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libtdevnc/x11vnc/README

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x11vnc README file Date: Tue Aug 3 21:54:01 EDT 2004
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)
x11vnc allows one to remotely view 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.
I wrote x11vnc 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 few
enhancements to improve the interactive response, add esoteric
features, etc.
Background:
VNC is a very useful network graphics protocol 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:
* [4]http://www.uk.research.att.com/vnc/
* [5]http://www.realvnc.com
* [6]http://www.tightvnc.com
For Unix, the VNC implementation includes a virtual X11 server Xvnc
(usually launched via the vncserver command) that is not associated
with a real 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. 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 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. This is where x11vnc is
useful.
_________________________________________________________________
How to use x11vnc:
In this 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 ([7]see below) and have it available to run
(e.g. via PATH) on far-away.east. Similarly, have a VNC viewer (e.g.
vncviewer) ready to run on sitting-here.west.
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. x11vnc needs to be run on the same machine the X server
process is running on (because MIT-SHM shared memory is used to poll
the X11 framebuffer).
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:
far-away> x11vnc -display :0
You could have also set the environment variable DISPLAY=:0 to achieve
the same thing. This step attaches x11vnc to the far-away.east:0 X
display (no viewer clients yet).
There will then be much chatter printed out from x11vnc, 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 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 on how to obtain a viewer for your
platform. For Solaris, vncviewer is available in the [8]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 -forever [9]option to have
it wait for additional viewer connections).
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 -accept popup option
discussed in the [10]FAQ below may be of use to allow the user at
far-away.east:0 to accept or reject incoming connections.
_________________________________________________________________
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 -display :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 hextile" localhost:0
The -encodings option is very important: vncviewer will 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 ...".
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 or rsh) to the workstation machine 'otherhost' and then start up
x11vnc on it.
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. However, if you "know" port 5900 will be free on the
local and remote machines, you can automate the above two steps by
using the x11vnc option -bg (forks into background after connection to
the display is set up) or using the -f option of ssh. 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 -rfbauth .vnc/passwd"
enc="copyrect tight 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.
Another method is to start the VNC viewer in listen mode "vncviewer
-listen" and have x11vnc initiate the reverse connection using the
-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 :$disp -connect localhost" # <-- new option
enc="copyrect tight hextile zlib corre rre raw"
vncviewer -encodings "$enc" -listen &
pid=$!
ssh -R 5500:localhost:5500 $host "$cmd"
kill $pid
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 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 -rfbport 5900 -display :$disp; 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 inetd(1)), you can simply use
the TightVNC vncviewer -via gateway host:port in its default mode to
provide secure ssh tunneling.
VNC password file: Also note in the first example script that the
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 [11]-storepasswd
option can be used to create the password file. x11vnc also has the
slightly less secure [12]-passwdfile and -passwd XXXXX options.
It is up to you to tell x11vnc to use password protection, it will not
do it for you automatically. The same goes for encrypting the channel
between the viewer and x11vnc: it is up to you to use ssh, etc.
_________________________________________________________________
Downloading x11vnc:
x11vnc is a contributed program to the [13]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 Aug 2004, the [14]x11vnc 0.6.2 source package is released
(recommended download) . 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 [15]x11vnc.c file to replace
the one in the above packages or the one in the CVS tree and then
rebuild.
See the [16]FAQ below for information about where you might obtain a
precompiled x11vnc binary from 3rd parties.
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:
* [17]rx11vnc wrapper script
* [18]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 0.6.2 release of x11vnc:
replace with the version you downloaded):
(un-tar the x11vnc+libvncserver tarball)
# gzip -dc x11vnc-0.6.2.tar.gz | tar -xvf -
(cd to the source directory)
# cd x11vnc-0.6.2
(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 $HOME/bin
Or do make install, it will probably install to /usr/local/bin (run
./configure --help for information on customizing your configuration).
You can now run it via typing "x11vnc", "x11vnc -help", "x11vnc -nap
-display :0", etc.
Building on Solaris: Depending on your version of Solaris (or other
Unix OS), the jpeg and/or zlib libraries may be in non-standard places
(e.g. /usr/local). Note: if configure cannot find these two libraries
then TightVNC support will be disabled, and you don't want that! Here
is a build script that indicates one way to pass this information to
the libvncserver configuration:
#!/bin/sh
# Build script for Solaris, etc, with, gcc, libjpeg and libz in
# non-standard locations.
PATH=/path/to/gcc/bin:/usr/ccs/bin:$PATH # set to get gcc
JPEG=/path/to/jpeg # maybe "/usr/local" or "/opt/sfw"
ZLIB=/path/to/zlib # maybe "/usr/local" 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"
export PATH CPPFLAGS LDFLAGS
./configure
make
ls -l ./x11vnc/x11vnc
Then do make install or copy the binary to your desired destination.
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 utililties are
there too: ld, ar, etc. Also, it is probably a bad idea to have
/usr/ucb in your PATH while building.
One user had a problem where the above build script 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.
There is a build problem on Solaris 7 11/99 (update 4) where the
header file X11/extensions/XKBstr.h that X11/XKBlib.h uses was not
shipped. The x11vnc configure succeeds and sets
LIBVNCSERVER_HAVE_XKEYBOARD in rfb/rfbconfig.h but then the build of
x11vnc fails in the make. A workaround is to remove all lines
referring to LIBVNCSERVER_HAVE_XKEYBOARD in rfb/rfbconfig.h after
configure has been run. Alternatively, one could put #undef
LIBVNCSERVER_HAVE_XKEYBOARD after the rfb/rfb.h include in the
x11vnc/x11vnc.c file. We are working to fix this in the configure
script.
_________________________________________________________________
Some Notes:
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. I
suggest using xsetroot, dtstyle or similar utility to set a solid
background while using x11vnc.
I also find the [19]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 issue with the -rfbport NNNN
option.
Options: x11vnc has (far too) many features that may be activated
via its [20]command line options. Useful options are -nap to use fewer
resources (it sleeps more between polls when activity is low) and
-rfbauth passwd-file to use VNC password protection (the vncpasswd or
storepasswd programs, or the x11vnc [21]-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. x11vnc uses a 32 x 32 pixel
tile model (the desktop is decomposed into ~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.
