11 user will be prompted to set the
VNC session password. If =<hexnumber> is appended
that icon will attempt to embed itself in the window
given by hexnumber. Use =noadvanced to disable the
full gui. (To supply more than one, use "+" sign).
E.g. -gui tray=setpass and -gui icon=0x3600028
Other modes: "full", the default and need not be
specified. "-gui none", do not show a gui, useful
to override a ~/.x11vncrc setting, etc.
5) When "geom=+X+Y" is specified, that geometry
is passed to the gui toplevel. This is the icon in
icon/tray mode, or the full gui otherwise. You can
also specify width and height, i.e. WxH+X+Y, but it
is not recommended. In "tray" mode the geometry is
ignored unless the system tray manager does not seem
to be running. One could imagine using something like
"-gui tray,geom=+4000+4000" with a display manager
to keep the gui invisible until someone logs in...
More icon tricks, "icon=minimal" gives an icon just
with the VNC display number. You can also set the font
with "iconfont=...". The following could be useful:
"-gui icon=minimal,iconfont=5x8,geom=24x10+0-0"
General examples of the -gui option: "x11vnc -gui",
"x11vnc -gui ez" "x11vnc -gui localhost:10",
"x11vnc -gui conn,host:0", "x11vnc -gui tray,ez"
"x11vnc -gui tray=setpass"
If you do not intend to start x11vnc from the gui
(i.e. just remote control an existing one), then the
gui process can run on a different machine from the
x11vnc server as long as X permissions, etc. permit
communication between the two.
-remote command Remotely control some aspects of an already running
x11vnc server. "-R" and "-r" are aliases for
"-remote". After the remote control command is
sent to the running server the 'x11vnc -remote ...'
command exits. You can often use the -query command
(see below) to see if the x11vnc server processed your
-remote command.
The default communication channel is that of X
properties (specifically X11VNC_REMOTE), and so this
command must be run with correct settings for DISPLAY
and possibly XAUTHORITY to connect to the X server
and set the property. Alternatively, use the -display
and -auth options to set them to the correct values.
The running server cannot use the -novncconnect option
because that disables the communication channel.
See below for alternate channels.
For example: 'x11vnc -remote stop' (which is the same as
'x11vnc -R stop') will close down the x11vnc server.
'x11vnc -R shared' will enable shared connections, and
'x11vnc -R scale:3/4' will rescale the desktop.
The following -remote/-R commands are supported:
stop terminate the server, same as "quit"
"exit" or "shutdown".
ping see if the x11vnc server responds.
Return is: ans=ping:<xdisplay>
blacken try to push a black fb update to all
clients (due to timings a client
could miss it). Same as "zero", also
"zero:x1,y1,x2,y2" for a rectangle.
refresh send the entire fb to all clients.
reset recreate the fb, polling memory, etc.
id:windowid set -id window to "windowid". empty
or "root" to go back to root window
sid:windowid set -sid window to "windowid"
waitmapped wait until subwin is mapped.
nowaitmapped do not wait until subwin is mapped.
clip:WxH+X+Y set -clip mode to "WxH+X+Y"
flashcmap enable -flashcmap mode.
noflashcmap disable -flashcmap mode.
shiftcmap:n set -shiftcmap to n.
notruecolor enable -notruecolor mode.
truecolor disable -notruecolor mode.
overlay enable -overlay mode (if applicable).
nooverlay disable -overlay mode.
overlay_cursor in -overlay mode, enable cursor drawing.
overlay_nocursor disable cursor drawing. same as
nooverlay_cursor.
8to24 enable -8to24 mode (if applicable).
no8to24 disable -8to24 mode.
8to24_opts:str set the -8to24 opts to "str".
