x11vnc: a VNC server for real X displays
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x11vnc allows one to view remotely and interact with real X displays (i.e. a display corresponding to a physical monitor, keyboard, and mouse) with any VNC viewer. In this way it plays the role for Unix/X11 that WinVNC plays for Windows.

It has built-in SSL encryption and authentication, UNIX account and password support, server-side scaling, single port HTTPS and VNC, mDNS service advertising, and TightVNC and UltraVNC file-transfer. It has also been extended to work with non-X devices: webcams and TV tuner capture devices, embedded Linux systems such as Qtopia Core, and natively on Mac OS X Aqua/Quartz.

It also provides an encrypted Terminal Services mode (-create, -svc, or -xdmsvc options) based on Unix usernames and Unix passwords where the user does not need to memorize his VNC display/port number. See also the tsvnc terminal services mode of the SSVNC viewer.

I wrote x11vnc back in 2002 because x0rfbserver was basically impossible to build on Solaris and had poor performance. The primary x0rfbserver build problems centered around esoteric C++ toolkits. x11vnc is written in plain C and needs only standard libraries and so should work on nearly all Unixes. I also added some enhancements to improve the interactive response, add many features, and etc.

This page including the FAQ contains much information [*]; solutions to many problems; and interesting applications, but nevertheless please feel free to contact me if you have problems or questions. Please do check the FAQ; I realize this page is massive, but you can often use your browser's find-in-page action to find the discussion of your problem or question.

Please help beta test the new performance speedup feature using viewer-side pixel caching "ncache". Let me know how it goes; thanks.

SSVNC:  An x11vnc side-project provides an Enhanced TightVNC Viewer package (SSVNC) for Unix, Windows, and Mac OS X with automatic SSL and/or SSH tunnelling support, SSL Certificate creation, saved connection profiles, and built-in Proxy support. And for the Unix viewer: NewFBSize, ZRLE, cursor alphablending, and low color modes. Also on Unix the UltraVNC File Transfer, Text Chat, Single Window, Server Input, and 1/n Scaling extensions are supported. This bundle could be placed on, say, a USB memory stick for SSL/SSH VNC viewing from nearly any networked computer. Please help test out some recently added features: automatic service tunnelling via SSH for: CUPS and SMB Printing, ESD/ARTSD Audio, and SMB (Windows/Samba) filesystem mounting; Port Knocking; and the sshvnc/tsvnc modes.

Background:

Some VNC links:

• http://www.realvnc.com
• http://www.tightvnc.com
• http://www.ultravnc.com/
• 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, firefox, 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 because it involves far fewer "roundtrips" (an exception is the cached pixmap data on the viewing-end provided by X). 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 the 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 (see below) and have it available to run on far-away.east (on some linux distros it is as easy as "apt-get install x11vnc", "emerge x11vnc", etc.) Similarly, have a VNC viewer (e.g. vncviewer) ready to run on sitting-here.west. We recommend TightVNC Viewers (see also here.)

Step 1. By some means log in to far-away.east and get a command shell running there. You can use ssh, or even rlogin, telnet, or any other method to do this. We do this because 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

Common Gotcha: To get X11 permissions right, you may also need to set the XAUTHORITY environment variable (or use the -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 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 below.

Note as of Feb/2007 you can also try the -find option instead of "-display ..." and see if that finds your display and Xauthority. (End of Common Gotcha)

When x11vnc starts up there will then be much chatter printed out (use "-q" to quiet it), 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

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 this FAQ. For Solaris, vncviewer is available in the 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

Common Gotcha: Nowadays there will likely be a host-level firewall on the x11vnc side that is blocking remote access to the VNC port (e.g. 5900). You will either have to open up that port (or a range of ports) in your firewall administration tool, or try the SSH tunnelling method below (even still the firewall must allow in the SSH port, 22).

 
Shortcut: Of course if you left x11vnc running on far-away.east:0 in a terminal window with the -forever option or as a service, you'd only have to do Step 3 as you moved around. Be sure to use a VNC Password or other measures if you do that.

 
Super Shortcut: Here is a potentially very easy way to get all of it working.