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 "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 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!
SunRay notes: You can run x11vnc on your (connected or disconnected)
[22]SunRay session (Please remember to use -nap and maybe -wait 200 to
avoid being a resource hog! It also helps a bit to have a solid
background color). You have to know the name of the machine your
SunRay session X server is running on. 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...).
SunRay Gotcha: Note that even though your SunRay X11 DISPLAY is
something like :137, x11vnc still tries for port 5900 as its listening
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 -rfbport NNNN option.
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). Work is in progress to attempt to speed
things up using the copyrect encoding and other things, but they
will likely 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 10-50, and it usually takes about 0.5-1 sec to read
in the whole video hardware framebuffer (5MB for 1280x1024 at
depth 24). So whenever activity changes most of the screen there
is a delay of this length while x11vnc reads the changed regions
in. To get a sense of the read and write speeds of your video
card, you can run the 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).
On XFree86 it is actually possible to increase the framebuffer
read speed considerably (5-50 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" (and depending on video card driver,
Option "NoAccel" "true" may be needed too) in the Device section
of the /etc/X11/XF86Config 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 speed at the physical display was tolerable.
Unfortunately it does not seem shadowfb can't be turned on and off
dynamically...
* Somewhat surprisingly, the X11 mouse (cursor) shape is write-only
and cannot be queried from the X server. So in x11vnc the cursor
shape stays fixed at an arrow. (see the -mouseX option, however,
for a partial hack for the root window).
* Audio from applications is of course not redirected (separate
redirectors do exist, e.g. esd). 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).
* Occasionally a patch of tiles will not get updated correctly.
Evidently a timing related bug and difficult to reproduce...
* Using -threads can expose some bugs in libvncserver.
Please feel free to [23]contact me if you have any questions,
problems, or comments about x11vnc, etc.
_________________________________________________________________
x11vnc FAQ:
[24]Q-1: I can't get x11vnc to start up. It says "XOpenDisplay failed
((null))" or "Xlib: connection to ":0.0" refused by server". What do I
need to do?
[25]Q-2: I can't get x11vnc and/or libvncserver to compile.
[26]Q-3: Where can I get a precompiled x11vnc binary for my Operating
System?
[27]Q-4: How can I see all of x11vnc's command line options and
documentation on how to use them?
[28]Q-5: I don't like typing arcane command line options every time I
start x11vnc. What can I do? Is there a config file?
[29]Q-6: 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?
[30]Q-7: 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?
[31]Q-8: I am running Win2VNC on my windows machine and trying to
create a dual-screen mode with my second display by running x11vnc
-nofb. Whenever I initiate the connection Win2VNC quickly disconnects
and x11vnc says something like: rfbProcessClientNormalMessage: read:
Connection reset by peer
[32]Q-9: The X display I run x11vnc on is only 8bpp PseudoColor (only
256 distinct colors). x11vnc starts out OK, but after a while the
colors are incorrect in certain windows.
[33]Q-10: Color problems: I have an X display that has nice
"overlay-like" visuals of multiple color depths. E.g. there are both
depth 8 and 24 visuals available. Why are some of the colors messed up
in x11vnc?
[34]Q-11: How do I figure out the window id to supply to the -id
windowid option?
[35]Q-12: Why don't menus or other transient windows come up when I am
using the -id windowid option to view a single application window?
[36]Q-13: 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?
[37]Q-14: Can I make x11vnc more quiet and also go into the background
after starting up?
[38]Q-15: Can I limit which machines incoming VNC clients can connect
from?
[39]Q-16: How do I build x11vnc/libvncserver with libwrap
(tcp_wrappers) support?
[40]Q-17: 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?
[41]Q-18: How do I create a VNC password for use with x11vnc?
[42]Q-19: How can I tunnel my connection to x11vnc via an encrypted
SSH channel between two Unix machines?
[43]Q-20: How can I tunnel my connection to x11vnc via an encrypted
SSH channel from Windows using an SSH client like Putty?
[44]Q-21: Does x11vnc support Unix usernames and passwords? Can I
further limit the set of Unix usernames who can connect to the VNC
desktop?
[45]Q-22: Can I have two passwords for VNC viewers, one for full
access and the other for view-only access to the display?
[46]Q-23: 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?
[47]Q-24: Can I have x11vnc automatically lock the screen when I
disconnect the VNC viewer?
[48]Q-25: Are reverse connections (i.e. the VNC server connecting to
the VNC viewer) using "vncviewer -listen" and vncconnect(1) supported?
[49]Q-26: 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.
[50]Q-27: How can I use x11vnc to connect to an X login screen like
xdm, GNOME gdmgreeter, KDE kdm, or CDE dtlogin?
[51]Q-28: Can I run x11vnc out of inetd(1)?
[52]Q-29: How do I make x11vnc work with the Java VNC viewer applet in
a web browser?
[53]Q-30: Why isn't the mouse cursor shape (the little icon shape
where the mouse pointer is) correct as I move from window to window?
[54]Q-31: Why does the mouse arrow just stay in one corner in my
vncviewer, whereas my cursor (that does move) is just a dot?
[55]Q-32: 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)?
[56]Q-33: 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?
[57]Q-34: 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?
[58]Q-35: 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)?
[59]Q-36: How can I make x11vnc use less system resources?
[60]Q-37: How can I make x11vnc use MORE system resources?
[61]Q-38: I use x11vnc over a slow link with high latency (i.e. dialup
modem), is there anything I can do to speed things up?
[62]Q-39: How can I get my AltGr and Shift modifiers to work between
keyboards for different languages?
[63]Q-40: When I try to type a "<" (i.e. less than) instead I get ">"
(i.e. greater than)! Strangely, typing ">" works OK!!
[64]Q-41: 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?
[65]Q-42: 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?
[66]Q-43: 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?
[67]Q-44: 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)
[68]Q-45: Can I map a keystroke to a mouse button click on the remote
machine?
[69]Q-46: 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?
[70]Q-47: Does x11vnc support server-side framebuffer scaling? (E.g.
to make the desktop smaller).
[71]Q-48: Does x11vnc work with Xinerama? (i.e. multiple monitors
joined together to form one big, single screen).