24to32 enable -24to32 mode (if applicable).
no24to32 disable -24to32 mode.
visual:vis set -visual to "vis"
scale:frac set -scale to "frac"
scale_cursor:f set -scale_cursor to "f"
viewonly enable -viewonly mode.
noviewonly disable -viewonly mode.
shared enable -shared mode.
noshared disable -shared mode.
forever enable -forever mode.
noforever disable -forever mode.
timeout:n reset -timeout to n, if there are
currently no clients, exit unless one
connects in the next n secs.
filexfer enable filetransfer for new clients.
nofilexfer disable filetransfer for new clients.
http enable http client connections.
nohttp disable http client connections.
deny deny any new connections, same as "lock"
nodeny allow new connections, same as "unlock"
connect:host do reverse connection to host, "host"
may be a comma separated list of hosts
or host:ports. See -connect. Passwords
required as with fwd connections.
See X11VNC_REVERSE_CONNECTION_NO_AUTH=1
disconnect:host disconnect any clients from "host"
same as "close:host". Use host
"all" to close all current clients.
If you know the client internal hex ID,
e.g. 0x3 (returned by "-query clients"
and RFB_CLIENT_ID) you can use that too.
allowonce:host For the next connection only, allow
connection from "host".
allow:hostlist set -allow list to (comma separated)
"hostlist". See -allow and -localhost.
Do not use with -allow /path/to/file
Use "+host" to add a single host, and
use "-host" to delete a single host
localhost enable -localhost mode
nolocalhost disable -localhost mode
listen:str set -listen to str, empty to disable.
nolookup enable -nolookup mode.
lookup disable -nolookup mode.
input:str set -input to "str", empty to disable.
grabkbd enable -grabkbd mode.
nograbkbd disable -grabkbd mode.
grabptr enable -grabptr mode.
nograbptr disable -grabptr mode.
client_input:str set the K, M, B -input on a per-client
basis. select which client as for
disconnect, e.g. client_input:host:MB
or client_input:0x2:K
accept:cmd set -accept "cmd" (empty to disable).
afteraccept:cmd set -afteraccept (empty to disable).
gone:cmd set -gone "cmd" (empty to disable).
noshm enable -noshm mode.
shm disable -noshm mode (i.e. use shm).
flipbyteorder enable -flipbyteorder mode, you may need
to set noshm for this to do something.
noflipbyteorder disable -flipbyteorder mode.
onetile enable -onetile mode. (you may need to
set shm for this to do something)
noonetile disable -onetile mode.
solid enable -solid mode
nosolid disable -solid mode.
solid_color:color set -solid color (and apply it).
blackout:str set -blackout "str" (empty to disable).
See -blackout for the form of "str"
(basically: WxH+X+Y,...)
Use "+WxH+X+Y" to append a single
rectangle use "-WxH+X+Y" to delete one
xinerama enable -xinerama mode. (if applicable)
noxinerama disable -xinerama mode.
xtrap enable -xtrap input mode(if applicable)
noxtrap disable -xtrap input mode.
xrandr enable -xrandr mode. (if applicable)
noxrandr disable -xrandr mode.
xrandr_mode:mode set the -xrandr mode to "mode".
padgeom:WxH set -padgeom to WxH (empty to disable)
If WxH is "force" or "do" the padded
geometry fb is immediately applied.
quiet enable -quiet mode.
noquiet disable -quiet mode.
modtweak enable -modtweak mode.
nomodtweak enable -nomodtweak mode.
xkb enable -xkb modtweak mode.
noxkb disable -xkb modtweak mode.
capslock enable -capslock mode.
nocapslock disable -capslock mode.
skip_lockkeys enable -skip_lockkeys mode.
noskip_lockkeys disable -skip_lockkeys mode.
skip_keycodes:str enable -xkb -skip_keycodes "str".
sloppy_keys enable -sloppy_keys mode.
nosloppy_keys disable -sloppy_keys mode.
skip_dups enable -skip_dups mode.
noskip_dups disable -skip_dups mode.
add_keysyms enable -add_keysyms mode.
noadd_keysyms stop adding keysyms. those added will
still be removed at exit.
clear_mods enable -clear_mods mode and clear them.
noclear_mods disable -clear_mods mode.
clear_keys enable -clear_keys mode and clear them.
noclear_keys disable -clear_keys mode.
remap:str set -remap "str" (empty to disable).
