x11vnc README file Date: Sun Apr 16 12:51:24 EDT 2006 The following information is taken from these URLs: http://www.karlrunge.com/x11vnc/index.html http://www.karlrunge.com/x11vnc/x11vnc_opts.html ... they contain the most up to date info. ======================================================================= http://www.karlrunge.com/x11vnc/index.html: _________________________________________________________________ x11vnc: a VNC server for real X displays (to [1]FAQ) (to [2]Downloads) (to [3]Building) (to [4]Beta Test) (to [5]Donations) [6][PayPal] x11vnc allows one to 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 some enhancements to improve the interactive response, add esoteric features, etc. This page and the [7]FAQ contain a lot of information [8][*] and solutions to many problems, but please feel free to [9]contact me if you have problems or questions. Background: VNC (Virtual Network Computing) is a very useful network graphics protocol (applications running on one computer but displaying their windows on another) in the spirit of X, however, unlike X, the viewing-end is very simple and maintains no state. It is a remote framebuffer (RFB) protocol Some VNC links: * [10]http://www.realvnc.com * [11]http://www.tightvnc.com * [12]http://www.ultravnc.com/ * [13]http://www.redstonesoftware.com/ For Unix, the traditional VNC implementation includes a virtual X11 server Xvnc (usually launched via the vncserver command) that is not associated with a physical display, but provides a "fake" one X11 clients (xterm, mozilla, etc.) can attach to. A remote user then connects to Xvnc via the VNC client vncviewer from anywhere on the network to view and interact with the whole virtual X11 desktop. The VNC protocol is in most cases better suited for remote connections with low bandwidth and high latency than is the X11 protocol (the exception is cached pixmap data on the viewing-end). Also, with no state maintained the viewing-end can crash, be rebooted, or relocated and the applications and desktop continue running. Not so with X11. So the standard Xvnc/vncserver program is very useful, I use it for things like: * Desktop conferencing with other users (e.g. codereviews). * Long running apps/tasks I want to be able to view from many places. * Motif, GNOME, and similar applications that would yield very poor performance over a high latency link. However, sometimes one wants to connect to a real X11 display (i.e. one attached to a physical monitor, keyboard, and mouse: a Workstation or a SunRay session) from far away. Maybe you want to close down an application cleanly rather than using kill, or want to work a bit in an already running application, or would like to help a distant colleague solve a problem with their desktop, or would just like to work out on your deck for a while. This is where x11vnc is useful. _________________________________________________________________ How to use x11vnc: In this basic example let's assume the remote machine with the X display you wish to view is "far-away.east:0" and the workstation you are presently working at is "sitting-here.west". Step 0. Download x11vnc ([14]see below) and have it available to run on far-away.east. Similarly, have a VNC viewer (e.g. vncviewer) ready to run on sitting-here.west. We recommend [15]TightVNC Viewers. Step 1. By some means log in to far-away.east and get a command shell running there. You can use ssh, rlogin, telnet, or any other method to do this. The x11vnc process needs to be run on the same machine the X server process is running on (otherwise things would be extremely slow). Step 2. In that far-away.east shell (with command prompt "far-away>" in this example) run x11vnc directed at the far-away.east X session display: far-away> x11vnc -display :0 You could have also set the environment variable DISPLAY=:0 instead of using -display. This step attaches x11vnc to the far-away.east:0 X display (i.e. no viewer clients yet). Common Gotcha: To get X11 permissions right, you may also need to set the XAUTHORITY environment variable (or use the [16]-auth option) to point to the correct MIT-MAGIC-COOKIE file (e.g. /home/joe/.Xauthority). If x11vnc does not have the authority to connect to the display it exits immediately. More on how to fix this [17]below. If you suspect an X11 permissions problem do this simple test: while sitting at the physical X display open a terminal window (gnome-terminal, xterm, etc). You should be able to run x11vnc successfully in that terminal without any need for command line options. If that works OK then you know X11 permissions are the only thing preventing it from working when you try to start x11vnc via a remote shell. Then fix this with the tips [18]below. When x11vnc starts up there will then be much chatter printed out, until it finally says something like: . . 13/05/2004 14:59:54 Autoprobing selected port 5900 13/05/2004 14:59:54 screen setup finished. 13/05/2004 14:59:54 13/05/2004 14:59:54 The VNC desktop is far-away:0 PORT=5900 which means all is OK, and we are ready for the final step. Step 3. At the place where you are sitting (sitting-here.west in this example) you now want to run a VNC viewer program. There are VNC viewers for Unix, Windows, MacOS, Java-enabled web browsers, and even for PDA's like the Palm Pilot! You can use any of them to connect to x11vnc (see the above VNC links under "Background:" on how to obtain a viewer for your platform or see [19]this FAQ. For Solaris, vncviewer is available in the [20]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 [21]-forever option to have it wait for additional viewer connections). Shortcut: Of course if you left x11vnc running on far-away.east:0 in a terminal window with the [22]-forever option or as a [23]service, you'd only have to do Step 3 as you moved around. Be sure to use a VNC [24]Password or [25]other measures if you do that. Desktop Sharing: The above more or less assumed nobody was sitting at the workstation display "far-away.east:0". This is often the case: a user wants to access her workstation remotely. Another usage pattern has the user sitting at "far-away.east:0" and invites one or more other people to view and interact with his desktop. Perhaps the user gives a demo or presentation this way (using the telephone for vocal communication). A "Remote Help Desk" mode would be similar: a technician remotely connects to the user's desktop to interactively solve a problem the user is having. For these cases it should be obvious how it is done. The above steps will work, but more easily the user sitting at far-away.east:0 simply starts up x11vnc from a terminal window, after which the guests would start their VNC viewers. For this usage mode the "[26]-connect host1,host2" option may be of use automatically connect to vncviewers in "-listen" mode on the list of hosts. _________________________________________________________________ Tunnelling x11vnc via ssh: The above example had no security or privacy at all. When logging into remote machines (certainly when going over the internet) it is best to use ssh, or use a VPN. For x11vnc one can tunnel the VNC protocol through the encrypted ssh channel. It would look something like this: sitting-here> ssh -L 5900:localhost:5900 far-away.east 'x11vnc -localhost -di splay :0' (you will likely have to provide passwords/passphrases for the ssh login) and then in another terminal window on sitting-here run the command: sitting-here> vncviewer -encodings "copyrect tight zrle hextile" localhost:0 Note: The -encodings option is very important: vncviewer will often default to "raw" encoding if it thinks the connection is to the local machine, and so vncviewer gets tricked this way by the ssh redirection. "raw" encoding will be extremely slow over a networked link, so you need to force the issue with -encodings "copyrect tight ...". Note that "x11vnc -localhost ..." limits incoming vncviewer connections to only those from the same machine. This is very natural for ssh tunnelling (the redirection appears to come from the same machine). Use of a [27]VNC password is also strongly recommended. Some VNC viewers will do the ssh tunnelling for you automatically, the TightVNC vncviewer does this when the "-via far-away.east" option is supplied to it (this requires x11vnc to be already running on far-away.east or having it started by [28]inetd(1)). See the 3rd script example [29]below for more info. If the machine you SSH into is not the same machine with the X display you wish to view (e.g. your company provides incoming SSH access to a gateway machine), then you need to change the above to, e.g.: "-L 5900:OtherHOST:5900". Once logged in, you'll need to do a second login (ssh, rsh, etc.) to the workstation machine 'otherhost' and then start up x11vnc on it (if it isn't already running). For an automatic way to use a gateway and have all the network traffic encrypted (including inside the firewall) see [30]chaining ssh's _________________________________________________________________ Scripts to automate ssh tunneling: As discussed below, there may be some problems with port 5900 being available. If that happens, the above port and display numbers may change a bit (e.g. -> 5901 and :1). However, if you "know" port 5900 will be free on the local and remote machines, you can easily automate the above two steps by using the x11vnc option [31]-bg (forks into background after connection to the display is set up) or using the -f option of ssh. Some example scripts are shown below. _________________________________________________________________ #1. A simple example script, assuming no problems with port 5900 being taken on the local or remote sides, looks like: #!/bin/sh # usage: x11vnc_ssh : # e.g.: x11vnc_ssh snoopy.peanuts.com:0 host=`echo $1 | awk -F: '{print $1}'` disp=`echo $1 | awk -F: '{print $2}'` if [ "x$disp" = "x" ]; then disp=0; fi cmd="x11vnc -display :$disp -localhost -rfbauth .vnc/passwd" enc="copyrect tight zrle hextile zlib corre rre raw" ssh -f -L 5900:localhost:5900 $host "$cmd" for i in 1 2 3 do sleep 2 if vncviewer -encodings "$enc" :0; then break; fi done See also rx11vnc.pl below. _________________________________________________________________ #2. Another method is to start the VNC viewer in listen mode "vncviewer -listen" and have x11vnc initiate a reverse connection using the [32]-connect option: #!/bin/sh # usage: x11vnc_ssh : # e.g.: x11vnc_ssh snoopy.peanuts.com:0 host=`echo $1 | awk -F: '{print $1}'` disp=`echo $1 | awk -F: '{print $2}'` if [ "x$disp" = "x" ]; then disp=0; fi cmd="x11vnc -display :$disp -localhost -connect localhost" # <== note new opt ion enc="copyrect tight zrle hextile zlib corre rre raw" vncviewer -encodings "$enc" -listen & pid=$! ssh -R 5500:localhost:5500 $host "$cmd" kill $pid Note the use of the ssh option "-R" instead of "-L" to set up a remote port redirection. _________________________________________________________________ #3. A third way is specific to the TightVNC vncviewer special option -via for gateways. The only tricky part is we need to start up x11vnc and give it some time (5 seconds in this example) to start listening for connections (so we cannot use the TightVNC default setting for VNC_VIA_CMD): #!/bin/sh # usage: x11vnc_ssh : # e.g.: x11vnc_ssh snoopy.peanuts.com:0 host=`echo $1 | awk -F: '{print $1}'` disp=`echo $1 | awk -F: '{print $2}'` if [ "x$disp" = "x" ]; then disp=0; fi VNC_VIA_CMD="ssh -f -L %L:%H:%R %G x11vnc -localhost -rfbport 5900 -display :$d isp; sleep 5" export VNC_VIA_CMD vncviewer -via $host localhost:0 # must be TightVNC vncviewer. Of course if you already have the x11vnc running waiting for connections (or have it started out of [33]inetd(1)), you can simply use the TightVNC "vncviewer -via gateway host:port" in its default mode to provide secure ssh tunnelling. _________________________________________________________________ VNC password file: Also note in the #1. example script that the [34]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 [35]-storepasswd option can be used to create the password file. x11vnc also has the slightly less secure [36]-passwdfile and "-passwd XXXXX" [37]options to specify passwords. Very Important: It is up to YOU to tell x11vnc to use password protection (-rfbauth or -passwdfile), it will NOT do it for you automatically or force you to. The same goes for encrypting the channel between the viewer and x11vnc: it is up to you to use ssh, stunnel, -ssl mode, a VPN, etc. For additional safety, also look into the -allow and -localhost [38]options and building x11vnc with [39]tcp_wrappers support to limit host access. _________________________________________________________________ Tunnelling x11vnc via SSL: One can also encrypt the VNC traffic using an SSL tunnel such as [40]stunnel or using the built-in (Mar/2006) [41]-ssl openssl mode. A SSL-enabled Java applet VNC Viewer is also provided (and https can be used to download it). Although not as ubiquitous as ssh, SSL tunnelling still provides a useful alternative. See [42]this FAQ on -ssl and -stunnel modes for details and examples. _________________________________________________________________ Downloading x11vnc: x11vnc is a contributed program to the [43]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 Feb 2006, the [44]x11vnc-0.8.tar.gz source package is released (recommended download). The [45]x11vnc 0.8 release notes. The x11vnc package is the subset of the libvncserver package needed to build the x11vnc program. Also, you can get a copy of my latest, bleeding edge [46]x11vnc-0.8.1.tar.gz tarball to build the most up to date one. Precompiled Binaries/Packages: See the [47]FAQ below for information about where you might obtain a precompiled x11vnc binary from 3rd parties and some ones I create. To obtain VNC viewers for the viewing side (Windows, Mac OS, or Unix) try these links: * [48]http://www.tightvnc.com/download.html * [49]http://www.realvnc.com/download-free.html * [50]http://sourceforge.net/projects/cotvnc/ * [51]http://www.ultravnc.com/ More tools: Here is a rsh/ssh wrapper script rx11vnc that attempts to automatically do the above Steps 1-3 for you (provided you have rsh/ssh login permission on the machine x11vnc is to be run on). The above example would be: "rx11vnc far-away.east:0" typed into a shell on sitting-here.west. Also included is an experimental script rx11vnc.pl that attempts to tunnel the vnc traffic through an ssh port redirection (and does not assume port 5900 is free). Have a look at them to see what they do and customize as needed: * [52]rx11vnc wrapper script * [53]rx11vnc.pl wrapper script to tunnel traffic thru ssh _________________________________________________________________ Building x11vnc: If your OS has libjpeg.so and libz.so in standard locations you can build as follows (example given for the 0.8 release of x11vnc: replace with the version you downloaded): (un-tar the x11vnc+libvncserver tarball) # gzip -dc x11vnc-0.8.tar.gz | tar -xvf - (cd to the source directory) # cd x11vnc-0.8 (run configure and then run make) # ./configure # make (if all went OK, copy x11vnc to the desired destination, e.g. $HOME/bin) # cp ./x11vnc/x11vnc $HOME/bin Or do make install, it will probably install to /usr/local/bin (run ./configure --help for information on customizing your configuration, e.g. --prefix=/my/place). You can now run it via typing "x11vnc", "x11vnc -help | more", "x11vnc -forever -shared -display :0", etc. Note: Currently gcc is required to build libvncserver. In some cases it will build with non-gcc compilers, but the resulting binary sometimes fails to run properly. For Solaris pre-built gcc binaries are at [54]http://www.sunfreeware.com/. Some Solaris pre-built x11vnc binaries are [55]here. However, one user reports it does work fine when built with Sun Studio 10, so YMMV. In fact, here is a little build script to do this on Solaris 10: #!/bin/sh PATH=/usr/ccs/bin:/opt/SUNWspro/bin:$PATH; export PATH CC='cc' \ CFLAGS='-xO4' \ LDFLAGS='-L/usr/sfw/lib -L/usr/X11/lib -R/usr/sfw/lib -R/usr/X11/lib' \ CPPFLAGS='-I /usr/sfw/include -I/usr/X11/include' \ ./configure MAKE="make -e" AM_CFLAGS="" export MAKE AM_CFLAGS $MAKE In general you can use the "make -e" trick if you don't like libvncserver's choice of AM_CFLAGS. See the [56]build scripts below for more ideas. You can find information on [57]Misc. Build problems here. _________________________________________________________________ Building on Solaris, FreeBSD, etc: Depending on your version of Solaris or other Unix OS the jpeg and/or zlib libraries may be in non-standard places (e.g. /usr/local, /usr/sfw, /opt/sfw, etc). Note: If configure cannot find these two libraries then TightVNC and ZRLE encoding support will be disabled, and you don't want that!!! The TightVNC encoding gives very good compression and performance, it even makes a noticeable difference over a fast LAN. Shortcuts: On Solaris 10 you can pick up almost everything just by insuring that your PATH has /usr/sfw/bin (for gcc) and /usr/ccs/bin (for other build tools), e.g.: env PATH=/usr/sfw/bin:/usr/ccs/bin:$PATH sh -c './configure; make' (The only thing this misses is /usr/X11/lib/libXrandr.so.2, which is for the little used -xrandr option, see the script below to pick it up as well). libjpeg is included in Solaris 9 and later (/usr/sfw/include and /usr/sfw/lib), and zlib in Solaris 8 and later (/usr/include and /usr/lib). So on Solaris 9 you can pick up everything with something like this: env PATH=/usr/local/bin:/usr/ccs/bin:$PATH sh -c './configure --with-jpeg=/us r/sfw; make' assuming your gcc is in /usr/local/bin and x11vnc 0.7.1 or later. These are getting pretty long, see those assignments split up in the build script below. If your system does not have these libraries at all you can get the source for the libraries to build them: libjpeg is available at [58]ftp://ftp.uu.net/graphics/jpeg/ and zlib at [59]http://www.gzip.org/zlib/. See also [60]http://www.sunfreeware.com/ for Solaris binary packages of these libraries as well as for gcc. Normally they will install into /usr/local but you can install them anywhere with the --prefix=/path/to/anywhere, etc. Here is a build script that indicates one way to pass the library locations information to the libvncserver configuration via the CPPFLAGS and LDFLAGS environment variables. ---8<---8<---8<---8<---8<---8<---8<---8<---8<---8<---8<---8<---8<---8<---8<---8 <--- #!/bin/sh # Build script for Solaris, etc, with gcc, libjpeg and libz in # non-standard locations. # set to get your gcc, etc: # PATH=/path/to/gcc/bin:/usr/ccs/bin:/usr/sfw/bin:$PATH JPEG=/path/to/jpeg # set to maybe "/usr/local", "/usr/sfw", or "/opt/sfw" ZLIB=/path/to/zlib # set to maybe "/usr/local", "/usr/sfw", or "/opt/sfw" # Below we assume headers in $JPEG/include and $ZLIB/include and the # shared libraries are in $JPEG/lib and $ZLIB/lib. If your situation # is different change the locations in the two lines below. # CPPFLAGS="-I $JPEG/include -I $ZLIB/include" LDFLAGS="-L $JPEG/lib -R $JPEG/lib -L $ZLIB/lib -R $ZLIB/lib" # These two lines may not be needed on more recent Solaris releases: # CPPFLAGS="$CPPFLAGS -I /usr/openwin/include" LDFLAGS="$LDFLAGS -L /usr/openwin/lib -R /usr/openwin/lib" # These are for libXrandr.so on Solaris 10: # CPPFLAGS="$CPPFLAGS -I /usr/X11/include" LDFLAGS="$LDFLAGS -L /usr/X11/lib -R /usr/X11/lib" # Everything needs to built with _REENTRANT for thread safe errno: # CPPFLAGS="$CPPFLAGS -D_REENTRANT" export PATH CPPFLAGS LDFLAGS ./configure make ls -l ./x11vnc/x11vnc ---8<---8<---8<---8<---8<---8<---8<---8<---8<---8<---8<---8<---8<---8<---8<---8 <--- Then do make install or copy the x11vnc binary to your desired destination. BTW, To run a shell script, just cut-and-paste the above into a file, say "myscript", then modify the "/path/to/..." items to correspond to your system/environment, and then type: "sh myscript" to run it. Note that on Solaris make is /usr/ccs/bin/make, so that is why the above puts /usr/ccs/bin in PATH. Other important build utilities are there too: ld, ar, etc. Also, it is probably a bad idea to have /usr/ucb in your PATH while building. Starting with the 0.7.1 x11vnc release the "configure --with-jpeg=DIR --with-zlib=DIR" options are handy if you want to avoid making a script. If you need to build on Solaris 2.5.1 or earlier or other older Unix OS's, see [61]this workaround FAQ. Building on FreeBSD, OpenBSD, ...: The jpeg libraries seem to be in /usr/local or /usr/pkg on these OS's. You won't need the openwin stuff in the above script (but you may need /usr/X11R6/...). Also starting with the 0.7.1 x11vnc release, this usually works: ./configure --with-jpeg=/usr/local make Building on HP-UX: For jpeg and zlib you will need to do the same sort of thing as described above for Solaris. You set CPPFLAGS and LDFLAGS to find them (see below for an example). You do not need to do any of the above /usr/openwin stuff. Also, HP-UX does not seem to support -R, so get rid of the -R items in LDFLAGS. Because of this, at runtime you may need to set LD_LIBRARY_PATH or SHLIB_PATH to indicate the directory paths so the libraries can be found. It is a good idea to have static archives, e.g. libz.a and libjpeg.a for the nonstandard libraries so that they get bolted into the x11vnc binary (and so won't get "lost"). Here is what we recently did to build x11vnc 0.7.2 on HP-UX 11.11 ./configure --with-jpeg=$HOME/hpux/jpeg --with-zlib=$HOME/hpux/zlib make Where we had static archives (libjpeg.a, libz.a) only and header files in the $HOME/hpux/... directories as discussed for the build script. _________________________________________________________________ Beta Testing: I don't have any formal beta-testers for the releases of x11vnc, so I'd appreciate any additional testing very much! Thanks to those who helped beta test x11vnc 0.8 released in Feb 2006! Please help test and debug the 0.8.1 version for release sometime in Spring 2006. The version 0.8.1 beta tarball is kept here: [62]x11vnc-0.8.1.tar.gz There are also some Linux, Solaris, and other OS test binaries [63]here. Please kick the tires and report bugs, performance regressions, undesired behavior, etc. to [64]me. Here are some features that will appear in the 0.8.1 release: * The [65]-unixpw option supports Unix username and password authentication (a variant is the [66]-unixpw_nis option that works in NIS environments). The [67]-ssl or [68]-localhost + [69]-stunnel options are enforced in this mode to prevent password sniffing. As a convenience, the -ssl or -stunnel requirements are lifted if a SSH tunnel can be deduced (but -localhost still applies). * The [70]-ssl option provides SSL encryption and authentication natively via the [71]www.openssl.org library. One can use from a simple self-signed certificate server certificate up to full CA and client certificate authentication schemes. * The [72]-stunnel option starts up a SSL tunnel server stunnel (that must be installed separately on the system: [73]www.stunnel.org) to allow only encrypted SSL connections from the network. * The [74]-sslverify option allows for authenticating VNC clients via their certificates in either -ssl or -stunnel modes. * An SSL enabled Java applet VNC Viewer applet is provided in classes/ssl/VncViewer.jar. It may also be loaded into the web browser via https (http over SSL) in addition to http. (via the VNC port or also by the separate [75]-https port option). * The [76]-usepw option will try to use your existing ~/.vnc/passwd or ~/.vnc/passwfile passwords or otherwise prompt you to create one (the server exits unless a password file is found and used). * The X CLIPBOARD selection is now managed in addition to PRIMARY. Use [77]-noclipboard and [78]-nosetclipboard for the previous PRIMARY-only behavior. * The [79]-xinerama option is now on by default. Use -noxinerama option to disable. Here are the release notes for the recent 0.8 release: * TightVNC file transfer added to libvncserver by Rohit Kumar is enabled (use [80]-nofilexfer to disable). * The [81]-passwdfile option has been enhanced to handle any number of full-access and view only passwords in an easy to maintain format. Automatic rereading or file removal can be enabled. * The [82]-8to24 option enables some multi-depth viewing on systems that don't support [83]-overlay. The 8bpp regions are transformed to depth 24 TrueColor. * The [84]-loop option will run x11vnc in an outer loop restarting each time (useful for situations where the X server restarts often). * The [85]-afteraccept option is like [86]-accept however it enables running a user supplied command after client authentication has taken place. The RFB_* environment variables have been extended. * The [87]-slow_fb allows for slow polling for special purpose applications (e.g. video). * [88]-blackout noptr,WxH+X+Y,... will prevent the pointer from going into a blacked out region. * The x11vnc source code has gone through a major reorganization. The build has been enhanced and many bugs fixed. Here are some notes about features added in 0.7.2. Checking/Testing them is still useful and appreciated! Note that the [89]X DAMAGE feature will be on by default and so I am interested if that causes any problems. I'd also like to have the new [90]wireframe move/resize, the [91]wireframe copyrect translation, and the [92]scroll detection+copyrect features all on by default as well since when they work they give a great speedup! (CopyRect is a VNC encoding and is very fast because the viewer already has the image data that needs to be copied: e.g. it just moves it to another part of its screen). The scroll copyrect is currently the least stable, you can toggle it off via "-noscr" or via the gui (all of the other new features can also be toggled by cmdline option or gui, see -help output for more info). _________________________________________________________________ Some Notes: Both a client and a server: It is sometimes confusing to people that x11vnc is both a client and a server at the same time. It is an X client because it connects to the running X server to do the screen polls. Think of it as a rather efficient "screenshot" program running continuously. It is a server in the sense that it is a VNC server that VNC viewers on the network can connect to and view the screen framebuffer it manages. When trying to debug problems, remember to think of both roles. E.g. "how is x11vnc connecting to the X server?", "how is the vncviewer connecting to x11vnc?", "what permits/restricts the connection?". Both links may have reachability, permission, and other issues. Network performance: Whether you are using Xvnc or x11vnc it is always a good idea to have a solid background color instead of a pretty background image. Each and every re-exposure of the background must be resent over the network: better to have that background be a solid color that compresses very well compared to a photo image. (This is one place where the X protocol has an advantage over the VNC protocol.) I suggest using xsetroot, dtstyle or similar utility to set a solid background while using x11vnc. You can turn the pretty background image back on when you are using the display directly. Update: As of Feb/2005 x11vnc has the [93]-solid [color] option that works on recent GNOME, KDE, and CDE and also on classic X (background image is on the root window). I also find the [94]TightVNC encoding gives the best response for my usage (Unix <-> Unix over cable modem). One needs a tightvnc-aware vncviewer to take advantage of this encoding. TCP port issues: Notice the lines 18/07/2003 14:36:31 Autoprobing selected port 5900 PORT=5900 in the output. 5900 is the default VNC listening port (just like 6000 is X11's default listening port). Had port 5900 been taken by some other application, x11vnc would have next tried 5901. That would mean the viewer command above should be changed to vncviewer far-away.east:1. You can force the port with the "[95]-rfbport NNNN" option where NNNN is the desired port number. If that port is already taken, x11vnc will exit immediately. (also see the "SunRay Gotcha" note below) Options: x11vnc has (far too) many features that may be activated via its [96]command line options. Useful options are, e.g., -scale to do server-side scaling, and -rfbauth passwd-file to use VNC password protection (the vncpasswd or storepasswd programs, or the x11vnc [97]-storepasswd option can be used to create the password file). Algorithm: How does x11vnc do it? Rather brute-forcedly: it continuously polls the X11 framebuffer for changes using XShmGetImage(). When changes are discovered, it instructs libvncserver which rectangular regions of the framebuffer have changed, and libvncserver compresses the changes and sends them off to any connected VNC viewers. A number of applications do similar things, such as x0rfbserver, krfb, x0vncserver, vino. x11vnc uses a 32 x 32 pixel tile model (the desktop is decomposed into roughly 1000 such tiles), where changed tiles are found by pseudo-randomly polling 1 pixel tall horizontal scanlines. This is a surprisingly effective algorithm for finding changed regions. For keyboard and mouse user input the XTEST extension is used to pass the input events to the X server. To detect XBell "beeps" the XKEYBOARD extension is used. If available, the XFIXES extension is used to retrieve the current mouse cursor shape. Also, if available the X DAMAGE extension is used to receive hints from the X server where modified regions on the screen are. This greatly reduces the system load when not much is changing on the screen and also improves how quickly the screen is updated. Barbershop mirrors effect: What if x11vnc is started up, and vncviewer is then started up on the same machine and displayed on the same display x11vnc is polling? One might "accidentally" do this when first testing out the programs. You get an interesting recursive/feedback effect where vncviewer images keep popping up each one contained in the previous one and slightly shifted a bit by the window manager decorations. There will be an [98]even more interesting effect if -scale is used. Also, if the XKEYBOARD is supported and the XBell "beeps" once, you get an infinite loop of beeps going off. Although all of this is mildly exciting it is not much use: you will normally run and display the viewer on a different machine! _________________________________________________________________ Sun Ray Notes: You can run x11vnc on your (connected or disconnected) [99]SunRay session. Here are some [100]notes on SunRay usage with x11vnc. _________________________________________________________________ Limitations: * Due to the polling nature, some activities (opaque window moves, scrolling), can be pretty choppy/ragged and others (exposures of large areas) slow. Experiment with interacting a bit differently than you normally do to minimize the effects (e.g. do fullpage paging rather than line-by-line scrolling, and move windows in a single, quick motion). Recent work has provided the [101]-scrollcopyrect and [102]-wireframe speedups using the CopyRect VNC encoding and other things, but they only speed up certain activities, not all. * A rate limiting factor for x11vnc performance is that video hardware is optimized for writing, not reading (x11vnc reads the video framebuffer for the screen image data). The difference can be a factor of 10 to 1000, and so it usually takes about 0.5-1 sec to read in the whole video hardware framebuffer (e.g. 5MB for 1280x1024 at depth 24 with a read rate of 5-10MB/sec). So whenever activity changes most of the screen (e.g. moving or iconifying a large window) there is a delay of 0.5-1 sec while x11vnc reads the changed regions in. Note: A quick way to get a 2X speedup for x11vnc is to switch from depth 24 (32bpp) to depth 16 (16bpp). You get a 4X speedup going to 8bpp, but the lack of color cells is usually unacceptable. To get a sense of the read and write speeds of your video card, you can run benchmarks like: x11perf -getimage500, x11perf -putimage500, x11perf -shmput500 and for XFree86 displays with direct graphics access the dga command (press "b" to run the benchmark and then after a few seconds press "q" to quit). Even this "dd if=/dev/fb0 of=/dev/null" often gives a good estimate. We have seen a few cases where the hardware fb read speed is greater than 65 MB/sec: on high end graphics workstations from SGI and Sun, and also from a Linux user using nvidia proprietary drivers for his nvidia video card. If you have a card with a fast read speed please send us the details. On XFree86/Xorg it is actually possible to increase the framebuffer read speed considerably (5-100 times) by using the Shadow Framebuffer (a copy of the framebuffer is kept in main memory and this can be read much more quickly). To do this one puts the line Option "ShadowFB" "true" in the Device section of the /etc/X11/XF86Config or /etc/X11/xorg.conf file. Note that this disables 2D acceleration at the physical display and so likely defeats the purpose. Nevertheless this could be handy in some circumstances, e.g. if the slower speed while sitting at the physical display was acceptable (this seems to be true for most video cards these days). Unfortunately it does not seem shadowfb can be turned on and off dynamically... Another amusing thing one can do is use Xvfb as the X server, e.g. "xinit $HOME/.xinitrc -- /usr/X11R6/bin/Xvfb :1 -screen 0 1024x768x16" x11vnc can poll Xvfb efficiently via main memory. It's not exactly clear why one would want to do this (perhaps to take advantage of an x11vnc feature, such as framebuffer scaling), instead of using vncserver/Xvnc, but we mention it because it may be of use for special purpose applications. Also, a faster and more accurate way is to use the "dummy" XFree86/Xorg device driver (or our Xdummy wrapper script). See [103]this FAQ for details. * Somewhat surprisingly, the X11 mouse (cursor) shape is write-only and cannot be queried from the X server. So traditionally in x11vnc the cursor shape stays fixed at an arrow. (see the "-cursor X" and "-cursor some" [104]options, however, for a partial hack for the root window, etc.). However, on Solaris using the SUN_OVL overlay extension, x11vnc can show the correct mouse cursor when the [105]-overlay option is also supplied. A similar thing is done on IRIX as well when -overlay is supplied. More generally, as of Dec/2004 x11vnc supports the new XFIXES extension (in Xorg and Solaris 10) to query the X server for the exact cursor shape, this works pretty well except that cursors with transparency (alpha channel) need to approximated to solid RGB values (some cursors look worse than others). * Audio from applications is of course not redirected (separate redirectors do exist, e.g. esd). The XBell() "beeps" will work if the X server supports the XKEYBOARD extension. (Note that on Solaris XKEYBOARD is disabled by default. Passing +kb to Xsun enables it). * The scroll detection algorithm for the [106]-scrollcopyrect option can give choppy or bunched up transient output and occasionally painting errors. * 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 [107]contact me if you have any questions, problems, or comments about x11vnc, etc. Also, some people ask if they can make a donation, see [108]this link for that. _________________________________________________________________ x11vnc FAQ: [Building and Starting] [109]Q-1: I can't get x11vnc to start up. It says "XOpenDisplay failed (null)" or "Xlib: connection to ":0.0" refused by server Xlib: No protocol specified" and then exits. What do I need to do? [110]Q-2: I can't get x11vnc and/or libvncserver to compile. [111]Q-3: I just built x11vnc successfully, but when I use it my keystrokes and mouse button clicks are ignored (I am able to move the mouse though). [112]Q-4: Help, I need to run x11vnc on Solaris 2.5.1 (or other old Unix/Linux) and it doesn't compile! [113]Q-5: Where can I get a precompiled x11vnc binary for my Operating System? [114]Q-6: Where can I get a VNC Viewer binary (or source code) for the Operating System I will be viewing from? [115]Q-7: How can I see all of x11vnc's command line options and documentation on how to use them? [116]Q-8: I don't like typing arcane command line options every time I start x11vnc. What can I do? Is there a config file? Or a GUI? [117]Q-9: How can I get the GUI to run in the System Tray, or at least be a smaller, simpler icon? [118]Q-10: Can I make x11vnc more quiet and also go into the background after starting up? [119]Q-11: Sometimes when a VNC viewer dies abruptly, x11vnc also dies with the error message like: "Broken pipe". I'm using the -forever mode and I want x11vnc to keep running. [120]Q-12: Are there any build-time customizations possible, e.g. change defaults, create a smaller binary, etc? [Win2VNC Related] [121]Q-13: I have two separate machine displays in front of me, one Windows the other X11: can I use x11vnc in combination with Win2VNC in dual-screen mode to pass the keystrokes and mouse motions to the X11 display? [122]Q-14: I am running Win2VNC on my Windows machine and "x11vnc -nofb" on Unix to pass keyboard and mouse to the Unix monitor. Whenever I start Win2VNC it quickly disconnects and x11vnc says: rfbProcessClientNormalMessage: read: Connection reset by peer [Color Issues] [123]Q-15: The X display I run x11vnc on is only 8 bits per pixel (bpp) PseudoColor (i.e. only 256 distinct colors). The x11vnc colors may start out OK, but after a while they are incorrect in certain windows. [124]Q-16: Color problems: Why are the colors for some windows incorrect in x11vnc? BTW, my X display has nice overlay/multi-depth visuals of different color depths: e.g. there are both depth 8 and 24 visuals available at the same time. [125]Q-17: How do I figure out the window id to supply to the -id windowid option? [126]Q-18: Why don't menus or other transient windows come up when I am using the -id windowid option to view a single application window? [127]Q-19: My X display is depth 24 at 24bpp (instead of the normal depth 24 at 32bpp). I'm having lots of color and visual problems with x11vnc and/or vncviewer. What's up? [Xterminals] [128]Q-20: Can I use x11vnc to view and interact with an Xterminal (e.g. NCD) that is not running UNIX and so x11vnc cannot be run on it directly? [129]Q-21: How do I get my X permissions (MIT-MAGIC-COOKIE file) correct for a Unix/Linux machine acting as an Xterminal? [Sun Rays] [130]Q-22: I'm having trouble using x11vnc with my Sun Ray session. [Remote Control] [131]Q-23: How do I stop x11vnc once it is running in the background? [132]Q-24: Can I change settings in x11vnc without having to restart it? Can I remote control it? [Security and Permissions] [133]Q-25: How do I create a VNC password for use with x11vnc? [134]Q-26: Can I make it so -storepasswd doesn't show my password on the screen? [135]Q-27: Can I have two passwords for VNC viewers, one for full access and the other for view-only access to the display? [136]Q-28: Can I have as many full-access and view-only passwords as I like? [137]Q-29: Does x11vnc support Unix usernames and passwords? Can I further limit the set of Unix usernames who can connect to the VNC desktop? [138]Q-30: Why does x11vnc exit as soon as the VNC viewer disconnects? And why doesn't it allow more than one VNC viewer to connect at the same time? [139]Q-31: Can I limit which machines incoming VNC clients can connect from? [140]Q-32: How do I build x11vnc/libvncserver with libwrap (tcp_wrappers) support? [141]Q-33: Can I have x11vnc only listen on one network interface (e.g. internal LAN) rather than having it listen on all network interfaces and relying on -allow to filter unwanted connections out? [142]Q-34: Now that -localhost implies listening only on the loopback interface, how I can occasionally allow in a non-localhost via the -R allowonce remote control command? [143]Q-35: Can I fine tune what types of user input are allowed? E.g. have some users just be able to move the mouse, but not click or type anything? [144]Q-36: Can I prompt the user at the local X display whether the incoming VNC client should be accepted or not? Can I decide to make some clients view-only? How about running an arbitrary program to make the decisions? [145]Q-37: I start x11vnc as root because it is launched via inetd(1) or a display manager like gdm(1). Can I have x11vnc later switch to a different user? [146]Q-38: I use a screen-lock when I leave my workstation (e.g. xscreensaver or xlock). When I remotely access my workstation desktop via x11vnc I can unlock the desktop fine, but I am worried people will see my activities on the physical monitor. What can I do to prevent this, or at least make it more difficult? [147]Q-39: Can I have x11vnc automatically lock the screen when I disconnect the VNC viewer? [Encrypted Connections] [148]Q-40: How can I tunnel my connection to x11vnc via an encrypted SSH channel between two Unix machines? [149]Q-41: How can I tunnel my connection to x11vnc via an encrypted SSH channel from Windows using an SSH client like Putty? [150]Q-42: How can I tunnel my connection to x11vnc via an encrypted SSL channel using an external tool like stunnel? [151]Q-43: Does x11vnc have built-in SSL tunneling? [152]Q-44: How do I use VNC Viewers with built-in SSL tunneling? [153]Q-45: How do I use VNC Viewers with built-in SSL tunneling when going through a Web Proxy? [154]Q-46: Can Apache web server act as a gateway for users to connect via SSL from the Internet with a Web browser to x11vnc running on their workstations behind a firewall? [155]Q-47: Can I create and use my own SSL Certificate Authority (CA) with x11vnc? [Display Managers and Services] [156]Q-48: How can I run x11vnc as a "service" that is always available? [157]Q-49: How can I use x11vnc to connect to an X login screen like xdm, GNOME gdm, KDE kdm, or CDE dtlogin? (i.e. nobody is logged into an X session yet). [158]Q-50: Can I run x11vnc out of inetd(1)? How about xinetd(1)? [159]Q-51: Can I have x11vnc restart itself after it terminates? [160]Q-52: How do I make x11vnc work with the Java VNC viewer applet in a web browser? [161]Q-53: Are reverse connections (i.e. the VNC server connecting to the VNC viewer) using "vncviewer -listen" and vncconnect(1) supported? [162]Q-54: Can I use x11vnc as a replacement for Xvnc? (i.e. not for a real display, but for a virtual one I keep around). [163]Q-55: How can I use x11vnc on "headless" machines? Why might I want to? [Resource Usage and Performance] [164]Q-56: 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)? [165]Q-57: How can I make x11vnc use less system resources? [166]Q-58: How can I make x11vnc use MORE system resources? [167]Q-59: I use x11vnc over a slow link with high latency (e.g. dialup modem), is there anything I can do to speed things up? [168]Q-60: Does x11vnc support the X DAMAGE Xserver extension to find modified regions of the screen quickly and efficiently? [169]Q-61: 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? [170]Q-62: Why not do something like wireframe animations to avoid the windows "lurching" when being moved or resized? [171]Q-63: Can x11vnc try to apply heuristics to detect when an window is scrolling its contents and use the CopyRect encoding for a speedup? [Mouse Cursor Shapes] [172]Q-64: Why isn't the mouse cursor shape (the little icon shape where the mouse pointer is) correct as I move from window to window? [173]Q-65: When using XFIXES cursorshape mode, some of the cursors look really bad with extra black borders around the cursor and other cruft. How can I improve their appearance? [174]Q-66: In XFIXES mode, are there any hacks to handle cursor transparency ("alpha channel") exactly? [Mouse Pointer] [175]Q-67: Why does the mouse arrow just stay in one corner in my vncviewer, whereas my cursor (that does move) is just a dot? [176]Q-68: 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)? [177]Q-69: Is it possible to swap the mouse buttons (e.g. left-handed operation), or arbitrarily remap them? How about mapping button clicks to keystrokes, e.g. to partially emulate Mouse wheel scrolling? [Keyboard Issues] [178]Q-70: How can I get my AltGr and Shift modifiers to work between keyboards for different languages? [179]Q-71: When I try to type a "<" (i.e. less than) instead I get ">" (i.e. greater than)! Strangely, typing ">" works OK!! [180]Q-72: When I try to type a "<" (i.e. less than) instead I get "<," (i.e. an extra comma). [181]Q-73: 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? [182]Q-74: 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? [183]Q-75: The x11vnc -norepeat mode is in effect, but I still get repeated keystrokes!! [184]Q-76: 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? [185]Q-77: 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) [186]Q-78: Can I map a keystroke to a mouse button click on the remote machine? [Screen Related Issues and Features] [187]Q-79: 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? [188]Q-80: Does x11vnc support server-side framebuffer scaling? (E.g. to make the desktop smaller). [189]Q-81: Does x11vnc work with Xinerama? (i.e. multiple monitors joined together to form one big, single screen). [190]Q-82: Can I use x11vnc on a multi-headed display that is not Xinerama (i.e. separate screens :0.0, :0.1, ... for each monitor)? [191]Q-83: Can x11vnc show only a portion of the display? (E.g. for a special purpose rfb application). [192]Q-84: Does x11vnc support the XRANDR (X Resize, Rotate and Reflection) extension? Whenever I rotate or resize the screen x11vnc just seems to crash. [193]Q-85: Why is the view in my VNC viewer completely black? Or why is everything flashing around randomly? [194]Q-86: 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? [195]Q-87: Can I use x11vnc to view my VMWare session remotely? [196]Q-88: Can non-X devices (e.g. a raw framebuffer) be viewed and/or controlled by x11vnc? [197]Q-89: I am using x11vnc where my local machine has "popup/hidden taskbars" (e.g. GNOME or MacOS X) and the remote display where x11vnc runs also has "popup/hidden taskbars" (e.g. GNOME). When I move the mouse to the edge of the screen where the popups happen, the taskbars interfere and fight with each other in strange ways. What can I do? [Misc: Clipboard, File Transfer, Beeps, Thanks, etc.] [198]Q-90: Does the Clipboard/Selection get transferred between the vncviewer and the X display? [199]Q-91: Can I transfer files back and forth with x11vnc? [200]Q-92: Why don't I hear the "Beeps" in my X session (e.g. when typing tput bel in an xterm)? [201]Q-93: Thanks for your program and for your help! Can I make a donation? _________________________________________________________________ [Building and Starting] Q-1: I can't get x11vnc to start up. It says "XOpenDisplay failed (null)" or "Xlib: connection to ":0.0" refused by server Xlib: No protocol specified" and then exits. What do I need to do? For the former error, you need to specify the X display to connect to (it also needs to be on the same machine the x11vnc process is to run on). Set your DISPLAY environment variable or use the [202]-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 correctly. To make sure X11 permissions are the problem do this simple test: while sitting at the physical X display open a terminal window (gnome-terminal, xterm, etc). You should be able to run x11vnc successfully without any need for special steps or command line options in that terminal. If that works OK then you know X11 permissions are the only thing preventing it from working when you try to start x11vnc via, say, a remote shell. How to Solve: See the xauth(1), Xsecurity(7), and xhost(1) man pages for much info on X11 permissions. For example, you may need to set your XAUTHORITY environment variable or use the [203]-auth option to point to the correct MIT-MAGIC-COOKIE file (e.g. /home/joe/.Xauthority or /var/gdm/:0.Xauth or /var/lib/kdm/A:0-crWk72K), or simply be sure you run x11vnc as the correct user (i.e. the user who is logged into the X session you wish to view). The MIT cookie file contains the secret key that allows x11vnc to connect to the desired X display. If, say, sshd has set XAUTHORITY to point to a random file it has created for X forwarding that will cause problems. (Under some circumstances even su(1) and telnet(1) can set XAUTHORITY.) Running x11vnc as root is often not enough: you need to know where the MIT-MAGIC-COOKIE file for the desired X display is. Example solution: x11vnc -display :0 -auth /var/gdm/:0.Xauth (this is for the display manager gdm and requires root permission to read the gdm cookie file, see [204]this faq for other display manager cookie file names). While running x11vnc as root, remember it comes with no warranty ;-). Less safe, but to avoid figuring out where the correct XAUTHORITY file is, if the person sitting at the physical X session types "xhost +localhost" then one should be able to attach x11vnc to the session (from the same machine). The person could then type "xhost -localhost" after x11vnc has connected to go back to the default permissions. Also, for some situations the "-users lurk=" option may be of use (please read the documentation on the [205]-users option). To test out your X11 permissions from a remote shell, set DISPLAY and possibly XAUTHORITY (see your shell's man page, bash(1), tcsh(1), on how to set environment variables) and type xdpyinfo in the same place you will be typing (or otherwise running) x11vnc. If information is printed out about the X display (screen sizes, supported extensions, color visuals info) that means the X11 permissions are set up properly: xdpyinfo successfully connected to DISPLAY! You could also type xclock and make sure no errors are reported (a clock should appear on the X display, press Ctrl-C to stop it). If these work, then typing "x11vnc" should also work. Important: if you cannot get your X11 permissions so that the xdpyinfo or xclock tests work, x11vnc also will not work (all of these X clients must be allowed to connect to the X server to function properly). Q-2: I can't get x11vnc and/or libvncserver to compile. Make sure you have all of the required -devel packages installed. These include X11/XFree86, libjpeg, libz, ... After running the libvncserver configure, carefully examine the output and the messages in the config.log file looking for missing components. For example, if the configure output looks like: checking how to run the C preprocessor... gcc -E checking for X... no checking for XkbSelectEvents in -lX11... no checking for XineramaQueryScreens in -lXinerama... no checking for XTestFakeKeyEvent in -lXtst... no there is quite a bit wrong with the build environment. Hopefully simply adding -devel packages will fix it. For Debian the list seems to be: gcc make libc6-dev libjpeg62-dev libx11-dev libxext-dev libxrandr-dev libxtst-dev x-dev xlibs-static-dev zlib1g-dev For Redhat the list seems to be: gcc make glibc-devel libjpeg-devel XFree86-devel or xorg-x11-devel zlib-devel Q-3: I just built x11vnc successfully, but when I use it my keystrokes and mouse button clicks are ignored (I am able to move the mouse though). This is most likely due to you not having a working build environment for the XTEST client library libXtst.so. The library is probably present on your system, but the package installing the development header file is missing. If you were watching carefully while configure was running you would have seen: checking for XTestFakeKeyEvent in -lXtst... no The solution is to add the necessary build environment package (and the library package if that is missing too). On Debian the build package is libxtst-dev. Other distros/OS's may have it in another package. x11vnc will build without support for this library (e.g. perhaps one wants a view-only x11vnc on a stripped down or embedded system...). At runtime it will also continue to run even if the X server it connects to does not support XTEST. In both cases it cannot inject keystrokes or button clicks since XTEST is needed for that (it can still move the mouse pointer using the X API XWarpPointer()). You will see a warning message something like this at run time: 20/03/2005 22:33:09 WARNING: XTEST extension not available (either missing fr om 20/03/2005 22:33:09 display or client library libXtst missing at build time ). 