[72]Q-49: Can I use x11vnc on a multi-headed display that is not
Xinerama (i.e. separate screens :0.0, :0.1, ... for each monitor)?
[73]Q-50: Why is the view in my VNC viewer completely black? Or why is
everything flashing around randomly?
[74]Q-51: 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?
[75]Q-52: Does the Clipboard/Selection get transferred between the
vncviewer and the X display?
[76]Q-53: Why don't I hear the "Beeps" in my X session (e.g. when
typing tput bel in an xterm)?
[77]Q-54: 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?
_________________________________________________________________
Q-1: I can't get x11vnc to start up. It says "XOpenDisplay failed
((null))" or "Xlib: connection to ":0.0" refused by server". 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 x11vnc is to run on). Set
your DISPLAY environment variable or use the -display option to
specify it. Nearly always the correct value will be ":0"
For the latter error, you need to set up the X11 permissions. See the
xauth(1), Xsecurity(1), and xhost(1) man pages. For example, you may
need to set your XAUTHORITY environment variable to point to the
correct cookie file (e.g. /home/joe/.Xauthority or
/var/lib/xdm/authdir/authfiles/A:0-nRySEi), or simply be sure you run
x11vnc as the correct user (i.e. the user who owns the X session you
wish to view). Less safe, but if the owner of the X session runs xhost
+localhost one should be able to attach x11vnc to the session (from
the same machine).
We have been informed that some recent Linux distribution display
managers set XAUTHORITY to random local filenames, e.g.:
/tmp/.gdmHaVtYy. So logging in as the correct user may not be
enough... you need to dig out where they have hidden the
MIT-MAGIC-COOKIE. The -e option to ps(1) may help, e.g.: ps wwwweaux |
tr ' ' '\n' | grep XAUTHORITY | sort -u
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
45be51... was found from an xauth -f /var/... list) or other reasons.
See xauth(1) manpage for full details on how to transfer an
MIT-MAGIC-COOKIE between machines and displays.
To test out your X11 permissions, set DISPLAY and type xclock in the
same place you will be typing (or otherwise running) x11vnc. If a
little clock comes up on the display, that means the X11 permissions
are OK. To test your X11 permissions when logged into the display
machine remotely, use xdpyinfo (if you see the informational output
about the display you know it connected to the X server successfully).
Important: if you cannot get your X11 permissions so that the xclock
or xdpyinfo tests work, x11vnc also will not work (all of these X
clients must be able to connect to the X server to function).
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. 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
libxtst-dev
x-dev
xlibs-static-dev
zlib1g-dev
For Redhat the list seems to be:
gcc
make
glibc-devel
libjpeg-devel
XFree86-devel
zlib-devel
Q-3: Where can I get a precompiled x11vnc binary for my Operating
System?
Hopefully the [78]build steps above and [79]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 made by other groups available
at the following locations:
Debian: [80]http://packages.debian.org/x11vnc
Slackware: [81]http://www.linuxpackages.net/ Redhat/Fedora:
[82]http://dag.wieers.com/packages/x11vnc/ wwexptools:
[83]http://www.bell-labs.com/project/wwexptools/packages.html The last
one, wwexptools, provides a variety of Unix binaries (Linux, Solaris,
HP-UX, Irix, ...) with the intent of being compatible on a wide range
of OS releases. Find x11vnc at that link and select 'download info'.
If any of the above binaries don't work and building x11vnc on your OS
fails, and all else fails, you can contact me as I occasionally have a
test binary I could give you.
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-4: How can I see all of x11vnc's command line options and
documentation on how to use them?
Run: x11vnc -help The output is listed [84]here as well.
Q-5: I don't like typing arcane command line options every time I
start x11vnc. What can I do? Is there a config file?
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 -nap -wait 50 -localhost -rfbauth $HOME/.vnc/passwd -display :0 $*
a similar thing can be via aliases in your shell (bash, tcsh, csh,
etc..).
Or as of Jun/2004 in the libvncserver CVS 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
nap
wait 50 # comment to the end of the line
-localhost # note: the leading "-" is optional.
rfbauth /home/fred/.vnc/passwd
display :0
At some point this config file support will be expanded.
Q-6: 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 -forever option (aka -many) to have x11vnc
wait for more connections after the first client disconnects. Use the
-shared option to have x11vnc allow multiple clients to connect
simultaneously.
Recommended additional safety measures include using ssh (see above)
or a VPN to authenticate and encrypt the viewer connections or to at
least use the -rfbauth passwd-file [85]option to use VNC password
protection.
Q-7: 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 "-nofb" option
(disables framebuffer polling, and does other optimizations) on the
secondary display (X11). Then start up Win2VNC on the primary display
(Windows) referring it to the secondary display.
This will also work X11 to X11 using [86]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:
* [87]Original Win2VNC
* [88]Enhanced Win2VNC and [89]sourceforge link
* [90]x2vnc
* [91]x2x also [92]here
* [93]zvnc (MorphOS)
All of them (except x2x) will work with x11vnc.
Q-8: I am running Win2VNC on my windows machine and trying to create a
dual-screen mode with my second display by running x11vnc -nofb.
Whenever I initiate the connection Win2VNC quickly disconnects and
x11vnc says something like: rfbProcessClientNormalMessage: read:
Connection reset by peer
Is the default visual of the X display you run x11vnc on low color
(e.g. 8bpp PseudoColor)? (you can run xdpyinfo to check). 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 visuals, and you can make the default visual depth 24
TrueColor (see fbconfig(1) and Xsun(1)). 2) As of Feb/2004, in the
libvncserver CVS, x11vnc has the -visual option to allow you to force
the framebuffer visual to whatever you want. This 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 there should be no
problems in doing this.
Q-9: The X display I run x11vnc on is only 8bpp PseudoColor (only 256
distinct colors). x11vnc starts out OK, but after a while the colors
are incorrect in certain windows.
Use the -flashcmap to have x11vnc watch for changes in the colormap,
and propagate those changes back to connected clients. This can be
slow. The incorrect colors 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.
Q-10: Color problems: I have an X display that has nice "overlay-like"
visuals of multiple color depths. E.g. there are both depth 8 and 24
visuals available. Why are some of the colors messed up in x11vnc?