See -remap for the form of "str"
(basically: key1-key2,key3-key4,...)
Use "+key1-key2" to append a single
keymapping, use "-key1-key2" to delete.
norepeat enable -norepeat mode.
repeat disable -norepeat mode.
nofb enable -nofb mode.
fb disable -nofb mode.
bell enable bell (if supported).
nobell disable bell.
nosel enable -nosel mode.
sel disable -nosel mode.
noprimary enable -noprimary mode.
primary disable -noprimary mode.
nosetprimary enable -nosetprimary mode.
setprimary disable -nosetprimary mode.
noclipboard enable -noclipboard mode.
clipboard disable -noclipboard mode.
nosetclipboard enable -nosetclipboard mode.
setclipboard disable -nosetclipboard mode.
seldir:str set -seldir to "str"
cursor:mode enable -cursor "mode".
show_cursor enable showing a cursor.
noshow_cursor disable showing a cursor. (same as
"nocursor")
arrow:n set -arrow to alternate n.
xfixes enable xfixes cursor shape mode.
noxfixes disable xfixes cursor shape mode.
alphacut:n set -alphacut to n.
alphafrac:f set -alphafrac to f.
alpharemove enable -alpharemove mode.
noalpharemove disable -alpharemove mode.
alphablend disable -noalphablend mode.
noalphablend enable -noalphablend mode.
cursorshape disable -nocursorshape mode.
nocursorshape enable -nocursorshape mode.
cursorpos disable -nocursorpos mode.
nocursorpos enable -nocursorpos mode.
xwarp enable -xwarppointer mode.
noxwarp disable -xwarppointer mode.
buttonmap:str set -buttonmap "str", empty to disable
dragging disable -nodragging mode.
nodragging enable -nodragging mode.
wireframe enable -wireframe mode. same as "wf"
nowireframe disable -wireframe mode. same as "nowf"
wireframe:str enable -wireframe mode string.
wireframe_mode:str enable -wireframe mode string.
wirecopyrect:str set -wirecopyrect string. same as "wcr:
"
scrollcopyrect:str set -scrollcopyrect string. same "scr
"
noscrollcopyrect disable -scrollcopyrect mode. "noscr"
scr_area:n set -scr_area to n
scr_skip:list set -scr_skip to "list"
scr_inc:list set -scr_inc to "list"
scr_keys:list set -scr_keys to "list"
scr_term:list set -scr_term to "list"
scr_keyrepeat:str set -scr_keyrepeat to "str"
scr_parms:str set -scr_parms parameters.
fixscreen:str set -fixscreen to "str".
noxrecord disable all use of RECORD extension.
xrecord enable use of RECORD extension.
reset_record reset RECORD extension (if avail.)
pointer_mode:n set -pointer_mode to n. same as "pm"
input_skip:n set -input_skip to n.
allinput enable use of -allinput mode.
noallinput disable use of -allinput mode.
speeds:str set -speeds to str.
wmdt:str set -wmdt to str.
debug_pointer enable -debug_pointer, same as "dp"
nodebug_pointer disable -debug_pointer, same as "nodp"
debug_keyboard enable -debug_keyboard, same as "dk"
nodebug_keyboard disable -debug_keyboard, same as "nodk"
defer:n set -defer to n ms,same as deferupdate:n
wait:n set -wait to n ms.
wait_ui:f set -wait_ui factor to f.
wait_bog disable -nowait_bog mode.
nowait_bog enable -nowait_bog mode.
slow_fb:f set -slow_fb to f seconds.
readtimeout:n set read timeout to n seconds.
nap enable -nap mode.
nonap disable -nap mode.