• Have x11vnc (0.9.3 or later) available to run on the remote host (i.e. in $PATH).
• Download and unpack a SSVNC bundle (1.0.19 or later, e.g. ssvnc_no_windows-1.0.19.tar.gz) on the Viewer-side machine.
• Start the SSVNC Terminal Services mode GUI: ./ssvnc/bin/tsvnc
• Enter your remote username@hostname (e.g. fred@far-away.east) in the "VNC Terminal Server" entry.
• Click "Connect".

There are a number of things assumed here, first that you are able to SSH into the remote host; i.e. that you have a Unix account there and the SSH server is running. On Unix and MacOS X it is assumed that the ssh client command is available on the local machine (on Windows a plink binary is included in the SSVNC bundle). Finally, it is assumed that you are already logged into an X session on the remote machine, e.g. your workstation (otherwise, a virtual X server, e.g. Xvfb, will be started for you).

In some cases the remote SSH server will not run commands with the same $PATH that you normally have in your shell there. In this case click on Options -> Advanced -> X11VNC Options, and type in the location of the x11vnc binary under "Full Path". (End of Super Shortcut)

 
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 connects remotely 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 "-connect host1,host2" option may be of use to automatically connect to the 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 a VPN, Virtual Private Network, the above example should be pretty safe).

For x11vnc one can tunnel the VNC protocol through an encrypted ssh channel. It would look something like running the following commands:

  sitting-here> ssh -t -L 5900:localhost:5900 far-away.east 'x11vnc -localhost -display :0'

And then in another terminal window on sitting-here run the command:

  sitting-here> vncviewer -encodings "copyrect tight zrle hextile" localhost:0

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 VNC password is also strongly recommended.

Note also the -t we used above (force allocate pseudoterminal), it actually seems to improve interactive typing response via VNC!

You may want to add the -C option to ssh to enable compression. The VNC compression is not perfect, and so this may help a bit. However, over a fast LAN you probably don't want to enable SSH compression because it can slow things down. Try both and see which is faster.

If your username is different on the remote machine use something like: "fred@far-away.east" in the above ssh command line.

Some VNC viewers will do the ssh tunnelling for you automatically, the TightVNC Unix 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 inetd(8)). See the 3rd script example below for more info.

SSVNC:  You may also want to look at the Enhanced TightVNC Viewer (ssvnc) bundles because they contain scripts and GUIs to automatically set up SSH tunnels (e.g. the GUI, "ssvnc", does it automatically and so does this command: "ssvnc_cmd -ssh user@far-away.east:0") and can even start up x11vnc as well.

The Terminal Services mode of SSVNC is perhaps the easiest way to use x11vnc. You just need to have x11vnc available in $PATH on the remote side (and can SSH to the host), and then on the viewer-side you type something like:

  tsvnc fred@far-away.east

Gateways:  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":

  sitting-here> ssh -t -L 5900:OtherHost:5900 gateway.east

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). (The "-connect gateway:59xx" option may be another alternative here with the viewer already in -listen mode). For an automatic way to use a gateway and have all the network traffic encrypted (including inside the firewall) see Chaining SSH's.

These gateway access modes also can be done automatically for you via the "Proxy/Gateway" setting in SSVNC (including the Chaining SSH's case, "Double Proxy").

Firewalls/Routers: 

A lot of people have inexpensive devices for home or office that act as a Firewall and Router to the machines inside on a private LAN. One can usually configure the Firewall/Router from inside the LAN via a web browser.

Often having a Firewall/Router sitting between the vncviewer and x11vnc will make it impossible for the viewer to connect to x11vnc.

One thing that can be done is to redirect a port on the Firewall/Router to, say, the SSH port (22) on an inside machine (how to do this depends on your particular Firewall/Router, often the router config URL is http://192.168.100.1 See www.portforward.com for more info). This way you reach these computers from anywhere on the Internet and use x11vnc to view X sessions running on them.