First off, try the (rather slow) -flashcmap option just to be sure
your color problem isn't simply due to x11vnc not following the
changing 256 element colormap. The -notruecolor option has also been
known to resolve some color problems on 8bpp displays.
If that doesn't help, run xdpyinfo to see what the default visual is.
Does it have a depth of 8? If it does, can you possibly re-configure
your X server to make the 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). I do this on an old Sparcstation 20 with SX
graphics
xinit -- -dev /dev/fb defclass TrueColor defdepth 24
and it works nicely (to log into console from the dtlogin window,
select "Options -> Command Line Login", then login and enter the above
command). A more permanent and convenient option is to put a line
like:
:0 Local local_uid@console root /usr/openwin/bin/Xsun -dev /dev/fb defclass Tr
ueColor defdepth 24
in /etc/dt/config/Xservers (see /usr/dt/config/Xservers).
Still not working? Run xwininfo on the application with the messed up
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 -id option to point x11vnc at the
application window itself. If the application is complicated this may
not be acceptable, and may even crash x11vnc (but not the
application).
It is theoretically possible to solve this problem (see xwd(1) for
example), but it does not seem trivial or sufficiently fast for x11vnc
to be able to do.
Q-11: 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.
Note that some VNC viewers will have problems rendering screens that
have a width that is not a multiple of 4. Try to manually adjust the
window width before starting x11vnc -id ....
Q-12: 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 man page for more details.
If things are not working and you still want to do the single window
polling, feel free to ask for a version of x11vnc that has an
experimental -sid windowid option ("shifted" windowid). x11vnc is
known to crash under both -id and -sid, so both modes are still
experimental.
Q-13: 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 to the Xterminal machine. Use the
-display to point the display to that of the Xterminal (you'll of
course need basic X11 permission to do that) and also supply the
-noshm option (this enables the polling over the network).
The response will likely be sluggish. 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
-flipbyteorder if the colors get messed up due to endian byte order
differences.
Q-14: Can I make x11vnc more quiet and also go into the background
after starting up?
Use the -q and -bg options, respectively. (also: -quiet is an alias
for -q)
Note that under -bg the stderr messages will be lost unless you use
the "-o logfile" option.
Q-15: Can I limit which machines incoming VNC clients can connect
from?
Yes, look at the -allow and -localhost options to limit connections by
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. Note that -localhost is the same as "-allow 127.0.0.1"
For more control, build libvncserver with libwrap support
(tcp_wrappers) and then use /etc/hosts.allow.
Q-16: 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.
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 [94]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-17: 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 "-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.
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 -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 [95]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 [96]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. (use of -threads may or may not alter
this behavior).
To run a command when a client disconnects, use the "-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"
Q-18: 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. The libvncserver package
also comes with a simple program: storepasswd in the examples
directory. And as of Jun/2004 in the libvncserver CVS x11vnc supports
the -storepasswd "pass" "file" option, which is the the same
functionality of storepasswd. Be sure to quote the "pass" if it
contains shell meta characters, spaces, etc.
You then use the password via the x11vnc option: -rfbauth filename
Compared to vncpasswd(1) the latter two methods are a somewhat unsafe
because the password is specified on the command line and so someone
may see it by using ps(1) or looking over your shoulder. Also watch
out for the command winding up in your shell's history file (history
-c is often a way to clear it).
x11vnc also has the [97]-passwdfile and -passwd/-viewpasswd plain text
(i.e. not obscured like the -rfbauth VNC passwords) password options.
Q-19: 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 [98]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.
Q-20: How can I tunnel my connection to x11vnc via an encrypted SSH
channel from Windows using an SSH client like Putty?
[99]Above we described how to tunnel VNC via SSH from Unix to Unix. 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.
* 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 -localhost and
-rfbauth/-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.
As discussed [100]above another option is to first start the VNC
viewer in "listen" mode, and then launch x11vnc with the "-connection
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-21: Does x11vnc support Unix usernames and passwords? Can I further
limit the set of Unix usernames who can connect to the VNC desktop?
Until the VNC protocol and libvncserver support this things will be
approximate at best. Hopefully, it will not be too long to wait for
such support.
One approximate method involves starting x11vnc with the -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 username -L
5900:localhost:5900 hostname ... See the ssh wrapper scripts mentioned
[101]elsewhere on this page. 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.
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). A scheme that avoids a second password
involves using the -accept option that runs a program to examine the
connection information to determine which user is connecting from the
local machine. 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!). 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.
Q-22: 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 in the libvncserver CVS there is the -viewpasswd
option to supply the view-only password. Note the full-access password
option -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
-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.
View-only passwords currently do not work for the -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-23: 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 [102]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 -accept option and told to
exit via the -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-24: Can I have x11vnc automatically lock the screen when I
disconnect the VNC viewer?
Yes, a user mentions he uses the -gone option under CDE to run a
screen lock program:
x11vnc -display :0.0 -forever -gone 'dtaction LockDisplay'
Other possibilities are:
x11vnc -display :0.0 -forever -gone 'xscreensaver-command -lock'
x11vnc -display :0.0 -forever -gone 'kdesktop_lock'
x11vnc -display :0.0 -forever -gone 'xlock &'
Q-25: Are reverse connections (i.e. the VNC server connecting to the
VNC viewer) using "vncviewer -listen" and vncconnect(1) supported?
As of Mar/2004 in the libvncserver CVS x11vnc supports reverse
connections. On Unix one starts the VNC viewer in listen mode:
vncviewer -listen, and then startus up x11vnc with the -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.
To use the vncconnect(1) program (from the core VNC package at
www.realvnc.com) specify the -vncconnect option to x11vnc.
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-26: 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 in the libvncserver CVS 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.
Currently (Apr/2004) the above fix only works for BSD signal systems
(Linux, FreeBSD, ...) For SYSV systems there is a workaround in my
[103]x11vnc.c file. It also has an option -sigpipe exit to have x11vnc
clean up and exit upon receiving SIGPIPE.
Q-27: How can I use x11vnc to connect to an X login screen like xdm,
GNOME gdmgreeter, KDE kdm, or CDE dtlogin?