sb:n set -sb to n s, same as screen_blank:n
fbpm disable -nofbpm mode.
nofbpm enable -nofbpm mode.
xdamage enable xdamage polling hints.
noxdamage disable xdamage polling hints.
xd_area:A set -xd_area max pixel area to "A"
xd_mem:f set -xd_mem remembrance to "f"
fs:frac set -fs fraction to "frac", e.g. 0.5
gaps:n set -gaps to n.
grow:n set -grow to n.
fuzz:n set -fuzz to n.
snapfb enable -snapfb mode.
nosnapfb disable -snapfb mode.
rawfb:str set -rawfb mode to "str".
uinput_accel:f set uinput_accel to f.
uinput_reset:n set uinput_reset to n ms.
uinput_always:n set uinput_always to 1/0.
progressive:n set libvncserver -progressive slice
height parameter to n.
desktop:str set -desktop name to str for new clients
.
rfbport:n set -rfbport to n.
httpport:n set -httpport to n.
httpdir:dir set -httpdir to dir (and enable http).
enablehttpproxy enable -enablehttpproxy mode.
noenablehttpproxy disable -enablehttpproxy mode.
alwaysshared enable -alwaysshared mode.
noalwaysshared disable -alwaysshared mode.
(may interfere with other options)
nevershared enable -nevershared mode.
nonevershared disable -nevershared mode.
(may interfere with other options)
dontdisconnect enable -dontdisconnect mode.
nodontdisconnect disable -dontdisconnect mode.
(may interfere with other options)
debug_xevents enable debugging X events.
nodebug_xevents disable debugging X events.
debug_xdamage enable debugging X DAMAGE mechanism.
nodebug_xdamage disable debugging X DAMAGE mechanism.
debug_wireframe enable debugging wireframe mechanism.
nodebug_wireframe disable debugging wireframe mechanism.
debug_scroll enable debugging scrollcopy mechanism.
nodebug_scroll disable debugging scrollcopy mechanism.
debug_tiles enable -debug_tiles
nodebug_tiles disable -debug_tiles
debug_grabs enable -debug_grabs
nodebug_grabs disable -debug_grabs
debug_sel enable -debug_sel
nodebug_sel disable -debug_sel
dbg enable -dbg crash shell
nodbg disable -dbg crash shell
noremote disable the -remote command processing,
it cannot be turned back on.
The vncconnect(1) command from standard VNC
distributions may also be used if string is prefixed
with "cmd=" E.g. 'vncconnect cmd=stop'. Under some
circumstances xprop(1) can used if it supports -set
(see the FAQ).
If "-connect /path/to/file" has been supplied to the
running x11vnc server then that file can be used as a
communication channel (this is the only way to remote
control one of many x11vnc's polling the same X display)
Simply run: 'x11vnc -connect /path/to/file -remote ...'
or you can directly write to the file via something
like: "echo cmd=stop > /path/to/file", etc.
-query variable Like -remote, except just query the value of
"variable". "-Q" is an alias for "-query".
Multiple queries can be done by separating variables
by commas, e.g. -query var1,var2. The results come
back in the form ans=var1:value1,ans=var2:value2,...
to the standard output. If a variable is read-only,
it comes back with prefix "aro=" instead of "ans=".
Some -remote commands are pure actions that do not make
sense as variables, e.g. "stop" or "disconnect", in
these cases the value returned is "N/A". To direct a
query straight to the X11VNC_REMOTE property or connect
file use "qry=..." instead of "cmd=..."