20/03/2005 22:33:09 MOST user input (pointer and keyboard) will be DISCARDE D. 20/03/2005 22:33:09 If display does have XTEST, be sure to build x11vnc wit h 20/03/2005 22:33:09 a working libXtst build environment (e.g. libxtst-dev, 20/03/2005 22:33:09 or other packages). 20/03/2005 22:33:09 No XTEST extension, switching to -xwarppointer mode for 20/03/2005 22:33:09 pointer motion input. Q-4: Help, I need to run x11vnc on Solaris 2.5.1 (or other old Unix/Linux) and it doesn't compile! We apologize that x11vnc does not build cleanly on older versions of Solaris, Linux, etc.: very few users are on these old releases. We have heard that since Dec/2004 a Solaris 2.6 built x11vnc will run on Solaris Solaris 2.5 and 2.5.1 (since a workaround for XConvertCase is provided). In any event, here is a workaround for Solaris 2.5.1 (and perhaps earlier and perhaps non-Solaris): First use the environment settings (CPPFLAGS, LDFLAGS, etc.) in the above [206]Solaris build script to run the configure command. That should succeed without failure. Then you have to hand edit the autogenerated rfb/rfbconfig.h file in the source tree, and just before the last #endif at the bottom of that file insert these workaround lines: struct timeval _tmp_usleep_tv; #define usleep(x) \ _tmp_usleep_tv.tv_sec = (x) / 1000000; \ _tmp_usleep_tv.tv_usec = (x) % 1000000; \ select(0, NULL, NULL, NULL, &_tmp_usleep_tv); int gethostname(char *name, int namelen); long random(); int srandom(unsigned int seed); #undef LIBVNCSERVER_HAVE_LIBPTHREAD #define SHUT_RDWR 2 typedef unsigned int in_addr_t; #define snprintf(a, n, args...) sprintf((a), ## args) Then run make with the Solaris build script environment, everything should compile without problems, and the resulting x11vnc binary should work OK. If some non-x11vnc related programs fail (e.g. test programs) and the x11vnc binary is not created try "make -k" to have it keep going. Similar sorts of kludges in rfb/rfbconfig.h can be done on other older OS (Solaris, Linux, ...) releases. Here are some notes for similar steps that need to be done to build on [207]SunOS 4.x Please let us know if you had to use the above workaround (and whether it worked or not). If there is enough demand we will try to push clean compilations back to earlier Solaris, Linux, etc, releases. Q-5: Where can I get a precompiled x11vnc binary for my Operating System? Hopefully the [208]build steps above and [209]FAQ provide enough info for a painless compile for most environments. Please report problems with the x11vnc configure, make, etc. on your system (if your system is known to compile other GNU packages successfully). There are precompiled x11vnc binaries built by other groups that are available at the following locations: Debian: (.deb) [210]http://packages.debian.org/x11vnc Slackware: (.tgz) [211]http://www.linuxpackages.net/ Redhat/Fedora: (.rpm) [212]http://dag.wieers.com/packages/x11vnc/ [213]http://dries.ulyssis.org/rpm/packages/x11vnc SuSE: (.rpm) [214]http://linux01.gwdg.de/~pbleser/ Solaris: (pkg) [215]http://www.sunfreeware.com/ Nokia 770 (.deb) [216]http://mike.saunby.net/770/x11vnc/ Sharp Zaurus [217]http://www.pdaxrom.org/ and [218]http://www.focv.com/ If the above binaries don't work and building x11vnc on your OS fails (and all else fails!) you can try one of [219]my collection of binaries for various OS's and x11vnc releases. As a general note, the x11vnc program is simple enough you don't really need to install a package: the binary will in most cases work as is and from any location (as long as your system libraries are not too old, etc). So, for Linux distributions that are not one of the above, the x11vnc binary from the above packages has a good chance of working. You can "install" it by just copying the x11vnc binary to the desired directory in your PATH. Tip on extracting files from a Debian package: extract the archive via a command like: "ar x x11vnc_0.6-2_i386.deb" and then you can find the binary in the resulting data.tar.gz tar file. Also, rpm2cpio(1) is useful in extracting files from rpm packages. Q-6: Where can I get a VNC Viewer binary (or source code) for the Operating System I will be viewing from? To obtain VNC viewers for the viewing side (Windows, Mac OS, or Unix) try here: * [220]http://www.tightvnc.com/download.html * [221]http://www.realvnc.com/download-free.html * [222]http://sourceforge.net/projects/cotvnc/ * [223]http://www.ultravnc.com/ Q-7: How can I see all of x11vnc's command line options and documentation on how to use them? Run: x11vnc -opts to list just the option names or run: x11vnc -help for long descriptions about each option. The output is listed [224]here as well. Q-8: I don't like typing arcane command line options every time I start x11vnc. What can I do? Is there a config file? Or a GUI? You could create a shell script that calls x11vnc with your options: #!/bin/sh # # filename: X11vnc (i.e. not "x11vnc") # It resides in a directory in $PATH. "chmod 755 X11vnc" has been run on it. # x11vnc -wait 50 -localhost -rfbauth $HOME/.vnc/passwd -display :0 $* a similar thing can be done via aliases in your shell (bash, tcsh, csh, etc..). Or as of Jun/2004 you can use the simple $HOME/.x11vncrc config file support. If that file exists, each line is taken as a command line option. E.g. the above would be: # this is a comment in my ~/.x11vncrc file wait 50 # this is a comment to the end of the line. -localhost # note: the leading "-" is optional. rfbauth /home/fred/.vnc/passwd display :0 As of Dec/2004 there is now a simple Tcl/Tk GUI based on the remote-control functionality ("-R") that was added. The /usr/bin/wish program is needed for operation. The gui is not particularly user-friendly, it just provides a point and click mode to set all the many x11vnc parameters and obtain help on them. See the [225]-gui option for more info. Examples: "x11vnc ... -gui" and "x11vnc ... -gui other:0" in the latter case the gui is displayed on other:0, not the X display x11vnc is polling. There is also a "[226]-gui tray" system tray mode. Q-9: How can I get the GUI to run in the System Tray, or at least be a smaller, simpler icon? As of Jul/2005 the gui can run in a more friendly small icon mode "-gui icon" or in the system tray: "-gui tray". It has balloon status, a simple menu, and a Properities dialog. The full, complicated, gui is only available under "Advanced". Other improvements were added as well. Try "Misc -> simple_gui" for a gui with fewer esoteric menu items. If the gui fails to embed itself in the system tray, do a retry via "Window View -> icon" followed by "Window View -> tray" with the popup menu. For inexperienced users starting up x11vnc and the GUI while sitting at the physical X display (not remotely), using something like "x11vnc -display :0 -gui tray=setpass" might be something for them that they are accustomed to in a Desktop environment (it prompts for an initial password, etc). This is a basic "Share My Desktop" mode. Q-10: Can I make x11vnc more quiet and also go into the background after starting up? Use the [227]-q and [228]-bg options, respectively. (also: -quiet is an alias for -q) Note that under -bg the stderr messages will be lost unless you use the "[229]-o logfile" option. Q-11: Sometimes when a VNC viewer dies abruptly, x11vnc also dies with the error message like: "Broken pipe". I'm using the -forever mode and I want x11vnc to keep running. As of Jan/2004 the SIGPIPE signal is ignored. So if a viewer client terminates abruptly, libvncserver will notice on the next I/O operation and will close the connection and continue on. Up until of Apr/2004 the above fix only works for BSD signal systems (Linux, FreeBSD, ...) For SYSV systems there is a workaround in place since about Jun/2004. Q-12: Are there any build-time customizations possible, e.g. change defaults, create a smaller binary, etc? There are some options. They are enabled by adding something like -Dxxxx=1 to the CPPFLAGS environment variable before running configure (see the [230]build notes for general background). /* * Mar/2006 * Build-time customization via CPPFLAGS. * * Summary of options to include in CPPFLAGS for custom builds: * * -DVNCSHARED to have the vnc display shared by default. * -DFOREVER to have -forever on by default. * -DNOREPEAT=0 to have -repeat on by default. * -DADDKEYSYMS=0 to have -noadd_keysyms the default. * * -DREMOTE_DEFAULT=0 to disable remote-control on by default (-yesremote). * -DREMOTE_CONTROL=0 to disable remote-control mechanism completely. * -DEXTERNAL_COMMANDS=0 to disable the running of all external commands. * -DFILEXFER=0 disable filexfer. * * -DHARDWIRE_PASSWD=... hardwired passwords, quoting necessary. * -DHARDWIRE_VIEWPASSWD=... * -DNOPW=1 make -nopw the default (skip warning) * -DUSEPW=1 make -usepw the default * -DPASSWD_REQUIRED=1 exit unless a password is supplied. * -DPASSWD_UNLESS_NOPW=1 exit unless a password is supplied and no -nopw. * * -DWIREFRAME=0 to have -nowireframe as the default. * -DWIREFRAME_COPYRECT=0 to have -nowirecopyrect as the default. * -DWIREFRAME_PARMS=... set default -wirecopyrect parameters. * -DSCROLL_COPYRECT=0 to have -noscrollcopyrect as the default. * -DSCROLL_COPYRECT_PARMS=... set default -scrollcopyrect parameters. * -DSCALING_COPYRECT=0 * -DXDAMAGE=0 to have -noxdamage as the default. * -DSKIPDUPS=0 to have -noskip_dups as the default or vice versa. * * -DPOINTER_MODE_DEFAULT={0,1,2,3,4} set default -pointer_mode. * -DBOLDLY_CLOSE_DISPLAY=0 to not close X DISPLAY under -rawfb. * -DSMALL_FOOTPRINT=1 for smaller binary size (no help, no gui, etc) * use 2 or 3 for even smaller footprint. * -DNOGUI do not include the gui tkx11vnc. * -DPOLL_8TO24_DELAY=N * -DDEBUG_XEVENTS=1 enable printout for X events. * * Set these in CPPFLAGS before running configure. E.g.: * * % env CPPFLAGS="-DFOREVER -DREMOTE_CONTROL=0" ./configure * % make */ If other things (e.g. "-I ...") are needed in CPPFLAGS add them as well. On some systems is seems you need to set LC_ALL=C for configure to work properly... Be careful the following two variables: HARDWIRE_PASSWD and HARDWIRE_VIEWPASSWD. If set (remember to include the double quotes around the string), they will be used as default values for the -passwd and -viewpasswd options. Of course the strings will exist unobscured in the x11vnc: the binary better not be readable by unintendeds. Perhaps this is of use in remote access for an embedded application, etc... Let us know if more build-time customizations would be useful. [Win2VNC Related] Q-13: I have two separate machine displays in front of me, one Windows the other X11: can I use x11vnc in combination with Win2VNC in dual-screen mode to pass the keystrokes and mouse motions to the X11 display? Yes, for best response start up x11vnc with the "[231]-nofb" option (disables framebuffer polling, and does other optimizations) on the secondary display (X11) machine. Then start up Win2VNC on the primary display (Windows) referring it to the secondary display. This will also work X11 to X11 using [232]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: * [233]Original Win2VNC * [234]Enhanced Win2VNC and [235]sourceforge link * [236]x2vnc * [237]x2x also [238]here * [239]zvnc (MorphOS) All of them will work with x11vnc (except x2x where it is not needed). Q-14: I am running Win2VNC on my Windows machine and "x11vnc -nofb" on Unix to pass keyboard and mouse to the Unix monitor. Whenever I start Win2VNC it quickly disconnects and x11vnc says: rfbProcessClientNormalMessage: read: Connection reset by peer Is the default visual of the X display you run x11vnc on low color (e.g. 8 bit per pixel PseudoColor)? (you can run xdpyinfo to check, look in the "screen" section). There seems to be a bug in Win2VNC in that it cannot deal correctly with colormaps (PseudoColor is the most common example of a visual with a colormap). If so, there are a couple options. 1) Can you set the default visual on your display to be depth 24 TrueColor? Sun machines often have 8+24 overlay/multi-depth visuals, and you can make the default visual depth 24 TrueColor (see fbconfig(1) and Xsun(1)). 2) As of Feb/2004 x11vnc has the [240]-visual option to allow you to force the framebuffer visual to whatever you want (this usually messes up the colors unless you are very clever). In this case, the option provides a convenient workaround for the Win2VNC bug: x11vnc -nofb -visual TrueColor -display :0 ... So the visual will be set to 8bpp TrueColor and Win2VNC can handle this. Since Win2VNC does not use the framebuffer data there should be no problems in doing this. [Color Issues] Q-15: The X display I run x11vnc on is only 8 bits per pixel (bpp) PseudoColor (i.e. only 256 distinct colors). The x11vnc colors may start out OK, but after a while they are incorrect in certain windows. Use the [241]-flashcmap option to have x11vnc watch for changes in the colormap, and propagate those changes back to connected clients. This can be slow (since the whole screen must be updated over the network whenever the colormap changes). This flashing colormap behavior often happens if an application installs its own private colormap when the mouse is in its window. "netscape -install" is a well-known historical example of this. Consider reconfiguring the system to 16 bpp or depth 24 TrueColor if at all possible. Also note the option [242]-8to24 (Jan/2006) can often remove the need for flashing the colormap. Everything is dynamically transformed to depth 24 at 32 bpp using the colormaps. There may be painting errors however (see the following FAQ for tips on reducing and correcting them). In some rare cases the [243]-notruecolor option has corrected colors on 8bpp displays. The red, green, and blue masks were non-zero in 8bpp PseudoColor on an obscure setup, and this option corrected the problems. Q-16: Color problems: Why are the colors for some windows incorrect in x11vnc? BTW, my X display has nice overlay/multi-depth visuals of different color depths: e.g. there are both depth 8 and 24 visuals available at the same time. You may want to review the [244]previous question regarding 8 bpp PseudoColor. On some hardware (Sun/SPARC and SGI), the [245]-overlay option discussed a couple paragraphs down may solve this for you (you may want to skip to it directly). On other hardware the less robust [246]-8to24 option may help (also discussed below). Run xdpyinfo(1) to see what the default visual is and what the depths of the other visuals are. Does the default visual have a depth of 8 but there are other visuals of depth 24? If it does, can you possibly re-configure your X server to make a depth 24 visual the default? If you can do it, this will save you a lot of grief WRT colors and x11vnc (and for general usage too!). Here is how I do this on an old Sparcstation 20 running Solaris 9 with SX graphics xinit -- -dev /dev/fb defclass TrueColor defdepth 24 and it works nicely (note: to log into console from the dtlogin window, select "Options -> Command Line Login", then login and enter the above command). See the -dev section of the Xsun(1) manpage for a description of the above arguments. If you have root permission, a more permanent and convenient thing to do is to record the arguments in a line like: :0 Local local_uid@console root /usr/openwin/bin/Xsun -dev /dev/fb defclass TrueColor defdepth 24 in /etc/dt/config/Xservers (copy /usr/dt/config/Xservers). Also look at the fbconfig(1) and related manpages (e.g. ffbconfig, m64config, pgxconfig, SUNWjfb_config, etc ...) for hardware framebuffer settings that may achieve the same effect. In general for non-Sun machines, look at the "-cc class" and related options in your X server manpage (perhaps Xserver(1)), it may allow modifying the default visual (e.g. "-cc 4", see for the visual class numbers). On XFree86 some video card drivers (e.g. Matrox mga) have settings like Option "Overlay" "24,8" to support multi-depth overlays. For these, use the "-cc 4" X server command line option to get a depth 24 default visual. The -overlay mode: Another option is if the system with overlay visuals is a Sun system running Solaris or SGI running IRIX you can use the [247]-overlay x11vnc option (Aug/2004) to have x11vnc use the Solaris XReadScreen(3X11) function to poll the "true view" of the whole screen at depth 24 TrueColor. XReadDisplay(3X11) is used on IRIX. This is useful for Legacy applications (older versions of Cadence CAD apps are mentioned by x11vnc users) that require the default depth be 8bpp, or the app will use a 8bpp visual even if depth 24 visuals are available, and so the default depth workaround described in the previous paragraph is not sufficient for these apps. It seems that Xorg is working toward supporting XReadDisplay(3X11) as part of the RENDER extension work. When it does support it and provides a library API x11vnc will be modified to take advantage of the feature to support -overlay on Linux, *BSD, etc. Until then see the -8to24 mode below. Misc. notes on -overlay mode: An amusing by-product of -overlay mode is that the mouse cursor shape is correct! (i.e. XFIXES is not needed). The -overlay mode may be somewhat slower than normal mode due to the extra framebuffer manipulations that must be performed. Also, on Solaris there is a bug in that for some popup menus, the windows they overlap will have painting errors (flashing colors) while the popup is up (a workaround is to disable SaveUnders by passing -su to Xsun, e.g. in your /etc/dt/config/Xservers file). The -8to24 mode: The [248]-8to24 x11vnc option (Jan/2006) is a kludge to try to dynamically rewrite the pixel values so that the 8bpp part of the screen is mapped onto depth 24 TrueColor. This is less robust than the -overlay mode because it is done by x11vnc outside of the X server. So only use it on OS's that do not support -overlay. The -8to24 mode will work if the default visual is depth 24 or depth 8. It scans for any windows within 3 levels of the root window that are 8bpp (i.e. legacy application), or in general ones that are not using the default visual. For the windows it finds it uses XGetSubImage() to retrieve the pixels values and uses the correct indexed colormap to create a depth 24 TrueColor view of the whole screen. This depth 24, 32bpp view is exported via VNC. Even on pure 8bpp displays it can be used as an alternative to [249]-flashcmap to avoid color flashing completely. This scheme is approximate and can often lead to painting errors. You can manually correct most painting errors by pressing 3 Alt_L's in a row, or by using something like: [250]-fixscreen V=3.0 to automatically refresh the screen every 3 seconds. Also -fixscreen 8=3.0 has been added to just refresh the non-default visual parts of the screen. In general the scheme uses many resources and may give rise to sluggish behavior. If multiple windows are using different 8bpp indexed colormaps all but one window may need to be iconified for the colors to be correct. There are a number of tunable parameters to try to adjust performance and painting accuracy. The option -8to24 nogetimage can give a nice speedup if the default depth 24 X server supports hiding the 8bpp bits in bits 25-32 of the framebuffer data. On very slow machines -8to24 poll=0.2,cachewin=5.0 gives an useful speedup. See the [251]-8to24 help description for information on tunable parameters, etc. Colors still not working correctly? Run xwininfo on the application with the incorrect colors to verify that the depth of its visual is different from the default visual depth (gotten from xdpyinfo). One possible workaround in this case is to use the [252]-id option to point x11vnc at the application window itself. If the application is complicated (lots of toplevel windows and popup menus) this may not be acceptable, and may even crash x11vnc (but not the application). It is theoretically possible to solve this problem in general (see xwd(1) for example), but it does not seem trivial or sufficiently fast for x11vnc to be able to do so in real time. The [253]-8to24 method does this approximately and is somewhat usable. Fortunately the [254]-overlay option works for Solaris machines with overlay visuals where most of this problem occurs. Q-17: How do I figure out the window id to supply to the -id windowid option? Run the xwininfo program in a terminal. It will ask you to click on the desired application window. After clicking, it will print out much information, including the window id (e.g. 0x6000010). Also, the visual and depth of the window printed out is often useful in debugging x11vnc [255]color problems. Also, as of Dec/2004 you can use "[256]-id pick" to have x11vnc run xwininfo(1) for you and after you click the window it extracts the windowid. Besides "pick" there is also "id:root" to allow you to go back to root window when doing remote-control. Q-18: Why don't menus or other transient windows come up when I am using the -id windowid option to view a single application window? This is related to the behavior of the XGetImage(3X11) and XShmGetImage() interfaces regarding backingstore, saveunders, etc. The way the image is retrieved depends on some aspects of how the X server maintains the display image data and whether other windows are clipping or obscuring it. See the XGetImage(3X11) man page for more details. If you disable BackingStore and SaveUnders in the X server you should be able to see these transient windows. If things are not working and you still want to do the single window polling, try the [257]-sid windowid option ("shifted" windowid). Q-19: My X display is depth 24 at 24bpp (instead of the normal depth 24 at 32bpp). I'm having lots of color and visual problems with x11vnc and/or vncviewer. What's up? First off, depth 24 at 24bpp (bpp=bits-per-pixel) is fairly uncommon and can cause problems in general. It also can be slower than depth 24 at 32bpp. You might want to switch to 32bpp (for XFree86 see the "-fbbpp 32", DefaultFbBpp, FbBpp and related options). Perhaps you have 24bpp because the video memory of the machine is low and the screen wouldn't fit in video RAM at 32bpp. For this case depth 16 at 16bpp might be an acceptable option. In any event x11vnc should handle depth 24 at 24bpp (although performance may be slower). There are some caveats involving the viewer however: The RealVNC Unix viewer cannot handle 24bpp from the server, it will say: "main: setPF: not 8, 16 or 32 bpp?" and exit. I have not checked the RealVNC Windows viewer. So you need to use the TightVNC Unix viewer. However there are some problems with that too. It seems libvncserver does not do 24bpp correctly with the Tight encoding. The colors and screen ultimately get messed up. So you have to use a different encoding with the TightVNC vncviewer, try "zlib", "hextile", or one of the other encodings (e.g. vncviewer -encodings "zlib hextile" ...). I have not checked the TightVNC or UltraVNC Windows viewers. It appears the older RealVNC Unix viewers (e.g. 3.3.3 and 3.3.7) can handle 24bpp from the server, so you may want to use those. They evidently request 32 bpp and libvncserver obliges. Now coming the opposite direction if you are running the vncviewer on the 24bpp display, TightVNC will fail with "Can't cope with 24 bits-per-pixel. Sorry." and RealVNC will fail with "main: Error: couldn't find suitable pixmap format" so evidently you cannot use 24bpp for the vncviewers to work on that X display. [Xterminals] Q-20: Can I use x11vnc to view and interact with an Xterminal (e.g. NCD) that is not running UNIX and so x11vnc cannot be run on it directly? You can, but it will likely be very wasteful of network bandwidth since you will be polling the X display over the network as opposed to over the local hardware. To do this, run x11vnc on a UNIX machine as close as possible network-wise (e.g. same switch) to the Xterminal machine. Use the [258]-display option to point the display to that of the Xterminal (you'll of course need basic X11 permission to do that) and also supply the [259]-noshm option (this enables the polling over the network). The response will likely be sluggish (maybe only one "frame" per second). This mode is not recommended except for "quick checks" of hard to get to X servers. Use something like "-wait 150" to cut down on the polling rate. You may also need [260]-flipbyteorder if the colors get messed up due to endian byte order differences. Q-21: How do I get my X permissions (MIT-MAGIC-COOKIE file) correct for a Unix/Linux machine acting as an Xterminal? If the X display machine is a traditional Xterminal (where the X server process runs on the Xterminal box, but all of the X client applications (mozilla, etc) run on a central server (aka "terminal server")), you will need to log into the Xterminal machine (i.e. get a shell running there) and then start the x11vnc program. If the Xterminal Linux/Unix machine is stripped down (e.g. no users besides root) that may be difficult. The next problem is the login Display Manager (e.g. gdm, kdm), and hence the MIT-MAGIC-COOKIE auth files, are on the central server and not on the Xterminal box where the X server and x11vnc processes are. So unless X permissions are completely turned off (e.g. "xhost +"), to run the x11vnc process on the Xterminal box the MIT-MAGIC-COOKIE auth file data (XAUTHORITY or $HOME/.Xauthority) must be accessible by or copied to the Xterminal. If $HOME/.Xauthority is exported via NFS (this is insecure of course, but has been going on for decades), then x11vnc can simply pick it up via NFS (you may need to use the [261]-auth option to point to the correct file). Other options include copying the auth file using scp, or something like: central-server> xauth nextract - xterm123:0 | ssh xterm123 xauth nmerge - and then, say, ssh from central-server to xterm123 to start x11vnc. Here "xterm123" refers to the computer acting as the Xterminal and "central-server" is the terminal server. You can use "xauth -f /path/to/cookie-file list" to examine the contents of the cookie(s) in a file "/path/to/cookie-file". See the xauth(1) manpage for more details. If the display name in the cookie file needs to be changed between the two hosts, see [262]this note on the "xauth add ..." command. A less secure option is to run something like "xhost +127.0.0.1" while sitting at the Xterminal box to allow cookie-free local access for x11vnc. You can run "xhost -127.0.0.1" after x11vnc connects if you want to go back to the original permissions. If the Xterminal is really stripped down and doesn't have any user accounts, NFS, etc. you'll need to contact your system administrator to set something up. It can be done!!! Some Xterminal projects have actually enabled "run locally" facilities for the running of an occasional app more efficiently locally on the Xterminal box (e.g. realplayer). Not recommended, but as a last resort, you could have x11vnc [263]poll the Xterminal Display over the network. For this you would run a "x11vnc -noshm ..." process on the central-server (and hope the network admin doesn't get angry...) Note: use of Display Manager (gdm, kdm, ...) auth cookie files (i.e. from /var/..., /tmp/..., or elsewhere) may require modification via xauth(1) to correctly include the display x11vnc refers to (e.g. "xauth -f cookie-file add :0 . 45be51ae2ce9dfbacd882ab3ef8e96b1", where the "45be51..." cookie value was found from an "xauth -f /path/to/original/cookie-file list") or other reasons. See xauth(1) manpage for full details on how to transfer an MIT-MAGIC-COOKIE between machines and displays. VNCviewer performance on Xterminals: This isn't related to x11vnc on Xterminals, but we mention it here anyway because of the similar issues. If you are on an Xterminal and want to use vncviewer to connect to a VNC server somewhere, then performance would be best if you ran the viewer on the Xterminal box. Otherwise, (i.e. running the viewer process on the central-server) all of the vncviewer screen drawing is done more inefficiently over the network. Something to consider, especially on a busy network. (BTW, this has all of the above permission, etc, problems: both vncviewer and x11vnc are X client apps desired to be run on the Xterminal box). [Sun Rays] Q-22: I'm having trouble using x11vnc with my Sun Ray session. The [264]Sun Ray technology is a bit like "VNC done in hardware" (the Sun Ray terminal device, DTU, playing the role of the vncviewer). Completely independent of that, the SunRay user's session is still an X server that speaks the X11 protocol and so x11vnc simply talks to the X server part to export the SunRay desktop to any place in the world (i.e. not only to a Sun Ray terminal device), creating a sort of "Soft Ray". Please see [265]this discussion of Sun Ray issues for solutions to problems. [Remote Control] Q-23: How do I stop x11vnc once it is running in the background? As of Dec/2004 there is a remote control feature. It can change a huge amount of things on the fly: see the [266]-remote and [267]-query options. To shut down the running x11vnc server just type "x11vnc -R stop". To disconnect all clients do "x11vnc -R disconnect:all", etc. If the [268]-forever option has not been supplied, x11vnc will automatically exit after the first client disconnects. In general you will have to kill the x11vnc process This can be done via: "kill NNNNN" (where NNNNN is the x11vnc process id number found from ps(1)), or "pkill x11vnc", or "killall x11vnc" (Linux only). If you have not put x11vnc in the background via the [269]-bg option or shell & operator, then simply press Ctrl-C in the shell where x11vnc is running to stop it. Potential Gotcha: If somehow your Keypress of Ctrl-C went through x11vnc to the Xserver that then delivered it to x11vnc it is possible one or both of the Ctrl or C keys will be left stuck in the pressed down state in the Xserver. Tapping the stuck key (either via a new x11vnc or at the physical console) will release it from the stuck state. If the keyboard seems to be acting strangely it is often fixed by tapping Ctrl, Shift, and Alt. Alternatively, the [270]-clear_mods option and [271]-clear_keys option can be used to release pressed keys at startup and exit. Q-24: Can I change settings in x11vnc without having to restart it? Can I remote control it? Look at the [272]-remote (same as -R) and [273]-query (same as -Q) options added in Dec/2004. They allow nearly everything to be changed dynamically and settings to be queried. Examples: "x11vnc -R shared", "x11vnc -R forever", "x11vnc -R scale:3/4", "x11vnc -Q modtweak", "x11vnc -R stop", "x11vnc -R disconnect:all", etc.. These commands do not start a x11vnc server, but rather communicate with one that is already running. The X display (X11VNC_REMOTE property) is used as the communication channel, so the X permissions and DISPLAY must be set up correctly for communication to be possible. There is also a simple Tcl/Tk gui based on this remote control mechanism. See the [274]-gui option for more info. You will need to have Tcl/Tk (i.e. /usr/bin/wish) installed for it to work. It can also run in the system tray: "-gui tray" or as a standalone icon window: "-gui icon". [Security and Permissions] Q-25: How do I create a VNC password for use with x11vnc? You may already have one in $HOME/.vnc/passwd if you have used, say, the vncserver program from the regular RealVNC or TightVNC packages (i.e. launching the Xvnc server). Otherwise, you could use the vncpasswd(1) program from those packages. As of Jun/2004 x11vnc supports the -storepasswd "pass" "file" [275]option, which is the same functionality of storepasswd. Be sure to quote the "pass" if it contains shell meta characters, spaces, etc. Example: x11vnc -storepasswd 'sword*fish' $HOME/myvncpasswd You then use the password via the x11vnc option: "[276]-rfbauth $HOME/myvncpasswd" If you do not supply any arguments: x11vnc -storepasswd you will be prompted for a password to save to ~/.vnc/passwd (your keystrokes when entering the password will not be echoed to the screen). x11vnc also has the [277]-passwdfile and -passwd/-viewpasswd plain text (i.e. not obscured like the -rfbauth VNC passwords) password options. You can use the [278]-usepw option to automatically use any password file you have in ~/.vnc/passwd or ~/.vnc/passwdfile (the latter is used with the -passwdfile option). x11vnc -usepw -display :0 ... If neither file exists you are prompted to store a password in ~/.vnc/passwd. If a password file cannot be found or created x11vnc exits immediately. Q-26: Can I make it so -storepasswd doesn't show my password on the screen? You can use the vncpasswd program from RealVNC or TightVNC mentioned above. As of Jan/2006 the -storepasswd option without any arguments will not echo your password as you type it and save the file to ~/.vnc/passwd: # x11vnc -storepasswd Enter VNC password: Verify password: Write password to /home/myname/.vnc/passwd? [y]/n Password written to: /home/myname/.vnc/passwd Q-27: Can I have two passwords for VNC viewers, one for full access and the other for view-only access to the display? Yes, as of May/2004 there is the [279]-viewpasswd option to supply the view-only password. Note the full-access password option [280]-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 [281]-passwdfile option to specify a file containing plain text passwords. Presumably this file is readable only by you, and ideally it is located on the machine x11vnc is run on (to avoid being snooped on over the network). The first line of this file is the full-access password. If there is a second line in the file and it is non-blank, it is taken as the view-only password. (use "__EMPTY__" to supply an empty one). View-only passwords currently do not work for the [282]-rfbauth password option (standard VNC password storing mechanism). FWIW, note that although the output (usually placed in $HOME/.vnc/passwd) by the vncpasswd or storepasswd programs (or from x11vnc -storepasswd) looks encrypted they are really just obscured to avoid "casual" password stealing. It takes almost no skill to figure out how to extract the plain text passwords from $HOME/.vnc/passwd since it is very straight-forward to work out what to do from the VNC source code. Q-28: Can I have as many full-access and view-only passwords as I like? Yes, as of Jan/2006 in the libvncserver CVS the [283]-passwdfile option has been extended to handle as many passwords as you like. You put the view-only passwords after a line __BEGIN_VIEWONLY__. You can also easily annotate and comment out passwords in the file. You can have x11vnc re-read the file dynamically when it is modified. Q-29: Does x11vnc support Unix usernames and passwords? Can I further limit the set of Unix usernames who can connect to the VNC desktop? Until the VNC protocol and libvncserver support this things will be approximate at best. Update: as of Feb/2006 x11vnc has the [284]-unixpw option that does this outside of the VNC protocol and libvncserver. The standard su(1) program is used to validate the user's password. A familiar "login:" and "Password:" dialog is presented to the user on a black screen inside the vncviewer. The connection is dropped if the user fails to supply the correct password in 3 tries or does not send one before a 25 second timeout. Existing clients are view-only during this period. A list of allowed Unix usernames may also be supplied along with per-user settings. There is also the [285]-unixpw_nis option for non-shadow-password (typically NIS environments, hence the name) systems where the traditional getpwnam() and crypt() functions are used instead of su(1). The encrypted user passwords must be accessible to the user running x11vnc in -unixpw_nis mode, otherwise the logins will always fail even when the correct password is supplied. See ypcat(1) and shadow(5). Two settings are enforced in the -unixpw and -unixpw_nis modes to provide extra security: the 1) [286]-localhost and 2) [287]-stunnel options. Without these one might send the Unix username and password data in clear text over the network which is a very bad idea. They can be relaxed if you want to provide encryption other than stunnel (the stunnel constraint is automatically relaxed if SSH_CONNECTION is set and indicates you have ssh-ed in, however the -localhost requirement is still enforced). The two -unixpw modes have been tested on Linux, Solaris, HP-UX, Tru64, FreeBSD, OpenBSD, and NetBSD. Additional testing is appreciated. For the last 4 it appears that su(1) will not prompt for a password if su-ing to oneself. Since x11vnc requires a password prompt from su, those logins will fail even when the correct password is supplied. On *BSD it appears this can be corrected by commenting out the pam_self.so entry in /etc/pam.d/su. Previous discussion: One approximate method involves starting x11vnc with the [288]-localhost option. This basically requires the viewer user to log into the workstation where x11vnc is running via their Unix username and password, and then somehow set up a port redirection of his vncviewer connection to make it appear to emanate from the local machine. As discussed above, ssh is useful for this: "ssh -L 5900:localhost:5900 user@hostname ..." See the ssh wrapper scripts mentioned [289]elsewhere on this page. [290]stunnel does this as well. Of course a malicious user could allow other users to get in through his channel, but that is a problem with every method. Another thing to watch out for is a malicious user on the viewer side (where ssh is running) trying to sneak in through the ssh port redirection there. Regarding limiting the set of Unix usernames who can connect, the traditional way would be to further require a VNC password to supplied (-rfbauth, -passwd, etc) and only tell the people allowed in what the VNC password is. A scheme that avoids a second password involves using the [291]-accept option that runs a program to examine the connection information to determine which user is connecting from the local machine. That may be difficult to do, but, for example, the program could use the ident service on the local machine (normally ident should not be trusted over the network, but on the local machine it should be accurate: otherwise root has been compromised and so there are more serious problems! Unfortunately recent Linux distros seem to provide a random string (MD5 hash?) instead of the username). An example script passed in via -accept scriptname that deduces the Unix username and limits who can be accepted might look something like this: #!/bin/sh if [ "$RFB_CLIENT_IP" != "127.0.0.1" -o "$RFB_SERVER_IP" != "127.0.0.1" ]; then exit 1 # something fishy... reject it. fi user=`echo "$RFB_CLIENT_PORT, $RFB_SERVER_PORT" | nc -w 1 $RFB_CLIENT_IP 113 \ | grep 'USERID.