One time only. If the X login screen is running and you just want to
connect to it once:
On Linux it seems it is possible to do this by just adjusting the
XAUTHORITY to point to the MIT-COOKIE auth file while running x11vnc
as root, e.g. for the gnome display manager, gdm:
env XAUTHORITY=/var/gdm/:0.Xauth x11vnc -display :0
or equivalently with newer x11vnc:
x11vnc -auth /var/gdm/:0.Xauth -display :0
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).
Another place to look for the auth file is via ps(1) output for the X
server process to find any -auth argument.
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 /etc/X11/gdm/gdm.conf may avoid this.
For dtlogin in addition to the above sort of trick (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). 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 the X server (please consider
the security implications of this!) including the login screen you
will need to add a command to the display manager startup script. The
name of the script file depends on desktop used and seem to be:
GNOME /etc/X11/gdm/PreSession/Default
KDE /etc/kde*/kdm/Xsetup
XDM /etc/X11/xdm/Xsetup
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. The above
Dtlogin*grabServer:False step will be needed for dtlogin here as well.
There may also be display number specific scripts: e.g. Xsetup_0 vs.
Xsetup.
In any event, the line you will add to the script will look something
like:
/usr/local/bin/x11vnc -rfbauth /path/to/my/vnc/passwd -forever -bg
where you should customize the exact command to your needs. You may
want to redirect the x11vnc output to a separate log file for
debugging. In that case replace the -bg above with something like:
1>> /var/tmp/x11vnc.log 2>&1 &
(or use the "-o logfile" option).
If you do not want to deal with the display manager startup scripts,
here is a kludgey script that can be run manually or out of a boot
file like rc.local. [104]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 above is
preferred.
Xterminals: Note that if the display machine is a traditional
Xterminal (where the X server runs on the Xterminal box, but all of
the X client applications run on a central server), the login display
manager, and hence the auth files, are on the central server and not
on the Xterminal where the X server and x11vnc processes are running.
Somehow the MIT-COOKIE auth file data must be copied to the Xterminal
(e.g. via ssh, possibly using xauth nextract). You can use xauth -f
cookie.file list to test the contents of the cookie in a file
"cookie.file"
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
45be51... was found from an xauth -f /var/... list) or other reasons.
See xauth(1) manpage for full details on how to transfer an
MIT-MAGIC-COOKIE between machines and displays.
Q-28: Can I run x11vnc out of inetd(1)?
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 looks something like
(you'll need to customize to your settings).
#!/bin/sh
XAUTHORITY=/home/fred/.Xauthority; export XAUTHORITY
/usr/local/bin/x11vnc -inetd -display :0 -rfbauth /home/fred/.vnc/passwd 2>> /t
mp/x11vnc_sh.log
Note that you must redirect the standard error output to a log file or
/dev/null for proper operation via inetd (otherwise the standard error
also goes to the VNC vncviewer, and that confuses it greatly). If you
do not use a wrapper script as above but rather call x11vnc directly
in /etc/inetd.conf and do not redirect stderr, then you must specify
the -q (aka -quiet) option: /usr/local/bin/x11vnc -q -inetd ... or use
the -o logfile to collect the output in a file. The wrapper script
with stderr redirection to a log file is the recommended method
because the errors and warnings printed out are very useful in
troubleshooting problems.
Note also the need to set XAUTHORITY to point to the MIT-COOKIE auth
file to get permission to connect to the X display (the x11vnc -auth
option could also have been used). See the x11vnc_loop file in the
previous question for more ideas on what that auth file may be, etc.
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.
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.
Q-29: 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 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.
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.
Q-30: Why isn't the mouse cursor shape (the little icon shape where
the mouse pointer is) correct as I move from window to window?
As mentioned above, 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 -mouseX 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.
It should be possible to apply some heuristics where x11vnc tries to
build up a table of cursors for the windows it sees, perhaps using a
user supplied hints file, but that has not been explored yet.
Q-31: 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 [105]tightvnc extension that allows
specifying a cursor shape for the local VNC viewer. You may disable it
with the -nocursor option to x11vnc if your viewer does not have this
extension.
Q-32: 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 -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).
Q-33: 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: -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 -debug_pointer option prints out much info for every
mouse/pointer event.
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. 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 -buttonmap but rather configuring the X server to
think it has a mouse with 5 buttons even though the physical mouse
does not.
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).
Q-34: 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?
As of Jan/2004 there are some improvements in the libvncserver CVS
tree. 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 -old_pointer option.
Also added was the -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).
Q-35: 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 [106]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
-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 -noshm option.
Performance will be somewhat degraded but when done over local machine
sockets it should be acceptable (see an [107]earlier question
discussing -noshm).
Q-36: How can I make x11vnc use less system resources?
The -nap and "-wait n" (where n is the sleep between polls in
milliseconds, the default is 30 or so) option are good places to
start. 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. Using the
-onetile option will use less memory and use fewer shared memory slots
(add -fs 1.0 for one less slot).
Q-37: How can I make x11vnc use MORE system resources?
You can try -threads and dial down the wait time (e.g. -wait 1) and
possibly dial down -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 -id option) can be streamed over a LAN or wireless at a
reasonable frame rate.
Q-38: I use x11vnc over a slow link with high latency (i.e. dialup
modem), is there anything I can do to speed things up?
Some things you might want to experiment with (most of which will help
performance on faster links as well):
X server/session parameters:
* Configure the X server bits per pixel to 16bpp or even 8bpp.
(reduces amount of data needed to be 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)
* Configure your window manager or desktop "theme" to not use fancy
images, shading, and gradients for the window decorations, etc.
Disable Opaque moves, resizes, and animations.
* Avoid small scrolls of large windows using the Arrow keys or
scrollbar. Try to use PageUp/PageDown instead.
* On XFree86 turn on the Shadow Framebuffer to speed up reading.
(Option "ShadowFB" "true", and possibly Option "NoAccel" "true" as
well, in the Device section of /etc/X11/XF86Config) This disables
2D acceleration on the physical display and so is probably not
worth it, but could be of use in some situations.
VNC viewer parameters:
* Use a [108]TightVNC enabled viewer!
* Make sure the tight 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)
* The -depth option is similar to -bgr233 in reducing the requested
number of bits per pixel.