ans= stop quit exit shutdown ping blacken zero
refresh reset close disconnect id sid waitmapped
nowaitmapped clip flashcmap noflashcmap shiftcmap
truecolor notruecolor overlay nooverlay overlay_cursor
overlay_yescursor nooverlay_nocursor nooverlay_cursor
nooverlay_yescursor overlay_nocursor 8to24 no8to24
8to24_opts 24to32 no24to32 visual scale scale_cursor
viewonly noviewonly shared noshared forever noforever
once timeout filexfer nofilexfer deny lock nodeny
unlock connect allowonce allow localhost nolocalhost
listen lookup nolookup accept afteraccept gone shm
noshm flipbyteorder noflipbyteorder onetile noonetile
solid_color solid nosolid blackout xinerama noxinerama
xtrap noxtrap xrandr noxrandr xrandr_mode padgeom
quiet q noquiet modtweak nomodtweak xkb noxkb capslock
nocapslock skip_lockkeys noskip_lockkeys skip_keycodes
sloppy_keys nosloppy_keys skip_dups noskip_dups
add_keysyms noadd_keysyms clear_mods noclear_mods
clear_keys noclear_keys remap repeat norepeat fb nofb
bell nobell sel nosel primary noprimary setprimary
nosetprimary clipboard noclipboard setclipboard
nosetclipboard seldir cursorshape nocursorshape
cursorpos nocursorpos cursor show_cursor noshow_cursor
nocursor arrow xfixes noxfixes xdamage noxdamage
xd_area xd_mem alphacut alphafrac alpharemove
noalpharemove alphablend noalphablend xwarppointer
xwarp noxwarppointer noxwarp buttonmap dragging
nodragging wireframe_mode wireframe wf nowireframe
nowf wirecopyrect wcr nowirecopyrect nowcr scr_area
scr_skip scr_inc scr_keys scr_term scr_keyrepeat
scr_parms scrollcopyrect scr noscrollcopyrect noscr
fixscreen noxrecord xrecord reset_record pointer_mode
pm input_skip allinput noallinput input grabkbd
nograbkbd grabptr nograbptr client_input speeds wmdt
debug_pointer dp nodebug_pointer nodp debug_keyboard
dk nodebug_keyboard nodk deferupdate defer wait_ui
wait_bog nowait_bog slow_fb wait readtimeout nap
nonap sb screen_blank fbpm nofbpm fs gaps grow
fuzz snapfb nosnapfb rawfb uinput_accel uinput_reset
uinput_always progressive rfbport http nohttp httpport
httpdir enablehttpproxy noenablehttpproxy alwaysshared
noalwaysshared nevershared noalwaysshared dontdisconnect
nodontdisconnect desktop debug_xevents nodebug_xevents
debug_xevents debug_xdamage nodebug_xdamage
debug_xdamage debug_wireframe nodebug_wireframe
debug_wireframe debug_scroll nodebug_scroll debug_scroll
debug_tiles dbt nodebug_tiles nodbt debug_tiles
debug_grabs nodebug_grabs debug_sel nodebug_sel dbg
nodbg noremote
aro= noop display vncdisplay desktopname guess_desktop
http_url auth xauth users rootshift clipshift
scale_str scaled_x scaled_y scale_numer scale_denom
scale_fac scaling_blend scaling_nomult4 scaling_pad
scaling_interpolate inetd privremote unsafe safer nocmds
passwdfile unixpw unixpw_nis unixpw_list ssl ssl_pem
sslverify stunnel stunnel_pem https usepw using_shm
logfile o flag rc norc h help V version lastmod bg
sigpipe threads readrate netrate netlatency pipeinput
clients client_count pid ext_xtest ext_xtrap ext_xrecord
ext_xkb ext_xshm ext_xinerama ext_overlay ext_xfixes
ext_xdamage ext_xrandr rootwin num_buttons button_mask
mouse_x mouse_y bpp depth indexed_color dpy_x dpy_y
wdpy_x wdpy_y off_x off_y cdpy_x cdpy_y coff_x coff_y
rfbauth passwd viewpasswd
-QD variable Just like -query variable, but returns the default
value for that parameter (no running x11vnc server
is consulted)
-sync By default -remote commands are run asynchronously, that
is, the request is posted and the program immediately
exits. Use -sync to have the program wait for an
acknowledgement from the x11vnc server that command was
processed (somehow). On the other hand -query requests
are always processed synchronously because they have
to wait for the answer.