Suppose you configured the Firewall/Router to redirect these ports to two internal machines:

  Port 12300 -> 192.168.1.3, Port 22 (SSH)
  Port 12301 -> 192.168.1.4, Port 22 (SSH)

  sitting-here> ssh -t -p 12300 -L 5900:localhost:5900 jill@far-away.east 'x11vnc -localhost -display :0'
  sitting-here> ssh -t -p 12301 -L 5900:localhost:5900 fred@far-away.east 'x11vnc -localhost -display :0'

It is a good idea to add some obscurity to accessing your system via SSH by using some high random port (e.g. 12300 in the above example). If you can't remember it, or are otherwise not worried about port scanners detecting the presence of your SSH server and there is just one internal PC involved you could map 22:

  Port 22 -> 192.168.1.3, Port 22 (SSH)

Again, this SSH gateway access can be done automatically for you via the "Proxy/Gateway" setting in SSVNC. And under the "Remote SSH Command" setting you can enter the x11vnc -localhost -display :0.

Host-Level-Firewalls: even with the hardware Firewall/Router problem solved via a port redirection, most PC systems have their own Host level "firewalls" enabled to protect users from themselves. I.e. the system itself blocks all incoming connections. So you will need to see what is needed to configure it to allow in the port (e.g. 22) that you desire. E.g. Yast, Firestarter, iptables(1), etc..

VNC Ports and Firewalls: The above discussion was for configuring the Firewall/Router to let in port 22 (SSH), but the same thing can be done for the default VNC port 5900:

  Port 5900 -> 192.168.1.3, Port 5900 (VNC)
  Port 5901 -> 192.168.1.4, Port 5900 (VNC)

The the VNC displays to enter in the VNC viewer would be, say, "far-away.east:0" to reach jills-pc and "far-away.east:1" to reach freds-pc. We assume above that x11vnc is using port 5900 (and any Host-Level-firewalls on jills-pc has been configured to let that port in).

For a home system one likely does not have a hostname and would have to use the IP address, say, "24.56.78.93:0". E.g.:

  vncviewer 24.56.78.93:0

#!/bin/sh
# usage: x11vnc_ssh <host>:<xdisplay>
#  e.g.: x11vnc_ssh snoopy.peanuts.com:0
#  (user@host:N also works)

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 -t -L 5900:localhost:5900 $host "$cmd"

for i in 1 2 3
do
        sleep 2
        if vncviewer -encodings "$enc" :0; then break; fi
done

#!/bin/sh
# usage: x11vnc_ssh <host>:<xdisplay>
#  e.g.: x11vnc_ssh snoopy.peanuts.com:0
#  (user@host:N also works)

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 option
enc="copyrect tight zrle hextile zlib corre rre raw"

vncviewer -encodings "$enc" -listen &
pid=$!
ssh -t -R 5500:localhost:5500 $host "$cmd"
kill $pid

#!/bin/sh
# usage: x11vnc_ssh <host>:<xdisplay>
#  e.g.: x11vnc_ssh snoopy.peanuts.com:0

host=`echo $1 | awk -F: '{print $1}'`
disp=`echo $1 | awk -F: '{print $2}'`
if [ "x$disp" = "x" ]; then disp=0; fi

VNC_VIA_CMD="ssh -f -t -L %L:%H:%R %G x11vnc -localhost -rfbport 5900 -display :$disp; sleep 5" 
export VNC_VIA_CMD

vncviewer -via $host localhost:0      # must be TightVNC vncviewer.

 
 
VNC password file: Also note in the #1. example script that the option "-rfbauth .vnc/passwd" provides additional protection by requiring a VNC password for every VNC viewer that connects. The vncpasswd or storepasswd programs, or the x11vnc -storepasswd option can be used to create the password file. x11vnc also has the slightly less secure -passwdfile and "-passwd XXXXX" 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 (use -usepw if you want to be forced to). The same goes for encrypting the channel between the viewer and x11vnc: it is up to you to use ssh, stunnel, -ssl mode, a VPN, etc. (use the Enhanced TightVNC Viewer (SSVNC) GUI if you want to be forced to use SSL or SSH). For additional safety, also look into the -allow and -localhost options and building x11vnc with tcp_wrappers support to limit host access.

Tunnelling x11vnc via SSL:

One can also encrypt the VNC traffic using an SSL tunnel such as stunnel (also stunnel.mirt.net) or using the built-in (Mar/2006) -ssl openssl mode. A SSL-enabled Java applet VNC Viewer is also provided in the x11vnc package (and https can be used to download it).

Although not as ubiquitous as ssh, SSL tunnelling still provides a useful alternative. See this FAQ on -ssl and -stunnel modes for details and examples.