* 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)
* Try other VNC encodings via -encodings (tight is probably fastest,
but you should check)
* On the machine where vncviewer is run, make sure Backing Store is
enabled (XFree86 disables it by default causing re-exposures of
vncviewer to be very slow)
x11vnc parameters:
* Try using -nodragging (no screen updates when dragging mouse, but
sometimes you miss visual feedback)
* Try the -progressive pixelheight mode with the block pixelheight
100 or so (delays sending vertical blocks since they may change
while viewer is receiving earlier ones)
* Set -fs 1.0 (disables fullscreen updates)
* Enable server-side scaling via -scale m/n to make the VNC
frambuffer smaller. (less data needs to be sent, but image may not
be sharp and requires extra resources on the server end, may
actually slow down transfers of text due to poorer compression)
* Try increasing -wait or -defer (reduces the maximum "frame rate",
but won't help much for large screen changes)
* If you just want to watch one (simple) window use -id (cuts down
extraneous polling and updates, but can be buggy or insufficient)
* Set -nosel (disables all clipboard selection exchange)
* Do not use -mouse or -mouseX (repainting the remote mouse takes
resources and round trips)
Q-39: How can I get my AltGr and Shift modifiers to work between
keyboards for different languages?
The option -modtweak should be of some use for this. 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 in the libvncserver CVS, -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 [109]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 [110]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, that the
-debug_keyboard option prints out much info for every keystroke and so
can be useful debugging things.
Q-40: 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).
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 is a mode that monitors the state of the Shift
and AltGr modifiers and tries to deduce the correct keycode sequence
to send. The latter 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 [111]FAQ about the -xkb option as a possible workaround
using the XKEYBOARD extension. Note that of Jul/2004 in the
libvncserver CVS the -modtweak option is now that default.
Note that the -debug_keyboard option prints out much info for every
keystroke to aid debugging keyboard problems.
Q-41: 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 -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 in the libvncserver CVS 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 -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).
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 while ISO_Level3_Shift was attached to
keycode 113. The keycode skipping option was used to disable the
ghost key: -skip_keycodes 93
* In implementing -xkb we noticed that some keys 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.
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 -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.
* To complement the above workaround using the -remap, an option
-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.
Q-42: 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) -norepeat x11vnc option. You will still have
autorepeating because that is taken care of on your VNC viewer side.
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. < 500 ms)? If you increase it to a very large delay, e.g.
"xset r rate 1500" or turn off autorepeat completely: "xset r off",
does the problem go away?
We are looking into a good way to fix this, but in the meantime as a
workaround try to use xset r rate N for large enough delay N or xset r
off to get rid of the problem. Also, as of Jul/2004 in the
libvncserver CVS there is the -norepeat option to automatically
disable autorepeating in the X server whenever VNC viewers are
attached. Note that 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-43: 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 "-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-44: 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 -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.
Q-45: 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 -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 that has a touchpad with only two
buttons. It is difficult to do a middle button "paste" because (using
XFree86 Emulate3Buttons) you have to click both buttons on the touch
pad at the same time. This remapping:
-remap Super_R-Button2
maps the Super_R "flag" key press to the Button2 click, thereby making
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-46: 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 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 on Windows)
that automatically shrink or expand the remote framebuffer to fit the
local display. Especially for hand-held devices. See also [112]this
FAQ
Q-47: Does x11vnc support server-side framebuffer scaling? (E.g. to
make the desktop smaller).
As of Jun/2004 in the libvncserver CVS x11vnc provides basic
server-side scaling. It is a global scaling of the desktop, not a
per-client setting. To enable it use the "-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 2/3).
The current implementation is experimental in that it still needs to
be optimized and there are some painting errors (evidently only with
fraction > 1; which is probably the less interesting case). 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.
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).
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 TightVNC 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 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.
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 (-rfbport option,
etc.).
Q-48: 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.
There are a couple potential issues 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 -blackout x11vnc option allows you to
blacken-out rectangles by specifying their WxH+X+Y geometries. If your
system has the libXinerama library, the -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).
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 -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-49: 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 [113]FAQ to increase the limit. It
is probably also a good idea to run with the -onetile option in this
case (to limit each x11vnc to 3 shm segments), or even -noshm to use
no shm segments.
Q-50: 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-51: 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.
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), one can use the switchto(1) command, e.g.
switchto 7 for VC #7.
Q-52: Does the Clipboard/Selection get transferred between the
vncviewer and the X display?
As of Jan/2004 in the libvncserver CVS x11vnc supports the "CutText"
part of the rfb protocol. Furthermore, x11vnc is able to hold the
PRIMARY selection (Xvnc does not seem to do this). If you don't want
the Clipboard/Selection exchanged use the -nosel option. If you don't
want the PRIMARY selection to be polled for changes use the -noprimary
option.
Q-53: Why don't I hear the "Beeps" in my X session (e.g. when typing
tput bel in an xterm)?
As of Dec/2003 in the libvncserver CVS "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),
and so you won't hear them if the extension is not present.
If you don't want to hear the beeps use the -nobell option. If you
want to hear the audio from the remote applications, consider trying a
redirector such as esd.
Q-54: 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?
No useful answer so far. Is there a way to temporarily disable one or
both of these magic desktop taskbars?