Also note that if both -remote and -query requests are
supplied on the command line, the -remote is processed
first (synchronously: no need for -sync), and then
the -query request is processed in the normal way.
This allows for a reliable way to see if the -remote
command was processed by querying for any new settings.
Note however that there is timeout of a few seconds so
if the x11vnc takes longer than that to process the
requests the requestor will think that a failure has
taken place.
-noremote Do not process any remote control commands or queries.
-yesremote Do process remote control commands or queries.
Default: -yesremote
A note about security wrt remote control commands.
If someone can connect to the X display and change
the property X11VNC_REMOTE, then they can remotely
control x11vnc. Normally access to the X display is
protected. Note that if they can modify X11VNC_REMOTE
on the X server, they have enough permissions to also
run their own x11vnc and thus have complete control
of the desktop. If the "-connect /path/to/file"
channel is being used, obviously anyone who can write
to /path/to/file can remotely control x11vnc. So be
sure to protect the X display and that file's write
permissions. See -privremote below.
If you are paranoid and do not think -noremote is
enough, to disable the X11VNC_REMOTE property channel
completely use -novncconnect, or use the -safer option
that shuts many things off.
-unsafe A few remote commands are disabled by default
(currently: id:pick, accept:<cmd>, gone:<cmd>, and
rawfb:setup:<cmd>) because they are associated with
running external programs. If you specify -unsafe, then
these remote-control commands are allowed. Note that
you can still specify these parameters on the command
line, they just cannot be invoked via remote-control.
-safer Equivalent to: -novncconnect -noremote and prohibiting
-gui and the -connect file. Shuts off communcation
channels.
-privremote Perform some sanity checks and disable remote-control
commands if it appears that the X DISPLAY and/or
connectfile can be accessed by other users. Once
remote-control is disabled it cannot be turned back on.
-nocmds No external commands (e.g. system(3), popen(3), exec(3))
will be run.
-allowedcmds list "list" contains a comma separated list of the only
external commands that can be run. The full list of
associated options is:
stunnel, ssl, unixpw, WAIT, id, accept, afteraccept,
gone, pipeinput, v4l-info, rawfb-setup, dt, gui,
storepasswd, crash.
See each option's help to learn the associated external
command. Note that the -nocmds option takes precedence
and disables all external commands.
-deny_all For use with -remote nodeny: start out denying all
incoming clients until "-remote nodeny" is used to
let them in.
These options are passed to libvncserver:
-rfbport port TCP port for RFB protocol
-rfbwait time max time in ms to wait for RFB client
-rfbauth passwd-file use authentication on RFB protocol
(use 'storepasswd' to create a password file)
-rfbversion 3.x Set the version of the RFB we choose to advertise
-permitfiletransfer permit file transfer support
-passwd plain-password use authentication
(use plain-password as password, USE AT YOUR RISK)
-deferupdate time time in ms to defer updates (default 40)
-deferptrupdate time time in ms to defer pointer updates (default none)
-desktop name VNC desktop name (default "LibVNCServer")
-alwaysshared always treat new clients as shared
-nevershared never treat new clients as shared
-dontdisconnect don't disconnect existing clients when a new non-shared
connection comes in (refuse new connection instead)
-httpdir dir-path enable http server using dir-path home
-httpport portnum use portnum for http connection
-enablehttpproxy enable http proxy support
-progressive height enable progressive updating for slow links
-listen ipaddr listen for connections only on network interface with
addr ipaddr. '-listen localhost' and hostname work too.
libvncserver-tight-extension options:
-disablefiletransfer disable file transfer
-ftproot string set ftp root
Pretty wild huh? [1]Contact me if you have any questions or problems.
Personally, I use:
x11vnc -rfbauth $HOME/.vnc/passwd -solid
References
1. mailto:xvml@karlrunge.com
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