*UNIX' | head -1 | sed -e 's/[\r ]//g' | awk -F: '{print $4}'` for okuser in fred barney wilma betty do if [ "X$user" = "X$okuser" ]; then exit 0 # accept it fi done exit 1 # reject it For this to work with ssh port redirection, the ssh option UsePrivilegeSeparation must be enabled otherwise the userid will always be "root". Q-30: Why does x11vnc exit as soon as the VNC viewer disconnects? And why doesn't it allow more than one VNC viewer to connect at the same time? These defaults are simple safety measures to avoid someone unknowingly leaving his X11 desktop exposed (to the internet, say) for long periods of time. Use the [292]-forever option (aka -many) to have x11vnc wait for more connections after the first client disconnects. Use the [293]-shared option to have x11vnc allow multiple clients to connect simultaneously. Recommended additional safety measures include using ssh ([294]see above), stunnel, or a VPN to authenticate and encrypt the viewer connections or to at least use the -rfbauth passwd-file [295]option to use VNC password protection (or [296]-passwdfile) It is up to YOU to apply these security measures, they will not be done for you automatically. Q-31: Can I limit which machines incoming VNC clients can connect from? Yes, look at the [297]-allow and [298]-localhost options to limit connections by hostname or IP address. E.g. x11vnc -allow 192.168.0.1,192.168.0.2 for those two hosts or x11vnc -allow 192.168.0. for a subnet. For individual hosts you can use the hostname instead of the IP number, e.g.: "-allow snoopy", and "-allow darkstar,wombat". Note that -localhost is the same as "-allow 127.0.0.1" For more control, build libvncserver with libwrap support [299](tcp_wrappers) and then use /etc/hosts.allow See hosts_access(5) for complete details. Q-32: How do I build x11vnc/libvncserver with libwrap (tcp_wrappers) support? Here is one way to pass this information to the configure script: env CPPFLAGS=-DUSE_LIBWRAP LDFLAGS=-lwrap ./configure then run make as usual. This requires libwrap and its development package (tcpd.h) to be installed on the build machine. If additional CPPFLAGS or LDFLAGS options are needed supply them as well using quotes. The resulting x11vnc then uses libwrap/tcp_wrappers for connections. The service name you will use in /etc/hosts.allow and /etc/hosts.deny is "vnc", e.g.: vnc: 192.168.100.3 .example.com Note that if you run x11vnc out of [300]inetd you do not need to build x11vnc with libwrap support because the /usr/sbin/tcpd reference in /etc/inetd.conf handles the tcp_wrappers stuff. Q-33: Can I have x11vnc only listen on one network interface (e.g. internal LAN) rather than having it listen on all network interfaces and relying on -allow to filter unwanted connections out? As of Mar/2005 there is the "[301]-listen ipaddr" option that enables this. For ipaddr either supply the desired network interface's IP address (or use a hostname that resolves to it) or use the string "localhost". For additional filtering simultaneously use the "[302]-allow host1,..." option to allow only specific hosts in. This option is useful if you want to insure that no one can even begin a dialog with x11vnc from untrusted network interfaces (e.g. ppp0). The option [303]-localhost now implies "-listen localhost" since that is what most people expect it to do. Q-34: Now that -localhost implies listening only on the loopback interface, how I can occasionally allow in a non-localhost via the -R allowonce remote control command? To do this specify "[304]-allow localhost". Unlike [305]-localhost this will leave x11vnc listening on all interfaces (but of course only allowing in local connections, e.g. ssh redirs). Then you can later run "x11vnc -R allowonce:somehost" or use to gui to permit a one-shot connection from a remote host. Note that if you do a lot of changing of the listening interface ([306]-listen option) via remote control or gui, you may need to also manually adjust the [307]-allow list if you unexpectedly get into a state where the allow list cannot match any hosts that would be coming in on the listening interface. If you just toggle [308]-localhost on and off x11vnc should see to it that you never get into such a state. Q-35: Can I fine tune what types of user input are allowed? E.g. have some users just be able to move the mouse, but not click or type anything? As of Feb/2005, the [309]-input option allows you to do this. "K", "M", and "B" stand for Keystroke, Mouse-motion, and Button-clicks, respectively. The setting: "-input M" makes attached viewers only able to move the mouse. "-input KMB,M" lets normal clients do everything and enables view-only clients to move the mouse. These settings can also be applied on a per-viewer basis via the remote control mechanism or the GUI. E.g. x11vnc -R input:hostname:M Q-36: Can I prompt the user at the local X display whether the incoming VNC client should be accepted or not? Can I decide to make some clients view-only? How about running an arbitrary program to make the decisions? Yes, look at the "[310]-accept command" option, it allows you to specify an external command that is run for each new client. (use quotes around the command if it contains spaces, etc.). If the external command returns 0 the client is accepted, otherwise the client is rejected. See below how to also accept clients view-only. The external command will have the RFB_CLIENT_IP environment variable set to the client's numerical IP address, RFB_CLIENT_PORT its port number. Similarly for RFB_SERVER_IP and RFB_SERVER_PORT to allow identification of the tcp virtual circuit. DISPLAY will be set to that of the X11 display being polled. Also, RFB_X11VNC_PID is set to the x11vnc process id (e.g. in case you decided to kill it), RFB_CLIENT_ID will be an id number, and RFB_CLIENT_COUNT the number of other clients currently connected. RFB_MODE will be "accept". As a special case, "-accept popup" will instruct x11vnc to create its own simple popup window. To accept the client press "y" or click mouse on the "Yes" button. To reject the client press "n" or click mouse on the "No" button. To accept the client View-only, press "v" or click mouse on the "View" button. If the [311]-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 [312]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 [313]dtVncPopup for use in CDE environments to do the same sort of thing. Information on how to use it is found at the top of the file. He encourages you to provide feedback to him to help improve the script. Note that in all cases x11vnc will block while the external command or popup is being run, so attached clients will not receive screen updates, etc during this period. To run a command when a client disconnects, use the "[314]-gone command" option. This is for the user's convenience only: the return code of the command is not interpreted by x11vnc. The same environment variables are set as in "-accept command" (except that RFB_MODE will be "gone"). Q-37: I start x11vnc as root because it is launched via inetd(1) or a display manager like gdm(1). Can I have x11vnc later switch to a different user? As of Feb/2005 x11vnc has the [315]-users option that allows things like this. Please read the documentation on it (also in the x11vnc -help output) carefully for features and caveats. It's use can often decrease security unless care is taken. BTW, a nice use of it is "-users +nobody" that switches to the Unix user nobody right after connections to the X display are established. In any event, while running x11vnc as root, remember it comes with no warranty ;-). Q-38: I use a screen-lock when I leave my workstation (e.g. xscreensaver or xlock). When I remotely access my workstation desktop via x11vnc I can unlock the desktop fine, but I am worried people will see my activities on the physical monitor. What can I do to prevent this, or at least make it more difficult? Probably most work environments would respect your privacy if you powered off the monitor. Also remember if people have physical access to your workstation they basically can do anything they want with it (e.g. install a backdoor for later use, etc). In any event, as of Jun/2004 there is an experimental utility to make it more difficult for nosey people to see your x11vnc activities. The source for it is [316]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 [317]-accept option and told to exit via the [318]-gone option (the vnc client user should obviously re-lock the screen before disconnecting!). Instructions can be found in the source code for the utility at the above link. Q-39: Can I have x11vnc automatically lock the screen when I disconnect the VNC viewer? Yes, a user mentions he uses the [319]-gone option under CDE to run a screen lock program: x11vnc -display :0 -forever -gone 'dtaction LockDisplay' Other possibilities are: x11vnc -display :0 -forever -gone 'xscreensaver-command -lock' x11vnc -display :0 -forever -gone 'kdesktop_lock' x11vnc -display :0 -forever -gone 'xlock &' Here is a scheme using the [320]-afteraccept option (in version 0.7.3) to unlock the screen after the first valid VNC login and to lock the screen after the last valid VNC login disconnects: x11vnc -display :0 -forever -shared -afteraccept ./myxlocker -gone ./myxlocke r Where the script ./myxlocker is: #!/bin/sh #/usr/bin/env | grep RFB_ | sort # for viewing RFB_* settings. if [ "X$RFB_MODE" = "Xafteraccept" ]; then if [ "X$RFB_STATE" = "XNORMAL" ]; then # require valid login if [ "X$RFB_CLIENT_COUNT" = "X1" ]; then killall xlock # Linux only. fi fi elif [ "X$RFB_MODE" = "Xgone" ]; then if [ "X$RFB_STATE" = "XNORMAL" ]; then # require valid login if [ "X$RFB_CLIENT_COUNT" = "X0" ]; then xlock -mode blank & fi fi fi [Encrypted Connections] Q-40: How can I tunnel my connection to x11vnc via an encrypted SSH channel between two Unix machines? See the description earlier on this page on [321]how to tunnel VNC via SSH from Unix to Unix. A number of ways are described along with some issues you may encounter. Other secure encrypted methods exists, e.g. stunnel, IPSEC, various VPNs, etc. Q-41: How can I tunnel my connection to x11vnc via an encrypted SSH channel from Windows using an SSH client like Putty? [322]Above we described how to tunnel VNC via SSH from Unix to Unix, you may want to review it. To do this from Windows using Putty it would go something like this: * In the Putty dialog window under 'Session' enter the hostname or IP number of the Unix machine with display to be viewed. * Make sure the SSH protocol is selected and the server port is correct. * Under 'Connections/SSH/Tunnels' Add a Local connection with 'Source port: 5900' and 'Destination: localhost:5900' * Log into the remote machine by pressing 'Open' and supplying username, password, etc. * In that SSH shell, start up x11vnc by typing the command: x11vnc -display :0 plus any other desired options (e.g. -localhost). * Finally, start up your VNC Viewer in Windows and enter 'localhost:0' as the VNC server. You can keep all of the settings in a Putty 'Saved Session'. Also, once everything is working, you can consider putting x11vnc -display :0 (plus other cmdline options) in the 'Remote command' Putty setting under 'Connections/SSH'. It is likely possible to script the whole process in a BAT file including launching the VNC viewer by using the plink Putty utility. Send us the script if you get that working. For extra protection feel free to run x11vnc with the [323]-localhost and [324]-rfbauth/[325]-passwdfile options. If the machine you SSH into via Putty is not the same machine with the X display you wish to view (e.g. your company provides incoming SSH access to a gateway machine), then you need to change the above Putty dialog setting to: 'Destination: otherhost:5900', Once logged in, you'll need to do a second login (ssh or rsh) to the workstation machine 'otherhost' and then start up x11vnc on it. This can also be automated by [326]chaining ssh's. As discussed [327]above another option is to first start the VNC viewer in "listen" mode, and then launch x11vnc with the "[328]-connect localhost" option to establish the reverse connection. In this case a Remote port redirection (not Local) is needed for port 5500 instead of 5900 (i.e. 'Source port: 5500' and 'Destination: localhost:5500' for a Remote connection). Q-42: How can I tunnel my connection to x11vnc via an encrypted SSL channel using an external tool like stunnel? It is possible to use a "lighter weight" encryption setup than SSH or IPSEC. SSL tunnels such as [329]stunnel provide an encrypted channel without the need for Unix users, passwords, and key passphrases required for ssh (and at the other extreme can also provide a complete signed certificate chain of trust). OTOH, since SSH is usually installed everywhere and firewalls often let its port through, ssh is frequently the path of least resistance (it also nicely manages public keys for you). Update: As of Feb/2006 x11vnc has the options [330]-ssl, [331]-stunnel, and [332]-sslverify to provide integrated SSL schemes. They are discussed [333]in the Next FAQ (you may want to skip to it now). Here are some basic examples using [334]stunnel but the general idea for any SSL tunnel utility is the same: * Start up x11vnc and constrain it to listen on localhost. * Then start up the SSL tunnel running on the same machine to forward incoming connections to that x11vnc. * Set up and run a similar SSL tunnel for the outgoing connection on the VNC viewer machine pointing it to the SSL/x11vnc server. * Optionally, set up server (or even client) public/private keys for use in authenticating one side to the other. * Finally, start the VNC Viewer and tell it to connect to the local port (e.g. a vnc display localhost:0) where its outgoing SSL tunnel is listening. We'll first use the stunnel version 3 syntax since it is the most concise and Unixy. Start up x11vnc listening on port 5900: x11vnc -display :0 -rfbport 5900 -localhost -bg -passwdfile ~/mypass Then start stunnel (version 3) with this command: stunnel -d 5901 -r 5900 -p /path/to/stunnel.pem The above two commands are run on host "far-away.east". The stunnel.pem is the self-signed PEM file certificate created when stunnel is built. One can also create certificates [335]signed by Certificate Authorities or self-signed if desired using the x11vnc utilities described there. Next, on the VNC viewer side we need an SSL tunnel to encrypt the outgoing connection. The nice thing is any SSL tunnel can be used because the protocol is a standard. For this example we'll also use stunnel on the viewer side on Unix. First start up the client-side stunnel: stunnel -c -d localhost:5902 -r far-away.east:5901 Then point the viewer to the local tunnel on port 5902: vncviewer -encodings "copyrect tight zrle hextile" localhost:2 That's it. (note that the [336]ssl_vncviewer script can automate this.) Be sure to use a VNC password because unlike ssh by default the encrypted SSL channel provides no authentication (only privacy). With some extra configuration one could also set up certificates to provide authentication of either or both sides as well (and hence avoid man-in-the-middle attacks). See the stunnel and openssl documentation and also [337]the key management section for details. stunnel has also been ported to Windows, and there are likely others to choose from for that OS. Much info for using it on Windows can be found at the stunnel site and in this [338]article The article also shows the detailed steps to set up all the authentication certificates. (for both server and clients, see also the [339]x11vnc utilities that do this). The default Windows client setup (no certs) is simpler and only 4 files are needed in a folder: stunnel.exe, stunnel.conf, libssl32.dll, libeay32.dll. We used an stunnel.conf containing: # stunnel.conf: client = yes options = ALL [myvncssl] accept = 5902 connect = far-away.east:5901 then double click on the stunnel.exe icon to launch it (followed by pointing the VNC viewer to localhost:2). stunnel inetd-like mode: As an aside, if you don't like the little "gap" of unencrypted TCP traffic (and a localhost listening socket) on the local machine between stunnel and x11vnc it can actually be closed by having stunnel start up x11vnc in [340]-inetd mode: stunnel -p /path/to/stunnel.pem -P none -d 5900 -l ./x11vnc_sh Where the script x11vnc_sh starts up x11vnc: #!/bin/sh x11vnc -q -inetd -display :0 -passwdfile ~/mypass Note that this creates a separate x11vnc process for each incoming connection (as any inetd x11vnc usage would), but for the case of normally just one viewer at a time it should not be a big problem. stunnel 4 syntax: Somewhat sadly, the stunnel version 4 syntax is not so amenable to the command line or scripts. You need to create a config file with the parameters. E.g.: stunnel x11vnc.cfg Where the file x11vnc.cfg contains: foreground = yes pid = cert = /path/to/stunnel.pem [x11vnc_stunnel] accept = 5901 connect = 5900 One nice thing about version 4 is often the PEM file does not need to be specified because stunnel finds it in its installed area. One other gotcha the PEM file is usually only readable by root (it has the private key afterall), so you'll need to relax the permissions or make a copy that the user running x11vnc/stunnel can read. SSL VNC Viewers: Regarding VNC viewers that "natively" do SSL unfortunately there do not seem to be many. UltraVNC has encryption plugin, but we have not tried it (it does not seem to be SSL). Commercial versions of VNC seem to have some SSL built in, but we haven't tried those either and they probably wouldn't work since the SSL negotiation is likely embedded in the VNC protocol unlike our case where it is external. Note: as of Mar/2006 libvncserver/x11vnc provides a [341]SSL-enabled Java applet that can be served up via the [342]-httpdir or [343]-http options when [344]-ssl is enabled. It will also be served via HTTPS via either the VNC port (e.g. https://host:5900/) or a 2nd port via the [345]-https option. In general current SSL VNC solutions are not particularly "seemless". But it can be done, and with a wrapper script on the viewer side and the [346]-stunnel option on the server side it works well and is convenient. Here is a simple script [347]ssl_vncviewer that automates running stunnel on the VNC viewer side on Unix a little more carefully than the commands printed above. (One could probably do a similar thing with a .BAT file on Windows in the stunnel folder.) Q-43: Does x11vnc have built-in SSL tunneling? You can read about non-built-in methods [348]in the Previous FAQ SSL tunnels provide an encrypted channel without the need for Unix users, passwords, and key passphrases required for ssh (and at the other extreme can also provide a complete signed certificate chain of trust). OTOH, since SSH is usually installed everywhere and firewalls often let its port through, ssh is frequently the path of least resistance. Built-in SSL x11vnc options: As of Feb/2006 the x11vnc [349]-ssl and [350]-stunnel options automate the SSL tunnel creation on the x11vnc server side. An [351]SSL-enabled Java Viewer applet also provided that can be served via http or https to automate SSL on the client side. The [352]-ssl mode uses the [353]www.openssl.org library if available at build time. The [354]-stunnel mode requires the [355]www.stunnel.org command stunnel(8) to be installed on the system. Both modes require an SSL certificate and key (i.e. .pem file). These are usually created via the openssl(1) (in fact in for options "-ssl" or "-stunnel SAVE" it will run openssl for you automatically). So the SSL is not completely "built-in" since these external tools need to be installed, but at least x11vnc runs them for you automatically. An -stunnel example: x11vnc -display :0 -stunnel /path/to/stunnel.pem -passwdfile ~/mypass You'll get output like this: The VNC desktop is: localhost:50 The SSL VNC desktop is: far-away.east:0 PORT=5950 SSLPORT=5900 That indicates stunnel is listening on port 5900 for incoming SSL-wrapped VNC connections from viewers. x11vnc is listening for local connections on port 5950 in this case (remote viewers cannot connect to it directly). For -stunnel to work the stunnel command must be installed on the machine and available in PATH (note stunnel is often installed in sbin directories rather than bin). An -ssl example: x11vnc -display :0 -ssl -passwdfile ~/mypass You'll get output like this: 09/04/2006 19:27:35 Creating a temporary, self-signed PEM certificate... 09/04/2006 19:27:35 ... The SSL VNC desktop is: far-away.east:0 PORT=5900 SSLPORT=5900 In this case openssl(1) was used to create a temporary PEM automatically. As seen above, the PEM (privacy enhanced mail) file does not need to be supplied if the openssl(1) command is available in PATH, in that case a self-signed, temporary certificate good only for the single x11vnc session is created (this may take a while on very slow machines). In general, the PEM file contains both the Certificate (i.e. public key) and the Private Key. Because of the latter, the file should be protected from being read by untrusted users. The best way to do this is to encrypt the key with a passphrase (note however this requires supplying the passphrase each time x11vnc is started up). See the discussion on [356]x11vnc Key Management for some utilities provided for creating and managing certificates and keys and even for creating your own Certificate Authority (CA) for signing VNC server and client certificates. This may be done by importing the certificate into Web Browser or Java plugin keystores, or pointing stunnel to it. The wrapper script [357]ssl_vncviewer provides an example on unix (-verify option). Here are some notes on the simpler default (non-CA) operation. To have x11vnc save the generated certificate and key, use the "SAVE" keyword like this: x11vnc -ssl SAVE -display :0 ... x11vnc -stunnel SAVE -display :0 ... This way it will be saved in the default directory ~/.vnc/certs/ as server.crt (the certificate only) and server.pem (both certificate and private key). This opens up the possibility of copying the server.crt to machines where the VNC Viewer will be run to enable authenticating the x11vnc SSL VNC server to the clients. When authentication takes place this way (or via the more sophisticated CA signing described [358]here), then Man-In-The-Middle-Attacks are prevented. Otherwise, the SSL encryption only provides protection against passive network traffic "sniffing". Nowadays, most people seem mostly concerned about only the latter (and the default x11vnc SSL modes protect against it.) One can test to some degree that SSL is working after starting x11vnc with the -stunnel or -ssl option. From another machine one can use the openssl command something like this: openssl s_client -debug -msg -showcerts -connect far-away.east:5900 After all of the debugging output and informational messages you'll see the string "RFB 003.007" that came from x11vnc. Pointing a web browser connecting to: https://far-away.east:5900/ and then viewing the SSL certificate information about the connection in the panels will also work. Note: If you serve up the SSL enabled Java VNC Viewer via something like: x11vnc -ssl -httpdir /usr/local/share/x11vnc/classes/ssl (or just the -http option), you can test it out completely using that, including using https to download it into the browser and connect to x11vnc. See the [359]next FAQ for SSL enabled VNC Viewers. Q-44: How do I use VNC Viewers with built-in SSL tunneling? Notes on the SSL enabled Java VNC Viewer provided in classes/ssl/VncViewer.jar: The SSL enabled Java VNC Viewer (VncViewer.jar) in the x11vnc package supports only SSL based connections by default (set the applet parameter disableSSL=yes in index.vnc to override). As mentioned above the [360]-httpdir can be used to specify the path to .../classes/ssl. A typical location might be /usr/local/share/x11vnc/classes/ssl. Or the [361]-http can be used to try to have it find the directory automatically. The Java viewer uses SSL to communicate securely with x11vnc. Note that the applet can optionally also be downloaded into your web browser via https (i.e. http over SSL). This way the HTML page and the Java applet itself are delivered securely (as opposed to only the VNC traffic being encrypted). For this case the output will be something like this: x11vnc -ssl -http ... The SSL VNC desktop is: far-away.east:0 Java SSL viewer URL: https://far-away.east:5900/ Java SSL viewer URL: http://far-away.east:5800/ PORT=5900 SSLPORT=5900 Indicating the two URLs (the first one encrypted, the second not) one could point the web browser at to get the VNC viewer applet. The https service provided thru the actual VNC port (5900 in the above example) can be slow or unreliable at times (it has to read some input and try to guess if the connection is VNC or HTTP). If it is unreliable and you still want to serve the Java applet via https, use the [362]-https option to get an additional port dedicated to https (its URL will also be printed in the output). Another possibility is to add the GET applet parameter: https://far-away.east:5900/?GET=1 This will have the VNC Viewer send a special HTTP GET string "GET /request.https.vnc.connection HTTP/1.0 that x11vnc will more quickly notice is a request for a VNC connection. Otherwise it must wait for a timeout to expire before it assumes a VNC connection. You may also use "?GET=somestring" to have /somestring prepended to /request.https.vnc.connection". If you need to have slashes "/" in the string use "_2F_" (a deficiency in libvncserver prevents using the more natural "%2F". If you do serve the SSL enabled Java viewer via https be prepared for quite a number of "are you sure you trust this site?" dialogs: * First from the Web browser that cannot verify the self-signed certificate when it downloads index.vnc. * From the Web browser noting that the common name on the certificate does not match the hostname of the remote machine. * Next from the Java VM that cannot verify the self-signed certificate when it downloads VncViewer.jar. * And also from the Java VM noting that the common name on the certificate does not match the hostname of the remote machine. * Finally from the Java VncViewer applet itself saying it cannot verify the certificate! (or a popup asking you if you want to see the certificate.) Note that sometimes if you pause too long at one of the above dialogs then x11vnc may exceed a timeout and assume the current socket connection is VNC instead of the HTTPS it actually is (but since you have paused too long at the dialog the GET request comes too late). Often hitting Reload and going through the dialogs more quickly will let you connect. Use the [363]-https option if you want a dedicated port for HTTPS connections instead of sharing the VNC port. Notes on the VNC Viewer ssl_vncviewer wrapper script: If you want to use a native VNC Viewer with the SSL enabled x11vnc you will need to run an external SSL tunnel on the Viewer side. There do not seem to be any native SSL VNC Viewers outside of the x11vnc package. The basic ideas of doing this were discussed [364]for external tunnel utilities here. The [365]ssl_vncviewer script provided with x11vnc can set up the stunnel tunnel automatically on unix as long as the stunnel command is installed on the Viewer machine and available in PATH (and vncviewer too of course). Here are some examples: 1) ssl_vncviewer far-away.east:0 2) ssl_vncviewer far-away.east:0 -encodings "copyrect tight zrle hextile" 3) ssl_vncviewer -verify ./server.crt far-away.east:0 4) ssl_vncviewer -mycert ./client.pem far-away.east:0 5) ssl_vncviewer -proxy far-away.east:8080 myworkstation:0 The first one is the default mode and accepts the x11vnc certificate without question. The second one is as the first, but adds the -encodings options to the vncviewer command line. The third one requires that the x11vnc server authenticate itself against the certificate in the file ./server.crt (e.g. one created by "x11vnc -ssl SAVE" and copied to the VNC viewer machine). The fourth one is for VNC Viewer authentication, it uses ./client.pem to authenticate itself to x11vnc. One can supply both -verify and -mycert simultaneously. The fifth one shows that Web proxies can be used if that is the only way to get out of the firewall. If the "double proxy" situation arises separate the two by commas. See [366]this page for more information on how Web proxies come into play. If one uses a Certificate Authority (CA) scheme described [367]here, the wrapper script would use the CA cert instead of the server cert: 3') ssl_vncviewer -verify ./cacert.crt far-away.east:0 Q-45: How do I use VNC Viewers with built-in SSL tunneling when going through a Web Proxy? The SSL enabled Java VNC Viewer and firewall Proxies: SSL/https aside, there is a general problem with Firewall Proxies and Java Applets that open sockets. The applet is downloaded successfully (through the browser) using http and the proxy, but when the applet tries to reconnect to the originating host (the only one allowed by security) it does not use the proxy channel. So it cannot reconnect to the server the applet came from! We have found a convenient workaround: in the directory where VncViewer.jar resides there is a digitally signed version of the same applet called SignedVncViewer.jar. Since the applet is digitally signed, there will be an additional dialog from the Java VM plugin asking you if you want to trust the applet fully. You should say "Yes". If you do, the applet will be run in a mode where it can try to determine the firewall proxy host name and port (it will ask you for them if it cannot find them). This way it can connect directly to the Proxy and then request the CONNECT method to be redirected to the originating host (the x11vnc VNC Server). SSL is then layered over this socket. To do this you should use the proxy.vnc HTML file like via this URL in your browser: https://yourmachine.com:5900/proxy.vnc (instead of the unsigned one in https://yourmachine.com:5900/ that gives the default index.vnc) Note that the [368]ssl_vncviewer stunnel wrapper script can use Web proxies as well. Proxies that limit CONNECT to ports 443 and 563: Things become trickier if the proxy restricts which CONNECT ports can be redirected to. For security, some (most?) proxies only allow port 443 (HTTPS) and 563 (SNEWS) by default. In this case, the only thing to do is run x11vnc on that low port, e.g. "-rfbport 443", (or use a port redirection on, say, a firewall or router port 443 to the internal machine). If you do such a redirection to an internal machine and x11vnc is not listening on port 443, you will probably need to edit proxy.vnc. Suppose the SSL x11vnc server was listening on port 5901. YOu should change the line in proxy.vnc from: to: Since otherwise $PORT will be expanded to 5901 by x11vnc and the viewer applet will fail to connect to that port. Another way to acheive the same thing is to use the applet PORT parameter: https://yourmachine.com/proxy.vnc?PORT=443 this is cleaner because it avoids editing the file, but requires more parameters in the URL. To use the GET [369]trick discussed above, do: https://yourmachine.com/proxy.vnc?PORT=443&GET=1 Q-46: Can Apache web server act as a gateway for users to connect via SSL from the Internet with a Web browser to x11vnc running on their workstations behind a firewall? Yes. You will need to configure apache to forward these connections. It is discussed [370]here. This provides a clean alternative to the traditional method where the user uses SSH to log in through the gateway to create the encrypted port redirection to x11vnc running on her desktop. Q-47: Can I create and use my own SSL Certificate Authority (CA) with x11vnc? Yes, see [371]this page for how to do this and the utility commands x11vnc provides to create and manage many types of certificates and private keys. [Display Managers and Services] Q-48: How can I run x11vnc as a "service" that is always available? There are a number of ways to do this. The primary thing you need to decide is whether you want x11vnc to connect to the X session on the machine 1) regardless of who (or if anyone) has the X session, or 2) only if a certain user has the X session. Because X sessions are protected by X permissions (MIT-MAGIC-COOKIE files XAUTHORITY and $HOME/.Xauthority) the automatically started x11vnc will of course need to have sufficient permissions to connect to the X display. Here are some ideas: * Use the description under "Continuously" in the [372]FAQ on x11vnc and Display Managers * Use the description in the [373]FAQ on x11vnc and inetd(1) * Start x11vnc from your $HOME/.xsession (or $HOME/.xinitrc) * Although less reliable, see the [374]x11vnc_loop rc.local hack below. The display manager scheme will not be specific to which user has the X session unless a test is specifically put into the display startup script (often named Xsetup). The inetd(1) scheme may or may not be specific to which user has the X session (and it may not be able to do all users via the XAUTHORITY permission issues). The $HOME/.xsession scheme is obviously is specific to a particular user. If you do not know what a $HOME/.xsession script is or how to use one, perhaps your desktop has a "session startup commands" configuration option. The command to be run in the .xsession or .xinitrc file may look like this: x11vnc -logfile $HOME/.x11vnc.log -rfbauth $HOME/.vnc/passwd -forever -bg plus any other options you desire. Q-49: How can I use x11vnc to connect to an X login screen like xdm, GNOME gdm, KDE kdm, or CDE dtlogin? (i.e. nobody is logged into an X session yet). One time only. If the X login screen is running and you just want to connect to it once (i.e. a one-shot): It is usually possible to do this by just adjusting the XAUTHORITY environment variable to point to the correct MIT-COOKIE auth file while running x11vnc as root, e.g. for the gnome display manager, gdm: x11vnc -auth /var/gdm/:0.Xauth -display :0 (the [375]-auth option sets the XAUTHORITY variable for you). There will be a similar thing for xdm using however a different auth directory path (perhaps something like /var/lib/xdm/authdir/authfiles/A:0-XQvaJk for xdm or /var/lib/kdm/A:0-crWk72 for kdm, where the random characters in basename will vary a bit). Read your system docs to find out where the display manager cookie files are kept. Trick: sometimes ps(1) can reveal the X server process -auth argument (e.g. "ps wwwwaux | grep auth"). You next connect to x11vnc with a VNC viewer, give your username and password to the X login prompt to start your session. Note: gdm seems to have an annoying setting that causes x11vnc (and any other X clients) to be killed after the user logs in. Setting KillInitClients=false in the [daemon] section of /etc/X11/gdm/gdm.conf avoids this. Otherwise, just restart x11vnc and then reconnect your viewer. Note: For dtlogin in addition to the above sort of trick (BTW, the auth file should be in /var/dt), you'll also need to add something like Dtlogin*grabServer:False to the Xconfig file (/etc/dt/config/Xconfig or /usr/dt/config/Xconfig on Solaris, see [376]the example at the end of this FAQ). Then restart dtlogin, e.g.: /etc/init.d/dtlogin stop; /etc/init.d/dtlogin start or reboot. Continuously. Have x11vnc reattach each time the X server is restarted (i.e. after each logout): To make x11vnc always attached to the X server including the login screen you will need to add a command to a display manager startup script. Please consider the security implications of this! Besides having the VNC display for the X session always available, there are other issues: .e.g. if you run the tkx11vnc gui (via say -gui or -gui tray), then the gui controls (insecure) are available on the physical X display before anyone has logged in (maybe doing "-gui tray,geom=+4000+4000" is a good idea...) The name of the display manager startup script file depends on desktop used and seem to be: GNOME /etc/X11/gdm/Init/Default (or Init/:0) KDE /etc/kde*/kdm/Xsetup XDM /etc/X11/xdm/Xsetup (or xdm/Xsetup_0) CDE /etc/dt/config/Xsetup although the exact location can depend on operating system and distribution. See the documentation for your display manager: gdm(1), kdm(1), xdm(1), dtlogin(1) for additional details. There may also be display number specific scripts: e.g. Xsetup_0 vs. Xsetup, you need to watch out for. Note: The above gdm setting of KillInitClients=false in /etc/X11/gdm/gdm.conf is needed here as well. Note: The above Dtlogin*grabServer:False step will be needed for dtlogin here as well. In any event, the line you will add to the display manager script will look something like: /usr/local/bin/x11vnc -rfbauth /path/to/the/vnc/passwd -o /tmp/x11vnc.log -fo rever -bg where you should customize the exact command to your needs. Happy, happy, joy, joy: Note that we do not need to specify -display or -auth because happily they are already set for us in the DISPLAY and XAUTHORITY environment variables for the Xsetup script!!! You may also want to force the VNC port with something like "-rfbport 5900" _________________________________________________________________ Fedora/gdm: Here is an example of what we did on a vanilla install of Fedora-C3 (seems to use gdm by default). Add a line like this to /etc/X11/gdm/Init/:0 /usr/local/bin/x11vnc -rfbauth /etc/x11vnc.passwd -forever -bg -o /tmp/x11vnc .log And then add this line to /etc/X11/gdm/gdm.conf in the [daemon] section: KillInitClients=false Then restart: /usr/sbin/gdm-restart (or reboot). The KillInitClients=false setting is important: without it x11vnc will be killed immediately after the user logs in. Here are [377]full details on how to configure gdm _________________________________________________________________ Solaris/dtlogin: Here is an example of what we did on a vanilla install of Solaris: Make the directory /etc/dt/config: mkdir -p /etc/dt/config Copy over the Xconfig file for customization: cp /usr/dt/config/Xconfig /etc/dt/config/Xconfig Edit /etc/dt/config/Xconfig and uncomment the line: Dtlogin*grabServer: False Next, copy over Xsetup for customization: cp /usr/dt/config/Xsetup /etc/dt/config/Xsetup Edit /etc/dt/config/Xsetup and at the bottom put a line like: /usr/local/bin/x11vnc -forever -o /var/tmp/x11vnc.log -bg (tweaked to your local setup and preferences, a password via -rfbauth, etc. would be a very good idea). Restart the X server and dtlogin: /etc/init.d/dtlogin stop /etc/init.d/dtlogin start (or reboot or maybe just restart the X session). _________________________________________________________________ KDM: One user running the kdm display manager reports putting this line: x11vnc -forever -rfbauth /home/xyz/.vnc/passwd -bg -o /tmp/x11vnc.log in /etc/kde/kdm/Xsetup. After rebooting the system it all seemed to work fine. _________________________________________________________________ If you do not want to deal with any display manager startup scripts, here is a kludgey script that can be run manually or out of a boot file like rc.local: [378]x11vnc_loop It will need some local customization before running. Because the XAUTHORITY auth file must be guessed by this script, use of the display manager script method described above is greatly preferred. If the machine is a traditional Xterminal you may want to read [379]this FAQ. Q-50: Can I run x11vnc out of inetd(1)? How about xinetd(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 uses the [380]-inetd option and looks something like (you'll need to customize to your settings). #!/bin/sh /usr/local/bin/x11vnc -inetd -display :0 -auth /home/fred/.Xauthority \ -rfbauth /home/fred/.vnc/passwd -o /tmp/x11vnc_sh.log Important: Note that you must redirect the standard error output to a log file (e.g. -o logfile) or "2>/dev/null" for proper operation via inetd (otherwise the standard error also goes to the VNC vncviewer, and that confuses it greatly, causing it to abort). If you do not use a wrapper script as above but rather call x11vnc directly in /etc/inetd.conf and do not redirect stderr to a file, then you must specify the -q (aka [381]-quiet) option: "/usr/local/bin/x11vnc -q -inetd ...". When you supply both -q and -inet and no "-o logfile" then stderr will automatically be closed (to prevent, e.g. library stderr messages leaking out to the viewer). The recommended practice is to use "-o logfile" to collect the output in a file or wrapper script with "2>logfile" redirection because the errors and warnings printed out are very useful in troubleshooting problems. Note also the need to set XAUTHORITY via [382]-auth to point to the MIT-COOKIE auth file to get permission to connect to the X display (setting and exporting the XAUTHORITY variable accomplishes the same thing). See the x11vnc_loop file in the previous question for more ideas on what that auth file may be, etc. Note: On Solaris you cannot have the bare number 5900 in /etc/inetd.conf, you'll need to replace it with a word like x11vnc an then put something like "x11vnc 5900/tcp" in /etc/services. Since the process runs as root, it might be a bad idea to have the logfile in a world-writable area like /tmp if there are untrustworthy users on the machine. Perhaps /var/log would be a better place. Also, while running x11vnc as root, remember it comes with no warranty ;-). Be sure to look at your /etc/hosts.allow and /etc/hosts.deny settings to limit the machines that can connect to this service (your desktop!). For the above example with /etc/hosts.allow: x11vnc_sh : 123.45.67.89 A really safe way to do things is to limit the above inetd to localhost only (via /etc/hosts.allow) and use ssh to tunnel the incoming connection. Using inetd for this prevents there being a tiny window of opportunity between x11vnc starting up and your vncviewer connecting to it. Always use a VNC password to further protect against unwanted access. For xinetd(1), one user reports he created the file /etc/xinetd.d/x11vncservice containing the following: # default: off # description: service x11vncservice { flags = REUSE NAMEINARGS port = 5900 type = UNLISTED socket_type = stream protocol = tcp wait = no user = root server = /usr/sbin/tcpd server_args = /usr/local/bin/x11vnc_sh disable = no } With the contents of /usr/local/bin/x11vnc_sh similar to the example given above. One user reports this works with avoiding the wrapper script: service x11vncservice { port = 5900 type = UNLISTED socket_type = stream protocol = tcp wait = no user = root server = /usr/local/bin/x11vnc server_args = -inetd -q -display :0 -auth /var/gdm/:0.Xauth disable = no } (or one can replace the -q with say "-o /var/log/x11vnc.log" to capture a log) Q-51: Can I have x11vnc restart itself after it terminates? One could do this in a shell script, but now there is an option [383]-loop that makes it easier. Of course when x11vnc restarts it needs to have permissions to connect to the (potentially new) X display. This mode could be useful if the X server restarts often. Use e.g. "-loop5000" to sleep 5000 ms between restarts. Also "-loop2000,5" to sleep 2000 ms and only restart 5 times. Q-52: 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 [384]option: -httpdir /path/to/the/java/classes/dir (this directory will contain the files index.vnc and, for example, VncViewer.jar) Note that libvncserver contains the TightVNC Java classes jar file for your convenience. (it is the file classes/VncViewer.jar in the source tree). You will see output something like this: 14/05/2004 11:13:56 Autoprobing selected port 5900 14/05/2004 11:13:56 Listening for HTTP connections on TCP port 5800 14/05/2004 11:13:56 URL http://walnut:5800 14/05/2004 11:13:56 screen setup finished. 14/05/2004 11:13:56 The VNC desktop is walnut:0 PORT=5900 then you can connect to that URL with any Java enabled browser. Feel free to customize the default index.vnc file in the classes directory. As of May/2005 the [385]-http option will try to guess where the Java classes jar file is by looking a expected locations. Also note that if you wanted to, you could also start the Java viewer entirely from the viewer-side by having the jar file there and using either the java or appletviewer commands to run the program. Q-53: Are reverse connections (i.e. the VNC server connecting to the VNC viewer) using "vncviewer -listen" and vncconnect(1) supported? As of Mar/2004 x11vnc supports reverse connections. On Unix one starts the VNC viewer in listen mode: vncviewer -listen (see your documentation for Windows, etc), and then starts up x11vnc with the [386]-connect option. To connect immediately at x11vnc startup time use the "-connect host:port" option (use commas for a list of hosts to connect to). The ":port" is optional (default is 5500). If a file is specified instead: -connect /path/to/some/file then that file is checked periodically (about once a second) for new hosts to connect to. The [387]-remote control option (aka -R) can also be used to do this during an active x11vnc session, e.g.: x11vnc -display :0 -R connect:hostname.domain Note that as of Mar/2006 x11vnc requires password authentication for reverse connections as well as for forward ones (assuming password auth has been enabled, e.g. via -rfbauth, -passwdfile, etc). Many VNC servers do not require any password for reverse connections. To regain the old behavior set: X11VNC_REVERSE_CONNECTION_NO_AUTH=1 before starting x11vnc. To use the vncconnect(1) program (from the core VNC package at www.realvnc.com) specify the [388]-vncconnect option to x11vnc (Note: as of Dec/2004 -vncconnect is now the default). vncconnect(1) must be pointed to the same X11 DISPLAY as x11vnc (since it uses X properties to communicate with x11vnc). If you do not have or do not want to get the vncconnect(1) program, the following script (named "Vncconnect") may work if your xprop(1) supports the -set option: #!/bin/sh # usage: Vncconnect # Vncconnect # note: not all xprop(1) support -set. # xprop -root -f VNC_CONNECT 8s -set VNC_CONNECT "$1" Q-54: Can I use x11vnc as a replacement for Xvnc? (i.e. not for a real display, but for a virtual one I keep around). You can, but you would not be doing this for performance reasons (for virtual X sessions via VNC, Xvnc will give the fastest response). You may want to do this because Xvnc does not support an X server extension you desire, or you want to take advantage of one of x11vnc's unending number of options and features. One way to acheive this is to have a Xvfb(1) virtual framebuffer X server running in the background and have x11vnc attached to it. Another method, faster and more accurate is to use the "dummy" Device Driver in XFree86/Xorg (see below). One could view this desktop both remotely and also locally using vncviewer. Make sure vncviewer's "-encodings raw" is in effect for local viewing (compression seems to slow things down locally). For local viewing you set up a "bare" window manager that just starts up vncviewer and nothing else. Here is one way to start up Xvfb: xinit -- /usr/X11R6/bin/Xvfb :1 -screen 0 1024x768x16 This starts up a 16bpp virtual display. To export it via VNC use "x11vnc -display :1 ...". One good thing about Xvfb is that the virtual framebuffer exists in main memory (rather than in the video hardware), and so x11vnc can "screen scrape" it efficiently (more than, say, 100X faster than normal video hardware). There are some annoyances WRT Xvfb though. The default keyboard mapping seems to be very poor. One should run x11vnc with [389]-add_keysyms option to have keysyms added automatically. Also, to add the Shift_R and Control_R modifiers something like this is needed: #!