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.uk.research.att.com/vnc/
5. http://www.realvnc.com/
6. http://www.tightvnc.com/
7. http://www.karlrunge.com/x11vnc/index.html#downloading
8. http://www.sun.com/software/solaris/freeware/
9. http://www.karlrunge.com/x11vnc/x11vnc_opts.html
10. http://www.karlrunge.com/x11vnc/index.html#accept
11. http://www.karlrunge.com/x11vnc/index.html#passwd
12. http://www.karlrunge.com/x11vnc/index.html#passwdfile
13. http://sourceforge.net/projects/libvncserver/
14. http://sourceforge.net/project/showfiles.php?group_id=32584&package_id=119006&release_id=257442
15. http://www.karlrunge.com/x11vnc/x11vnc.c
16. http://www.karlrunge.com/x11vnc/index.html#binaries
17. http://www.karlrunge.com/x11vnc/rx11vnc
18. http://www.karlrunge.com/x11vnc/rx11vnc.pl
19. http://www.tightvnc.com/
20. http://www.karlrunge.com/x11vnc/x11vnc_opts.html
21. http://www.karlrunge.com/x11vnc/index.html#passwd
22. http://wwws.sun.com/sunray/index.html
23. mailto:xvml@karlrunge.com
24. http://www.karlrunge.com/x11vnc/index.html#FAQ-1
25. http://www.karlrunge.com/x11vnc/index.html#FAQ-2
26. http://www.karlrunge.com/x11vnc/index.html#FAQ-3
27. http://www.karlrunge.com/x11vnc/index.html#FAQ-4
28. http://www.karlrunge.com/x11vnc/index.html#FAQ-5
29. http://www.karlrunge.com/x11vnc/index.html#FAQ-6
30. http://www.karlrunge.com/x11vnc/index.html#FAQ-7
31. http://www.karlrunge.com/x11vnc/index.html#FAQ-8
32. http://www.karlrunge.com/x11vnc/index.html#FAQ-9
33. http://www.karlrunge.com/x11vnc/index.html#FAQ-10
34. http://www.karlrunge.com/x11vnc/index.html#FAQ-11
35. http://www.karlrunge.com/x11vnc/index.html#FAQ-12
36. http://www.karlrunge.com/x11vnc/index.html#FAQ-13
37. http://www.karlrunge.com/x11vnc/index.html#FAQ-14
38. http://www.karlrunge.com/x11vnc/index.html#FAQ-15
39. http://www.karlrunge.com/x11vnc/index.html#FAQ-16
40. http://www.karlrunge.com/x11vnc/index.html#FAQ-17
41. http://www.karlrunge.com/x11vnc/index.html#FAQ-18
42. http://www.karlrunge.com/x11vnc/index.html#FAQ-19
43. http://www.karlrunge.com/x11vnc/index.html#FAQ-20
44. http://www.karlrunge.com/x11vnc/index.html#FAQ-21
45. http://www.karlrunge.com/x11vnc/index.html#FAQ-22
46. http://www.karlrunge.com/x11vnc/index.html#FAQ-23
47. http://www.karlrunge.com/x11vnc/index.html#FAQ-24
48. http://www.karlrunge.com/x11vnc/index.html#FAQ-25
49. http://www.karlrunge.com/x11vnc/index.html#FAQ-26
50. http://www.karlrunge.com/x11vnc/index.html#FAQ-27
51. http://www.karlrunge.com/x11vnc/index.html#FAQ-28
52. http://www.karlrunge.com/x11vnc/index.html#FAQ-29
53. http://www.karlrunge.com/x11vnc/index.html#FAQ-30
54. http://www.karlrunge.com/x11vnc/index.html#FAQ-31
55. http://www.karlrunge.com/x11vnc/index.html#FAQ-32
56. http://www.karlrunge.com/x11vnc/index.html#FAQ-33
57. http://www.karlrunge.com/x11vnc/index.html#FAQ-34
58. http://www.karlrunge.com/x11vnc/index.html#FAQ-35
59. http://www.karlrunge.com/x11vnc/index.html#FAQ-36
60. http://www.karlrunge.com/x11vnc/index.html#FAQ-37
61. http://www.karlrunge.com/x11vnc/index.html#FAQ-38
62. http://www.karlrunge.com/x11vnc/index.html#FAQ-39
63. http://www.karlrunge.com/x11vnc/index.html#FAQ-40
64. http://www.karlrunge.com/x11vnc/index.html#FAQ-41
65. http://www.karlrunge.com/x11vnc/index.html#FAQ-42
66. http://www.karlrunge.com/x11vnc/index.html#FAQ-43
67. http://www.karlrunge.com/x11vnc/index.html#FAQ-44
68. http://www.karlrunge.com/x11vnc/index.html#FAQ-45
69. http://www.karlrunge.com/x11vnc/index.html#FAQ-46
70. http://www.karlrunge.com/x11vnc/index.html#FAQ-47
71. http://www.karlrunge.com/x11vnc/index.html#FAQ-48
72. http://www.karlrunge.com/x11vnc/index.html#FAQ-49
73. http://www.karlrunge.com/x11vnc/index.html#FAQ-50
74. http://www.karlrunge.com/x11vnc/index.html#FAQ-51
75. http://www.karlrunge.com/x11vnc/index.html#FAQ-52
76. http://www.karlrunge.com/x11vnc/index.html#FAQ-53
77. http://www.karlrunge.com/x11vnc/index.html#FAQ-54
78. http://www.karlrunge.com/x11vnc/index.html#building
79. http://www.karlrunge.com/x11vnc/index.html#buildfaq
80. http://packages.debian.org/x11vnc
81. http://www.linuxpackages.net/search_view.php?by=name&name=x11vnc
82. http://dag.wieers.com/packages/x11vnc/
83. http://www.bell-labs.com/project/wwexptools/packages.html
84. http://www.karlrunge.com/x11vnc/x11vnc_opts.html
85. http://www.karlrunge.com/x11vnc/index.html#passwd
86. http://fredrik.hubbe.net/x2vnc.html
87. http://www.hubbe.net/~hubbe/win2vnc.html
88. http://www.deboer.gmxhome.de/
89. http://sourceforge.net/projects/win2vnc/
90. http://fredrik.hubbe.net/x2vnc.html
91. http://freshmeat.net/projects/x2x/
92. http://ftp.digital.com/pub/Digital/SRC/x2x/
93. http://zapek.com/software/zvnc/
94. http://www.karlrunge.com/x11vnc/index.html#inetd
95. ftp://ftp.x.org/
96. http://www.karlrunge.com/x11vnc/dtVncPopup
97. http://www.karlrunge.com/x11vnc/index.html#passwdfile
98. http://www.karlrunge.com/x11vnc/index.html#tunnelling
99. http://www.karlrunge.com/x11vnc/index.html#tunnelling
100. http://www.karlrunge.com/x11vnc/index.html#tunnelling
101. http://www.karlrunge.com/x11vnc/index.html#tunnelling
102. http://www.karlrunge.com/x11vnc/blockdpy.c
103. http://www.karlrunge.com/x11vnc/x11vnc.c
104. http://www.karlrunge.com/x11vnc/x11vnc_loop
105. http://www.tightvnc.com/
106. http://www.karlrunge.com/x11vnc/shm_clear
107. http://www.karlrunge.com/x11vnc/index.html#noshm
108. http://www.tightvnc.com/
109. http://www.karlrunge.com/x11vnc/index.html#greaterless
110. http://www.karlrunge.com/x11vnc/index.html#xkbmodtweak
111. http://www.karlrunge.com/x11vnc/index.html#xkbmodtweak
112. http://www.karlrunge.com/x11vnc/index.html#scaling
113. http://www.karlrunge.com/x11vnc/index.html#solshm
=======================================================================
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 -help
x11vnc: allow VNC connections to real X11 displays. 0.6.2 lastmod: 2004-07-31
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 port). One would next run something
like this on the local machine: "vncviewer host:N" where N is XXXX - 5900,
i.e. usually "vncviewer host:0"
By default x11vnc will not allow the screen to be shared and it will
exit as soon as a client disconnects. See -shared and -forever below
to override these protections.