/bin/sh xmodmap -e "keycode any = Shift_R" xmodmap -e "add Shift = Shift_L Shift_R" xmodmap -e "keycode any = Control_R" xmodmap -e "add Control = Control_L Control_R" Perhaps the Xvfb options -xkbdb or -xkbmap could be used to get a better default keyboard mapping. A user points out a faster and more accurate method is to use the "dummy" Device Driver of XFree86/Xorg instead of Xvfb. He uses this to create a persistent and resizable desktop accessible from anywhere. In the Device Section of the config file set Driver "dummy". You may also need to set VideoRam NNN to be large enough to hold the framebuffer. The framebuffer is kept in main memory like Xvfb except that the server code is closely correlated with the real XFree86/Xorg Xserver unlike Xvfb. The main drawback to this method (besides requiring extra configuration and possibly root permission) is that it also does the Linux Virtual Console/Terminal (VC/VT) [390]switching even though it does not need to (since it doesn't use a real framebuffer). There are some "dual headed" (actually multi-headed/multi-user) patches to the X server that turn off the VT usage in the X server. Update: As of Jul/2005 we have an LD_PRELOAD script [391]Xdummy that allows you to use a stock (i.e. unpatched) Xorg or XFree86 server with the "dummy" driver and not have any VT switching problems! Currently Xdummy needs to be run as root, but with some luck that may be relaxed in the future. The standard way to start the "dummy" driver would be: startx -- :1 -config /etc/X11/xorg.conf.dummy where the file /etc/X11/xorg.conf.dummy has its Device Section modified as described above. To use the LD_PRELOAD wrapper script: startx -- /path/to/Xdummy :1 An xdm(1) example is also provided. In general, one can use these sorts of schemes to use x11vnc to export other virtual X sessions, say Xnest or even Xvnc itself (useful for testing x11vnc). Q-55: How can I use x11vnc on "headless" machines? Why might I want to? An interesting application of x11vnc is to let it export displays of "headless" machines. For example, you may have some lab or server machines with no keyboard, mouse, or monitor, but each one still has a video card. One can use x11vnc to provide a simple "desktop service" from these server machines. An X server can be started on the headless machine (sometimes this requires configuring the X server to not fail if it cannot detect a keyboard or mouse, see the next paragraph). Then you can export that X display via x11vnc (e.g. see [392]this FAQ) and access it from anywhere on the network via a VNC viewer. Some tips on getting X servers to start on machines without keyboard or mouse: For XFree86/Xorg the Option "AllowMouseOpenFail" "true" "ServerFlags" config file option is useful. On Solaris Xsun the +nkeyboard and +nmouse options are useful (put them in the server command line args in /etc/dt/config/Xservers). See Xserver(1) for more info. Although this usage may sound strange it can be quite useful for a GUI (or other) testing or QA setups: the engineers do not need to walk to lab machines running different hardware, OS's, versions, etc (or have many different machines in their office). They just connect to the various test machines over the network via VNC. The advantage to testing this way instead of using Xvnc or even Xvfb is that the test is done using the real X server, fonts, video hardware, etc. that will be used in the field. One can imagine a single server machine crammed with as many video cards as it can hold to provide multiple simultaneous access or testing on different kinds of video hardware. [Resource Usage and Performance] Q-56: 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 [393]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 [394]-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 [395]-noshm option. Performance will be somewhat degraded but when done over local machine sockets it should be acceptable (see an [396]earlier question discussing -noshm). Q-57: How can I make x11vnc use less system resources? The [397]-nap and "[398]-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. The ShadowFB will make x11vnc's screen polling less severe. Using the [399]-onetile option will use less memory and use fewer shared memory slots (add [400]-fs 1.0 for one less slot). Q-58: How can I make x11vnc use MORE system resources? You can try [401]-threads and dial down the wait time (e.g. -wait 1) and possibly dial down [402]-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 [403]-id option) can be streamed over a LAN or wireless at a reasonable frame rate. Q-59: I use x11vnc over a slow link with high latency (e.g. dialup modem), is there anything I can do to speed things up? Some things you might want to experiment with (many of which will help performance on faster links as well): X server/session parameters: * Configure the X server bits per pixel to be 16bpp or even 8bpp. (reduces amount of data needed to be polled, compressed, and sent) * Use a smaller desktop size (e.g. 1024x768 instead of 1280x1024) * Make sure the desktop background is a solid color (the background is resent every time it is re-exposed). Consider using the [404]-solid [color] option to try to do this automatically. * Configure your window manager or desktop "theme" to not use fancy images, shading, and gradients for the window decorations, etc. Disable window animations, etc. Maybe your desktop has a "low bandwidth" theme you can easily switch into and out of. * Avoid small scrolls of large windows using the Arrow keys or scrollbar. Try to use PageUp/PageDown instead. (not so much of a problem in x11vnc 0.7.2 if [405]-scrollcopyrect is active and detecting scrolls for the application). * If the [406]-wireframe option is not available (earlier than x11vnc 0.7.2 or you have disabled it via -nowireframe) then Disable Opaque Moves and Resizes in the window manager/desktop. * However if -wireframe is active (on by default in x11vnc 0.7.2) then you should Enable Opaque Moves and Resizes in the window manager! This seems counter-intuitive, but because x11vnc detects the move/resize events early there is a huge speedup over a slow link when Opaque Moves and Resizes are enabled. (e.g. CopyRect encoding will be used). * Turn off Anti-aliased fonts on your system, web browser, terminal windows, etc. AA fonts do not compress as well as traditional fonts (sometimes 10X less). * On XFree86 turn on the Shadow Framebuffer to speed up reading. (Option "ShadowFB" "true" in the Device section of /etc/X11/XF86Config) This disables 2D acceleration on the physical display and so may not be worth it, but could be of use in some situations. If the link is very slow, this speedup may not be noticed. VNC viewer parameters: * Use a [407]TightVNC enabled viewer! (Actually, RealVNC 4.x viewer with ZRLE encoding is not too bad either; some claim it is faster). * Make sure the tight (or zrle) encoding is being used (look at vncviewer and x11vnc outputs) * Request 8 bits per pixel using -bgr233 (up to 4X speedup over depth 24 TrueColor (32bpp), but colors will be off) * RealVNC 4.x viewer has some extremely low color modes (only 64 and even 8 colors). The colors are poor, but it is usually noticeably faster than bgr233 (256 colors). * Try increasing the TightVNC -compresslevel (compresses more on server side before sending, but uses more CPU) * Try reducing the TightVNC -quality (increases JPEG compression, but is lossy with painting artifacts) * Try other VNC encodings via -encodings (tight is may be the fastest, but you should compare it to zrle and maybe some of the others) * On the machine where vncviewer is run, make sure Backing Store is enabled (XFree86/Xorg disables it by default causing re-exposures of vncviewer to be very slow) Option "backingstore" in config file. x11vnc parameters: * Try using [408]-nodragging (no screen updates when dragging mouse, but sometimes you miss visual feedback) * Make sure the [409]-wireframe option is active (it should be on by default) and you have Opaque Moves/Resizes Enabled in the window manager. * Make sure the [410]-scrollcopyrect option is active (it should be on by default). This detects scrolls in many (but not all) applications an applies the CopyRect encoding for a big speedup. * Set [411]-fs 1.0 (disables fullscreen updates) * Try increasing [412]-wait or [413]-defer (reduces the maximum "frame rate", but won't help much for large screen changes) * Try the [414]-progressive pixelheight mode with the block pixelheight 100 or so (delays sending vertical blocks since they may change while viewer is receiving earlier ones) * If you just want to watch one (simple) window use [415]-id (cuts down extraneous polling and updates, but can be buggy or insufficient) * Set [416]-nosel (disables all clipboard selection exchange) * Use [417]-nocursor and [418]-nocursorpos (repainting the remote cursor position and shape takes resources and round trips) * On very slow links (e.g. <= 28.8) you may need to increase the [419]-readtimeout n setting if it sometimes takes more than 20sec to paint the full screen, etc. Q-60: Does x11vnc support the X DAMAGE Xserver extension to find modified regions of the screen quickly and efficiently? Yes, as of Mar/2005 x11vnc will use the X DAMAGE extension by default if it is available on the display. This requires libXdamage to be available in the build environment as well (recent Linux distros and Solaris 10 have it). The DAMAGE extension enables the X server to report changed regions of the screen back to x11vnc. So x11vnc doesn't have to guess where the changes are (by polling every pixel of the entire screen every 2-4 seconds). The use of X DAMAGE dramatically reduces the load when the screen is not changing very much (i.e. most of the time). It also noticeably improves updates, especially for very small changed areas (e.g. clock ticking, cursor flashing, typing, etc). Note that the DAMAGE extension does not speed up the actual reading of pixels from the video card framebuffer memory, by, say, mirroring them in main memory. So reading the fb is still painfully [420]slow (e.g. 5MB/sec), and so even using X DAMAGE when large changes occur on the screen the bulk of the time is still spent retrieving them. Not ideal, but use of the ShadowFB XFree86/Xorg option speeds up the reading considerably (at the cost of h/w acceleration). Unfortunately the current Xorg DAMAGE extension implementation can at times be overly conservative and report very large rectangles as "damaged" even though only a small portion of the pixels have actually been modified. This behavior is often the fault of the window manager (e.g. it redraws the entire, unseen, frame window underneath the application window when it gains focus), or the application itself (e.g. does large, unnecessary repaints). To work around this deficiency, x11vnc currently only trusts small DAMAGE rectangles to contain real damage. The larger rectangles are only used as hints to focus the traditional scanline polling (i.e. if a scanline doesn't intersect a recent DAMAGE rectangle, the scan is skipped). You can use the "[421]-xd_area A" option to adjust the size of the trusted DAMAGE rectangles. The default is 20000 pixels (e.g. a 140x140 square, etc). Use "-xd_area 0" to disable the cutoff and trust all DAMAGE rectangles. The option "[422]-xd_mem f" may also be of use in tuning the algorithm. To disable using DAMAGE entirely use "[423]-noxdamage". Q-61: When I drag windows around with the mouse or scroll up and down things really bog down (unless I do the drag in a single, quick motion). Is there anything to do to improve things? This problem is primarily due to [424]slow hardware read rates from video cards: as you scroll or move a large window around the screen changes are much too rapid for x11vnc to keep up them (it can usually only read the video card at about 5-10 MB/sec, so it can take a good fraction of a second to read the changes induce from moving a large window, if this to be done a number of times in succession the window or scroll appears to "lurch" forward). See the description in the [425]-pointer_mode option for more info. The next bottleneck is compressing all of these changes and sending them out to connected viewers, however the VNC protocol is pretty much self-adapting with respect to that (updates are only packaged and sent when viewers ask for them). As of Jan/2004 there are some improvements to libvncserver. The default should now be much better than before and dragging small windows around should no longer be a huge pain. If for some reason these changes make matters worse, you can go back to the old way via the "[426]-pointer_mode 1" option. Also added was the [427]-nodragging option that disables all screen updates while dragging with the mouse (i.e. mouse motion with a button held down). This gives the snappiest response, but might be undesired in some circumstances when you want to see the visual feedback while dragging (e.g. menu traversal or text selection). As of Dec/2004 the [428]-pointer_mode n option was introduced. n=1 is the original mode, n=2 an improvement, etc.. See the -pointer_mode n help for more info. Also, in some circumstances the [429]-threads option can improve response considerably. Be forewarned that if more than one vncviewer is connected at the same time then libvncserver may not be thread safe (try to get the viewers to use different VNC encodings, e.g. tight and ZRLE). As of Apr/2005 two new options (see the [430]wireframe FAQ and [431]scrollcopyrect FAQ below) provide schemes to sweep this problem under the rug for window moves or resizes and for some (but not all) window scrolls. Q-62: Why not do something like wireframe animations to avoid the windows "lurching" when being moved or resized? Nice idea for a hack! As of Apr/2005 x11vnc by default will apply heuristics to try to guess if a window is being (opaquely) moved or resized. If such a change is detected framebuffer polling and updates will be suspended and only an animated "wireframe" (a rectangle outline drawn where the moved/resized window would be) is shown. When the window move/resize stops, it returns to normal processing: you should only see the window appear in the new position. This spares you from interacting with a "lurching" window between all of the intermediate steps. BTW the lurching is due to [432]slow video card read rates (see [433]here too). A displacement, even a small one, of a large window requires a non-negligible amount of time, a good fraction of a second, to read in from the hardware framebuffer. Note that Opaque Moves/Resizes must be Enabled by your window manager for -wireframe to do any good. The mode is currently on by default because most people are inflicted with the problem. It can be disabled with the [434]-nowireframe option (aka -nowf). Why might one want to turn off the wireframing? Since x11vnc is merely guessing when windows are being moved/resized, it may guess poorly for your window-manager or desktop, or even for the way you move the pointer. If your window-manager or desktop already does its own wireframing then this mode is a waste of time and could do the wrong thing occasionally. There may be other reasons the new mode feels unnatural. If you have very expensive video hardware (SGI) or are using an in-RAM video framebuffer (SunRay, ShadowFB, Xvfb), the read rate from that framebuffer may be very fast (100's of MB/sec) and so you don't really see much lurching: opaque moves look smooth in x11vnc. Note: ShadowFB is often turned on when you are using the vesafb or fbdev XFree86 video driver instead of a native one so you might be using it already and not know. The heuristics used to guess window motion or resizing are simple, but are not fool proof: x11vnc is sometimes tricked and so you'll occasionally see the lurching opaque move and rarely something even worse. First it assumes that the move/resize will occur with a mouse button pressed, held down and dragged (of course this is only mostly true). Next it will only consider a window for wireframing if the mouse pointer is initially "close enough" to the edges of the window frame, e.g. you have grabbed the title bar or a resizer edge (this requirement can be disabled and it also not applied if a modifier key, e.g. Alt, is pressed). If these are true, it will wait an amount of time to see if the window starts moving or resizing. If it does, it starts drawing the wireframe "outline" of where the window would be. When the mouse button is released, or a timeout occurs, it goes back to the standard mode to allow the actual framebuffer changes to propagate to the viewers. These parameters can be tweaked: * Color/Shade of the wireframe. * Linewidth of the outline frame. * Cutoff size of windows to not apply wireframing to. * Cutoffs for closeness to Top, Bottom, Left, and Right edges of window. * Modifier keys to enable interior window grabbing. * Maximum time to wait for dragging pointer events. * Maximum time to wait for the window to start moving/resizing. * Maximum time to show a wireframe animation. * Minimum time between sending wireframe outlines. See the [435]"-wireframe tweaks" option for more details. On a slow link, e.g. dialup modem, the parameters may be automatically adjusted for better response. CopyRect encoding: In addition to the above there is the [436]"-wirecopyrect mode" option. It is also on by default. This instructs x11vnc to not only show the wireframe animation, but to also instruct all connected VNC viewers to locally translate the window image data from the original position to the new position on the screen when the animation is done. This speedup is the VNC CopyRect encoding: the framebuffer update doesn't need to send the actual new image data. This is nice in general, and very convenient over a slow link, but since it is based on heuristics you may need to disable it with the -nowirecopyrect option (aka -nowcr) if it works incorrectly or unnaturally for you. The -wirecopyrect modes are: "never" (same as -nowirecopyrect); "top", only apply the CopyRect if the window is appears to be on the top of the window stack and is not obstructed by other windows; and "always" to always try to apply the CopyRect (obstructed regions are usually clipped off and not translated). Note that some desktops (KDE and xfce) appear to mess with the window stacking in ways that are not yet clear. In these cases x11vnc works around the problem by applying the CopyRect even if obscuring windows' data is translated! Use -nowirecopyrect if this yields undesirable effects for your desktop. Also, the CopyRect encoding may give incorrect results under -scale (depending on the scale factor the CopyRect operation is often only approximate: the correctly scaled framebuffer will be slightly different from the translated one). x11vnc will try to push a "cleanup" update after the CopyRect if -scale is in effect. Use -nowirecopyrect if this or other painting errors are unacceptable. Q-63: Can x11vnc try to apply heuristics to detect when an window is scrolling its contents and use the CopyRect encoding for a speedup? Another nice idea for a hack! As of May/2005 x11vnc will by default apply heuristics to try to detect if the window that has the input focus is scrolling its contents (but only when x11vnc is feeding user input, keystroke or pointer, to the X server). So, when detected, scrolls induced by dragging on a scrollbar or by typing (e.g. Up or Down arrows, hitting Return in a terminal window, etc), will show up much more quickly than via the standard x11vnc screen polling update mechanism. There will be a speedup for both slow and fast links to viewers. For slow links the speedup is mostly due to the CopyRect encoding not requiring the image data to be transmitted over the network. For fast links the speedup is primarily due to x11vnc not having to read the scrolled framebuffer data from the X server (recall that reading from the hardware framebuffer is [437]slow). To do this x11vnc uses the RECORD X extension to snoop the X11 protocol between the X client with the focus window and the X server. This extension is usually present on most X servers (but SuSE disables it for some reason). On XFree86/Xorg it can be enabled via Load "record" in the Module section of the config file if it isn't already. Currently the RECORD extension is used as little as possible so as to not slow down regular use. Only simple heuristics are applied to detect XCopyArea and XConfigureWindow calls from the application. These catch a lot of scrolls, e.g. in mozilla/firefox and in terminal windows like gnome-terminal and xterm. Unfortunately the toolkits KDE applications use make scroll detection less effective (only rarely are they detected: i.e. Konqueror and Konsole don't work). An interesting project, that may be the direction x11vnc takes, is to record all of the X11 protocol from all clients and try to "tee" the stream into a modified Xvfb watching for CopyRect and other VNC speedups. A potential issue is the RECORD stream is delayed from actual view on the X server display: if one falls too far behind it could become a mess... The initial implementation of [438]-scrollcopyrect option is useful in that it detects many scrolls and thus gives a much nicer working environment (especially when combined with the [439]-wireframe [440]-wirecopyrect [441]options, which are also on by default; and if you are willing to enable the ShadowFB things are very fast). The fact that there aren't long delays or lurches during scrolling is the primary improvement. But there are some drawbacks: * Not all scrolls are detected. Some apps scroll windows in ways that cannot currently be detected, and other times x11vnc "misses" the scroll due to timeouts, etc. Sometimes it is more distracting that a speedup occasionally doesn't work as opposed to being consistently slow! * For rapid scrolling (i.e. sequence of many scrolls over a short period) there can be painting errors (tearing, bunching up, etc.) during the scroll. These will repair themselves after the scroll is over, but when they are severe it can be distracting. Try to think of the approximate window contents as a quicker and more useful "animation" compared to the slower polling scheme... * Scrolling inside shells in terminal windows (gnome-terminal, xterm), can lead to odd painting errors. This is because x11vnc did not have time to detect a screen change just before the scroll (most common is the terminal undraws the block cursor before scrolling the text up: in the viewer you temporarily see multiple block cursors). Another issue is with things like more(1): scroll detection for 5-6 lines happens nicely, but then it can't keep up and so there is a long pause for the standard polling method to deliver the remaining updates. * More rarely sometimes painting errors are not repaired after the scroll is over. This may be a bug in x11vnc or libvncserver, or it may be an inescapable fact of the CopyRect encoding and the delay between RECORD callbacks and what is actually on the X display. One can tap the Alt_L key (Left "Alt" key) 3 times in a row to signal x11vnc to refresh the screen to all viewers. Your VNC-viewer may have its own screen refresh hot-key or button. See also: [442]-fixscreen * Some applications, notably OpenOffice, do XCopyArea scrolls in weird ways that assume ancestor window clipping is taking place. See the [443]-scr_skip option for ways to tweak this on a per-application basis. * Selecting text while dragging the mouse may be slower, especially if the Button-down event happens near the window's edge. This is because the scrollcopyrect scheme is watching for scrolls via RECORD and has to wait for a timeout to occur before it does the update. * For reasons not yet understood the RECORD extension can stop responding (and hence scrolls are missed). As a workaround x11vnc attempts to reset the RECORD connection every 60 seconds or so. Another workaround is to type 4 Super_L (Left Super/Windows-Flag key) in a row to reset RECORD. Work is in progress to try to fix this bug. * Sometimes you need to "retrain" x11vnc for a certain window because it fails to detect scrolls in it. Sometimes clicking inside the application window or selecting some text in it to force the focus helps. * When using the [444]-scale option there will be a quick CopyRect scroll, but it needs to be followed by a slower "cleanup" update. This is because for a fixed finite screen resolution (e.g. 75 dpi) scaling and copyrect-ing are not exactly independent. Scaling involves a blending of nearby pixels and if you translate a pixel the neighbor pixel weighting may be different. So you have to wait a bit for the cleanup update to finish. On slow links x11vnc may automatically decide to not detect scrolls when -scale is in effect. In general it will also try to defer the cleanup update if possible. If you find the -scrollcopyrect behavior too approximate or distracting you can go back to the standard polling-only update method with the [445]-noscrollcopyrect (or -noscr for short). If you find some extremely bad and repeatable behavior for -scrollcopyrect please report a bug. Alternatively, as with -wireframe, there are many tuning parameters to try to improve the situation. You can also access these parameters inside the gui under "Tuning". These parameters can be tweaked: * The minimum pixel area of a rectangle to be watched for scrolls. * A list if application names to skip scroll detection. * Which keystrokes should trigger scroll detection. * Which applications should have a "terminal" tweak applied to them. * When repeating keys (e.g. Up arrow) should be discarded to preserve a scroll. * Cutoffs for closeness to Top, Bottom, Left, and Right edges of window for mouse induced scrolls. * Set timeout parameters for keystroke induced scrolls. * Set timeout parameters for mouse pointer induced scrolls. * Have the full screen be periodically refreshed to fix painting errors. [Mouse Cursor Shapes] Q-64: Why isn't the mouse cursor shape (the little icon shape where the mouse pointer is) correct as I move from window to window? On X servers supporting XFIXES or Solaris/IRIX Overlay extensions it is possible for x11vnc to do this correctly. See a few paragraphs down for the answer. Historically, the X11 mouse cursor shape (i.e. little picture: an arrow, X, I-beam, resizer, etc) is one of the few WRITE-only objects in X11. That is, an application can tell the X server what the cursor shape should be when the pointer is in a given window, but a program (like x11vnc) unfortunately cannot read this information. I believe this is because the cursor shape is often downloaded to the graphics hardware (video card), but I could be mistaken. A simple kludge is provided by the "[446]-cursor X" option that changes the cursor when the mouse is on the root background (or any window has the same cursor as the root background). Note that desktops like GNOME or KDE often cover up the root background, so this won't work for those cases. Also see the "[447]-cursor some" option for additional kludges. Note that as of Aug/2004 on Solaris using the SUN_OVL overlay extension and IRIX, x11vnc can show the correct mouse cursor when the [448]-overlay option is supplied. See [449]this FAQ for more info. Also as of Dec/2004 XFIXES X extension support has been added to allow exact extraction of the mouse cursor shape. XFIXES fixes the problem of the cursor-shape being write-only: x11vnc can now query the X server for the current shape and send it back to the connected viewers. XFIXES is available on recent Linux Xorg based distros and [450]Solaris 10. The only XFIXES issue is the handling of alpha channel transparency in cursors. If a cursor has any translucency then in general it must be approximated to opaque RGB values for use in VNC. There are some situations where the cursor transparency can also handled exactly: when the VNC Viewer requires the cursor shape be drawn into the VNC framebuffer or if you apply a patch to your VNC Viewer to extract hidden alpha channel data under 32bpp. [451]Details can be found here. Q-65: When using XFIXES cursorshape mode, some of the cursors look really bad with extra black borders around the cursor and other cruft. How can I improve their appearance? This happens for cursors with transparency ("alpha channel"); regular X cursors (bitmaps) should be correct. Unfortunately x11vnc 0.7 was released with a very poor algorithm for approximating the transparency, which led to the ugly black borders. The problem is as follows: XFIXES allows x11vnc to retrieve the current X server cursor shape, including the alpha channel for transparency. For traditional bitmap cursors the alpha value will be 0 for completely transparent pixels and 255 for completely opaque pixels; whereas for modern, eye-candy cursors an alpha value between 0 and 255 means to blend in the background colors to that degree with the cursor colors. The pixel color blending formula is something like this: Red = Red_cursor * a + Red_background * (1 - a), (where here 0 =< a =< 1), with similar for Green and Blue. The VNC protocol does not currently support an alpha channel in cursors: it only supports regular X bitmap cursors and Rich Cursors that have RGB (Red, Green, Blue) color data, but no "A" = alpha data. So in general x11vnc has to approximate a cursor with transparency to create a Rich Cursor. This is easier said than done: some cursor themes have cursors with complicated drop shadows and other forms of translucency. Anyway, for the x11vnc 0.7.1 release the algorithm for approximating transparency is much improved and hopefully gives decent cursor shapes for most cursor themes and you don't have to worry about it. In case it still looks bad for your cursor theme, there are (of course!) some tunable parameters. The "[452]-alphacut n" option lets you set the threshold "n" (between 0 and 255): cursor pixels with alpha values below n will be considered completely transparent while values equal to or above n will be completely opaque. The default is 240. The "[453]-alphafrac f" option tries to correct individual cursors that did not fare well with the default -alphacut value: if a cursor has less than fraction f (between 0.0 and 1.0) of its pixels selected by the default -alphacut, the threshold is lowered until f of its pixels are selected. The default fraction is 0.33. Finally, there is an option [454]-alpharemove that is useful for themes where many cursors are light colored (e.g. "whiteglass"). XFIXES returns the cursor data with the RGB values pre-multiplied by the alpha value. If the white cursors look too grey, specify -alpharemove to brighten them by having x11vnc divide out the alpha value. One user played with these parameters and reported back: Of the cursor themes present on my system: gentoo and gentoo-blue: alphacut:192 - noalpharemove gentoo-silver: alphacut:127 and alpharemove whiteglass and redglass (presumably also handhelds, which is based heavily on redglass) look fine with the apparent default of alphacut:255. Q-66: In XFIXES mode, are there any hacks to handle cursor transparency ("alpha channel") exactly? As of Jan/2005 libvncserver has been modified to allow an alpha channel (i.e. RGBA data) for Rich Cursors. So x11vnc can now send the alpha channel data to libvncserver. However, this data will only be used for VNC clients that do not support the CursorShapeUpdates VNC extension (or have disabled it). It can be disabled for all clients with the [455]-nocursorshape x11vnc option. In this case the cursor is drawn, correctly blended with the background, into the VNC framebuffer before being sent out to the client. So the alpha blending is done on the x11vnc side. Use the [456]-noalphablend option to disable this behavior (always approximate transparent cursors with opaque RGB values). The CursorShapeUpdates VNC extension complicates matters because the cursor shape is sent to the VNC viewers supporting it, and the viewers draw the cursor locally. This improves response over slow links. Alpha channel data for these locally drawn cursors is not supported by the VNC protocol. However, in the libvncserver CVS there is a patch to the TightVNC viewer to make this work for CursorShapeUpdates under some circumstances. This hack is outside of the VNC protocol. It requires the screens on both sides to be depth 24 at 32bpp (it uses the extra 8 bits to secretly hide the cursor alpha channel data). Not only does it require depth 24 at 32bpp, but it also currently requires the client and server to be of the same endianness (otherwise the hidden alpha data gets reset to zero by a libvncserver translation function; we can fix this at some point if there is interest). The patch is for the TightVNC 1.3dev5 Unix vncviewer and it enables the TightVNC viewer to do the cursor alpha blending locally. The patch code should give an example on how to change the Windows TightVNC viewer to achieve the same thing (send me the patch if you get that working). [Mouse Pointer] Q-67: 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 [457]tightvnc extension (CursorShapeUpdates) that allows specifying a cursor image shape for the local VNC viewer. You may disable it with the [458]-nocursor option to x11vnc if your viewer does not have this extension. Note: as of Aug/2004 this should be fixed: the default for non-tightvnc viewers (or ones that do not support CursorShapeUpdates) will be to draw the moving cursor into the x11vnc framebuffer. This can also be disabled via -nocursor. Q-68: 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 [459]-cursorpos option when starting x11vnc. A VNC viewer must support the Cursor Positions Updates for the user to see the mouse motions (the TightVNC viewers support this). As of Aug/2004 -cursorpos is the default. See also [460]-nocursorpos and [461]-nocursorshape. Q-69: 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: [462]-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 [463]-debug_pointer option prints out much info for every mouse/pointer event and is handy in solving problems. To map mouse button clicks to keystrokes you can use the alternate format where the keystrokes are enclosed between colons like this :: in place of the mouse button digit. For a sequence of keysyms separate them with "+" signs. Look in the include file , or use xev(1), or -debug_keyboard to fine the keysym names. Button clicks can also be included in the sequence via the fake keysyms Button1, etc. As an example, suppose the VNC viewer machine has a mouse wheel (these generate button 4 and 5 events), but the machine that x11vnc is run on only has the 3 regular buttons. In normal operation x11vnc will discard the button 4 and 5 events. However, either of the following button maps could possibly be of use emulating the mouse wheel events in this case: -buttonmap 12345-123:Prior::Next: -buttonmap 12345-123:Up+Up+Up::Down+Down+Down: Exactly what keystroke "scrolling" events they should be bound to depends on one's taste. If this method is too approximate, one could consider not using [464]-buttonmap but rather configuring the X server to think it has a mouse with 5 buttons even though the physical mouse does not. (e.g. 'Option "ZAxisMapping" "4 5"'). Note that when a keysym-mapped mouse button is clicked down this immediately generates the key-press and key-release events (for each keysym in turn if the mapping has a sequence of keysyms). When the mouse button goes back up nothing is generated. If you include modifier keys like Shift_L instead of key-press immediately followed by key-release the state of the modifier key is toggled (however the initial state of the modifier key is ignored). So to map the right button to type my name 'Karl Runge' I could use this: -buttonmap 3-:Shift_L+k+Shift_L+a+r+l+space+Shift_L+r+Shift_L+u+n+g+e: (yes, this is getting a little silly). BTW, Coming the other way around, if the machine you are sitting at does not have a mouse wheel, but the remote machine does (or at least has 5 buttons configured), this key remapping can be useful: -remap Super_R-Button4,Menu-Button5 you just tap those two keys to get the mouse wheel scrolls (this is more useful than the Up and Down arrow keys because a mouse wheel "click" usually gives a multi-line scroll). [Keyboard Issues] Q-70: How can I get my AltGr and Shift modifiers to work between keyboards for different languages? The option [465]-modtweak should help here. It is a mode that monitors the state of the Shift and AltGr Modifiers and tries to deduce the correct keycode to send, possibly by sending fake modifier key presses and releases in addition to the actual keystroke. Update: As of Jul/2004 -modtweak is now the default (use -nomodtweak to get the old behavior). This was done because it was noticed on newer XFree86 setups even on bland "us" keyboards like "pc104 us" XFree86 included a "ghost" key with both "<" and ">" it. This key does not exist on the keyboard (see [466]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 [467]FAQ about the -xkb option for a more powerful method of modifier tweaking for use on X servers with the XKEYBOARD extension. When trying to resolve keyboard mapping problems, note that the [468]-debug_keyboard option prints out much info for every keystroke and so can be useful debugging things. Q-71: When I try to type a "<" (i.e. less than) instead I get ">" (i.e. greater than)! Strangely, typing ">" works OK!! Does your keyboard have a single key with both "<" and ">" on it? Even if it doesn't, your X server may think your keyboard has such a key (e.g. pc105 in the XF86Config file when it should be something else, say pc104). Short Cut: Try the [469]-xkb or [470]-sloppy_keys options and see if that helps the situation. The discussion below is a bit outdated (e.g. [471]-modtweak is now the default) but is useful reference for various tricks and so is kept. The problem here is that on the Xserver where x11vnc is run there are two keycodes that correspond to the "<" keysym. Run something like this to see: xmodmap -pk | egrep -i 'KeyCode|less|greater' There are 4 KeySyms per KeyCode; KeyCodes range from 8 to 255. KeyCode Keysym (Keysym) ... 59 0x002c (comma) 0x003c (less) 60 0x002e (period) 0x003e (greater) 94 0x003c (less) 0x003e (greater) That keycode 94 is the special key with both "<" and ">". When x11vnc receives the "<" keysym over the wire from the remote VNC client, it unfortunately maps it to keycode 94 instead of 59, and sends 94 to the X server. Since Shift is down (i.e. you are Shifting the comma key), the X server interprets this as Shifted-94, which is ">". A workaround in the X server configuration is to "deaden" that special key: xmodmap -e "keycode 94 = " However, one user said he had to do this: xmodmap -e "keycode 94 = 0x002c 0x003c" (If the numerical values are different for your setup, substitute the ones that correspond to your display. The above xmodmap scheme can often be used to work around other ambiguous keysym to keycode mappings). Alternatively, here are some x11vnc options to try to work around the problem: -modtweak and -remap less-comma These are convenient in that they do not modify the actual X server settings. The former ([472]-modtweak) is a mode that monitors the state of the Shift and AltGr modifiers and tries to deduce the correct keycode sequence to send. Since Jul/2004 -modtweak is now the default. The latter ([473]-remap less-comma) is an immediate remapping of the keysym less to the keysym comma when it comes in from a client (so when Shift is down the comma press will yield "<"). See also the [474]FAQ about the -xkb option as a possible workaround using the XKEYBOARD extension. Note that the [475]-debug_keyboard option prints out much info for every keystroke to aid debugging keyboard problems. Q-72: When I try to type a "<" (i.e. less than) instead I get "<," (i.e. an extra comma). This is likely because you press "Shift" then "<" but then released the Shift key before releasing the "<". Because of a [476]keymapping ambiguity the last event "< up" is interpreted as "," because that key unshifted is the comma. This should not happen in [477]-xkb mode, because it works hard to resolve the ambiguities. If you do not want to use -xkb, try the option [478]-sloppy_keys to attempt a similar type of algorithm. Q-73: 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 [479]-modtweak option (it figures out how to adjust the Modifier keys (Shift or AltGr) to get the "@"). However it fails under recent versions of XFree86 (and the X.org fork). These run the XKEYBOARD extension by default and make heavy use of it to handle international keyboards. To make a long story short, on these newer XFree86 setups the traditional X keymap lookup x11vnc uses is no longer accurate. x11vnc can't find the keysym "@" anywhere in the keymapping! (even though it is in the XKEYBOARD extended keymapping). How to Solve: As of Jul/2004 x11vnc has two changes: * -modtweak (tweak Modifier keys) is now the default (use -nomodtweak to go back to the old way) * there is a new option -xkb to use the XKEYBOARD extension API to do the Modifier key tweaking. The [480]-xkb option seems to fix all of the missing keys: "@", "<", ">", etc.: it is recommended that you try it if you have this sort of problem. Let us know if there are any remaining problems (see the next paragraph for some known problems). If you specify the -debug_keyboard (aka -dk) option twice you will get a huge amount of keystroke debugging output (send it along with any problems you report). Update: as of Jun/2005 x11vnc will try to automatically enable [481]-xkb if it appears that would be beneficial (e.g. if it sees any of "@", "<", ">", "[" and similar keys are mapped in a way that needs the -xkb to access them). To disable this automatic check use -noxkb. Known problems: * One user had to disable a "ghost" Mode_switch key that was causing problems under -xkb. His physical AltGr key was bound to ISO_Level3_Shift (which seems to be the XKEYBOARD way of doing things), while there was a ghost key Mode_switch (which seems to be obsolete) in the mapping as well. Both of these keysyms were bound to Mod5 and x11vnc was unfortunately choosing Mode_switch. From the x11vnc -xkb -dk -dk output it was noted that Mode_switch was attached to keycode 93 (no physical key generates this keycode) while ISO_Level3_Shift was attached to keycode 113. The keycode skipping option was used to disable the ghost key: [482]-skip_keycodes 93 * In implementing -xkb we noticed that some characters were still not getting through, e.g. "~" and "^". This is not really an XKEYBOARD problem. What was happening was the VNC viewer was sending the keysyms asciitilde and asciicircum to x11vnc, but on the X server with the international keyboard those keysyms were not mapped to any keys. So x11vnc had to skip them. 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. "ã" 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 [483]-remap x11vnc option: -remap asciitilde-dead_tilde,asciicircum-dead_circumflex etc. Use -remap filename if the list is long. Please send us your workarounds for this problem on your keyboard. Perhaps we can have x11vnc adjust automatically at some point. Also see the [484]-add_keysyms option in the next paragraph. Update: for convenience "[485]-remap DEAD" does many of these mappings at once. * To complement the above workaround using the [486]-remap, an option [487]-add_keysyms was added. This option instructs x11vnc to bind any unknown Keysyms coming in from VNC viewers to unused Keycodes in the X server. This modifies the global state of the X server. When x11vnc exits it removes the extra keymappings it created. Note that the -remap mappings are applied first, right when the Keysym is received from a VNC viewer, and only after that would -add_keysyms, or anything else, come into play. Update: -add_keysyms is now on by default. Use -noadd_keysyms to disable. Q-74: 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) [488]-norepeat x11vnc option. You will still have autorepeating because that is taken care of on your VNC viewer side. Update: as of Dec/2004 -norepeat is now the default. Use -repeat to disable it. Details: suppose you press a key DOWN and it generates changes in large regions of the screen. The CPU and I/O work x11vnc does for the large screen change could be longer than your X server's key autorepeat delay. x11vnc may not get to processing the key UP event until after the screen work is completed. The X server believes the key has been held down all this time, and applies its autorepeat rules. Even without inducing changes in large regions of the screen, this problem could arise when accessing x11vnc via a dialup modem or otherwise high latency link (e.g. > 250 ms latency). Look at the output of "xset q" for the "auto repeat delay" setting. Is it low (e.g. < 300 ms)? If you turn off autorepeat completely: "xset r off", does the problem go away? The workaround is to manually apply "xset r off" and "xset r on" as needed, or to use the [489]-norepeat (which has since Dec/2004 been made the default). Note that with X server autorepeat turned off the VNC viewer side of the connection will (nearly always) do its own autorepeating so there is no big loss here, unless someone is also working at the physical display and misses his autorepeating. Q-75: The x11vnc -norepeat mode is in effect, but I still get repeated keystrokes!! Are you using x11vnc to log in to an X session? (as described in [490]this FAQ) If so, x11vnc is starting before your session and it disables autorepeat when you connect, but then after you log in your session startup (GNOME, KDE, ...) could be resetting the autorepeat to be on. Or it could be something inside your desktop trying to be helpful that decides to turn it back on. x11vnc in -norepeat mode will by default reset autorepeat to off 2 times (to help get thru the session startup problem), but it will not continue to battle with things turning autorepeat back on. It will also turn autorepeat off whenever it goes from a state of zero clients to one client. You can adjust the number of resets via "-norepeat N", or use "-norepeat -1" to have it keep resetting it whenever autorepeat gets turned back on when clients are connected. In general you can manually turn autorepeating off by typing "xset r off", or a using desktop utility/menu, or "x11vnc -R norepeat". If something in your desktop is automatically turning it back on you should figure out how to disable that somehow. Q-76: 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 "[491]-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-77: 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 [492]-remap Alt_L-Meta_L to x11vnc may be sufficient for ones needs, and does not modify the X server environment. Note that you cannot send Alt_L in this case, maybe -remap Super_L-Meta_L would be a better choice if the Super_L key is typically unused in Unix. Q-78: 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 [493]-remap option using the fake "keysyms" Button1, Button2, etc. as the "to" keys (i.e. the ones after the "-") As an example, consider a laptop where the VNC viewer is run that has a touchpad with only two buttons. It is difficult to do a middle button "paste" because (using XFree86/Xorg Emulate3Buttons) you have to click both buttons on the touch pad at the same time. This remapping: [494]-remap Super_R-Button2 maps the Super_R "flag" key press to the Button2 click, thereby making X pasting a bit easier. Note that once the key goes down, the button down and button up events are generated immediately on the x11vnc side. When the key is released (i.e. goes up) no events are generated. [Screen Related Issues and Features] Q-79: The remote display is larger (in number of pixels) than the local display I am running the vncviewer on. I don't like the vncviewer scrollbars, what I can do? vncviewer has a option (usually accessible via F8 key or -fullscreen option) for vncviewer to run in full screen, where it will automatically scroll when the mouse is near the edge of the current view. For quick scrolling, also make sure Backing Store is enabled on the machine vncviewer is run on. (XFree86/Xorg disables it by default for some reason, add Option "backingstore" to XF86Config on the vncviewer side). BTW, contact me if you are having problems with vncviewer in fullscreen mode with your window manager (i.e. no keyboard response). I have a workaround for vncviewer using XGrabServer(). There may also be scaling viewers out there (e.g. TightVNC or UltraVNC on Windows) that automatically shrink or expand the remote framebuffer to fit the local display. Especially for hand-held devices. See also [495]this FAQ on x11vnc scaling. Q-80: Does x11vnc support server-side framebuffer scaling? (E.g. to make the desktop smaller). As of Jun/2004 x11vnc provides basic server-side scaling. It is a global scaling of the desktop, not a per-client setting. To enable it use the "[496]-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). Note that if fraction is greater than one the display is magnified. Extra resources (CPU, memory I/O, and memory) are required to do the scaling. If the machine is slow where x11vnc is run with scaling enabled, the interactive response can be unacceptable. OTOH, if run with scaling on a fast machine the performance degradation is usually not a big issue or even noticeable. Also, if you just want a quick, rough "thumbnail" of the display you can append ":nb" to the fraction to turn on "no blending" mode. E.g.: "-scale 1/3:nb" Fonts will be difficult to read, but the larger features will be recognizable. BTW, "no blending" mode is forced on when scaling 8bpp PseudoColor displays (because blending an indexed colormap is a bad idea and leads to random colors, use :fb to force it on). One can also use the ":nb" with an integer scale factor (say "-scale 2:nb") to use x11vnc as a screen magnifier for vision impaired [497]applications. Since with integer scale factors the framebuffers become huge and scaling operations time consuming, be sure to use ":nb" for the fastest response. In general for a scaled display if you are using a TightVNC viewer you may want to turn off jpeg encoding (e.g. vncviewer -nojpeg host:0). There appears to be a noise enhancement effect, especially for regions containing font/text: the scaling can introduce some pixel artifacts that evidently causes the tight encoding algorithm to incorrectly detect the regions as image data and thereby introduce additional pixel artifacts due to the lossiness of the jpeg compression algorithm. Experiment to see if -nojpeg vncviewer option improves the readability of text when using -scale to shrink the display size. Also note that scaling may actually slow down the transfer of text regions because after being scaled they do not compress as well. (this can often be a significant slowdown, e.g. 10X). Another issue is that it appears VNC viewers require the screen width to be a multiple of 4. When scaling x11vnc will round the width to the nearest multiple of 4. To disable this use the ":n4" sub option (like ":nb" in the previous paragraph; to specify both use a comma: ":nb,n4", etc.) If one desires per-client scaling for something like 1:1 from a workstation and 1:2 from a smaller device (e.g. handheld), currently the only option is to run two (or more) x11vnc processes with different scalings listening on separate ports ([498]-rfbport option, etc.). BTW, whenever you run two or more x11vnc's on the same X display and use the [499]GUI, then to avoid all of the x11vnc's simultaneously answering the gui you will need to use something like [500]"-connect file1 -gui ..." with different connect files for each x11vnc you want to control via the gui (or remote-control). The "-connect file1" usage gives separate communication channels between a x11vnc proces and the gui process. Otherwise they all share the same X property channels: VNC_CONNECT and X11VNC_REMOTE. Update: As of Mar/2005 x11vnc now scales the mouse cursor with the same scale factor as the screen. If you don't want that, use the [501]"-scale_cursor frac" option to set the cursor scaling to a different factor (e.g. use "-scale_cursor 1" to keep the cursor at its natural unscaled size). Q-81: Does x11vnc work with Xinerama? (i.e. multiple monitors joined together to form one big, single screen). Yes, it should generally work because it simply polls the big effective screen. If the viewing-end monitor is not as big as the remote Xinerama display, then the vncviewer scrollbars, etc, will have to be used to pan across the large area. However one user started two x11vnc's, one with "-clip 1280x1024+0+0" and the other with "-clip 1280x1024+1280+0" to split the big screen into two and used two VNC viewers to access them. There are a couple potential issues with Xinerama however. If the screen is not rectangular (e.g. 1280x1024 and 1024x768 monitors joined together), then there will be "non-existent" areas on the screen. The X server will return "garbage" image data for these areas and so they may be distracting to the viewer. The [502]-blackout x11vnc option allows you to blacken-out rectangles by manually specifying their WxH+X+Y geometries. If your system has the libXinerama library, the [503]-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 [504]-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-82: 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 [505]FAQ to increase the limit. It is probably also a good idea to run with the [506]-onetile option in this case (to limit each x11vnc to 3 shm segments), or even [507]-noshm to use no shm segments. Q-83: Can x11vnc show only a portion of the display? (E.g. for a special purpose rfb application). As of Mar/2005 x11vnc has the "[508]-clip WxH+X+Y" option to select a rectangle of width W, height H and offset (X, Y). Thus the VNC screen will be the clipped sub-region of the display and be only WxH in size. One user used -clip to split up a large [509]Xinerama screen into two more managable smaller screens. This also works to view a sub-region of a single application window if the [510]-id or [511]-sid options are used. The offset is measured from the upper left corner of the selected window. Q-84: Does x11vnc support the XRANDR (X Resize, Rotate and Reflection) extension? Whenever I rotate or resize the screen x11vnc just seems to crash. As of Dec/2004 x11vnc supports XRANDR. You enable it with the [512]-xrandr option to make x11vnc monitor XRANDR events and also trap X server errors if the screen change occurred in the middle of an X call like XGetImage. Once it traps the screen change it will create a new framebuffer using the new screen. If the connected vnc viewers support the NewFBSize VNC extension (Windows TightVNC viewer and RealVNC 4.0 windows and Unix viewers do) then the viewer will automatically resize. Otherwise, the new framebuffer is fit as best as possible into the original viewer size (portions of the screen may be clipped, unused, etc). For these viewers you can try the [513]-padgeom option to make the region big enough to hold all resizes and rotations. If you specify "-xrandr newfbsize" then vnc viewers that do not support NewFBSize will be disconnected before the resize. If you specify "-xrandr exit" then all will be disconnected and x11vnc will terminate. Q-85: 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-86: I use Linux Virtual Consoles (VC's) to implement 'Fast User Switching' between users' sessions (e.g. Betty is on Ctrl-Alt-F7, Bobby is on Ctrl-Alt-F8, and Sid is on Ctrl-Alt-F1: they use those keystrokes to switch between their sessions). How come the view in a VNC viewer connecting to x11vnc is either completely black or otherwise all messed up unless the X session x11vnc is attached to is in the active VC? This seems to have to do with how applications (the X server processes in this case) must "play nicely" if they are not on the active VC (sometimes called VT for virtual terminal). That is, they should not read from the keyboard or mouse or manage the video display unless they have the active VC. Given that it appears the XGetImage() call must ultimately retrieve the framebuffer data from the video hardware itself, it would make sense x11vnc's polling wouldn't work unless the X session had active control of the VC. There does not seem to be an easy way to work around this. Even xwd(1) doesn't work in this case (try it). Something would need to be done at a lower level, say in the XFree86 X server. Also, using the XFree86 Shadow Framebuffer (a copy of the video framebuffer is kept in main memory) does not appear to fix the problem. If no one is sitting at the workstation and you just want to remotely switch the VC over to the one associated with your X session (so x11vnc can poll it correctly), one can use the chvt(1) command, e.g. "chvt 7" for VC #7. Q-87: Can I use x11vnc to view my VMWare session remotely? Yes, since VMWare is an X application you can view it via x11vnc in the normal way. Note that VMWare has several viewing modes: * Normal X application window (with window manager frame) * Quick-Switch mode (with no window manager frame) * Fullscreen mode The way VMWare does Fullscreen mode on Linux is to display the Guest desktop in a separate Virtual Console (e.g. VC 8) (see [514]this FAQ on VC's for background). Unfortunately, this Fullscreen VC is not an X server. So x11vnc cannot access it (however, [515]see this for a possible partial workaround). x11vnc works fine with "Normal X application window" and "Quick-Switch mode" because these use X. One user reports he left his machine with VMWare in the Fullscreen mode, and even though his X session wasn't in the active VC, he could still connect x11vnc to the X session and pass the keystrokes Ctrl-Alt (typing "blind") to the VMWare X app. This induced VMWare to switch out of Fullscreen into Normal X mode and he could continue working in the Guest desktop remotely. Sometimes it is convenient (for performance, etc.) to start VMWare in its own X session using startx(1). This can be used to have a minimal window manger (e.g. twm or even no window manager), to improve response. One can also cut the display depth (e.g. to 16bpp) in this 2nd X session to improve video performance. This 2nd X session emulates Fullscreen mode to some degree and can be viewed via x11vnc as long as the VMWare X session [516]is in the active VC. Also note that with a little bit of playing with "xwininfo -all -children" output one can extract the (non-toplevel) windowid of the of the Guest desktop only when VMWare is running as a normal X application. Then one can export just the guest desktop (i.e. without the VMWare menu buttons) by use of the [517]-id windowid option. The caveats are the X session VMWare is in must be in the active VC and the window must be fully visible, so this mode is not terribly convenient, but could be useful in some circumstances (e.g. running VMWare on a very powerful server machine in a server room that happens to have a video card, (but need not have a monitor, Keyboard or mouse)). Q-88: Can non-X devices (e.g. a raw framebuffer) be viewed and/or controlled by x11vnc? As of Apr/2005 there is rudimentary support for this. Two options were added: "-rawfb string" (to indicate the raw framembuffer and its parameters) and "-pipeinput cmd" (to provide an external program that will inject or otherwise process mouse and keystroke input). This non-X mode for x11vnc is experimental because it is so removed in scope from the intended usage of the tool. Little attempt is made to make all of the other options consistent with non-X framebuffer polling. So all of the X-related options (e.g. -add_keysyms, -xkb) are just ignored or in the worst case will cause a crash. Be careful applying such an option via the command line or remote control. The format for the -rawfb string is: -rawfb :@xx[://][+] Some examples: -rawfb shm:210337933@800x600x32:ff/ff00/ff0000 -rawfb map:/dev/fb0@1024x768x16 -rawfb map:/tmp/Xvfb_screen0@640x480x8+3232 -rawfb file:/tmp/my.pnm@250x200x24+37 So the type can be "shm" for shared memory objects, and "map" or "file" for file objects. "map" uses mmap(2) to map the file into memory and is preferred over "file" (that uses the slower lseek(2) access method). Only use file if map isn't working. BTW, "mmap" is an alias for "map" and if you do not supply a type and the file exists, map is assumed. Also, if the string is of the form "setup:cmd" then cmd is run and the first line of its output retrieved and used as the rawfb string. This allows initializing the device, determining WxHxB, etc. The object will be the numerical shared memory id for the case of shm. The idea here is some other program has created this shared memory segment and periodically updates it with new framebuffer data. x11vnc polls the area for changes. See shmat(2) and ipcs(8) for more info. The ipcs command will list current shared memory segments on the system. The object will be the path to the regular or character special file for the cases of map and file. The idea here is that in the case of a regular file some other program is writing/updating framebuffer image data to it. In the case of a character special (e.g. /dev/fb0) it is the kernel that is "updating" the framebuffer data. In all cases x11vnc needs to be told the width, height, and number of bits per pixel (bpp) of the framebuffer. This is the @WxHxB field. For the case of the Linux framebuffer device, /dev/fb0, the fbset(8) may be of use (but may not always be accurate for what is currently viewable). In general some guessing may be required, especially for the bpp. Based on the bpp x11vnc will try to guess the red, green, and blue masks (these indicate which bits correspond to each color). It if gets it wrong you can specify them manually via the optional ":R/G/B" field. E.g. ":0xff0000/0x00ff00/0x0000ff" (this is the default for 32bpp). Finally, the framebuffer may not begin at the beginning of the memory object, so use the optional "+offset" parameter to indicate where the framebuffer information starts. So as an example, the Xvfb virtual framebuffer has options -shmem and -fbdir for exporting its virtual screen to either shm or a mapped file. The format of these is XWD and so the initial header should be skipped. BTW, since XWD is not strictly RGB the view will only be approximate. Of course for the case of Xvfb x11vnc can poll it much better via the [518]X API, but you get the idea. By default in -rawfb mode x11vnc will actually close any X display it happened to open. This is basically to shake out bugs (e.g it will crash rather than mysteriously interacting with the X display). If you want x11vnc to keep the X display open while polling the raw framebuffer capitalize the type (i.e. "SHM:", "MAP:", or "FILE:"). This could be convenient for keeping the remote control channel active (it uses X properties). The "-connect /path/to/file" mechanism could also be used for remote control to avoid the X property channel. Rare usage, but if you also supply -noviewonly in this mode then the mouse and keyboard input are still sent to the X display, presumably for doing something strange with /dev/fb... All of the above was just for viewing the raw framebuffer. That may be enough for certain applications of this feature (e.g. suppose a video camera mapped its framebuffer into memory). To handle the pointer and keyboard input from the viewer users the "-pipeinput cmd" option was added to indicate a helper program to process the user input. The input is streamed to it and looks something like this: Pointer 1 205 257 0 None Pointer 1 198 253 0 None Pointer 1 198 253 1 ButtonPress-1 Pointer 1 198 253 0 ButtonRelease-1 Pointer 1 198 252 0 None Keysym 1 1 119 w KeyPress Keysym 1 0 119 w KeyRelease Keysym 1 1 65288 BackSpace KeyPress Keysym 1 0 65288 BackSpace KeyRelease Keysym 1 1 112 p KeyPress Keysym 1 0 112 p KeyRelease Run "-pipeinput tee:/bin/cat" to get a description of the format. Note that the -pipeinput option is independent of -rawfb mode and so may have some other interesting uses. BTW, the "tee:" prefix means x11vnc will both process the user input and pipe it to the command. The default is to just pipe it to the -pipeinput command. Note the -pipeinput helper program could actually control the raw framebuffer. In the libvncserver CVS a simple example program x11vnc/misc/slide.pl is provided that demonstrates a simple jpeg "slideshow" application. The -pipeinput program is run with these environment variables set: X11VNC_PID, X11VNC_PROG, X11VNC_CMDLINE, X11VNC_RAWFB_STR to aid its knowing what is up. Another example provided in libvncserver CVS is a script to inject keystrokes into the Linux console (e.g. the virtual consoles: /dev/tty1, /dev/tty2, etc) in x11vnc/misc/vcinject.pl. It is based on the vncterm/LinuxVNC.c program also in the libvncserver CVS. So to view and interact with VC #2 (assuming it is the [519]active VC) one can run something like: x11vnc -rawfb map:/dev/fb0@1024x768x16 -pipeinput './vcinject.pl 2' This assumes your Linux framebuffer device (/dev/fb0) is properly configured. See fbset(8) and other documentation. Try "file:/dev/fb0@WxHxB" as a last resort. The above is just an example of what can be done. If you really want to view and interact with the Linux console it is better to use the more accurate and faster LinuxVNC program. The only advantage x11vnc -rawfb might have is that it can presumably allow interaction with a non-text application, e.g. one based on svgalib. For example the [520]VMWare Fullscreen mode is actually viewable under -rawfb. But this isn't much use until one figures out how to inject keystrokes and mouse events... The -rawfb and -pipeinput features are intended to help one creatively "get out of a jam" (say on a legacy or embedded device) where X is absent or doesn't work properly. Feedback and bug reports are welcome. For more control and less overhead use libvncserver in your own C program that passes the framebuffer to libvncserver. Q-89: I am using x11vnc where my local machine has "popup/hidden taskbars" (e.g. GNOME or MacOS X) and the remote display where x11vnc runs also has "popup/hidden taskbars" (e.g. GNOME). When I move the mouse to the edge of the screen where the popups happen, the taskbars interfere and fight with each other in strange ways. What can I do? Is there a way to temporarily disable one or both of these magic desktop taskbars? One x11vnc user suggests: it should be straightforward to right mouse click on the task bar panel, and uncheck "enable auto-hide" from the panel properties dialog box. This will make the panel always visible. [Misc: Clipboard, File Transfer, Beeps, Thanks, etc.] Q-90: Does the Clipboard/Selection get transferred between the vncviewer and the X display? As of Jan/2004 x11vnc supports the "CutText" part of the rfb protocol. Furthermore, x11vnc is able to hold the PRIMARY selection (Xvnc does not seem to do this). If you don't want the Clipboard/Selection exchanged use the [521]-nosel option. If you don't want the PRIMARY selection to be polled for changes use the [522]-noprimary option. You can also fine-tune it a bit with the [523]-seldir dir option. You may need to watch out for desktop utilities such as KDE's "Klipper" that do odd things with the selection, clipboard, and cutbuffers. Q-91: Can I transfer files back and forth with x11vnc? As of Oct/2005 x11vnc enables the TightVNC file transfer implementation that was added to libvncserver. This currently only works with TightVNC viewers (and Windows only it appears). It is on by default, to disable it use the [524]-nofilexfer option. Q-92: Why don't I hear the "Beeps" in my X session (e.g. when typing tput bel in an xterm)? As of Dec/2003 "Beep" XBell events are tracked by default. The X server must support the XKEYBOARD extension (this is not on by default in Solaris, see Xserver(1) for how to turn it on via +kb), and so you won't hear them if the extension is not present. If you don't want to hear the beeps use the [525]-nobell option. If you want to hear the audio from the remote applications, consider trying a redirector such as esd. Contributions: Q-93: Thanks for your program and for your help! Can I make a donation? Please do (any amount is appreciated) and thank you for your support! Click on the PayPal button below for more info. 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_________________________________________________________________ Chaining ssh's: Note that for use of a ssh gateway and -L redirection to an internal host (e.g. "-L 5900:otherhost:5900") the VNC traffic inside the firewall is not encrypted and you have to manually log into otherhost to start x11vnc. Kyle Amon shows a method where you chain two ssh's together that encrypts all network traffic and also automatically starts up x11vnc on the internal workstation: #!/bin/sh # gateway="example.com" # or "user@example.com" host="labyrinth" # or "user@hostname" user="kyle" # Need to sleep long enough for all of the passwords and x11vnc to start up. # The /dev/null) & # Chain the vnc connection thru 2 ssh's, and connect x11vnc to user's display: # exec /usr/bin/ssh -t -L 5900:localhost:5900 $gateway \ /usr/bin/ssh -t -L 5900:localhost:5900 $host \ sudo /usr/bin/x11vnc -localhost -auth /home/$user/.Xauthority \ -rfbauth .vnc/passwd -display :0 Also note the use of sudo(1) to switch to root so that the different user's .Xauthority file can be accessed. See the visudo(8) manpage for details on how to set this up. One can also chain together ssh's for reverse connections with vncviewers using the -listen option. For this case -R would replace the -L (and 5500 the 5900, see the #2 example script above). If the gateway machine's sshd is configured with GatewayPorts=no (the default) then the double chaining of "ssh -R ..." will be required for reverse connections to work. ======================================================================= http://www.karlrunge.com/x11vnc/miscbuild.html: _________________________________________________________________ Misc. Build problems: We collect here rare build problems some users have reported and the corresponding workarounds. See also the [1]FAQ's on building. One user had a problem where the build script below was failing because his work environment had the ENV variable set to a script that was resetting his PATH so that gcc could no longer be found. Make sure you do not have any ENV or BASH_ENV in your environment doing things like that. Typing "unset ENV", etc. before configuring and building should clear it. One user had his bash shell compiled with --enable-xpg-echo-default that causes some strange behavior with things like echo "\\1 ..." the configure script executes. In particular instead of getting "\1" the non-printable character "^A" is produced, and causes failures at compile time like: ../rfb/rfbconfig.h:9:22: warning: extra tokens at end of #ifndef directive The workaround is to configure like this: env CONFIG_SHELL=/bin/sh /bin/sh ./configure i.e. avoid using the bash with the misbehavior. A bug has been filed against autoconf to guard against this. References 1. http://www.karlrunge.com/x11vnc/miscbuild.html#faq-build ======================================================================= http://www.karlrunge.com/x11vnc/sunray.html: Sun Ray Notes: You can run x11vnc on your (connected or disconnected) [1]SunRay session (Please remember to use settings like [2]-wait 200, [3]-sb 15, and not running a screensaver animation (blank instead) to avoid being a resource hog! x11vnc does induce a lot of memory I/O from polling the X server. It also helps to have a solid background color, e.g. [4]-solid). You have to know the name of the machine your SunRay session X server is running on (so you can ssh into it and start x11vnc). You also need to know the X11 DISPLAY number for the session: on a SunRay it could be a large number, e.g. :137, since there are many people with X sessions (Xsun processes) on the same machine. If you don't know it, you can get it by running who(1) in a shell on the SunRay server and looking for the dtlocal entry with your username (and if you don't even know which server machine has your session, you could login to all possible ones looking at the who output for your username...). I put some code in my ~/.dtprofile script that stores $DISPLAY in my ~/.sunray_current file at session startup and deletes it when the session ends to make it easy to get at the hostname and X11 display number info for my current X sessions. SunRay Gotcha #1: Note that even though your SunRay X11 DISPLAY is something like :137, x11vnc still tries for port 5900 as its listening port if it can get it, in which case the VNC display (i.e. the information you supply to the VNC viewer) is something like sunray-server:0 (note the :0 corresponding to port 5900, it is not :137). If it cannot get 5900, it tries for 5901, and so on. You can also try to force the port (and thereby the VNC display) using the [5]-rfbport NNNN option. Especially on a busy Sun Ray server it is often difficult to find free ports for both VNC and the HTTP Java applet server to listen on. This script, [6]vnc_findports may be of use for doing this automatically. It suggests x11vnc command line options based on netstat output that lists the occupied ports. It is even more difficult to start vncserver/Xvnc on a busy Sun Ray because then 3 ports (HTTP, VNC, and X11), all separated by 100 are needed! This script, [7]findvncports may be helpful as well. Both scripts start at VNC display :10 and work their way up. SunRay Gotcha #2: If you get an error like: shmget(tile) failed. shmget: No space left on device when starting up x11vnc that most likely means all the shared memory (shm) slots are filled up on your machine. The Solaris default is only 100, and that can get filled up in a week or so on a SunRay server with lots of users. If the shm slot is orphaned (e.g. creator process dies) the slot is not reclaimed. You can view the shm slots with the "ipcs -mA" command. If there are about 100 then you've probably hit this problem. They can be cleaned out (by the owner or by root) using the ipcrm command. I wrote a script [8]shm_clear that finds the orphans and lists or removes them. Longer term, have your SunRay sysadmin add something like this to /etc/system: set shmsys:shminfo_shmmax = 0x2000000 set shmsys:shminfo_shmmni = 0x1000 SunRay Gotcha #3: Some SunRay installations have implemented suspending certain applications when a SunRay session is in a disconnected state (e.g. Java Badge pulled out, utdetach, etc). This is a good thing because it limits hoggy or runaway apps from wasting the shared CPU resource. Think how much CPU and memory I/O is wasted by a bunch of Firefox windows running worthless Flash animations while your session is disconnected! So some sites have implemented scripts to suspend (e.g. kill -STOP) certain apps when your badge is removed from the SunRay terminal. When you reattach, it kill -CONT them. This causes problems for viewing the detached SunRay session via x11vnc: those suspended apps will not respond (their windows will be blank or otherwise inactive). What to do? Well, since you are going to be using the application you might as well unfreeze it rather than starting up a 2nd instance. Here is one way to do it using the kill -CONT mechanism: kill -CONT `ps -ealf | grep ' T ' | grep $LOGNAME | awk '{print $4}'` If you want to be a good citizen and re-freeze them before you exit x11vnc this script could be of use: #!/bin/sh # # kill -STOP/-CONT script for x11vnc (or other) SunRay usage ("freezes" # certain apps from hogging resources when disconnected). # # Put here a pattern that matches the apps that are frozen: # appmatch="java_vm|jre|netscape-bin|firefox-bin|realplay|acroread|mozilla-bin" if [ "X$1" = "Xfreeze" ]; then pkill -STOP -U $LOGNAME "$appmatch" elif [ "X$1" = "Xthaw" ]; then pkill -CONT -U $LOGNAME "$appmatch" elif [ "$RFB_MODE" = "afteraccept" -a "$RFB_STATE" = "NORMAL" ]; then # a valid x11vnc login. if [ "$RFB_CLIENT_COUNT" = "1" ]; then # only one client present. pkill -CONT -U $LOGNAME "$appmatch" fi elif [ "$RFB_MODE" = "gone" -a "$RFB_STATE" = "NORMAL" ]; then # a valid x11vnc login. if [ "$RFB_CLIENT_COUNT" = "0" ]; then # last client present has just left. pkill -STOP -U $LOGNAME "$appmatch" fi fi exit 0 If you called the script "goodcitizen" you could type "goodcitizen thaw" to unfreeze them, and then "goodcitizen freeze" to refreeze them. One could also use these x11vnc options "-afteraccept goodcitizen -gone goodcitizen" to do it automatically. SunRay Gotcha #4: Recent versions of the Sun Ray Server Software SRSS (seems to be version 3.0 or 3.1) have a "misfeature" that when the session is disconnected (i.e. badge/smartcard out) the screen locker (xscreensaver) will freeze the X server just when the "Enter Password" dialog box appears. So you cannot unlock the screen remotely via x11vnc! Here "freeze" means "stop other X clients from inserting keyboard and mouse input and from viewing the current contents of the screen". Or something like that; the upshot is x11vnc can't do its normal thing. There are several workarounds for this. 1) The easiest one by far is to put these lines in your $HOME/.dtprofile file: SUN_SUNRAY_UTXLOCK_PREF="/usr/openwin/bin/xlock -mode blank" export SUN_SUNRAY_UTXLOCK_PREF One might argue that xlock isn't particularly "pretty". (Just IMHO, but if something like this not being pretty actually gets in the way of your work I think some introspection may be in order. :-) 2) The problem has been traced to the pam_sunray.so PAM module. Evidently xscreensaver invokes this pam module and it communicates with utsessiond who in turn instructs the Xsun server to not process any synthetic mouse/keyboard input or to update the screen framebuffer. It is not clear if this is by design (security?) or something else. In any event, the problem can be avoided by commenting out the corresponding line in /etc/pam.conf: #xscreensaver auth sufficient /opt/SUNWut/lib/pam_sunray.so syncondisplay Leave the other xscreensaver pam authentication lines unchanged. The dtsession-SunRay line may also need to be commented out to avoid the problem for CDE sessions. N.B. it is possible the application of a SSRS patch, etc, may re-enable that /etc/pam.conf line. 3) A more drastic way is to kill the xscreensaver process from a shell prompt whenever you connect via x11vnc and the screen is in a locked state: pkill -U $LOGNAME '^xscreensaver$' And then after you are in be sure to restart it by typing something like: xscreensaver & You may want to avoid restarting it until you are about to disconnect your VNC viewer (since if it locks the screen while you are working you'll be stuck again). 3') The above idea can be done a bit more cleanly by having x11vnc do it. Suppose we called the following script xss_killer: #!/bin/sh # # xss_killer: kill xscreensaver after a valid x11vnc client logs in. # Restart xscreensaver and lock it when the last client # disconnects. PATH=/usr/openwin/bin:/usr/bin:$PATH export PATH if [ "$RFB_MODE" = "afteraccept" -a "$RFB_STATE" = "NORMAL" ]; then # a valid x11vnc login. if [ "$RFB_CLIENT_COUNT" = "1" ]; then # only one client present. pkill -U $LOGNAME '^xscreensaver$' pkill -KILL -U $LOGNAME -f xscreensaver/hacks fi elif [ "$RFB_MODE" = "gone" -a "$RFB_STATE" = "NORMAL" ]; then # a valid x11vnc login. if [ "$RFB_CLIENT_COUNT" = "0" ]; then # last client present has just left. xscreensaver -nosplash & sleep 1 xscreensaver-command -lock & fi fi Then we would run x11vnc with these options: "-afteraccept xss_killer -gone xss_killer". The [9]-afteraccept option (introduced in version 0.8) is used to run a command after a vncviewer has successfully logged in (note that this is a VNC login, not a Unix login, so you may not want to do this if you are really paranoid...) Note if you use the above script and also plan to Ctrl-C (SIGINT) x11vnc you have to run the xscreensaver in a new process group to avoid killing it as well. One way to do this is via this kludge: perl -e 'setpgrp(0,0); exec "xscreensaver -nosplash &"' in the above script. 4) There appears to be a bug in pam_sunray.so in that it doesn't seem to honor the convention that, say, DISPLAY=unix:3 means to use Unix sockets to connect to display 3 on the local machine (this is a bit faster than TCP sockets). Rather, it thinks the display is a non-local one to a machine named "unix" (that usually does not resolve to an IP address). Amusingly, this can be used to bypass the pam_sunray.so blocking of Xsun that prevents one from unlocking the screen remotely via x11vnc. One could put something like this in $HOME/.dtprofile to kill any existing xscreensavers and then start up a fresh xscreensaver using DISPLAY=unix:N # stop/kill any running xscreensavers (probably not running yet, but to be sure ) xscreensaver-command -exit pkill -U $LOGNAME '^xscreensaver$' env DISPLAY=`echo $DISPLAY | sed -e 's/^.*:/unix:/'` xscreensaver & Note that all of the above workarounds side-step the pam_sunray.so PAM module in one way or another. You'll need to see if that is appropriate for your site's SunRay / smartcard usage. Also, these hacks may break other things and so you may want to test various scenarios carefully. E.g. check corner cases like XDMCP/dtremote, NSCM, etc. References 1. http://wwws.sun.com/sunray/index.html 2. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-wait 3. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-sb 4. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-solid 5. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-rfbport 6. http://www.karlrunge.com/x11vnc/vnc_findports 7. http://www.karlrunge.com/x11vnc/findvncports 8. http://www.karlrunge.com/x11vnc/shm_clear 9. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-afteraccept ======================================================================= http://www.karlrunge.com/x11vnc/ssl.html: Notes on x11vnc SSL Certificates and Key Management: The simplest scheme ("x11vnc -ssl") is where x11vnc generates a temporary, self-signed certificate each time (automatically using openssl(1)) and the VNC viewer client accepts the certificate without question (e.g. user clicks "Yes" in a dialog box. Perhaps the dialog allows them to view the certificate too). Also note stunnel's default is to quietly accept all certificates. The encryption this provides protects against all passive sniffing of the VNC traffic and passwords on the network and so it is quite good, but it does not prevent a Man-In-The-Middle attack: e.g. an attacker intercepts the VNC client stream and sends it his own Public key for SSL negotiation (pretending to be the server). Then it makes a connection to SSL x11vnc itself and forwards the data back and forth. He can see all the traffic and modify it as well. Most people don't seem to worry about Man-In-The-Middle attacks these days; they are more concerned about passive sniffing. Perhaps someday that will change if attack tools are created that make it simpler to perform the attack. If you are not worried about Man-In-The-Middle attacks you do not have to read the techniques described in the rest of this section. To prevent Man-In-The-Middle attacks, certificates must somehow be verified. This requires the VNC client side have some piece of information that can be used to verify the SSL x11vnc server. Alternatively, although rarely done, x11vnc could verify VNC Clients' certificates, see the [1]-sslverify option that is discussed briefly below. There are a number of ways to have the client authenticate x11vnc. The quickest way perhaps would be to copy (safely) the certificate x11vnc prints out: 26/03/2006 21:12:00 Creating a temporary, self-signed PEM certificate... ... -----BEGIN CERTIFICATE----- MIIC4TCCAkqgAwIBAgIJAMnwCaOjvEKaMA0GCSqGSIb3DQEBBAUAMIGmMQswCQYD VQQGEwJBVTEOMAwGA1UEBxMFTGludXgxITAfBgNVBAsTGGFuZ2VsYS0xMTQzNDI1 NTIwLjQxMTE2OTEPMA0GA1UEChMGeDExdm5jMS4wLAYDVQQDEyV4MTF2bmMtU0VM (more lines) ... -----END CERTIFICATE----- to the client machine(s) and have the client's SSL machinery (e.g. stunnel, Web Browser, or Java plugin) import the certificate. That way when the connection to x11vnc is made the client can verify that is it the desired server on the other side of the SSL connection. So, for example suppose the user is using the SSL enabled Java VNC Viewer and has incorporated the x11vnc certificate into his Web browser on the viewing side. If he gets a dialog that the certificate is not verified he knows something is wrong. It may be a Man-In-The-Middle attack, but more likely x11vnc certificate has changed or expired or his browser was reinstalled and lost the certificate, etc, etc. As another example, if the user was using [2]stunnel with his VNC viewer (this is mentioned [3]in this FAQ), e.g. STUNNEL.EXE on Windows, then he would have to set the "CAfile = path-to-the-cert" and "verify = 2" options in the stunnel.conf file before starting up the tunnel. If a x11vnc certificate cannot be verified, stunnel will drop the connection (and print a failure message in its log file). A third example, using the VNC viewer on Unix with stunnel the wrapper script can be used this way: "[4]ssl_vncviewer -verify ./x11vnc.crt far-away.east:0" where ./x11vnc.crt is the copied certificate x11vnc printed out. Note that in principle the copying of the certificate to the client machine(s) itself could be altered in a Man-In-The-Middle attack! You can't win. It is unlikely the attacker could predict how you were going to send it unless you had, say, done it many times before the same way. SSH is a very good way to send it (but of course it too depends on public keys being sent unaltered between the two machines!). If you are really paranoid, I'm sure you'll figure out a really good way to transport the certificates. See the Certificate Authority scheme below for a way to make this easier (you just have to do it once). Saving SSL certificates and keys: Now, it would be very inconvenient to copy the new temporary certificate every time x11vnc is run in SSL mode. So for convenience there is the "SAVE" keyword to instruct x11vnc to save the certificate it creates: x11vnc -ssl SAVE -display :0 ... This way it will save the certificate and private key in these files: ~/.vnc/certs/server.crt ~/.vnc/certs/server.pem The ".crt" file contains only the certificate and should be copied to the VNC Viewer machine(s) that will be authenticating the x11vnc server. The ".pem" file contains both the certificate and the private key and should be kept secret. (If you don't like the default location ~/.vnc/certs, e.g. it is on an NFS share and you are worried about local network sniffing, use the [5]-ssldir dir option to point to a different directory.) So the next time you run "x11vnc -ssl SAVE ..." it will read the server.pem file directly instead of creating a new one. You can manage multiple SSL x11vnc server keys in this simple way by using: x11vnc -ssl SAVE-key2 -display :0 ... etc, where you put whatever name you choose for the key after "SAVE-". E.g. "-ssl SAVE-fred". Also, if you want to be prompted to possibly change the made up names, etc. that x11vnc creates (e.g. "x11vnc-SELF-SIGNED-CERT-7762" for the CommonName) for the certificates distinguished name (DN), then use "x11vnc -ssl SAVE_PROMPT ...", "x11vnc -ssl SAVE_PROMPT-fred ..." etc. when you create the key the first time. Tip: when prompting, if you choose the CommonName entry to be the full internet hostname of the machine the clients will be connecting to then that will avoid an annoying dialog box in their Web browsers that warn that the CommonName doesn't match the hostname. Passphrases for server keys: Well, since now with the "SAVE" keyword the certificate and key will be longer lived, one can next worry about somebody stealing the private key and pretending to be the x11vnc server! How to guard against this? The first is that the file is created with perms 600 (i.e. -rw-------) to make it harder for an untrusted user to copy the file. A better way is to also encrypt the private key with a passphrase. You are prompted whether you want to do this or not when the key is first created under "-ssl SAVE" mode ("Protect key with a passphrase? [y]/n"). It is suggested that you use a passphrase. The inconvenience is every time you run "x11vnc -ssl SAVE ..." you will need to supply the passphrase to access the private key: 06/04/2006 11:39:11 using PEM /home/runge/.vnc/certs/server.pem 0.000s A passphrase is needed to unlock an OpenSSL private key (PEM file). Enter passphrase> before x11vnc can continue. Being your own Certificate Authority: A very sophisticated way that scales well if the number of users is large is to use a Certificate Authority (CA) whose public certificate is available to all of the VNC clients and whose private key has been used to digitally sign the x11vnc server certificate(s). The idea is as follows: * A special CA cert and key is generated. * Its private key is always protected by a good passphrase since it is only used for signing. * The CA cert is (safely) distributed to all machines where VNC clients will run. * One or more x11vnc server certs and keys are generated. * The x11vnc server cert is signed with the CA private key. * x11vnc is run using the server key. (e.g. "[6]-ssl SAVE") * VNC clients (viewers) can now authenticate the x11vnc server because they have the CA certificate. The advantage is the CA cert only needs to be distributed once to the various machines, that can be done even before x11vnc server certs are generated. As above, it is important the CA private key and the x11vnc server key are kept secret, otherwise someone could steal them and pretend to be the CA or the x11vnc server if they copied the key. It is recommended that the x11vnc server keys are also protected via a passphrase (see the previous section). Optionally, VNC viewer certs and keys could also be generated to enable the x11vnc server to authenticate each client. This is not normally done (usually a simple viewer password scheme is used), but this can be useful in some situations. These optional steps go like this: * One or more VNC client certs and keys are generated. * These VNC client certs are signed with the CA private key. * The VNC client certs+keys are safely distributed to the corresponding client machines. * x11vnc is told to verify clients by using the CA cert. (e.g. "[7]-sslverify CA") * When VNC clients (viewers) connect, they must authenticate themselves to x11vnc by using their client key. Again, it is a good idea if the client private keys are protected with a passphrase, otherwise if stolen they could be used to gain access to the x11vnc server. Once distributed to the client machines, there is no need to keep the client key on the CA machine that generated and signed it. You can keep the client certs if you like because they are public, and they could also be used let in only a subset of all the clients. (see [8]-sslverify) How to do the above CA steps with x11vnc: Some utility commands are provided to ease the cert+key creation, signing, and management: [9]-sslGenCA, [10]-sslGenCert, [11]-sslDelCert, [12]-sslEncKey, [13]-sslCertInfo. They basically run the openssl(1) command for you to manage the certs/keys. It is required that openssl(1) is installed on the machine and available in PATH. All commands can be pointed to an alternate toplevel certificate directory via the [14]-ssldir option if you don't want to use the default ~/.vnc/certs. 1) To generate your Certificate Authority (CA) cert and key run this: x11vnc -sslGenCA Follow the prompts, you can modify any information strings you care to. You will also be required to encrypt the CA private key with a passphrase. This generates these files: ~/.vnc/certs/CA/cacert.pem (the CA public certificate) ~/.vnc/certs/CA/private/cakey.pem (the CA private key) If you want to use a different directory use [15]-ssldir It must supplied with all subsequent SSL utility options to point them to the correct directory. 2) To generate a signed x11vnc server cert and key run this: x11vnc -sslGenCert server As with the CA generation, follow the prompts and you can modify any information strings you care to. This will create the files: ~/.vnc/certs/server.crt (the server public certificate) ~/.vnc/certs/server.pem (the server private key + public cert) It is recommended to protect the server private key with a passphrase (you will be prompted whether you want to). You will need to provide it whenever you start x11vnc using this key. 3) Start up x11vnc using this server key: x11vnc -ssl SAVE -display :0 ... (SAVE corresponds to server.pem, see [16]-sslGenCert server somename info on creating additional server keys, server-somename.crt ...) 4) Next, safely copy the CA certificate to the VNC viewer (client) machine(s). Perhaps: scp ~/.vnc/CA/cacert.pem clientmachine:. 5) Then the tricky part, make it so the SSL VNC Viewer uses this certificate. There are a number of ways this might be done, it depends on what your client and/or SSL tunnel is. Some examples: For the SSL Java VNC viewer supplied with x11vnc in classes/ssl/VncViewer.jar or classes/ssl/SignedVncViewer.jar: * Import the cacert.pem cert into your Web Browser (e.g. Edit -> Preferences -> Privacy & Security -> Manage Certificates -> WebSites -> Import) * Or Import the cacert.pem cert into your Java Plugin (e.g. run ControlPanel, then Security -> Certificates -> Secure Site -> Import) When importing, one would give the browser/java-plugin the path to the copied cacert.pem file in some dialog. Note that the Web browser or Java plugin is used for the server authentication. If the user gets a "Site not verified" message while connecting he should investigate further. For the use of stunnel (e.g. on Windows) one would add this to the stunnel.conf: # stunnel.conf: client = yes options = ALL CAfile = /path/to/cacert.pem # or maybe C:\path\to\cacert.pem [myvncssl] accept = 5901 connect = far-away.east:5900 (then point the VNC viewer to localhost:1). Here is an example for the Unix stunnel wrapper script [17]ssl_vncviewer: ssl_vncviewer -verify ./cacert.pem far-away.east:0 Tricks for server keys: To create additional x11vnc server keys do something like this: x11vnc -sslGenCert server myotherkey and use it this way: x11vnc -ssl SAVE-myotherkey ... The files will be ~/.vnc/certs/server-myotherkey.