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 "nap" or "-nap" 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.
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".
-auth file Set the X authority file to be "file", equivalent to
setting the XAUTHORITY environment varirable to "file"
before startup. See Xsecurity(7), xauth(1) man pages.
-id windowid Show the window corresponding to <windowid> not the
entire display. Warning: bugs! new toplevels missed!...
-flashcmap In 8bpp indexed color, let the installed colormap flash
as the pointer moves from window to window (slow).
-notruecolor Force 8bpp indexed color even if it looks like TrueColor
.
-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... 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" for better
or for worse the visual depth is forced to be m.
-scale fraction Scale the framebuffer by factor "fraction". Values
less than 1 shrink the fb. 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, 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). For compatibility with vncviewers the scaled
width is adjusted to be a multiple of 4, to disable
this use ":n4". More esoteric options: ":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).
-viewonly All VNC clients can only watch (default off).
-shared VNC display is shared (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
-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. 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.
-vncconnect Monitor the VNC_CONNECT X property set by the standard
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 FAQ.
-inetd Launched by inetd(1): 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.
-allow addr1[,addr2..] Only allow client connections from IP addresses matching
the comma separated list of numerical addresses.
Can be a prefix, e.g. "192.168.100." to match a
simple subnet, for more control build libvncserver
with libwrap support. 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 Same as -allow 127.0.0.1
-viewpasswd string Supply a 2nd password for view-only logins. The -passwd
(full-access) password must also be supplied.
-passwdfile filename Specify libvncserver -passwd via the first line of
the file "filename" instead of via command line.
If a second non blank line exists in the file it is
taken as a view-only password (i.e. -viewpasswd) Note:
this is a simple plaintext passwd, see also -rfbauth
and -storepasswd below.
-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"
-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, 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.
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.
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)
If "string" is "xmessage" then an xmessage(1)
invocation is used for the command.
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
or popup is running (other clients may see no updates
during this period).
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. 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.
-gone string As -accept string, except to run a user supplied command
when a client goes away (disconnects). Unlike -accept,
the command return code is not interpreted by x11vnc.
-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. Same as -old_copytile.
Limits shm segments used to 3.
-blackout string Black out rectangles on the screen. string is a comma
separated list of WxH+X+Y type geometries for each rect.
-xinerama If your screen is composed of multiple monitors
glued together via XINERAMA, and that screen is
non-rectangular this option will try to guess the areas
to black out (if your system has libXinerama).
-o logfile Write stderr messages to file "logfile" instead of
to the terminal. Same as -logfile "file".
-rc filename Use "filename" instead of $HOME/.x11vncrc for rc file.
-norc Do not process any .x11vncrc file for options.
-h, -help Print this help text.
-V, -version Print program version (last modification date).
-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 it exists) to do the modifier tweaking.
-skip_keycodes string Skip keycodes not on your keyboard but your X server
thinks exist. Currently only applies to -xkb mode.
"string" is a comma separated list of decimal
keycodes. Use this option to help x11vnc in the reverse
problem it tries to solve: Keysym -> Keycode(s) when
ambiguities exist. E.g. -skip_keycodes 94,114
-add_keysyms If a Keysym is received from a VNC viewer and
that Keysym does not exist in the X server, then
add the Keysym to the X server's keyboard mapping.
Added Keysyms will be removed when exiting.
-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
-norepeat Option -norepeat disables X server key auto repeat
-repeat when VNC clients are connected. 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).
Note: your VNC viewer side will likely do autorepeating,
so this is no loss unless someone is simultaneously at
the real X display. Default: -repeat
-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.
-noprimary Do not poll the PRIMARY selection for changes to send
back to clients. (PRIMARY is still set on received
changes, however).
-nocursor Do not have the VNC viewer show a local cursor.
-mouse Draw a 2nd cursor at the current X pointer position.
-mouseX As -mouse, but also draw an "X" when pointer is on
root background.
-X Shorthand for -mouseX -nocursor.
-xwarppointer Move the pointer with XWarpPointer() instead of XTEST
(try as a workaround if pointer behaves poorly, e.g.
on touchscreens or other non-standard setups).
-cursorpos Option -cursorpos enables sending the X cursor position
-nocursorpos back to all vnc clients that support the TightVNC
CursorPosUpdates extension. Default: -cursorpos
-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 motion with a button held down). Greatly
improves response on slow setups, but you lose all
visual feedback for drags, text selection, and some
menu traversals.
-old_pointer Do not use the new pointer input handling mechanisms.
See check_input() and pointer() in source file for
details.
-input_skip n For the old 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.
-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
[rfbDeferUpdateTime] Default: 30
-wait time Time in ms to pause between screen polls. Used to cut
down on load. Default: 30
-nap Monitor activity and if low take longer naps between
polls to really cut down load when idle. Default: off
-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".
-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
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)
-passwd plain-password use authentication
(use plain-password as password, USE AT YOUR RISK)
-deferupdate time time in ms to defer updates (default 40)
-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
Pretty wild huh? [1]Contact me if you have any questions or problems.
Personally, I use:
x11vnc -rfbauth $HOME/.vnc/passwd -nap -flashcmap -cursorpos -norepeat
(the -flashcmap only matters on old 8-bit X displays)
[2]Back to main x11vnc page
References
1. mailto:xvml@karlrunge.com
2. http://www.karlrunge.com/x11vnc/index.html
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