{crt,pem} You can also create a self-signed server key: x11vnc -sslGenCert server self:third_key and use it this way: x11vnc -ssl SAVE-self:third_key ... This key is not signed by your CA. This can be handy to have a key set separate from your CA when you do not want to create a 2nd CA cert+key. Using external CA's: You don't have to use your own CA cert+key you can use a third party's. Perhaps you have a company-wide CA or you can even have your x11vnc certificate signed by a professional CA (e.g. www.thawte.com or www.verisign.com). The advantage to doing this is that the VNC client machines will already have the CA certificates installed and you don't have to install it on each machine. To generate an x11vnc server cert+key this way you should generate a "request" for a certicate signing something like this: x11vnc -sslGenCert server req:external This will create the request file: ~/.vnc/certs/server-req:external.req Which you should send to the external CA. When you get the signed certificate back from them, save it in the file: ~/.vnc/certs/server-req:external.crt and create the .pem this way: cp ~/.vnc/certs/server-req:external.key ~/.vnc/certs/server-req:external. pem chmod 600 ~/.vnc/certs/server-req:external.pem cat ~/.vnc/certs/server-req:external.crt >> ~/.vnc/certs/server-req:external. pem rm ~/.vnc/certs/server-req:external.key You also rename the two files (.crt and .pem) to have a shorter basename if you like. Using Client Keys for Authentication: You can optionally create certs+keys for your VNC client machines as well. After distributing them to the client machines you can have x11vnc verify the clients using SSL. Here is how to do this: x11vnc -sslGenCert client dilbert x11vnc -sslGenCert client wally x11vnc -sslGenCert client alice ... As usual, follow the prompts if you want to change any of the info field values. As always, it is a good idea to protect the private keys with a passphrase. These files are created: ~/.vnc/certs/clients/dilbert.crt ~/.vnc/certs/clients/dilbert.pem ... Note that these are kept in a clients subdirectory. Next, safely copy the .pem files to each corresponding client machine and incorporate them into the VNC viewer / SSL software (see the ideas mentioned above for the CA and server keys). The only difference is these certificates might be referred to as "My Certificates" or "Client Certificates". They are used for client authentication (which is relatively rare for SSL). After copying them you can delete the clients/*.pem files for extra safety because the private keys are not needed by the x11vnc server. You don't really need the clients/*.crt files either (because they have been signed by the CA). But they could come in handy if you wanted to let in just one client. Now start up x11vnc and instruct it to verify connecting clients via SSL and the CA cert: x11vnc -ssl SAVE -sslverify CA Finally, connect with your VNC viewer using the key. For the Java Applet viewer (TBD...). Here is an example for the Unix stunnel wrapper script [18]ssl_vncviewer: using client authentication (and the standard server authentication with the CA cert): ssl_vncviewer -mycert ./dilbert.pem -verify ./cacert.pem far-away.east:0 It is also possible to use [19]-sslverify on a per-client key basis, and also using self-signed client keys (x11vnc -sslGenCert client self:dilbert) Additional utlities: You can get information about your keys via [20]-sslCertInfo. These lists all your keys: x11vnc -sslCertInfo list x11vnc -sslCertInfo ll (the latter is long format). These print long output, including the public certificate, for individual keys: x11vnc -sslCertInfo server x11vnc -sslCertInfo dilbert x11vnc -sslCertInfo all (every key, very long) If you want to add a protecting passphrase to a key originally created without one: x11vnc -sslEncKey SAVE x11vnc -sslEncKey SAVE-fred To delete a cert+key: x11vnc -sslDelCert SAVE x11vnc -sslDelCert SAVE-fred x11vnc -sslDelCert wally (but rm(1) will be just as effective). More info: See also this [21]article for some some general info and examples using stunnel and openssl on Windows with VNC. References 1. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-sslverify 2. http://www.stunnel.org/ 3. http://www.karlrunge.com/x11vnc/index.html#faq-ssl-tunnel-ext 4. http://www.karlrunge.com/x11vnc/ssl_vncviewer 5. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-ssldir 6. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-ssl 7. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-sslverify 8. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-sslverify 9. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-sslGenCA 10. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-sslGenCert 11. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-sslDelCert 12. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-sslEncKey 13. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-sslCertInfo 14. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-ssldir 15. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-ssldir 16. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-ssldir 17. http://www.karlrunge.com/x11vnc/ssl_vncviewer 18. http://www.karlrunge.com/x11vnc/ssl_vncviewer 19. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-sslverify 20. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-sslCertInfo 21. http://www.securityfocus.com/infocus/1677 ======================================================================= http://www.karlrunge.com/x11vnc/ssl-portal.html: Using Apache as an SSL Gateway to x11vnc servers inside a firewall: The standard way to allow access to x11vnc running on workstations inside a firewall is via SSH. The user somewhere out on the Internet logs in to the SSH gateway machine and uses port forwarding (e.g. ssh -L 5900:myworkstation:5900 user@gateway) to set up the encrypted channel that VNC is then tunneled through. Next he starts up the VNC viewer on the machine where he is sitting directed to the local tunnel port. The SSH scheme is nice because it is a common and well tested login technique for users connecting to machines inside their company or home firewall. It is a bit awkward, however, because SSH needs to be installed on the Viewer machine and the user usually has to rig up his own port redirection plumbing. With the SSL support in x11vnc and the Java VNC viewer applet, a convenient and secure alternative exists that uses the Apache webserver. The idea is that the company or home internet connection is already running apache as a web server (either SSL or non-SSL) and we add to it the ability to act as a gateway for SSL VNC connections. The only thing needed on the Viewer side is a Java enabled Web Browser. The stunnel VNC viewer wrapper script provided (ssl_vncviewer) can also take advantage of the method described here. There are numerous ways to do this. We present the simplest one here. Important: these schemes allow incoming connections from anywhere on the Internet to specific ports on machines inside the firewall. Care must be taken to implement and test thoroughly. If one is paranoid one can (and should) add extra layers of protection. (e.g. extra passwords, packet filtering, SSL certificate verification, etc). The scheme described here sets up apache on the firewall/gateway as a regular Web proxy into the intranet and allows connections to a fixed port on a limited set of machines. In this example suppose the gateway machine running apache is named "www.gateway.east" (e.g. it may also provide normal web service). We also choose the Internet-facing port for this VNC service to be port 563. One could choose any port, including the default HTTP port 80. We choose 563 because it is the rarely used SNEWS port that is usually allowed by Web proxies for the CONNECT method. The idea is the user may be coming out of another firewall using a proxy (not the one we describe here, that is, the case when two proxies are involved; the "double proxy" problem) and using port 563 simplifies things because CONNECT's to it are usually allowed by default. We also assume all of the x11vnc servers on the internal machines are all listening on port 5915 ("-rfbport 5915") instead of the default 5900. This is to limit any unintended proxy redirections to a lesser used port, and also to stay out of the way of normal VNC servers on the same machines. One could obviously implement a scheme that handles different ports, but we just discuss this simplest setup here. So we assume x11vnc has been started this way on all of the workstations to be granted VNC access: x11vnc -ssl -http -display :0 -forever -rfbauth ~/.vnc/passwd -rfbport 5915 i.e. we force SSL VNC connections, port 5915, serve the Java VNC viewer applet, and require a VNC password (another option would be [1]-unixpw). These sections are added to the httpd.conf apache configuration file on www.gateway.east: Listen 563 # this is a "bounce" failure from the ProxyRemoteMatch below. ProxyRequests Off # for convenience, a rewrite to avoid having ...?CONNECT=..&PORT=... in the URL. RewriteEngine On RewriteRule /x11vnc/([^/]*)$ /x11vnc/$1/index.vnc?CONNECT=$1+5915 &PORT=563 [R,NE] RewriteRule /x11vnc/proxy/([^/]*)$ /x11vnc/$1/proxy.vnc?CONNECT=$1+5915 &PORT=563 [R,NE] # allow incoming proxy CONNECT requests to port 5915 only. ProxyRequests On AllowCONNECT 5915 # this will fetch the jar file from port 5815 via http (not https) # (list all allowed x11vnc servers here) ProxyPass /x11vnc/mach1/ http://mach1:5815/ ProxyPass /x11vnc/mach2/ http://mach2:5815/ ProxyPass /x11vnc/mach3/ http://mach3:5815/ ProxyPass /x11vnc/mach4/ http://mach4:5815/ # ... # force a reject for any CONNECT not to the known list of x11vnc servers: # (list all allowed x11vnc servers here) ProxyRemoteMatch ^(?!(http://|mach1:|mach2:|mach3:|mach4:)) http://localhos t:563/ Note that the listing of allowed internal workstations (mach1, mach2, ...) is done in two places. The above setup requires mod_rewrite (optional) and mod_proxy (required) be enabled in the apache web server. The user at the Java enabled Web browser would simply enter this URL into the browser: http://www.gateway.east:563/x11vnc/mach2 to connect to internal workstation mach2, etc. There will be a number of SSL certificate, etc, dialogs he will have to respond to in addition to any passwords he is required to provide (this depends on how you set up user authentication for x11vnc). If a second Web proxy is involved (i.e. the user's browser is inside another firewall that requires proxying) then use this URL: http://www.gateway.east:563/x11vnc/proxy/mach2 See [2]this FAQ for more info on how this works. Let's go through the httpd.conf additions in detail. The VirtualHost localhost:563 section is used as a bounce if anyone tries to connect to a workstation machine not listed in httpd.conf. See ProxyRemoteMatch below. The RewriteRule's are for convenience only so that the URL entered into the Web browser does not need the various extra parameters, e.g.: http://www.gateway.east:563/x11vnc/mach2/index.vnc?CONNECT=mach2+5915&PORT=5 63 (or otherwise make direct edits to index.vnc to set these parameters). Next, the "ProxyRequests On" and "AllowCONNECT 5915" enable the web server to forward proxy requests to port 5915 (and only this port) INSIDE the firewall. Test this carefully. The "ProxyPass /x11vnc/mach1/ ..." lines forward the initial page (e.g. index.vnc) and Java applet JAR file (e.g. VncViewer.jar) requests to port 5815 on the x11vnc server machines. Note that these index.vnc and VncViewer.jar downloads are not encrypted via SSL. The subsequent VNC connections are encrypted however. See below for how to have these initial downloads encrypted as well (if the apache web server has SSL, i.e. https, enabled and configured). Finally, the ProxyRemoteMatch redirects any request that is not a http: URL or a CONNECT to a valid machine (mach1, ... etc) to localhost:563 which has proxying disabled ("ProxyRequests Off") and so effectively drops the connection. Some Ideas for adding extra authentication for the paranoid: * VNC passwords: [3]-rfbauth, [4]-passwdfile, or [5]-usepw. * Unix passwords: [6]-unixpw * SSL Client certificates: [7]-sslverify * Apache AuthUserFile directive: .htaccess, etc. * Add proxy password authentication (requires Viewer changes?) Using non-Java viewers with this scheme: The [8]ssl_vncviewer stunnel wrapper script for VNC viewers has the -proxy option that can take advantage of this method. For the case of the "double proxy" situation (see below) supply both separated by a comma. Downloading the Java applet via HTTPS: To have the Java applet downloaded to the user's Web Browswer via an encrypted (and evidently safer) SSL connection the Apache webserver should be configured for SSL via [9]mod_ssl (this is probably not absolutely necessary; show us how you did it). It is actually possible to use the x11vnc [10]Key Management utility "[11]-sslGenCert" to generate your Apache/SSL .crt and .key files. (In brief, run something like "x11vnc -sslGenCert server self:apache" then copy the resulting self:apache.crt file to conf/ssl.crt/server.crt and extract the private key part from self:apache.pem and paste it into conf/ssl.key/server.key). Or you can use the standard methods described in the Apache mod_ssl documentation. In addition to the above sections in httpd.conf one should add the following to ssl.conf: SSLProxyEngine On # for convenience, a rewrite to avoid having ...?CONNECT=... in URL. RewriteEngine On RewriteRule /x11vnc/([^/]*)$ /x11vnc/$1/index.vnc?CONNECT=$1+5915&PO RT=563 [R,NE] RewriteRule /x11vnc/proxy/([^/]*)$ /x11vnc/$1/proxy.vnc?CONNECT=$1+5915&PO RT=563 [R,NE] # these "S11vnc" are for https applet downloading: RewriteRule /S11vnc/([^/]*)$ /S11vnc/$1/index.vnc?CONNECT=$1+5915&PO RT=563 [R,NE] RewriteRule /S11vnc/proxy/([^/]*)$ /S11vnc/$1/proxy.vnc?CONNECT=$1+5915&PO RT=563 [R,NE] # fetch the jar file from port 5815 via http or port 5915 via https # inside the firewall # (list all allowed x11vnc servers here) ProxyPass /x11vnc/mach1/ http://mach1:5815/ ProxyPass /x11vnc/mach2/ http://mach2:5815/ ProxyPass /x11vnc/mach3/ http://mach3:5815/ ProxyPass /x11vnc/mach4/ http://mach4:5815/ ProxyPass /S11vnc/mach1/ https://mach1:5915/ ProxyPass /S11vnc/mach2/ https://mach2:5915/ ProxyPass /S11vnc/mach3/ https://mach3:5915/ ProxyPass /S11vnc/mach4/ https://mach4:5915/ This is all in the "" section of ssl.conf. The user could then point the Web Browser to: https://www.gateway.east/x11vnc/mach2 or https://www.gateway.east/x11vnc/proxy/mach2 for the "double proxy" case. Note that inside the firewall the Java applet download traffic is not encrypted (only over the Internet is SSL used) for these cases: https://www.gateway.east/x11vnc/mach2 https://www.gateway.east/x11vnc/proxy/mach2 However for the special "S11vnc" rules above: https://www.gateway.east/S11vnc/mach2 the Java applet download is encrypted via SSL for both legs. Note that the two legs are two separate SSL sessions. So the data is uncrypted inside an apache process and reencrypted for the 2nd SSL session inside the same apache process (a very small gap one might overlook). In all of the above cases the VNC traffic from Viewer to x11vnc is encrypted end-to-end in a single SSL session, even for the "double proxy" case. This is the important part to have encrypted. Note that the Certificate dialogs the user has in his web browser will be for the Apache Certificate, while for the Java applet it will be the x11vnc certificate. Note also that you can have Apache serve up the Jar file VncViewer.jar instead of each x11vnc if you want to. INETD automation: The "single-port" (i.e. 5915) applet download and VNC connection aspect shown here is convenient and also enables having x11vnc run out of inetd. That way x11vnc is run on demand instead of being run all the time (the user does not have to remember to start it). The first connections to inetd download index.vnc and the Jar file (via https) and the the last connection to inetd establishes the SSL VNC connection. Since x11vnc is restarted for each connection, this will be slower than the (already slow) normal process. For example, the /etc/inetd.conf line could be: 5915 stream tcp nowait root /usr/sbin/tcpd /usr/local/bin/x11vnc_ssl.sh where the script x11vnc_ssl.sh looks something like this: #!/bin/sh /usr/local/bin/x11vnc -inetd -oa /var/log/x11vnc-15.log \ -ssl SAVE -http -unixpw \ -display :0 -auth /home/THE_USER/.Xauthority where, as always, the inetd launching needs to know which user is typically using the display on that machine. One could imagine giving different users different ports, 5915, 5916, etc. to distinguish (then the script would need to be passed the username). mod_rewrite could be used to automatically map username in the URL to his port number. Also note the use of "-ssl SAVE". This way a saved server.pem is used for each inetd invocation (rather generating a new one each time). Note that it cannot have a protecting passphrase because inetd will not be able to supply it. Other Ideas: - The above schemes work, but they are a bit complicated with all of the rigging. There should be better ways to configure Apache to do these, but we have not found them (please let us know if you discover something nice). However, once this scheme has been set up and is working it is easy to maintain and add workstations, etc. - In general Apache is not required, but it makes things convenient. The firewall itself could do the port redirection via its firewall rules. Evidently different Internet-facing ports would be required for each workstation. This could be set up using iptables rules for example. If there were just one or two machines this would be the easiest method. For example: iptables -t nat -A PREROUTING -p tcp -d 24.35.46.57 --dport 5901 -j DNAT --to -destination 192.168.1.2:5915 iptables -t nat -A PREROUTING -p tcp -d 24.35.46.57 --dport 5902 -j DNAT --to -destination 192.168.1.3:5915 Where 24.35.46.57 is the internet IP address of the gateway. In this example 24.35.46.57:5901 is redirected to the internal machine 192.168.1.2:5915 and 24.35.46.57:5902 is redirected to another internal machine 192.168.1.3:5915, both running x11vnc -ssl ... in SSL mode. For this example, the user would point the web browser to, e.g.: https://24.35.46.57:5901/?PORT=5901 or using the stunnel wrapper script: ssl_vncviewer 24.35.46.57:1 One can acheive similar things with dedicated firewall/routers (e.g. Linksys) using the device's web or other interface to configure the firewall. If the user may be coming out of a firewall using a proxy it may be better to redirect ports 443 and 563 (instead of 5901 and 5902) to the internal machines so that the user's proxy will allow CONNECTing to them. - The redirection could also be done at the application level using a TCP redirect program (e.g. ip_relay or fancier ones). Evidently more careful internal hostname checking, etc., could be performed by the special purpose application to add security. - One might imagine the ProxyPass could be done for the VNC traffic as well (for the ssl.conf case) to avoid the CONNECT proxying completely (which would be nice to avoid). Unfortunately we were not able to get this to work. Since HTTP is a request-response protocol (as opposed to a full bidirectional link required by VNC) this makes it difficult to do. It may be possible, but we haven't found out how yet. References 1. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-unixpw 2. http://www.karlrunge.com/x11vnc/index.html#faq-ssl-java-viewer-proxy 3. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-rfbauth 4. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-passwdfile 5. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-usepw 6. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-unixpw 7. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-sslverify 8. http://www.karlrunge.com/x11vnc/index.html#ssl_vncviewer 9. http://httpd.apache.org/docs/2.0/mod/mod_ssl.html 10. http://www.karlrunge.com/x11vnc/ssl.html 11. http://www.karlrunge.com/x11vnc/x11vnc_opts.html#opt-sslGenCert ======================================================================= http://www.karlrunge.com/x11vnc/x11vnc_opts.html: _________________________________________________________________ x11vnc: a VNC server for real X displays Here are all of x11vnc command line options: % x11vnc -opts (see below for -help long descriptions) x11vnc: allow VNC connections to real X11 displays. 0.8.1 lastmod: 2006-04-16 x11vnc options: -display disp -auth file -id windowid -sid windowid -clip WxH+X+Y -flashcmap -shiftcmap n -notruecolor -visual n -overlay -overlay_nocursor -8to24 [opts] -scale fraction -scale_cursor frac -viewonly -shared -once -forever -loop -timeout n -inetd -nofilexfer -http -connect string -vncconnect -novncconnect -allow host1[,host2..] -localhost -nolookup -input string -viewpasswd string -passwdfile filename -unixpw [list] -unixpw_nis [list] -ssl [pem] -ssldir [dir] -sslverify [path] -sslGenCA [dir] -sslGenCert type name -sslEncKey [pem] -sslCertInfo [pem] -sslDelCert [pem] -stunnel [pem] -stunnel3 [pem] -https [port] -usepw -storepasswd pass file -nopw -accept string -afteraccept string -gone string -users list -noshm -flipbyteorder -onetile -solid [color] -blackout string -xinerama -noxinerama -xtrap -xrandr [mode] -padgeom WxH -o logfile -flag file -rc filename -norc -h, -help -?, -opts -V, -version -dbg -q -bg -modtweak -nomodtweak -xkb -noxkb -skip_keycodes string -sloppy_keys -skip_dups -noskip_dups -add_keysyms -noadd_keysyms -clear_mods -clear_keys -remap string -norepeat -repeat -nofb -nobell -nosel -noprimary -nosetprimary -noclipboard -nosetclipboard -seldir string -cursor [mode] -nocursor -arrow n -noxfixes -alphacut n -alphafrac fraction -alpharemove -noalphablend -nocursorshape -cursorpos -nocursorpos -xwarppointer -buttonmap string -nodragging -wireframe [str] -nowireframe -wirecopyrect mode -nowirecopyrect -debug_wireframe -scrollcopyrect mode -noscrollcopyrect -scr_area n -scr_skip list -scr_inc list -scr_keys list -scr_term list -scr_keyrepeat lo-hi -scr_parms string -fixscreen string -debug_scroll -noxrecord -grab_buster -nograb_buster -debug_grabs -debug_sel -pointer_mode n -input_skip n -speeds rd,bw,lat -wmdt string -debug_pointer -debug_keyboard -defer time -wait time -wait_ui factor -nowait_bog -slow_fb time -readtimeout n -nap -nonap -sb time -nofbpm -fbpm -noxdamage -xd_area A -xd_mem f -sigpipe string -threads -nothreads -fs f -gaps n -grow n -fuzz n -debug_tiles -snapfb -rawfb string -pipeinput cmd -gui [gui-opts] -remote command -query variable -QD variable -sync -noremote -yesremote -unsafe -safer -privremote -nocmds -deny_all libvncserver options: -rfbport port TCP port for RFB protocol -rfbwait time max time in ms to wait for RFB client -rfbauth passwd-file use authentication on RFB protocol (use 'storepasswd' to create a password file) -passwd plain-password use authentication (use plain-password as password, USE AT YOUR RISK) -deferupdate time time in ms to defer updates (default 40) -deferptrupdate time time in ms to defer pointer updates (default none) -desktop name VNC desktop name (default "LibVNCServer") -alwaysshared always treat new clients as shared -nevershared never treat new clients as shared -dontdisconnect don't disconnect existing clients when a new non-shared connection comes in (refuse new connection instead) -httpdir dir-path enable http server using dir-path home -httpport portnum use portnum for http connection -enablehttpproxy enable http proxy support -progressive height enable progressive updating for slow links -listen ipaddr listen for connections only on network interface with addr ipaddr. '-listen localhost' and hostname work too. libvncserver-tight-extension options: -disablefiletransfer disable file transfer -ftproot string set ftp root % x11vnc -help x11vnc: allow VNC connections to real X11 displays. 0.8.1 lastmod: 2006-04-16 (type "x11vnc -opts" to just list the options.) Typical usage is: Run this command in a shell on the remote machine "far-host" with X session you wish to view: x11vnc -display :0 Then run this in another window on the machine you are sitting at: vncviewer far-host:0 Once x11vnc establishes connections with the X11 server and starts listening as a VNC server it will print out a string: PORT=XXXX where XXXX is typically 5900 (the default VNC server port). One would next run something like this on the local machine: "vncviewer hostname:N" where "hostname" is the name of the machine running x11vnc and N is XXXX - 5900, i.e. usually "vncviewer hostname:0". By default x11vnc will not allow the screen to be shared and it will exit as soon as the client disconnects. See -shared and -forever below to override these protections. See the FAQ for details how to tunnel the VNC connection through an encrypted channel such as ssh(1). In brief: ssh -L 5900:localhost:5900 far-host 'x11vnc -localhost -display :0' vncviewer -encodings 'copyrect tight zrle hextile' localhost:0 Also, use of a VNC password (-rfbauth or -passwdfile) is strongly recommend. For additional info see: http://www.karlrunge.com/x11vnc/ and http://www.karlrunge.com/x11vnc/#faq Rudimentary config file support: if the file $HOME/.x11vncrc exists then each line in it is treated as a single command line option. Disable with -norc. For each option name, the leading character "-" is not required. E.g. a line that is either "forever" or "-forever" may be used and are equivalent. Likewise "wait 100" or "-wait 100" are acceptable and equivalent lines. The "#" character comments out to the end of the line in the usual way (backslash it for a literal). Leading and trailing whitespace is trimmed off. Lines may be continued with a "\" as the last character of a line (it becomes a space character). Options: -display disp X11 server display to connect to, usually :0. The X server process must be running on same machine and support MIT-SHM. Equivalent to setting the DISPLAY environment variable to "disp". -auth file Set the X authority file to be "file", equivalent to setting the XAUTHORITY environment variable to "file" before startup. Same as -xauth file. See Xsecurity(7), xauth(1) man pages for more info. -id windowid Show the window corresponding to "windowid" not the entire display. New windows like popup menus, transient toplevels, etc, may not be seen or may be clipped. Disabling SaveUnders or BackingStore in the X server may help show them. x11vnc may crash if the window is initially partially obscured, changes size, is iconified, etc. Some steps are taken to avoid this and the -xrandr mechanism is used to track resizes. Use xwininfo(1) to get the window id, or use "-id pick" to have x11vnc run xwininfo(1) for you and extract the id. The -id option is useful for exporting very simple applications (e.g. the current view on a webcam). -sid windowid As -id, but instead of using the window directly it shifts a root view to it: this shows SaveUnders menus, etc, although they will be clipped if they extend beyond the window. -clip WxH+X+Y Only show the sub-region of the full display that corresponds to the rectangle with size WxH and offset +X+Y. The VNC display has size WxH (i.e. smaller than the full display). This also works for -id/-sid mode where the offset is relative to the upper left corner of the selected window. -flashcmap In 8bpp indexed color, let the installed colormap flash as the pointer moves from window to window (slow). Also try the -8to24 option to avoid flash altogether. -shiftcmap n Rare problem, but some 8bpp displays use less than 256 colorcells (e.g. 16-color grayscale, perhaps the other bits are used for double buffering) *and* also need to shift the pixels values away from 0, .., ncells. "n" indicates the shift to be applied to the pixel values. To see the pixel values set DEBUG_CMAP=1 to print out a colormap histogram. Example: -shiftcmap 240 -notruecolor For 8bpp displays, force indexed color (i.e. a colormap) even if it looks like 8bpp TrueColor (rare problem). -visual n Experimental option: probably does not do what you think. It simply *forces* the visual used for the framebuffer; this may be a bad thing... (e.g. messes up colors or cause a crash). It is useful for testing and for some workarounds. n may be a decimal number, or 0x hex. Run xdpyinfo(1) for the values. One may also use "TrueColor", etc. see for a list. If the string ends in ":m" then for better or for worse the visual depth is forced to be m. -overlay Handle multiple depth visuals on one screen, e.g. 8+24 and 24+8 overlay visuals (the 32 bits per pixel are packed with 8 for PseudoColor and 24 for TrueColor). Currently -overlay only works on Solaris via XReadScreen(3X11) and IRIX using XReadDisplay(3). On Solaris there is a problem with image "bleeding" around transient popup menus (but not for the menu itself): a workaround is to disable SaveUnders by passing the "-su" argument to Xsun (in /etc/dt/config/Xservers). Use -overlay as a workaround for situations like these: Some legacy applications require the default visual to be 8bpp (8+24), or they will use 8bpp PseudoColor even when the default visual is depth 24 TrueColor (24+8). In these cases colors in some windows will be incorrect in x11vnc unless -overlay is used. Another use of -overlay is to enable showing the exact mouse cursor shape (details below). Under -overlay, performance will be somewhat slower due to the extra image transformations required. For optimal performance do not use -overlay, but rather configure the X server so that the default visual is depth 24 TrueColor and try to have all apps use that visual (e.g. some apps have -use24 or -visual options). -overlay_nocursor Sets -overlay, but does not try to draw the exact mouse cursor shape using the overlay mechanism. -8to24 [opts] Try this option if -overlay is not supported on your OS, and you have a legacy 8bpp app that you want to view on a multi-depth display with default depth 24 (and is 32 bpp) OR have a default depth 8 display with depth 24 overlay windows for some apps. This option may not work on all X servers and hardware (tested on XFree86/Xorg mga driver and Xsun). The "opts" string is not required and is described below. This mode enables a hack where x11vnc monitors windows within 3 levels from the root window. If it finds any that are 8bpp it extracts the indexed color pixel values using XGetImage() and then applies a transformation using the colormap(s) to create TrueColor RGB values that it in turn inserts into bits 1-24 of the framebuffer. This creates a depth 24 "view" of the display that is then exported via VNC. Conversely, for default depth 8 displays, the depth 24 regions are read by XGetImage() and everything is transformed and inserted into a depth 24 TrueColor framebuffer. Note that even if there are *no* depth 24 visuals or windows (i.e. pure 8bpp), this mode is potentially an improvement over -flashcmap because it avoids the flashing and shows each window in the correct color. This method appear to work, but may still have bugs and it does hog resources. If there are multiple 8bpp windows using different colormaps, one may have to iconify all but one for the colors to be correct. There may be painting errors for clipping and switching between windows of depths 8 and 24. Heuristics are applied to try to minimize the painting errors. One can also press 3 Alt_L's in a row to refresh the screen if the error does not repair itself. Also the option -fixscreen 8=3.0 or -fixscreen V=3.0 may be used to periodically refresh the screen at the cost of bandwidth (every 3 sec for this example). The [opts] string can contain the following settings. Multiple settings are separated by commas. For for some X servers with default depth 24 a speedup may be achieved via the option "nogetimage". This enables a scheme were XGetImage() is not used to retrieve the 8bpp data. Instead, it assumes that the 8bpp data is in bits 25-32 of the 32bit X pixels. There is no reason the X server should put the data there for our poll requests, but some do and so the extra steps to retrieve it can be skipped. Tested with mga driver with XFree86/Xorg. For the default depth 8 case this option is ignored. To adjust how often XGetImage() is used to poll the non-default visual regions for changes, use the option "poll=t" where "t" is a floating point time. (default: 0.05) Setting the option "level2" will limit the search for non-default visual windows to two levels from the root window. Do this on slow machines where you know the window manager only imposes one extra window between the app window and the root window. Also for very slow machines use "cachewin=t" where t is a floating point amount of time to cache XGetWindowAttributes results. E.g. cachewin=5.0. This may lead to the windows being unnoticed for this amount of time when deiconifying, painting errors, etc. While testing on a very old SS20 these options gave tolerable response: -8to24 poll=0.2,cachewin=5.0. For this machine -overlay is supported and gives better response. Debugging for this mode can be enabled by setting "dbg=1", "dbg=2", or "dbg=3". -scale fraction Scale the framebuffer by factor "fraction". Values less than 1 shrink the fb, larger ones expand it. Note: image may not be sharp and response may be slower. If "fraction" contains a decimal point "." it is taken as a floating point number, alternatively the notation "m/n" may be used to denote fractions exactly, e.g. -scale 2/3 Scaling Options: can be added after "fraction" via ":", to supply multiple ":" options use commas. If you just want a quick, rough scaling without blending, append ":nb" to "fraction" (e.g. -scale 1/3:nb). No blending is the default for 8bpp indexed color, to force blending for this case use ":fb". To disable -scrollcopyrect and -wirecopyrect under -scale use ":nocr". If you need to to enable them use ":cr" or specify them explicitly on the command line. If a slow link is detected, ":nocr" may be applied automatically. Default: :cr More esoteric options: for compatibility with vncviewers the scaled width is adjusted to be a multiple of 4: to disable this use ":n4". ":in" use interpolation scheme even when shrinking, ":pad" pad scaled width and height to be multiples of scaling denominator (e.g. 3 for 2/3). -scale_cursor frac By default if -scale is supplied the cursor shape is scaled by the same factor. Depending on your usage, you may want to scale the cursor independently of the screen or not at all. If you specify -scale_cursor the cursor will be scaled by that factor. When using -scale mode to keep the cursor at its "natural" size use "-scale_cursor 1". Most of the ":" scaling options apply here as well. -viewonly All VNC clients can only watch (default off). -shared VNC display is shared, i.e. more than one viewer can connect at the same time (default off). -once Exit after the first successfully connected viewer disconnects, opposite of -forever. This is the Default. -forever Keep listening for more connections rather than exiting as soon as the first client(s) disconnect. Same as -many -loop Create an outer loop restarting the x11vnc process whenever it terminates. -bg and -inetd are ignored in this mode. Useful for continuing even if the X server terminates and restarts (you will need permission to reconnect of course). Use, e.g., -loop100 to sleep 100 millisecs between restarts, etc. Default is 2000ms (i.e. 2 secs) Use, e.g. -loop300,5 to sleep 300 ms and only loop 5 times. -timeout n Exit unless a client connects within the first n seconds after startup. -inetd Launched by inetd(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, otherwise the stderr goes to the viewer which will cause it to abort. Specifying both -inetd and -q and no -o will automatically close the stderr. -nofilexfer Disable the TightVNC file transfer extension. (same as -disablefiletransfer). Note that when the -viewonly option is supplied all file transfers are disabled. Also clients that log in viewonly cannot transfer files. However, if the remote control mechanism is used to change the global or per-client viewonly state the filetransfer permissions will NOT change. -http Instead of using -httpdir (see below) to specify where the Java vncviewer applet is, have x11vnc try to *guess* where the directory is by looking relative to the program location and in standard locations (/usr/local/share/x11vnc/classes, etc). -connect string For use with "vncviewer -listen" reverse connections. If "string" has the form "host" or "host:port" the connection is made once at startup. Use commas for a list of host's and host:port's. Note that unlike most vnc servers, x11vnc will require a password for reverse as well as for forward connections. (provided password auth has been enabled, -rfbauth, etc) If you do not want to require a password for reverse connections set X11VNC_REVERSE_CONNECTION_NO_AUTH=1 in your environment before starting x11vnc. If "string" contains "/" it is instead interpreted as a file to periodically check for new hosts. The first line is read and then the file is truncated. Be careful for this usage mode if x11vnc is running as root (e.g. via gdm(1), etc). -vncconnect Monitor the VNC_CONNECT X property set by the standard -novncconnect VNC program vncconnect(1). When the property is set to "host" or "host:port" establish a reverse connection. Using xprop(1) instead of vncconnect may work (see the FAQ). The -remote control mechanism uses X11VNC_REMOTE channel, and this option disables/enables it as well. Default: -vncconnect -allow host1[,host2..] Only allow client connections from hosts matching the comma separated list of hostnames or IP addresses. Can also be a numerical IP prefix, e.g. "192.168.100." to match a simple subnet, for more control build libvncserver with libwrap support (See the FAQ). If the list contains a "/" it instead is a interpreted as a file containing addresses or prefixes that is re-read each time a new client connects. Lines can be commented out with the "#" character in the usual way. -localhost Same as "-allow 127.0.0.1". Note: if you want to restrict which network interface x11vnc listens on, see the -listen option below. E.g. "-listen localhost" or "-listen 192.168.3.21". As a special case, the option "-localhost" implies "-listen localhost". For non-localhost -listen usage, if you use the remote control mechanism (-R) to change the -listen interface you may need to manually adjust the -allow list (and vice versa) to avoid situations where no connections (or too many) are allowed. -nolookup Do not use gethostbyname() or gethostbyaddr() to look up host names or IP numbers. Use this if name resolution is incorrectly set up and leads to long pauses as name lookups time out, etc. -input string Fine tuning of allowed user input. If "string" does not contain a comma "," the tuning applies only to normal clients. Otherwise the part before "," is for normal clients and the part after for view-only clients. "K" is for Keystroke input, "M" for Mouse-motion input, "B" for Button-click input, and "C" is for Clipboard input. Their presence in the string enables that type of input. E.g. "-input M" means normal users can only move the mouse and "-input KMBC,M" lets normal users do anything and enables view-only users to move the mouse. This option is ignored when a global -viewonly is in effect (all input is discarded in that case). -viewpasswd string Supply a 2nd password for view-only logins. The -passwd (full-access) password must also be supplied. -passwdfile filename Specify the libvncserver password via the first line of the file "filename" (instead of via -passwd on the command line where others might see it via ps(1)). See below for how to supply multiple passwords. If the filename is prefixed with "rm:" it will be removed after being read. Perhaps this is useful in limiting the readability of the file. In general, the password file should not be readable by untrusted users (BTW: neither should the VNC -rfbauth file: it is NOT encrypted). If the filename is prefixed with "read:" it will periodically be checked for changes and reread. Note that only the first 8 characters of a password are used. If multiple non-blank lines exist in the file they are all taken as valid passwords. Blank lines are ignored. Password lines may be "commented out" (ignored) if they begin with the charactor "#" or the line contains the string "__SKIP__". Lines may be annotated by use of the "__COMM__" string: from it to the end of the line is ignored. An empty password may be specified via the "__EMPTY__" string on a line by itself (note your viewer might not accept empty passwords). If the string "__BEGIN_VIEWONLY__" appears on a line by itself, the remaining passwords are used for viewonly access. For compatibility, as a special case if the file contains only two password lines the 2nd one is automatically taken as the viewonly password. Otherwise the "__BEGIN_VIEWONLY__" token must be used to have viewonly passwords. (tip: make the 3rd and last line be "__BEGIN_VIEWONLY__" to have 2 full-access passwords) -unixpw [list] Use Unix username and password authentication. x11vnc uses the su(1) program to verify the user's password. [list] is an optional comma separated list of allowed Unix usernames. See below for per-user options that can be applied. A familiar "login:" and "Password:" dialog is presented to the user on a black screen inside the vncviewer. The connection is dropped if the user fails to supply the correct password in 3 tries or does not send one before a 25 second timeout. Existing clients are view-only during this period. Since the detailed behavior of su(1) can vary from OS to OS and for local configurations, test the mode carefully on your systems before using it in production. Test different combinations of valid/invalid usernames and valid/invalid passwords to see if it behaves as expected. x11vnc will attempt to be conservative and reject a login if anything abnormal occurs. On FreeBSD and the other BSD's by default it is impossible for the user running x11vnc to validate his *own* password via su(1) (evidently commenting out the pam_self.so entry in /etc/pam.d/su eliminates this problem). So the x11vnc login will always *fail* for this case (even when the correct password is supplied). A possible workaround for this would be to start x11vnc as root with the "-users +nobody" option to immediately switch to user nobody. Another source of problems are PAM modules that prompt for extra info, e.g. password aging modules. These logins will fail as well even when the correct password is supplied. **IMPORTANT**: to prevent the Unix password being sent in *clear text* over the network, one of two schemes will be enforced: 1) the -ssl builtin SSL mode, or 2) require both -localhost and -stunnel be enabled. Method 1) ensures the traffic is encrypted between viewer and server. A PEM file will be required, see the discussion under -ssl below (under some circumstances a temporary one can be automatically generated). Method 2) requires the viewer connection to appear to come from the same machine x11vnc is running on (e.g. from a ssh -L port redirection). And that the -stunnel SSL mode be used for encryption over the network.(see the description of -stunnel below). Note: as a convenience, if you ssh(1) in and start x11vnc it will check if the environment variable SSH_CONNECTION is set and appears reasonable. If it does, then the -ssl or -stunnel requirement will be dropped since it is assumed you are using ssh for the encrypted tunnelling. -localhost is still enforced. Use -ssl or -stunnel to force SSL usage even if SSH_CONNECTION is set. To override the above restrictions you can set environment variables before starting x11vnc: Set UNIXPW_DISABLE_SSL=1 to disable requiring either -ssl or -stunnel. Evidently you will be using a different method to encrypt the data between the vncviewer and x11vnc: perhaps ssh(1) or an IPSEC VPN. Note that use of -localhost with ssh(1) is roughly the same as requiring a Unix user login (since a Unix password or the user's public key authentication is used by sshd on the machine where x11vnc runs and only local connections from that machine are accepted) Set UNIXPW_DISABLE_LOCALHOST=1 to disable the -localhost requirement in Method 2). One should never do this (i.e. allow the Unix passwords to be sniffed on the network). Regarding reverse connections (e.g. -R connect:host and -connect host), when the -localhost constraint is in effect then reverse connections can only be used to connect to the same machine x11vnc is running on (default port 5500). Please use a ssh or stunnel port redirection to the viewer machine to tunnel the reverse connection over an encrypted channel. Note that in -ssl mode reverse connection are disabled (see below). In -inetd mode the Method 1) will be enforced (not Method 2). With -ssl in effect reverse connections are disabled. If you override this via env. var, be sure to also use encryption from the viewer to inetd. Tip: you can also have your own stunnel spawn x11vnc in -inetd mode (thereby bypassing inetd). See the FAQ for details. The user names in the comma separated [list] can have per-user options after a ":", e.g. "fred:opts" where "opts" is a "+" separated list of "viewonly", "fullaccess", "input=XXXX", or "deny", e.g. "karl,fred:viewonly,boss:input=M". For "input=" it is the K,M,B,C described under -input. If a user in the list is "*" that means those options apply to all users. It also means all users are allowed to log in after supplying a valid password. Use "deny" to explicitly deny some users if you use "*" to set a global option. There are also some utilities for testing password if [list] starts with the "%" character. See the quick_pw() function in the source for details. -unixpw_nis [list] As -unixpw above, however do not use su(1) but rather use the traditional getpwnam(3) + crypt(3) method to verify passwords instead. This requires that the encrypted passwords be readable. Passwords stored in /etc/shadow will be inaccessible unless x11vnc is run as root. This is called "NIS" mode simply because in most NIS setups the user encrypted passwords are accessible (e.g. "ypcat passwd"). NIS is not required for this mode to work (only that getpwnam(3) return the encrypted password is required), but it is unlikely it will work for any other modern environment. All of the -unixpw options and contraints apply. -ssl [pem] Use the openssl library (www.openssl.org) to provide a built-in encrypted SSL tunnel between VNC viewers and x11vnc. This requires libssl support to be compiled into x11vnc at build time. If x11vnc is not built with libssl support it will exit immediately when -ssl is prescribed. [pem] is optional, use "-ssl /path/to/mycert.pem" to specify a PEM certificate file to use to identify and provide a key for this server. See openssl(1) for more info about PEMs and the -sslGenCert option below. The connecting VNC viewer SSL tunnel can optionally authenticate this server if they have the public key part of the certificate (or a common certificate authority, CA, is a more sophisicated way to verify this server's cert, see -sslGenCA below). This is used to prevent man-in-the-middle attacks. Otherwise, if the VNC viewer accepts this server's key without verification, at least the traffic is protected from passive sniffing on the network (but NOT from man-in-the-middle attacks). If [pem] is not supplied and the openssl(1) utility command exists in PATH, then a temporary, self-signed certificate will be generated for this session (this may take 5-30 seconds on slow machines). If openssl(1) cannot be used to generate a temporary certificate x11vnc exits immediately. If successful in using openssl(1) to generate a temporary certificate, the public part of it will be displayed to stderr (e.g. one could copy it to the client-side to provide authentication of the server to VNC viewers.) See following paragraphs for how to save keys to reuse when x11vnc is restarted. Set the env. var. X11VNC_SHOW_TMP_PEM=1 to have x11vnc print out the entire certificate, including the PRIVATE KEY part, to stderr. One could reuse this cert if saved in a [pem] file. Similarly, set X11VNC_KEEP_TMP_PEM=1 to not delete the temporary PEM file: the file name will be printed to stderr (so one could move it to a safe place for reuse). You will be prompted for a passphrase for the private key. If [pem] is "SAVE" then the certificate will be saved to the file ~/.vnc/certs/server.pem, or if that file exists it will be used directly. Similarly, if [pem] is "SAVE_PROMPT" the server.pem certificate will be made based on your answers to its prompts for info such as OrganizationalName, CommonName, etc. Use "SAVE-" and "SAVE_PROMPT-" to refer to the file ~/.vnc/certs/server-.pem instead. E.g. "SAVE-charlie" will store to the file ~/.vnc/certs/server-charlie.pem See -ssldir below to use a directory besides the default ~/.vnc/certs Example: x11vnc -ssl SAVE -display :0 ... Reverse connections are disabled in -ssl mode because there is no way to ensure that data channel will be encrypted. Set X11VNC_SSL_ALLOW_REVERSE=1 to override this. Your VNC viewer will also need to be able to connect via SSL. See the discussion below under -stunnel and the FAQ (ssl_vncviewer script) for how this might be achieved. E.g. on Unix it is easy to write a shell script that starts up stunnel and then vncviewer. Also in the x11vnc source a SSL enabled Java VNC Viewer applet is provided in the classes/ssl directory. -ssldir [dir] Use [dir] as an alternate ssl certificate and key management toplevel directory. The default is ~/.vnc/certs This directory is used to store server and other certificates and keys and also other materials. E.g. in the simplest case, "-ssl SAVE" will store the x11vnc server cert in [dir]/server.pem Use of alternate directories via -ssldir allows you to manage multiple VNC Certificate Authority (CA) keys. Another use is if ~/.vnc/cert is on an NFS share you might want your certificates and keys to be on a local filesystem to prevent network snooping (for example -ssldir /var/lib/x11vnc-certs). -ssldir affects nearly all of the other -ssl* options, e.g. -ssl SAVE, -sslGenCert, etc.. -sslverify [path] For either of the -ssl or -stunnel modes, use [path] to provide certificates to authenticate incoming VNC *Client* connections (normally only the server is authenticated in SSL.) This can be used as a method to replace standard password authentication of clients. If [path] is a directory it contains the client (or CA) certificates in separate files. If [path] is a file, it contains multiple certificates. See special tokens below. These correspond to the "CApath = dir" and "CAfile = file" stunnel options. See the stunnel(8) manpage for details. Examples: x11vnc -ssl -sslverify ~/my.pem x11vnc -ssl -sslverify ~/my_pem_dir/ Note that if [path] is a directory, it must contain the certs in separate files named like .0, where the value of is found by running the command "openssl x509 -hash -noout -in file.crt". Evidently one uses .1 if there is a collision... The the key-management utility "-sslCertInfo HASHON" and "-sslCertInfo HASHOFF" will create/delete these hashes for you automatically (via symlink) in the HASH subdirs it manages. Then you can point -sslverify to the HASH subdir. Special tokens: in -ssl mode, if [path] is not a file or a directory, it is taken as a comma separated list of tokens that are interpreted as follows: If a token is "CA" that means load the CA/cacert.pem file from the ssl directory. If a token is "clients" then all the files clients/*.crt in the ssl directory are loaded. Otherwise the file clients/token.crt is attempted to be loaded. As a kludge, use a token like ../server-foo to load a server cert if you find that necessary. Use -ssldir to use a directory different from the ~/.vnc/certs default. Note that if the "CA" cert is loaded you do not need to load any of the certs that have been signed by it. You will need to load any additional self-signed certs however. Examples: x11vnc -ssl -sslverify CA x11vnc -ssl -sslverify self:fred,self:jim x11vnc -ssl -sslverify CA,clients Usually "-sslverify CA" is the most effective. See the -sslGenCA and -sslGenCert options below for how to set up and manage the CA framework. NOTE: the following utilities, -sslGenCA, -sslGenCert, -sslEncKey, and -sslCertInfo are provided for completeness, but for casual usage they are overkill. They provide VNC Certificate Authority (CA) key creation and server / client key generation and signing. So they provide a basic Public Key management framework for VNC-ing with x11vnc. (note that they require openssl(1) be installed on the system) However, the simplest usage mode (where x11vnc automatically generates its own, self-signed, temporary key and the VNC viewers always accept it, e.g. accepting via a dialog box) is probably safe enough for most scenarios. CA management is not needed. To protect against Man-In-The-Middle attacks the simplest mode can be improved by using "-ssl SAVE" to have x11vnc create a longer term self-signed certificate, and then (safely) copy the corresponding public key cert to the desired client machines (care must be taken the private key part is not stolen; you will be prompted for a passphrase). So keep in mind no CA key creation or management (-sslGenCA and -sslGenCert) is needed for either of the above two common usage modes. One might want to use -sslGenCA and -sslGenCert if you had a large number of VNC client and server workstations. That way the administrator could generate a single CA key with -sslGenCA and distribute its certificate part to all of the workstations. Next, he could create signed VNC server keys (-sslGenCert server ...) for each workstation or user that then x11vnc would use to authenticate itself to any VNC client that has the CA cert. Optionally, the admin could also make it so the VNC clients themselves are authenticated to x11vnc (-sslGenCert client ...) For this -sslverify would be pointed to the CA cert (and/or self-signed certs). x11vnc will be able to use all of these cert and key files. On the VNC client side, they will need to be "imported" somehow. Web browsers have "Manage Certificates" actions as does the Java applet plugin Control Panel. stunnel can also use these files (see the ssl_vncviewer example script in the FAQ.) -sslGenCA [dir] Generate your own Certificate Authority private key, certificate, and other files in directory [dir]. If [dir] is not supplied, a -ssldir setting is used, or otherwise ~/.vnc/certs is used. This command also creates directories where server and client certs and keys will be stored. The openssl(1) program must be installed on the system and available in PATH. After the CA files and directories are created the command exits; the VNC server is not run. You will be prompted for information to put into the CA certificate. The info does not have to be accurate just as long as clients accept the cert for VNC connections. You will also need to supply a passphrase of at least 4 characters for the CA private key. Once you have generated the CA you can distribute its certificate part, [dir]/CA/cacert.pem, to other workstations where VNC viewers will be run. One will need to "import" this certicate in the applications, e.g. Web browser, Java applet plugin, stunnel, etc. Next, you can create and sign keys using the CA with the -sslGenCert option below. Examples: x11vnc -sslGenCA x11vnc -sslGenCA ~/myCAdir x11vnc -ssldir ~/myCAdir -sslGenCA (the last two lines are equivalent) -sslGenCert type name Generate a VNC server or client certificate and private key pair signed by the CA created previously with -sslGenCA. The openssl(1) program must be installed on the system and available in PATH. After the Certificate is generated the command exits; the VNC server is not run. The type of key to be generated is the string "type". It is either "server" (i.e. for use by x11vnc) or "client" (for a VNC viewer). Note that typically only "server" is used: the VNC clients authenticate themselves by a non-public-key method (e.g. VNC or unix password). "type" is required. An arbitrary default name you want to associate with the key is supplied by the "name" string. You can change it at the various prompts when creating the key. "name" is optional. If name is left blank for clients keys then "nobody" is used. If left blank for server keys, then the primary server key: "server.pem" is created (this is the saved one referenced by "-ssl SAVE" when the server is started) If "name" begins with the string "self:" then a self-signed certificate is created instead of one signed by your CA key. If "name" begins with the string "req:" then only a key (.key) and a certificate signing *request* (.req) are generated. You can then send the .req file to an external CA (even a professional one, e.g. Thawte) and then combine the .key and the received cert into the .pem file with the same basename. The distinction between "server" and "client" is simply the choice of output filenames and sub-directory. This makes it so the -ssl SAVE-name option can easily pick up the x11vnc PEM file this option generates. And similarly makes it easy for the -sslverify option to pick up your client certs. There is nothing special about the filename or directory location of either the "server" and "client" certs. You can rename the files or move them to wherever you like. Precede this option with -ssldir [dir] to use a directory other than the default ~/.vnc/certs You will need to run -sslGenCA on that directory first before doing any -sslGenCert key creation. Note you cannot recreate a cert with exactly the same distiguished name (DN) as an existing one. To do so, you will need to edit the [dir]/CA/index.txt file to delete the line. Similar to -sslGenCA, you will be prompted to fill in some information that will be recorded in the certificate when it is created. Tip: if you know the fully-quailified hostname other people will be connecting to you can use that as the CommonName "CN" to avoid some applications (e.g. web browsers and java plugin) complaining it does not match the hostname. You will also need to supply the CA private key passphrase to unlock the private key created from -sslGenCA. This private key is used to sign the server or client certicate. The "server" certs can be used by x11vnc directly by pointing to them via the -ssl [pem] option. The default file will be ~/.vnc/certs/server.pem. This one would be used by simply typing -ssl SAVE. The pem file contains both the certificate and the private key. server.crt file contains the cert only. The "client" cert + private key file will need to be copied and imported into the VNC viewer side applications (Web browser, Java plugin, stunnel, etc.) Once that is done you can delete the "client" private key file on this machine since it is only needed on the VNC viewer side. The, e.g. ~/.vnc/certs/clients/.pem contains both the cert and private key. The .crt contains the certificate only. NOTE: It is very important to know one should always generate new keys with a passphrase. Otherwise if an untrusted user steals the key file he could use it to masquerade as the x11vnc server (or VNC viewer client). You will be prompted whether to encrypt the key with a passphrase or not. It is recommended that you do. One inconvenience to a passphrase is that it must be suppled every time x11vnc or the client app is started up. Examples: x11vnc -sslGenCert server x11vnc -ssl SAVE -display :0 ... and then on viewer using ssl_vncviewer stunnel wrapper (see the FAQ): ssl_vncviewer -verify ./cacert.crt hostname:0 (this assumes the cacert.crt cert from -sslGenCA was safely copied to the VNC viewer machine where ssl_vncviewer is run) Example using a name: x11vnc -sslGenCert server charlie x11vnc -ssl SAVE-charlie -display :0 ... Example for a client certificate (rarely used): x11vnc -sslGenCert client roger scp ~/.vnc/certs/clients/roger.pem somehost:. rm ~/.vnc/certs/clients/roger.pem x11vnc is then started with the the option -sslverify ~/.vnc/certs/clients/roger.crt (or simply -sslverify roger), and on the viewer user on somehost could do for example: ssl_vncviewer -mycert ./roger.pem hostname:0 -sslEncKey [pem] Utility to encrypt an existing PEM file with a passphrase you supply when prompted. For that key to be used (e.g. by x11vnc) the passphrase must be supplied each time. The "SAVE" notation described under -ssl applies as well. (precede this option with -ssldir [dir] to refer a directory besides the default ~/.vnc/certs) The openssl(1) program must be installed on the system and available in PATH. After the Key file is encrypted the command exits; the VNC server is not run. Examples: x11vnc -sslEncKey /path/to/foo.pem x11vnc -sslEncKey SAVE x11vnc -sslEncKey SAVE-charlie -sslCertInfo [pem] Prints out information about an existing PEM file. In addition the public certificate is also printed. The openssl(1) program must be in PATH. Basically the command "openssl x509 -text" is run on the pem. The "SAVE" notation described under -ssl applies as well. Using "LIST" will give a list of all certs being managed (in the ~/.vnc/certs dir, use -ssldir to refer to another dir). "ALL" will print out the info for every managed key (this can be very long). Giving a client or server cert shortname will also try a lookup (e.g. -sslCertInfo charlie). Use "LISTL" or "LL" for a long (ls -l style) listing. Using "HASHON" will create subdirs [dir]/HASH and [dir]/HASH with OpenSSL hash filenames (e.g. 0d5fbbf1.0) symlinks pointing up to the corresponding *.crt file. ([dir] is ~/.vnc/certs or one given by -ssldir.) This is a useful way for other OpenSSL applications (e.g. stunnel) to access all of the certs without having to concatenate them. x11vnc will not use them unless you specifically reference them. "HASHOFF" removes these HASH subdirs. The LIST, LISTL, LL, ALL, HASHON, HASHOFF words can also be lowercase, e.g. "list". -sslDelCert [pem] Prompts you to delete all .crt .pem .key .req files associated with [pem]. "SAVE" and lookups as in -sslCertInfo apply as well. -stunnel [pem] Use the stunnel(8) (www.stunnel.org) to provide an encrypted SSL tunnel between viewers and x11vnc. This external tunnel method was implemented prior to the integrated -ssl encryption described above. It still works well. This requires stunnel to be installed on the system and available via PATH (n.b. stunnel is often installed in sbin directories). Version 4.x of stunnel is assumed (but see -stunnel3 below.) [pem] is optional, use "-stunnel /path/to/stunnel.pem" to specify a PEM certificate file to pass to stunnel. Whether one is needed or not depends on your stunnel configuration. stunnel often generates one at install time. See the stunnel documentation for details. stunnel is started up as a child process of x11vnc and any SSL connections stunnel receives are decrypted and sent to x11vnc over a local socket. The strings "The SSL VNC desktop is ..." and "SSLPORT=..." are printed out at startup to indicate this. The -localhost option is enforced by default to avoid people routing around the SSL channel. Set STUNNEL_DISABLE_LOCALHOST=1 before starting x11vnc to disable the requirement. Your VNC viewer will also need to be able to connect via SSL. Unfortunately not too many do this. UltraVNC has an encryption plugin but it does not seem to be SSL. Also, in the x11vnc distribution, a patched TightVNC Java applet is provided in classes/ssl that does SSL connections (only). It is also not too difficult to set up an stunnel or other SSL tunnel on the viewer side. A simple example on Unix using stunnel 3.x is: % stunnel -c -d localhost:5901 -r remotehost:5900 % vncviewer localhost:1 For Windows, stunnel has been ported to it and there are probably other such tools available. See the FAQ for more examples. -stunnel3 [pem] Use version 3.x stunnel command line syntax instead of version 4.x -https [port] Choose a separate HTTPS port (-ssl mode only). In -ssl mode, it turns out you can use the single VNC port (e.g. 5900) for both VNC and HTTPS connections. (HTTPS is used to retrieve a SSL-aware VncViewer.jar applet that is provided with x11vnc). Since both use SSL the implementation was extended to detect if HTTP traffic (i.e. GET) is taking place and handle it accordingly. The URL would be, e.g.: https://mymachine.org:5900/ This is convenient for firewalls, etc, because only one port needs to be allowed in. However, this heuristic adds a few seconds delay to each connection and can be unreliable (especially if the user takes much time to ponder the Certificate dialogs in his browser, Java VM, or VNC Viewer applet. That's right 3 separate "Are you sure you want to connect" dialogs!) So use the -https option to provide a separate, more reliable HTTPS port that x11vnc will listen on. If [port] is not provided (or is 0), one is autoselected. The URL to use is printed out at startup. The SSL Java applet directory is specified via the -httpdir option. If not supplied it will try to guess the directory as though the -http option was supplied. -usepw If no other password method was supplied on the command line, first look for ~/.vnc/passwd and if found use it with -rfbauth; next, look for ~/.vnc/passwdfile and use it with -passwdfile; otherwise, prompt the user for a password to create ~/.vnc/passwd and use it with the -rfbauth option. If none of these succeed x11vnc exits immediately. Note: -unixpw currently does not count as a password method by this option. -storepasswd pass file Store password "pass" as the VNC password in the file "file". Once the password is stored the program exits. Use the password via "-rfbauth file" If called with no arguments, "x11vnc -storepasswd", the user is prompted for a password and it is stored in the file ~/.vnc/passwd. Called with one argument, that will be the file to store the prompted password in. -nopw Disable the big warning message when you use x11vnc without some sort of password. -accept string Run a command (possibly to prompt the user at the X11 display) to decide whether an incoming client should be allowed to connect or not. "string" is an external command run via system(3) or some special cases described below. Be sure to quote "string" if it contains spaces, shell characters, etc. If the external command returns 0 the client is accepted, otherwise the client is rejected. See below for an extension to accept a client view-only. If x11vnc is running as root (say from inetd(1) or from display managers xdm(1), gdm(1), etc), think about the security implications carefully before supplying this option (likewise for the -gone option). Environment: The RFB_CLIENT_IP environment variable will be set to the incoming client IP number and the port in RFB_CLIENT_PORT (or -1 if unavailable). Similarly, RFB_SERVER_IP and RFB_SERVER_PORT (the x11vnc side of the connection), are set to allow identification of the tcp virtual circuit. The x11vnc process id will be in RFB_X11VNC_PID, a client id number in RFB_CLIENT_ID, and the number of other connected clients in RFB_CLIENT_COUNT. RFB_MODE will be "accept". RFB_STATE will be PROTOCOL_VERSION, SECURITY_TYPE, AUTHENTICATION, INITIALISATION, NORMAL, or UNKNOWN indicating up to which state the client has acheived. RFB_LOGIN_VIEWONLY will be 0, 1, or -1 (unknown). RFB_USERNAME, RFB_LOGIN_TIME, and RFB_CURRENT_TIME may also be set. If "string" is "popup" then a builtin popup window is used. The popup will time out after 120 seconds, use "popup:N" to modify the timeout to N seconds (use 0 for no timeout). If "string" is "xmessage" then an xmessage(1) invocation is used for the command. xmessage must be installed on the machine for this to work. Both "popup" and "xmessage" will present an option for accepting the client "View-Only" (the client can only watch). This option will not be presented if -viewonly has been specified, in which case the entire display is view only. If the user supplied command is prefixed with something like "yes:0,no:*,view:3 mycommand ..." then this associates the numerical command return code with the actions: accept, reject, and accept-view-only, respectively. Use "*" instead of a number to indicate the default action (in case the command returns an unexpected value). E.g. "no:*" is a good choice. Note that x11vnc blocks while the external command or popup is running (other clients may see no updates during this period). So a person sitting a the physical display is needed to respond to an popup prompt. (use a 2nd x11vnc if you lock yourself out). More -accept tricks: use "popupmouse" to only allow mouse clicks in the builtin popup to be recognized. Similarly use "popupkey" to only recognize keystroke responses. These are to help avoid the user accidentally accepting a client by typing or clicking. All 3 of the popup keywords can be followed by +N+M to supply a position for the popup window. The default is to center the popup window. -afteraccept string As -accept, except to run a user supplied command after a client has been accepted and authenticated. RFB_MODE will be set to "afteraccept" and the other RFB_* variables are as in -accept. Unlike -accept, the command return code is not interpreted by x11vnc. Example: -afteraccept 'killall xlock &' -gone string As -accept, except to run a user supplied command when a client goes away (disconnects). RFB_MODE will be set to "gone" and the other RFB_* variables are as in -accept. The "popup" actions apply as well. Unlike -accept, the command return code is not interpreted by x11vnc. Example: -gone 'xlock &' -users list If x11vnc is started as root (say from inetd(1) or from display managers xdm(1), gdm(1), etc), then as soon as possible after connections to the X display are established try to switch to one of the users in the comma separated "list". If x11vnc is not running as root this option is ignored. Why use this option? In general it is not needed since x11vnc is already connected to the X display and can perform its primary functions. The option was added to make some of the *external* utility commands x11vnc occasionally runs work properly. In particular under GNOME and KDE to implement the "-solid color" feature external commands (gconftool-2 and dcop) must be run as the user owning the desktop session. Since this option switches userid it also affects the userid used to run the processes for the -accept and -gone options. It also affects the ability to read files for options such as -connect, -allow, and -remap. Note that the -connect file is also sometimes written to. So be careful with this option since in many situations its use can decrease security. The switch to a user will only take place if the display can still be successfully opened as that user (this is primarily to try to guess the actual owner of the session). Example: "-users fred,wilma,betty". Note that a malicious user "barney" by quickly using "xhost +" when logging in may get x11vnc to switch to user "fred". What happens next? Under display managers it may be a long time before the switch succeeds (i.e. a user logs in). To make it switch immediately regardless if the display can be reopened prefix the username with the "+" character. E.g. "-users +bob" or "-users +nobody". The latter (i.e. switching immediately to user "nobody") is probably the only use of this option that increases security. To immediately switch to a user *before* connections to the X display are made or any files opened use the "=" character: "-users =bob". That user needs to be able to open the X display of course. The special user "guess=" means to examine the utmpx database (see who(1)) looking for a user attached to the display number (from DISPLAY or -display option) and try him/her. To limit the list of guesses, use: "-users guess=bob,betty". Even more sinister is the special user "lurk=" that means to try to guess the DISPLAY from the utmpx login database as well. So it "lurks" waiting for anyone to log into an X session and then connects to it. Specify a list of users after the = to limit which users will be tried. To enable a different searching mode, if the first user in the list is something like ":0" or ":0-2" that indicates a range of DISPLAY numbers that will be tried (regardless of whether they are in the utmpx database) for all users that are logged in. Examples: "-users lurk=" and also "-users lurk=:0-1,bob,mary" Be especially careful using the "guess=" and "lurk=" modes. They are not recommended for use on machines with untrustworthy local users. -noshm Do not use the MIT-SHM extension for the polling. Remote displays can be polled this way: be careful this can use large amounts of network bandwidth. This is also of use if the local machine has a limited number of shm segments and -onetile is not sufficient. -flipbyteorder Sometimes needed if remotely polled host has different endianness. Ignored unless -noshm is set. -onetile Do not use the new copy_tiles() framebuffer mechanism, just use 1 shm tile for polling. Limits shm segments used to 3. -solid [color] To improve performance, when VNC clients are connected try to change the desktop background to a solid color. The [color] is optional: the default color is "cyan4". For a different one specify the X color (rgb.txt name, e.g. "darkblue" or numerical "#RRGGBB"). Currently this option only works on GNOME, KDE, CDE, and classic X (i.e. with the background image on the root window). The "gconftool-2" and "dcop" external commands are run for GNOME and KDE respectively. Other desktops won't work, e.g. Xfce (send us the corresponding commands if you find them). If x11vnc is running as root (inetd(1) or gdm(1)), the -users option may be needed for GNOME and KDE. If x11vnc guesses your desktop incorrectly, you can force it by prefixing color with "gnome:", "kde:", "cde:" or "root:". -blackout string Black out rectangles on the screen. "string" is a comma separated list of WxH+X+Y type geometries for each rectangle. If one of the items on the list is the string "noptr" the mouse pointer will not be allowed to go into a blacked out region. -xinerama If your screen is composed of multiple monitors -noxinerama glued together via XINERAMA, and that screen is not a rectangle this option will try to guess the areas to black out (if your system has libXinerama). default: -xinerama In general, we have noticed on XINERAMA displays you may need to use the "-xwarppointer" option if the mouse pointer misbehaves. -xtrap Use the DEC-XTRAP extension for keystroke and mouse input insertion. For use on legacy systems, e.g. X11R5, running an incomplete or missing XTEST extension. By default DEC-XTRAP will be used if XTEST server grab control is missing, use -xtrap to do the keystroke and mouse insertion via DEC-XTRAP as well. -xrandr [mode] If the display supports the XRANDR (X Resize, Rotate and Reflection) extension, and you expect XRANDR events to occur to the display while x11vnc is running, this options indicates x11vnc should try to respond to them (as opposed to simply crashing by assuming the old screen size). See the xrandr(1) manpage and run 'xrandr -q' for more info. [mode] is optional and described below. Since watching for XRANDR events and trapping errors increases polling overhead, only use this option if XRANDR changes are expected. For example on a rotatable screen PDA or laptop, or using a XRANDR-aware Desktop where you resize often. It is best to be viewing with a vncviewer that supports the NewFBSize encoding, since it knows how to react to screen size changes. Otherwise, libvncserver tries to do so something reasonable for viewers that cannot do this (portions of the screen may be clipped, unused, etc). "mode" defaults to "resize", which means create a new, resized, framebuffer and hope all viewers can cope with the change. "newfbsize" means first disconnect all viewers that do not support the NewFBSize VNC encoding, and then resize the framebuffer. "exit" means disconnect all viewer clients, and then terminate x11vnc. -padgeom WxH Whenever a new vncviewer connects, the framebuffer is replaced with a fake, solid black one of geometry WxH. Shortly afterwards the framebuffer is replaced with the real one. This is intended for use with vncviewers that do not support NewFBSize and one wants to make sure the initial viewer geometry will be big enough to handle all subsequent resizes (e.g. under -xrandr, -remote id:windowid, rescaling, etc.) -o logfile Write stderr messages to file "logfile" instead of to the terminal. Same as "-logfile file". To append to the file use "-oa file" or "-logappend file". -flag file Write the "PORT=NNNN" (e.g. PORT=5900) string to "file" in addition to stdout. This option could be useful by wrapper script to detect when x11vnc is ready. -rc filename Use "filename" instead of $HOME/.x11vncrc for rc file. -norc Do not process any .x11vncrc file for options. -h, -help Print this help text. -?, -opts Only list the x11vnc options. -V, -version Print program version and last modification date. -dbg Instead of exiting after cleaning up, run a simple "debug crash shell" when fatal errors are trapped. -q Be quiet by printing less informational output to stderr. Same as -quiet. -bg Go into the background after screen setup. Messages to stderr are lost unless -o logfile is used. Something like this could be useful in a script: port=`ssh $host "x11vnc -display :0 -bg" | grep PORT` port=`echo "$port" | sed -e 's/PORT=//'` port=`expr $port - 5900` vncviewer $host:$port -modtweak Option -modtweak automatically tries to adjust the AltGr -nomodtweak and Shift modifiers for differing language keyboards between client and host. Otherwise, only a single key press/release of a Keycode is simulated (i.e. ignoring the state of the modifiers: this usually works for identical keyboards). Also useful in resolving cases where a Keysym is bound to multiple keys (e.g. "<" + ">" and "," + "<" keys). Default: -modtweak -xkb When in modtweak mode, use the XKEYBOARD extension (if -noxkb the X display supports it) to do the modifier tweaking. This is powerful and should be tried if there are still keymapping problems when using -modtweak by itself. The default is to check whether some common keysyms, e.g. !, @, [, are only accessible via -xkb mode and if so then automatically enable the mode. To disable this automatic detection use -noxkb. -skip_keycodes string Ignore the comma separated list of decimal keycodes. Perhaps these are keycodes not on your keyboard but your X server thinks exist. Currently only applies to -xkb mode. Use this option to help x11vnc in the reverse problem it tries to solve: Keysym -> Keycode(s) when ambiguities exist (more than one Keycode per Keysym). Run 'xmodmap -pk' to see your keymapping. Example: "-skip_keycodes 94,114" -sloppy_keys Experimental option that tries to correct some "sloppy" key behavior. E.g. if at the viewer you press Shift+Key but then release the Shift before Key that could give rise to extra unwanted characters (usually only between keyboards of different languages). Only use this option if you observe problems with some keystrokes. -skip_dups Some VNC viewers send impossible repeated key events, -noskip_dups e.g. key-down, key-down, key-up, key-up all for the same key, or 20 downs in a row for the same modifier key! Setting -skip_dups means to skip these duplicates and just process the first event. Note: some VNC viewers assume they can send down's without the corresponding up's and so you should not set this option for these viewers (symptom: some keys do not autorepeat) Default: -noskip_dups -add_keysyms If a Keysym is received from a VNC viewer and that -noadd_keysyms Keysym does not exist in the X server, then add the Keysym to the X server's keyboard mapping on an unused key. Added Keysyms will be removed periodically and also when x11vnc exits. Default: -add_keysyms -clear_mods At startup and exit clear the modifier keys by sending KeyRelease for each one. The Lock modifiers are skipped. Used to clear the state if the display was accidentally left with any pressed down. -clear_keys As -clear_mods, except try to release any pressed key. Note that this option and -clear_mods can interfere with a person typing at the physical keyboard. -remap string Read Keysym remappings from file named "string". Format is one pair of Keysyms per line (can be name or hex value) separated by a space. If no file named "string" exists, it is instead interpreted as this form: key1-key2,key3-key4,... See header file for a list of Keysym names, or use xev(1). To map a key to a button click, use the fake Keysyms "Button1", ..., etc. E.g: "-remap Super_R-Button2" (useful for pasting on a laptop) Dead keys: "dead" (or silent, mute) keys are keys that do not produce a character but must be followed by a 2nd keystroke. This is often used for accenting characters, e.g. to put "`" on top of "a" by pressing the dead key and then "a". Note that this interpretation is not part of core X11, it is up to the toolkit or application to decide how to react to the sequence. The X11 names for these keysyms are "dead_grave", "dead_acute", etc. However some VNC viewers send the keysyms "grave", "acute" instead thereby disabling the accenting. To work around this -remap can be used. For example "-remap grave-dead_grave,acute-dead_acute" As a convenience, "-remap DEAD" applies these remaps: g grave-dead_grave a acute-dead_acute c asciicircum-dead_circumflex t asciitilde-dead_tilde m macron-dead_macron b breve-dead_breve D abovedot-dead_abovedot d diaeresis-dead_diaeresis o degree-dead_abovering A doubleacute-dead_doubleacute r caron-dead_caron e cedilla-dead_cedilla If you just want a subset use the first letter label, e.g. "-remap DEAD=ga" to get the first two. Additional remaps may also be supplied via commas, e.g. "-remap DEAD=ga,Super_R-Button2". Finally, "DEAD=missing" means to apply all of the above as long as the left hand member is not already in the X11 keymap. -norepeat Option -norepeat disables X server key auto repeat when -repeat VNC clients are connected and VNC keyboard input is not idle for more than 5 minutes. This works around a repeating keystrokes bug (triggered by long processing delays between key down and key up client events: either from large screen changes or high latency). Default: -norepeat Note: your VNC viewer side will likely do autorepeating, so this is no loss unless someone is simultaneously at the real X display. Use "-norepeat N" to set how many times norepeat will be reset if something else (e.g. X session manager) undoes it. The default is 2. Use a negative value for unlimited resets. -nofb Ignore video framebuffer: only process keyboard and pointer. Intended for use with Win2VNC and x2vnc dual-monitor setups. -nobell Do not watch for XBell events. (no beeps will be heard) Note: XBell monitoring requires the XKEYBOARD extension. -nosel Do not manage exchange of X selection/cutbuffer between VNC viewers and the X server at all. -noprimary Do not poll the PRIMARY selection for changes to send back to clients. (PRIMARY is still set on received changes, however). -nosetprimary Do not set the PRIMARY selection for changes received from VNC clients. -noclipboard Do not poll the CLIPBOARD selection for changes to send back to clients. (CLIPBOARD is still set on received changes, however). -nosetclipboard Do not set the CLIPBOARD selection for changes received from VNC clients. -seldir string If direction string is "send", only send the selection to viewers, and if it is "recv" only receive it from viewers. To work around apps setting the selection too frequently and messing up the other end. You can actually supply a comma separated list of directions, including "debug" to turn on debugging output. -cursor [mode] Sets how the pointer cursor shape (little icon at the -nocursor mouse pointer) should be handled. The "mode" string is optional and is described below. The default is to show some sort of cursor shape(s). How this is done depends on the VNC viewer and the X server. Use -nocursor to disable cursor shapes completely. Some VNC viewers support the TightVNC CursorPosUpdates and CursorShapeUpdates extensions (cuts down on network traffic by not having to send the cursor image every time the pointer is moved), in which case these extensions are used (see -nocursorshape and -nocursorpos below to disable). For other viewers the cursor shape is written directly to the framebuffer every time the pointer is moved or changed and gets sent along with the other framebuffer updates. In this case, there will be some lag between the vnc viewer pointer and the remote cursor position. If the X display supports retrieving the cursor shape information from the X server, then the default is to use that mode. On Solaris this can be done with the SUN_OVL extension using -overlay (see also the -overlay_nocursor option). A similar overlay scheme is used on IRIX. Xorg (e.g. Linux) and recent Solaris Xsun servers support the XFIXES extension to retrieve the exact cursor shape from the X server. If XFIXES is present it is preferred over Overlay and is used by default (see -noxfixes below). This can be disabled with -nocursor, and also some values of the "mode" option below. Note that under XFIXES cursors with transparency (alpha channel) will usually not be exactly represented and one may find Overlay preferable. See also the -alphacut and -alphafrac options below as fudge factors to try to improve the situation for cursors with transparency for a given theme. The "mode" string can be used to fine-tune the displaying of cursor shapes. It can be used the following ways: "-cursor arrow" - just show the standard arrow nothing more or nothing less. "-cursor none" - same as "-nocursor" "-cursor X" - when the cursor appears to be on the root window, draw the familiar X shape. Some desktops such as GNOME cover up the root window completely, and so this will not work, try "X1", etc, to try to shift the tree depth. On high latency links or slow machines there will be a time lag between expected and the actual cursor shape. "-cursor some" - like "X" but use additional heuristics to try to guess if the window should have a windowmanager-like resizer cursor or a text input I-beam cursor. This is a complete hack, but may be useful in some situations because it provides a little more feedback about the cursor shape. "-cursor most" - try to show as many cursors as possible. Often this will only be the same as "some" unless the display has overlay visuals or XFIXES extensions available. On Solaris and IRIX if XFIXES is not available, -overlay mode will be attempted. -arrow n Choose an alternate "arrow" cursor from a set of some common ones. n can be 1 to 6. Default is: 1 Ignored when in XFIXES cursor-grabbing mode. -noxfixes Do not use the XFIXES extension to draw the exact cursor shape even if it is available. -alphacut n When using the XFIXES extension for the cursor shape, cursors with transparency will not usually be displayed exactly (but opaque ones will). This option sets n as a cutoff for cursors that have transparency ("alpha channel" with values ranging from 0 to 255) Any cursor pixel with alpha value less than n becomes completely transparent. Otherwise the pixel is completely opaque. Default 240 -alphafrac fraction With the threshold in -alphacut some cursors will become almost completely transparent because their alpha values are not high enough. For those cursors adjust the alpha threshold until fraction of the non-zero alpha channel pixels become opaque. Default 0.33 -alpharemove By default, XFIXES cursors pixels with transparency have the alpha factor multiplied into the RGB color values (i.e. that corresponding to blending the cursor with a black background). Specify this option to remove the alpha factor. (useful for light colored semi-transparent cursors). -noalphablend In XFIXES mode do not send cursor alpha channel data to libvncserver. The default is to send it. The alphablend effect will only be visible in -nocursorshape mode or for clients with cursorshapeupdates turned off. (However there is a hack for 32bpp with depth 24, it uses the extra 8 bits to store cursor transparency for use with a hacked vncviewer that applies the transparency locally. See the FAQ for more info). -nocursorshape Do not use the TightVNC CursorShapeUpdates extension even if clients support it. See -cursor above. -cursorpos Option -cursorpos enables sending the X cursor position -nocursorpos back to all vnc clients that support the TightVNC CursorPosUpdates extension. Other clients will be able to see the pointer motions. Default: -cursorpos -xwarppointer Move the pointer with XWarpPointer(3X) instead of the XTEST extension. Use this as a workaround if the pointer motion behaves incorrectly, e.g. on touchscreens or other non-standard setups. Also sometimes needed on XINERAMA displays. -buttonmap string String to remap mouse buttons. Format: IJK-LMN, this maps buttons I -> L, etc., e.g. -buttonmap 13-31 Button presses can also be mapped to keystrokes: replace a button digit on the right of the dash with :: or :+: 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 header file for a list of Keysyms, or use the xev(1) program. Note: mapping of button clicks to Keysyms may not work if -modtweak or -xkb is needed for the Keysym. If you include a modifier like "Shift_L" the modifier's up/down state is toggled, e.g. to send "The" use :Shift_L+t+Shift_L+h+e: (the 1st one is shift down and the 2nd one is shift up). (note: the initial state of the modifier is ignored and not reset) To include button events use "Button1", ... etc. -nodragging Do not update the display during mouse dragging events (mouse button held down). Greatly improves response on slow setups, but you lose all visual feedback for drags, text selection, and some menu traversals. It overrides any -pointer_mode setting. -wireframe [str] Try to detect window moves or resizes when a mouse -nowireframe button is held down and show a wireframe instead of the full opaque window. This is based completely on heuristics and may not always work: it depends on your window manager and even how you move things around. See -pointer_mode below for discussion of the "bogging down" problem this tries to avoid. Default: -wireframe Shorter aliases: -wf [str] and -nowf The value "str" is optional and, of course, is packed with many tunable parameters for this scheme: Format: shade,linewidth,percent,T+B+L+R,mod,t1+t2+t3+t4 Default: 0xff,3,0,32+8+8+8,all,0.15+0.30+5.0+0.125 If you leave nothing between commas: ",," the default value is used. If you don't specify enough commas, the trailing parameters are set to their defaults. "shade" indicate the "color" for the wireframe, usually a greyscale: 0-255, however for 16 and 32bpp you can specify an rgb.txt X color (e.g. "dodgerblue") or a value > 255 is treated as RGB (e.g. red is 0xff0000). "linewidth" sets the width of the wireframe in pixels. "percent" indicates to not apply the wireframe scheme to windows with area less than this percent of the full screen. "T+B+L+R" indicates four integers for how close in pixels the pointer has to be from the Top, Bottom, Left, or Right edges of the window to consider wireframing. This is a speedup to quickly exclude a window from being wireframed: set them all to zero to not try the speedup (scrolling and selecting text will likely be slower). "mod" specifies if a button down event in the interior of the window with a modifier key (Alt, Shift, etc.) down should indicate a wireframe opportunity. It can be "0" or "none" to skip it, "1" or "all" to apply it to any modifier, or "Shift", "Alt", "Control", "Meta", "Super", or "Hyper" to only apply for that type of modifier key. "t1+t2+t3+t4" specify four floating point times in seconds: t1 is how long to wait for the pointer to move, t2 is how long to wait for the window to start moving or being resized (for some window managers this can be rather long), t3 is how long to keep a wireframe moving before repainting the window. t4 is the minimum time between sending wireframe "animations". If a slow link is detected, these values may be automatically changed to something better for a slow link. -wirecopyrect mode Since the -wireframe mechanism evidently tracks moving -nowirecopyrect windows accurately, a speedup can be obtained by telling the VNC viewers to locally copy the translated window region. This is the VNC CopyRect encoding: the framebuffer update doesn't need to send the actual new image data. Shorter aliases: -wcr [mode] and -nowcr "mode" can be "never" (same as -nowirecopyrect) to never try the copyrect, "top" means only do it if the window was not covered by any other windows, and "always" means to translate the orginally unobscured region (this may look odd as the remaining pieces come in, but helps on a slow link). Default: "always" Note: there can be painting errors or slow response when using -scale so you may want to disable CopyRect in this case "-wirecopyrect never" on the command line or by remote-control. Or you can also use the "-scale xxx:nocr" scale option. -debug_wireframe Turn on debugging info printout for the wireframe heuristics. "-dwf" is an alias. Specify multiple times for more output. -scrollcopyrect mode Like -wirecopyrect, but use heuristics to try to guess -noscrollcopyrect if a window has scrolled its contents (either vertically or horizontally). This requires the RECORD X extension to "snoop" on X applications (currently for certain XCopyArea and XConfigureWindow X protocol requests). Examples: Hitting in a terminal window when the cursor was at the bottom, the text scrolls up one line. Hitting arrow in a web browser window, the web page scrolls up a small amount. Or scrolling with a scrollbar or mouse wheel. Shorter aliases: -scr [mode] and -noscr This scheme will not always detect scrolls, but when it does there is a nice speedup from using the VNC CopyRect encoding (see -wirecopyrect). The speedup is both in reduced network traffic and reduced X framebuffer polling/copying. On the other hand, it may induce undesired transients (e.g. a terminal cursor being scrolled up when it should not be) or other painting errors (window tearing, bunching-up, etc). These are automatically repaired in a short period of time. If this is unacceptable disable the feature with -noscrollcopyrect. Screen clearing kludges: for testing at least, there are some "magic key sequences" (must be done in less than 1 second) to aid repairing painting errors that may be seen when using this mode: 3 Alt_L's in a row: resend whole screen, 4 Alt_L's in a row: reread and resend whole screen, 3 Super_L's in a row: mark whole screen for polling, 4 Super_L's in a row: reset RECORD context, 5 Super_L's in a row: try to push a black screen note: Alt_L is the Left "Alt" key (a single key) Super_L is the Left "Super" key (Windows flag). Both of these are modifier keys, and so should not generate characters when pressed by themselves. Also, your VNC viewer may have its own refresh hot-key or button. "mode" can be "never" (same as -noscrollcopyrect) to never try the copyrect, "keys" means to try it in response to keystrokes only, "mouse" means to try it in response to mouse events only, "always" means to do both. Default: "always" Note: there can be painting errors or slow response when using -scale so you may want to disable CopyRect in this case "-scrollcopyrect never" on the command line or by remote-control. Or you can also use the "-scale xxx:nocr" scale option. -scr_area n Set the minimum area in pixels for a rectangle to be considered for the -scrollcopyrect detection scheme. This is to avoid wasting the effort on small rectangles that would be quickly updated the normal way. E.g. suppose an app updated the position of its skinny scrollbar first and then shifted the large panel it controlled. We want to be sure to skip the small scrollbar and get the large panel. Default: 60000 -scr_skip list Skip scroll detection for applications matching the comma separated list of strings in "list". Some applications implement their scrolling in strange ways where the XCopyArea, etc, also applies to invisible portions of the window: if we CopyRect those areas it looks awful during the scroll and there may be painting errors left after the scroll. Soffice.bin is the worst known offender. Use "##" to denote the start of the application class (e.g. "##XTerm") and "++" to denote the start of the application instance name (e.g. "++xterm"). The string your list is matched against is of the form "^^WM_NAME##Class++Instance" The "xlsclients -la" command will provide this info. If a pattern is prefixed with "KEY:" it only applies to Keystroke generated scrolls (e.g. Up arrow). If it is prefixed with "MOUSE:" it only applies to Mouse induced scrolls (e.g. dragging on a scrollbar). Default: ##Soffice.bin,##StarOffice -scr_inc list Opposite of -scr_skip: this list is consulted first and if there is a match the window will be monitored via RECORD for scrolls irrespective of -scr_skip. Use -scr_skip '*' to skip anything that does not match your -scr_inc. Use -scr_inc '*' to include everything. -scr_keys list For keystroke scroll detection, only apply the RECORD heuristics to the comma separated list of keysyms in "list". You may find the RECORD overhead for every one of your keystrokes disrupts typing too much, but you don't want to turn it off completely with "-scr mouse" and -scr_parms does not work or is too confusing. The listed keysyms can be numeric or the keysym names in the header file or from the xev(1) program. Example: "-scr_keys Up,Down,Return". One probably wants to have application specific lists (e.g. for terminals, etc) but that is too icky to think about for now... If "list" begins with the "-" character the list is taken as an exclude list: all keysyms except those list will be considered. The special string "builtin" expands to an internal list of keysyms that are likely to cause scrolls. BTW, by default modifier keys, Shift_L, Control_R, etc, are skipped since they almost never induce scrolling by themselves. -scr_term list Yet another cosmetic kludge. Apply shell/terminal heuristics to applications matching comma separated list (same as for -scr_skip/-scr_inc). For example an annoying transient under scroll detection is if you hit Enter in a terminal shell with full text window, the solid text cursor block will be scrolled up. So for a short time there are two (or more) block cursors on the screen. There are similar scenarios, (e.g. an output line is duplicated). These transients are induced by the approximation of scroll detection (e.g. it detects the scroll, but not the fact that the block cursor was cleared just before the scroll). In nearly all cases these transient errors are repaired when the true X framebuffer is consulted by the normal polling. But they are distracting, so what this option provides is extra "padding" near the bottom of the terminal window: a few extra lines near the bottom will not be scrolled, but rather updated from the actual X framebuffer. This usually reduces the annoying artifacts. Use "none" to disable. Default: "term" -scr_keyrepeat lo-hi If a key is held down (or otherwise repeats rapidly) and this induces a rapid sequence of scrolls (e.g. holding down an Arrow key) the "scrollcopyrect" detection and overhead may not be able to keep up. A time per single scroll estimate is performed and if that estimate predicts a sustainable scrollrate of keys per second between "lo" and "hi" then repeated keys will be DISCARDED to maintain the scrollrate. For example your key autorepeat may be 25 keys/sec, but for a large window or slow link only 8 scrolls per second can be sustained, then roughly 2 out of every 3 repeated keys will be discarded during this period. Default: "4-20" -scr_parms string Set various parameters for the scrollcopyrect mode. The format is similar to that for -wireframe and packed with lots of parameters: Format: T+B+L+R,t1+t2+t3,s1+s2+s3+s4+s5 Default: 0+64+32+32,0.02+0.10+0.9,0.03+0.06+0.5+0.1+5.0 If you leave nothing between commas: ",," the default value is used. If you don't specify enough commas, the trailing parameters are set to their defaults. "T+B+L+R" indicates four integers for how close in pixels the pointer has to be from the Top, Bottom, Left, or Right edges of the window to consider scrollcopyrect. If -wireframe overlaps it takes precedence. This is a speedup to quickly exclude a window from being watched for scrollcopyrect: set them all to zero to not try the speedup (things like selecting text will likely be slower). "t1+t2+t3" specify three floating point times in seconds that apply to scrollcopyrect detection with *Keystroke* input: t1 is how long to wait after a key is pressed for the first scroll, t2 is how long to keep looking after a Keystroke scroll for more scrolls. t3 is how frequently to try to update surrounding scrollbars outside of the scrolling area (0.0 to disable) "s1+s2+s3+s4+s5" specify five floating point times in seconds that apply to scrollcopyrect detection with *Mouse* input: s1 is how long to wait after a mouse button is pressed for the first scroll, s2 is how long to keep waiting for additional scrolls after the first Mouse scroll was detected. s3 is how frequently to try to update surrounding scrollbars outside of the scrolling area (0.0 to disable). s4 is how long to buffer pointer motion (to try to get fewer, bigger mouse scrolls). s5 is the maximum time to spend just updating the scroll window without updating the rest of the screen. -fixscreen string Periodically "repair" the screen based on settings in "string". Hopefully you won't need this option, it is intended for cases when the -scrollcopyrect or -wirecopyrect features leave too many painting errors, but it can be used for any scenario. This option periodically performs costly operations and so interactive response may be reduced when it is on. You can use 3 Alt_L's (the Left "Alt" key) taps in a row (as described under -scrollcopyrect) instead to manually request a screen repaint when it is needed. "string" is a comma separated list of one or more of the following: "V=t", "C=t", "X=t", and "8=t". In these "t" stands for a time in seconds (it is a floating point even though one should usually use values > 2 to avoid wasting resources). V sets how frequently the entire screen should be sent to viewers (it is like the 3 Alt_L's). C sets how long to wait after a CopyRect to repaint the full screen. X sets how frequently to reread the full X11 framebuffer from the X server and push it out to connected viewers. Use of X should be rare, please report a bug if you find you need it. 8= applies only for -8to24 mode: it sets how often the non-default visual regions of the screen (e.g. 8bpp windows) are refreshed. Examples: -fixscreen V=10 -fixscreen C=10 -debug_scroll Turn on debugging info printout for the scroll heuristics. "-ds" is an alias. Specify it multiple times for more output. -noxrecord Disable any use of the RECORD extension. This is currently used by the -scrollcopyrect scheme and to monitor X server grabs. -grab_buster Some of the use of the RECORD extension can leave a -nograb_buster tiny window for XGrabServer deadlock. This is only if the whole-server grabbing application expects mouse or keyboard input before releasing the grab. It is usually a window manager that does this. x11vnc takes care to avoid the the problem, but if caught x11vnc will freeze. Without -grab_buster, the only solution is to go the physical display and give it some input to satisfy the grabbing app. Or manually kill and restart the window manager if that is feasible. With -grab_buster, x11vnc will fork a helper thread and if x11vnc appears to be stuck in a grab after a period of time (20-30 sec) then it will inject some user input: button clicks, Escape, mouse motion, etc to try to break the grab. If you experience a lot of grab deadlock, please report a bug. -debug_grabs Turn on debugging info printout with respect to XGrabServer() deadlock for -scrollcopyrect mode. -debug_sel Turn on debugging info printout with respect to PRIMARY, CLIPBOARD, and CUTBUFFER0 selections. -pointer_mode n Various pointer motion update schemes. "-pm" is an alias. The problem is pointer motion can cause rapid changes on the screen: consider the rapid changes when you drag a large window around opaquely. Neither x11vnc's screen polling and vnc compression routines nor the bandwidth to the vncviewers can keep up these rapid screen changes: everything will bog down when dragging or scrolling. So a scheme has to be used to "eat" much of that pointer input before re-polling the screen and sending out framebuffer updates. The mode number "n" can be 0 to 4 and selects one of the schemes desribed below. Note that the -wireframe and -scrollcopyrect modes complement -pointer_mode by detecting (and improving) certain periods of "rapid screen change". n=0: does the same as -nodragging. (all screen polling is suspended if a mouse button is pressed.) n=1: was the original scheme used to about Jan 2004: it basically just skips -input_skip keyboard or pointer events before repolling the screen. n=2 is an improved scheme: by watching the current rate of input events it tries to detect if it should try to "eat" additional pointer events before continuing. n=3 is basically a dynamic -nodragging mode: it detects when the mouse motion has paused and then refreshes the display. n=4 attempts to measures network rates and latency, the video card read rate, and how many tiles have been changed on the screen. From this, it aggressively tries to push screen "frames" when it decides it has enough resources to do so. NOT FINISHED. The default n is 2. Note that modes 2, 3, 4 will skip -input_skip keyboard events (but it will not count pointer events). Also note that these modes are not available in -threads mode which has its own pointer event handling mechanism. To try out the different pointer modes to see which one gives the best response for your usage, it is convenient to use the remote control function, for example "x11vnc -R pm:4" or the tcl/tk gui (Tuning -> pointer_mode -> n). -input_skip n For the pointer handling when non-threaded: try to read n user input events before scanning display. n < 0 means to act as though there is always user input. Default: 10 -speeds rd,bw,lat x11vnc tries to estimate some speed parameters that are used to optimize scheduling (e.g. -pointer_mode 4, -wireframe, -scrollcopyrect) and other things. Use the -speeds option to set these manually. The triple "rd,bw,lat" corresponds to video h/w read rate in MB/sec, network bandwidth to clients in KB/sec, and network latency to clients in milliseconds, respectively. If a value is left blank, e.g. "-speeds ,100,15", then the internal scheme is used to estimate the empty value(s). Typical PC video cards have read rates of 5-10 MB/sec. If the framebuffer is in main memory instead of video h/w (e.g. SunRay, shadowfb, dummy driver, Xvfb), the read rate may be much faster. "x11perf -getimage500" can be used to get a lower bound (remember to factor in the bytes per pixel). It is up to you to estimate the network bandwith and latency to clients. For the latency the ping(1) command can be used. For convenience there are some aliases provided, e.g. "-speeds modem". The aliases are: "modem" for 6,4,200; "dsl" for 6,100,50; and "lan" for 6,5000,1 -wmdt string For some features, e.g. -wireframe and -scrollcopyrect, x11vnc has to work around issues for certain window managers or desktops (currently kde and xfce). By default it tries to guess which one, but it can guess incorrectly. Use this option to indicate which wm/dt. "string" can be "gnome", "kde", "cde", "xfce", or "root" (classic X wm). Anything else is interpreted as "root". -debug_pointer Print debugging output for every pointer event. -debug_keyboard Print debugging output for every keyboard event. Same as -dp and -dk, respectively. Use multiple times for more output. -defer time Time in ms to wait for updates before sending to client (deferUpdateTime) Default: 30 -wait time Time in ms to pause between screen polls. Used to cut down on load. Default: 30 -wait_ui factor Factor by which to cut the -wait time if there has been recent user input (pointer or keyboard). Improves response, but increases the load whenever you are moving the mouse or typing. Default: 2.00 -nowait_bog Do not detect if the screen polling is "bogging down" and sleep more. Some activities with no user input can slow things down a lot: consider a large terminal window with a long build running in it continously streaming text output. By default x11vnc will try to detect this (3 screen polls in a row each longer than 0.25 sec with no user input), and sleep up to 1.5 secs to let things "catch up". Use this option to disable that detection. -slow_fb time Floating point time in seconds delay all screen polling. For special purpose usage where a low frame rate is acceptable and desirable, but you want the user input processed at the normal rate so you cannot use -wait. -readtimeout n Set libvncserver rfbMaxClientWait to n seconds. On slow links that take a long time to paint the first screen libvncserver may hit the timeout and drop the connection. Default: 20 seconds. -nap Monitor activity and if it is low take longer naps -nonap between screen polls to really cut down load when idle. Default: take naps -sb time Time in seconds after NO activity (e.g. screen blank) to really throttle down the screen polls (i.e. sleep for about 1.5 secs). Use 0 to disable. Default: 60 -nofbpm If the system supports the FBPM (Frame Buffer Power -fbpm Management) extension (i.e. some Sun systems), then prevent the video h/w from going into a reduced power state when VNC clients are connected. FBPM capable video h/w save energy when the workstation is idle by going into low power states (similar to DPMS for monitors). This interferes with x11vnc's polling of the framebuffer data. "-nofbpm" means prevent FBPM low power states whenever VNC clients are connected, while "-fbpm" means to not monitor the FBPM state at all. See the xset(1) manpage for details. -nofbpm is basically the same as running "xset fbpm force on" periodically. Default: -fbpm -noxdamage Do not use the X DAMAGE extension to detect framebuffer changes even if it is available. Use -xdamage if your default is to have it off. x11vnc's use of the DAMAGE extension: 1) significantly reduces the load when the screen is not changing much, and 2) detects changed areas (small ones by default) more quickly. Currently the DAMAGE extension is overly conservative and often reports large areas (e.g. a whole terminal or browser window) as damaged even though the actual changed region is much smaller (sometimes just a few pixels). So heuristics were introduced to skip large areas and use the damage rectangles only as "hints" for the traditional scanline polling. The following tuning parameters are introduced to adjust this behavior: -xd_area A Set the largest DAMAGE rectangle area "A" (in pixels: width * height) to trust as truly damaged: the rectangle will be copied from the framebuffer (slow) no matter what. Set to zero to trust *all* rectangles. Default: 20000 -xd_mem f Set how long DAMAGE rectangles should be "remembered", "f" is a floating point number and is in units of the scanline repeat cycle time (32 iterations). The default (1.0) should give no painting problems. Increase it if there are problems or decrease it to live on the edge (perhaps useful on a slow machine). -sigpipe string Broken pipe (SIGPIPE) handling. "string" can be "ignore" or "exit". For "ignore" libvncserver will handle the abrupt loss of a client and continue, for "exit" x11vnc will cleanup and exit at the 1st broken connection. Default: "ignore". This option is obsolete. -threads Whether or not to use the threaded libvncserver -nothreads algorithm [rfbRunEventLoop] if libpthread is available Default: -nothreads -fs f If the fraction of changed tiles in a poll is greater than f, the whole screen is updated. Default: 0.75 -gaps n Heuristic to fill in gaps in rows or cols of n or less tiles. Used to improve text paging. Default: 4 -grow n Heuristic to grow islands of changed tiles n or wider by checking the tile near the boundary. Default: 3 -fuzz n Tolerance in pixels to mark a tiles edges as changed. Default: 2 -debug_tiles Print debugging output for tiles, fb updates, etc. -snapfb Instead of polling the X display framebuffer (fb) for changes, periodically copy all of X display fb into main memory and examine that copy for changes. Under some circumstances this will improve interactive response, or at least make things look smoother, but in others (most!) it will make the response worse. If the video h/w fb is such that reading small tiles is very slow this mode could help. To keep the "framerate" up the screen size x bpp cannot be too large. Note that this mode is very wasteful of memory I/O resources (it makes full screen copies even if nothing changes). It may be of use in video capture-like applications, or where window tearing is a problem. -rawfb string Experimental option, instead of polling X, poll the memory object specified in "string". For shared memory segments it is of the form: "shm:N@WxHxB" which specifies a shmid N and framebuffer Width, Height, and Bits per pixel. To memory map mmap(2) a file use: "map:/path/to/a/file@WxHxB". If there is trouble with mmap, use "file:/..." for slower lseek(2) based reading. If you do not supply a type "map" is assumed if the file exists. If string is "setup:cmd", then the command "cmd" is run and the first line from it is read and used as "string". This allows initializing the device, determining WxHxB, etc. These are often done as root so take care. Optional suffixes are ":R/G/B" and "+O" to specify red, green, and blue masks and an offset into the memory object. If the masks are not provided x11vnc guesses them based on the bpp. Examples: -rawfb shm:210337933@800x600x32:ff/ff00/ff0000 -rawfb map:/dev/fb0@1024x768x32 -rawfb map:/tmp/Xvfb_screen0@640x480x8+3232 -rawfb file:/tmp/my.pnm@250x200x24+37 (see ipcs(1) and fbset(1) for the first two examples) All user input is discarded by default (but see the -pipeinput option). Most of the X11 (screen, keyboard, mouse) options do not make sense and many will cause this mode to crash, so please think twice before setting/changing them. If you don't want x11vnc to close the X DISPLAY in rawfb mode, then capitalize the prefix, SHM:, MAP:, FILE: Keeping the display open enables the default remote-control channel, which could be useful. Also, if you also specify -noviewonly, then the mouse and keyboard input are STILL sent to the X display, this usage should be very rare, i.e. doing something strange with /dev/fb0. -pipeinput cmd Another experimental option: it lets you supply an external command in "cmd" that x11vnc will pipe all of the user input events to in a simple format. In -pipeinput mode by default x11vnc will not process any of the user input events. If you prefix "cmd" with "tee:" it will both send them to the pipe command and process them. For a description of the format run "-pipeinput tee:/bin/cat". Another prefix is "reopen" which means to reopen pipe if it exits. Separate multiple prefixes with commas. In combination with -rawfb one might be able to do amusing things (e.g. control non-X devices). To facilitate this, if -rawfb is in effect then the value is stored in X11VNC_RAWFB_STR for the pipe command to use if it wants. Do 'env | grep X11VNC' for more. -gui [gui-opts] Start up a simple tcl/tk gui based on the the remote control options -remote/-query described below. Requires the "wish" program to be installed on the machine. "gui-opts" is not required: the default is to start up both the full gui and x11vnc with the gui showing up on the X display in the environment variable DISPLAY. "gui-opts" can be a comma separated list of items. Currently there are these types of items: 1) a gui mode, a 2) gui "simplicity", 3) the X display the gui should display on, 4) a "tray" or "icon" mode, and 5) a gui geometry. 1) The gui mode can be "start", "conn", or "wait" "start" is the default mode above and is not required. "conn" means do not automatically start up x11vnc, but instead just try to connect to an existing x11vnc process. "wait" means just start the gui and nothing else (you will later instruct the gui to start x11vnc or connect to an existing one.) 2) The gui simplicity is off by default (a power-user gui with all options is presented) To start with something less daunting supply the string "simple" ("ez" is an alias for this). Once the gui is started you can toggle between the two with "Misc -> simple_gui". 3) Note the possible confusion regarding the potentially two different X displays: x11vnc polls one, but you may want the gui to appear on another. For example, if you ssh in and x11vnc is not running yet you may want the gui to come back to you via your ssh redirected X display (e.g. localhost:10). If you do not specify a gui X display in "gui-opts" then the DISPLAY environment variable and -display option are tried (in that order). Regarding the x11vnc X display the gui will try to communication with, it first tries -display and then DISPLAY. For example, "x11vnc -display :0 -gui otherhost:0", will remote control an x11vnc polling :0 and display the gui on otherhost:0 The "tray/icon" mode below reverses this preference, preferring to display on the x11vnc display. 4) When "tray" or "icon" is specified, the gui presents itself as a small icon with behavior typical of a "system tray" or "dock applet". The color of the icon indicates status (connected clients) and there is also a balloon status. Clicking on the icon gives a menu from which properties, etc, can be set and the full gui is available under "Advanced". To be fully functional, the gui mode should be "start" (the default). For "icon" the gui just a small standalone window. For "tray" it will attempt to embed itself in the "system tray" if possible. If "=setpass" is appended the n at startup the X11 user will be prompted to set the VNC session password. If = is appended that icon will attempt to embed itself in the window given by hexnumber. Use =noadvanced to disable the full gui. (To supply more than one, use "+" sign). E.g. -gui tray=setpass and -gui icon=0x3600028 Other modes: "full", the default and need not be specified. "-gui none", do not show a gui, useful to override a ~/.x11vncrc setting, etc. 5) When "geom=+X+Y" is specified, that geometry is passed to the gui toplevel. This is the icon in icon/tray mode, or the full gui otherwise. You can also specify width and height, i.e. WxH+X+Y, but it is not recommended. In "tray" mode the geometry is ignored unless the system tray manager does not seem to be running. One could imagine using something like "-gui tray,geom=+4000+4000" with a display manager to keep the gui invisible until someone logs in... More icon tricks, "icon=minimal" gives an icon just with the VNC display number. You can also set the font with "iconfont=...". The following could be useful: "-gui icon=minimal,iconfont=5x8,geom=24x10+0-0" General examples of the -gui option: "x11vnc -gui", "x11vnc -gui ez" "x11vnc -gui localhost:10", "x11vnc -gui conn,host:0", "x11vnc -gui tray,ez" "x11vnc -gui tray=setpass" If you do not intend to start x11vnc from the gui (i.e. just remote control an existing one), then the gui process can run on a different machine from the x11vnc server as long as X permissions, etc. permit communication between the two. -remote command Remotely control some aspects of an already running x11vnc server. "-R" and "-r" are aliases for "-remote". After the remote control command is sent to the running server the 'x11vnc -remote ...' command exits. You can often use the -query command (see below) to see if the x11vnc server processed your -remote command. The default communication channel is that of X properties (specifically X11VNC_REMOTE), and so this command must be run with correct settings for DISPLAY and possibly XAUTHORITY to connect to the X server and set the property. Alternatively, use the -display and -auth options to set them to the correct values. The running server cannot use the -novncconnect option because that disables the communication channel. See below for alternate channels. For example: 'x11vnc -remote stop' (which is the same as 'x11vnc -R stop') will close down the x11vnc server. 'x11vnc -R shared' will enable shared connections, and 'x11vnc -R scale:3/4' will rescale the desktop. The following -remote/-R commands are supported: stop terminate the server, same as "quit" "exit" or "shutdown". ping see if the x11vnc server responds. Return is: ans=ping: blacken try to push a black fb update to all clients (due to timings a client could miss it). Same as "zero", also "zero:x1,y1,x2,y2" for a rectangle. refresh send the entire fb to all clients. reset recreate the fb, polling memory, etc. id:windowid set -id window to "windowid". empty or "root" to go back to root window sid:windowid set -sid window to "windowid" waitmapped wait until subwin is mapped. nowaitmapped do not wait until subwin is mapped. clip:WxH+X+Y set -clip mode to "WxH+X+Y" flashcmap enable -flashcmap mode. noflashcmap disable -flashcmap mode. shiftcmap:n set -shiftcmap to n. notruecolor enable -notruecolor mode. truecolor disable -notruecolor mode. overlay enable -overlay mode (if applicable). nooverlay disable -overlay mode. overlay_cursor in -overlay mode, enable cursor drawing. overlay_nocursor disable cursor drawing. same as nooverlay_cursor. 8to24 enable -8to24 mode (if applicable). no8to24 disable -8to24 mode. 8to24_opts:str set the -8to24 opts to "str". visual:vis set -visual to "vis" scale:frac set -scale to "frac" scale_cursor:f set -scale_cursor to "f" viewonly enable -viewonly mode. noviewonly disable -viewonly mode. shared enable -shared mode. noshared disable -shared mode. forever enable -forever mode. noforever disable -forever mode. timeout:n reset -timeout to n, if there are currently no clients, exit unless one connects in the next n secs. filexfer enable filetransfer for new clients. nofilexfer disable filetransfer for new clients. http enable http client connections. nohttp disable http client connections. deny deny any new connections, same as "lock" nodeny allow new connections, same as "unlock" connect:host do reverse connection to host, "host" may be a comma separated list of hosts or host:ports. See -connect. Passwords required as with fwd connections. See X11VNC_REVERSE_CONNECTION_NO_AUTH=1 disconnect:host disconnect any clients from "host" same as "close:host". Use host "all" to close all current clients. If you know the client internal hex ID, e.g. 0x3 (returned by "-query clients" and RFB_CLIENT_ID) you can use that too. allowonce:host For the next connection only, allow connection from "host". allow:hostlist set -allow list to (comma separated) "hostlist". See -allow and -localhost. Do not use with -allow /path/to/file Use "+host" to add a single host, and use "-host" to delete a single host localhost enable -localhost mode nolocalhost disable -localhost mode listen:str set -listen to str, empty to disable. nolookup enable -nolookup mode. lookup disable -nolookup mode. input:str set -input to "str", empty to disable. client_input:str set the K, M, B -input on a per-client basis. select which client as for disconnect, e.g. client_input:host:MB or client_input:0x2:K accept:cmd set -accept "cmd" (empty to disable). afteraccept:cmd set -afteraccept (empty to disable). gone:cmd set -gone "cmd" (empty to disable). noshm enable -noshm mode. shm disable -noshm mode (i.e. use shm). flipbyteorder enable -flipbyteorder mode, you may need to set noshm for this to do something. noflipbyteorder disable -flipbyteorder mode. onetile enable -onetile mode. (you may need to set shm for this to do something) noonetile disable -onetile mode. solid enable -solid mode nosolid disable -solid mode. solid_color:color set -solid color (and apply it). blackout:str set -blackout "str" (empty to disable). See -blackout for the form of "str" (basically: WxH+X+Y,...) Use "+WxH+X+Y" to append a single rectangle use "-WxH+X+Y" to delete one xinerama enable -xinerama mode. (if applicable) noxinerama disable -xinerama mode. xtrap enable -xtrap input mode(if applicable) noxtrap disable -xtrap input mode. xrandr enable -xrandr mode. (if applicable) noxrandr disable -xrandr mode. xrandr_mode:mode set the -xrandr mode to "mode". padgeom:WxH set -padgeom to WxH (empty to disable) If WxH is "force" or "do" the padded geometry fb is immediately applied. quiet enable -quiet mode. noquiet disable -quiet mode. modtweak enable -modtweak mode. nomodtweak enable -nomodtweak mode. xkb enable -xkb modtweak mode. noxkb disable -xkb modtweak mode. skip_keycodes:str enable -xkb -skip_keycodes "str". sloppy_keys enable -sloppy_keys mode. nosloppy_keys disable -sloppy_keys mode. skip_dups enable -skip_dups mode. noskip_dups disable -skip_dups mode. add_keysyms enable -add_keysyms mode. noadd_keysyms stop adding keysyms. those added will still be removed at exit. clear_mods enable -clear_mods mode and clear them. noclear_mods disable -clear_mods mode. clear_keys enable -clear_keys mode and clear them. noclear_keys disable -clear_keys mode. remap:str set -remap "str" (empty to disable). See -remap for the form of "str" (basically: key1-key2,key3-key4,...) Use "+key1-key2" to append a single keymapping, use "-key1-key2" to delete. norepeat enable -norepeat mode. repeat disable -norepeat mode. nofb enable -nofb mode. fb disable -nofb mode. bell enable bell (if supported). nobell disable bell. nosel enable -nosel mode. sel disable -nosel mode. noprimary enable -noprimary mode. primary disable -noprimary mode. nosetprimary enable -nosetprimary mode. setprimary disable -nosetprimary mode. noclipboard enable -noclipboard mode. clipboard disable -noclipboard mode. nosetclipboard enable -nosetclipboard mode. setclipboard disable -nosetclipboard mode. seldir:str set -seldir to "str" cursor:mode enable -cursor "mode". show_cursor enable showing a cursor. noshow_cursor disable showing a cursor. (same as "nocursor") arrow:n set -arrow to alternate n. xfixes enable xfixes cursor shape mode. noxfixes disable xfixes cursor shape mode. alphacut:n set -alphacut to n. alphafrac:f set -alphafrac to f. alpharemove enable -alpharemove mode. noalpharemove disable -alpharemove mode. alphablend disable -noalphablend mode. noalphablend enable -noalphablend mode. cursorshape disable -nocursorshape mode. nocursorshape enable -nocursorshape mode. cursorpos disable -nocursorpos mode. nocursorpos enable -nocursorpos mode. xwarp enable -xwarppointer mode. noxwarp disable -xwarppointer mode. buttonmap:str set -buttonmap "str", empty to disable dragging disable -nodragging mode. nodragging enable -nodragging mode. wireframe enable -wireframe mode. same as "wf" nowireframe disable -wireframe mode. same as "nowf" wireframe:str enable -wireframe mode string. wireframe_mode:str enable -wireframe mode string. wirecopyrect:str set -wirecopyrect string. same as "wcr: " scrollcopyrect:str set -scrollcopyrect string. same "scr " noscrollcopyrect disable -scrollcopyrect mode. "noscr" scr_area:n set -scr_area to n scr_skip:list set -scr_skip to "list" scr_inc:list set -scr_inc to "list" scr_keys:list set -scr_keys to "list" scr_term:list set -scr_term to "list" scr_keyrepeat:str set -scr_keyrepeat to "str" scr_parms:str set -scr_parms parameters. fixscreen:str set -fixscreen to "str". noxrecord disable all use of RECORD extension. xrecord enable use of RECORD extension. reset_record reset RECORD extension (if avail.) pointer_mode:n set -pointer_mode to n. same as "pm" input_skip:n set -input_skip to n. speeds:str set -speeds to str. wmdt:str set -wmdt to str. debug_pointer enable -debug_pointer, same as "dp" nodebug_pointer disable -debug_pointer, same as "nodp" debug_keyboard enable -debug_keyboard, same as "dk" nodebug_keyboard disable -debug_keyboard, same as "nodk" defer:n set -defer to n ms,same as deferupdate:n wait:n set -wait to n ms. wait_ui:f set -wait_ui factor to f. wait_bog disable -nowait_bog mode. nowait_bog enable -nowait_bog mode. slow_fb:f set -slow_fb to f seconds. readtimeout:n set read timeout to n seconds. nap enable -nap mode. nonap disable -nap mode. sb:n set -sb to n s, same as screen_blank:n fbpm disable -nofbpm mode. nofbpm enable -nofbpm mode. xdamage enable xdamage polling hints. noxdamage disable xdamage polling hints. xd_area:A set -xd_area max pixel area to "A" xd_mem:f set -xd_mem remembrance to "f" fs:frac set -fs fraction to "frac", e.g. 0.5 gaps:n set -gaps to n. grow:n set -grow to n. fuzz:n set -fuzz to n. snapfb enable -snapfb mode. nosnapfb disable -snapfb mode. rawfb:str set -rawfb mode to "str". progressive:n set libvncserver -progressive slice height parameter to n. desktop:str set -desktop name to str for new clients . rfbport:n set -rfbport to n. httpport:n set -httpport to n. httpdir:dir set -httpdir to dir (and enable http). enablehttpproxy enable -enablehttpproxy mode. noenablehttpproxy disable -enablehttpproxy mode. alwaysshared enable -alwaysshared mode. noalwaysshared disable -alwaysshared mode. (may interfere with other options) nevershared enable -nevershared mode. nonevershared disable -nevershared mode. (may interfere with other options) dontdisconnect enable -dontdisconnect mode. nodontdisconnect disable -dontdisconnect mode. (may interfere with other options) debug_xevents enable debugging X events. nodebug_xevents disable debugging X events. debug_xdamage enable debugging X DAMAGE mechanism. nodebug_xdamage disable debugging X DAMAGE mechanism. debug_wireframe enable debugging wireframe mechanism. nodebug_wireframe disable debugging wireframe mechanism. debug_scroll enable debugging scrollcopy mechanism. nodebug_scroll disable debugging scrollcopy mechanism. debug_tiles enable -debug_tiles nodebug_tiles disable -debug_tiles debug_grabs enable -debug_grabs nodebug_grabs disable -debug_grabs debug_sel enable -debug_sel nodebug_sel disable -debug_sel dbg enable -dbg crash shell nodbg disable -dbg crash shell noremote disable the -remote command processing, it cannot be turned back on. The vncconnect(1) command from standard VNC distributions may also be used if string is prefixed with "cmd=" E.g. 'vncconnect cmd=stop'. Under some circumstances xprop(1) can used if it supports -set (see the FAQ). If "-connect /path/to/file" has been supplied to the running x11vnc server then that file can be used as a communication channel (this is the only way to remote control one of many x11vnc's polling the same X display) Simply run: 'x11vnc -connect /path/to/file -remote ...' or you can directly write to the file via something like: "echo cmd=stop > /path/to/file", etc. -query variable Like -remote, except just query the value of "variable". "-Q" is an alias for "-query". Multiple queries can be done by separating variables by commas, e.g. -query var1,var2. The results come back in the form ans=var1:value1,ans=var2:value2,... to the standard output. If a variable is read-only, it comes back with prefix "aro=" instead of "ans=". Some -remote commands are pure actions that do not make sense as variables, e.g. "stop" or "disconnect", in these cases the value returned is "N/A". To direct a query straight to the X11VNC_REMOTE property or connect file use "qry=..." instead of "cmd=..." Here is the current list of "variables" that can be supplied to the -query command. This includes the "N/A" ones that return no useful info. For variables names that do not correspond to an x11vnc option or remote command, we hope the name makes it obvious what the returned value corresponds to (hint: the ext_* variables correspond to the presence of X extensions): ans= stop quit exit shutdown ping blacken zero refresh reset close disconnect id sid waitmapped nowaitmapped clip flashcmap noflashcmap shiftcmap truecolor notruecolor overlay nooverlay overlay_cursor overlay_yescursor nooverlay_nocursor nooverlay_cursor nooverlay_yescursor overlay_nocursor 8to24 no8to24 8to24_opts visual scale scale_cursor viewonly noviewonly shared noshared forever noforever once timeout filexfer nofilexfer deny lock nodeny unlock connect allowonce allow localhost nolocalhost listen lookup nolookup accept afteraccept gone shm noshm flipbyteorder noflipbyteorder onetile noonetile solid_color solid nosolid blackout xinerama noxinerama xtrap noxtrap xrandr noxrandr xrandr_mode padgeom quiet q noquiet modtweak nomodtweak xkb noxkb skip_keycodes sloppy_keys nosloppy_keys skip_dups noskip_dups add_keysyms noadd_keysyms clear_mods noclear_mods clear_keys noclear_keys remap repeat norepeat fb nofb bell nobell sel nosel primary noprimary setprimary nosetprimary clipboard noclipboard setclipboard nosetclipboard seldir cursorshape nocursorshape cursorpos nocursorpos cursor show_cursor noshow_cursor nocursor arrow xfixes noxfixes xdamage noxdamage xd_area xd_mem alphacut alphafrac alpharemove noalpharemove alphablend noalphablend xwarppointer xwarp noxwarppointer noxwarp buttonmap dragging nodragging wireframe_mode wireframe wf nowireframe nowf wirecopyrect wcr nowirecopyrect nowcr scr_area scr_skip scr_inc scr_keys scr_term scr_keyrepeat scr_parms scrollcopyrect scr noscrollcopyrect noscr fixscreen noxrecord xrecord reset_record pointer_mode pm input_skip input client_input speeds wmdt debug_pointer dp nodebug_pointer nodp debug_keyboard dk nodebug_keyboard nodk deferupdate defer wait_ui wait_bog nowait_bog slow_fb wait readtimeout nap nonap sb screen_blank fbpm nofbpm fs gaps grow fuzz snapfb nosnapfb rawfb progressive rfbport http nohttp httpport httpdir enablehttpproxy noenablehttpproxy alwaysshared noalwaysshared nevershared noalwaysshared dontdisconnect nodontdisconnect desktop debug_xevents nodebug_xevents debug_xevents debug_xdamage nodebug_xdamage debug_xdamage debug_wireframe nodebug_wireframe debug_wireframe debug_scroll nodebug_scroll debug_scroll debug_tiles dbt nodebug_tiles nodbt debug_tiles debug_grabs nodebug_grabs debug_sel nodebug_sel dbg nodbg noremote aro= noop display vncdisplay desktopname guess_desktop http_url auth xauth users rootshift clipshift scale_str scaled_x scaled_y scale_numer scale_denom scale_fac scaling_blend scaling_nomult4 scaling_pad scaling_interpolate inetd privremote unsafe safer nocmds passwdfile unixpw unixpw_nis unixpw_list ssl ssl_pem sslverify stunnel stunnel_pem https usepw using_shm logfile o flag rc norc h help V version lastmod bg sigpipe threads readrate netrate netlatency pipeinput clients client_count pid ext_xtest ext_xtrap ext_xrecord ext_xkb ext_xshm ext_xinerama ext_overlay ext_xfixes ext_xdamage ext_xrandr rootwin num_buttons button_mask mouse_x mouse_y bpp depth indexed_color dpy_x dpy_y wdpy_x wdpy_y off_x off_y cdpy_x cdpy_y coff_x coff_y rfbauth passwd viewpasswd -QD variable Just like -query variable, but returns the default value for that parameter (no running x11vnc server is consulted) -sync By default -remote commands are run asynchronously, that is, the request is posted and the program immediately exits. Use -sync to have the program wait for an acknowledgement from the x11vnc server that command was processed (somehow). On the other hand -query requests are always processed synchronously because they have to wait for the answer. Also note that if both -remote and -query requests are supplied on the command line, the -remote is processed first (synchronously: no need for -sync), and then the -query request is processed in the normal way. This allows for a reliable way to see if the -remote command was processed by querying for any new settings. Note however that there is timeout of a few seconds so if the x11vnc takes longer than that to process the requests the requestor will think that a failure has taken place. -noremote Do not process any remote control commands or queries. -yesremote Do process remote control commands or queries. Default: -yesremote A note about security wrt remote control commands. If someone can connect to the X display and change the property X11VNC_REMOTE, then they can remotely control x11vnc. Normally access to the X display is protected. Note that if they can modify X11VNC_REMOTE on the X server, they have enough permissions to also run their own x11vnc and thus have complete control of the desktop. If the "-connect /path/to/file" channel is being used, obviously anyone who can write to /path/to/file can remotely control x11vnc. So be sure to protect the X display and that file's write permissions. See -privremote below. If you are paranoid and do not think -noremote is enough, to disable the X11VNC_REMOTE property channel completely use -novncconnect, or use the -safer option that shuts many things off. -unsafe A few remote commands are disabled by default (currently: id:pick, accept:, gone:, and rawfb:setup:) because they are associated with running external programs. If you specify -unsafe, then these remote-control commands are allowed. Note that you can still specify these parameters on the command line, they just cannot be invoked via remote-control. -safer Equivalent to: -novncconnect -noremote and prohibiting -gui and the -connect file. Shuts off communcation channels. -privremote Perform some sanity checks and disable remote-control commands if it appears that the X DISPLAY and/or connectfile can be accessed by other users. Once remote-control is disabled it cannot be turned back on. -nocmds No external commands (e.g. system(3), popen(3), exec(3)) will be run. -deny_all For use with -remote nodeny: start out denying all incoming clients until "-remote nodeny" is used to let them in. These options are passed to libvncserver: -rfbport port TCP port for RFB protocol -rfbwait time max time in ms to wait for RFB client -rfbauth passwd-file use authentication on RFB protocol (use 'storepasswd' to create a password file) -passwd plain-password use authentication (use plain-password as password, USE AT YOUR RISK) -deferupdate time time in ms to defer updates (default 40) -deferptrupdate time time in ms to defer pointer updates (default none) -desktop name VNC desktop name (default "LibVNCServer") -alwaysshared always treat new clients as shared -nevershared never treat new clients as shared -dontdisconnect don't disconnect existing clients when a new non-shared connection comes in (refuse new connection instead) -httpdir dir-path enable http server using dir-path home -httpport portnum use portnum for http connection -enablehttpproxy enable http proxy support -progressive height enable progressive updating for slow links -listen ipaddr listen for connections only on network interface with addr ipaddr. '-listen localhost' and hostname work too. libvncserver-tight-extension options: -disablefiletransfer disable file transfer -ftproot string set ftp root Pretty wild huh? [1]Contact me if you have any questions or problems. Personally, I use: x11vnc -rfbauth $HOME/.vnc/passwd -solid References 1. mailto:xvml@karlrunge.com