The Enhanced TightVNC Viewer (SSVNC) bundles contain some convenient utilities to automatically set up an SSL tunnel from the viewer-side (i.e. to connect to "x11vnc -ssl ..."). And many other enhancements too.

Downloading x11vnc:

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 x11vnc-0.9.4.tar.gz tarball to build the most up to date one.

Precompiled Binaries/Packages:  See the FAQ below for information about where you might obtain a precompiled x11vnc binary from 3rd parties and some ones I create.

VNC Viewers:  To obtain VNC viewers for the viewing side (Windows, Mac OS, or Unix) try these links:

• http://www.tightvnc.com/download.html
• http://www.realvnc.com/download-free.html
• http://sourceforge.net/projects/cotvnc/
• http://www.ultravnc.com/
• Our Enhanced TightVNC Viewer (SSVNC)
   
  

 
More tools: Here is a ssh/rsh wrapper script rx11vnc that attempts to automatically do the above Steps 1-3 for you (provided you have ssh/rsh 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:

• rx11vnc wrapper script
• 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 0.9.3 release of x11vnc: replace with the version you downloaded):

(un-tar the x11vnc+libvncserver tarball)
# gzip -dc x11vnc-0.9.3.tar.gz | tar -xvf -

(cd to the source directory)
# cd x11vnc-0.9.3

(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

Note: Currently gcc is recommended to build libvncserver. In some cases it will build with non-gcc compilers, but the resulting binary sometimes fails to run properly. For Solaris pre-built gcc binaries are at http://www.sunfreeware.com/. Some Solaris pre-built x11vnc binaries are 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

You can find information on Misc. Build problems here.

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'

 
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=/usr/sfw; make'

 
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 ftp://ftp.uu.net/graphics/jpeg/ and zlib at http://www.gzip.org/zlib/. See also 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<---

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 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

 
Building on AIX:   AIX: one user had to add the "X11.adt" package to AIX 4.3.3 and 5.2 to get build header files like XShm.h, etc. You may also want to make sure that /usr/lpp/X11/include, etc is being picked up by the configure and make.

 
Building on Mac OS X:   There is now native Mac OS X support for x11vnc by using the raw framebuffer feature. This mode does not use or need X11 at all. To build you may need to disable X11:

./configure --without-x ...
make

 
OpenSSL:   Starting with version 0.8.3 x11vnc can now be built with SSL support. For this to be enabled the libssl.so library needs to be available at build time. So you may need to have additional CPPFLAGS and LDFLAGS items if your libssl.so is in a non-standard place.

Beta Testing:

I don't have any formal beta-testers for the releases of x11vnc, so I'd appreciate any additional testing very much.

Thanks to those who suggested features and helped beta test x11vnc 0.9.3 released in Oct 2007!

Please help test and debug the 0.9.4 version for release sometime in Spring 2008.

The version 0.9.4 beta tarball is kept here:    x11vnc-0.9.4.tar.gz

There are also some Linux, Solaris, Mac OS X, and other OS test binaries here. Please kick the tires and report bugs, performance regressions, undesired behavior, etc. to me.

To aid testing of the built-in SSL support for x11vnc, a number of VNC Viewer packages for Unix, Mac OS X, and Windows have been created that provide SSL Support for the TightVNC Viewer (this is done by wrapper scripts and a GUI that start STUNNEL). It should be pretty convenient for automatic SSL and SSH connections. It is described in detail at and can be downloaded from the Enhanced TightVNC Viewer (SSVNC) page.

 
Here are some features that will appear in the 0.9.4 release:

• Improvements to the -find and -create X session finding or creating modes: new desktop types and service redirection options. Personal cupsd daemon and SSH port redirection helper for use with SSVNC's Terminal Services feature.
• Reverse VNC connections via -connect work in the -find, -create and related -display WAIT:... modes.
• Reverse VNC connections (either normal or SSL) can use a Web Proxy or a SOCKS proxy, or a SSH connection, or even a CGI URL to make the outgoing connection. See: -proxy. Forward connections can also use: -ssh.
• Reverse VNC connections via the UltraVNC repeater proxy (either normal or SSL) are supported. Use either the "-connect repeater=ID:NNNN+host:port" or "-connect repeater://host:port+ID:NNNN" notation. The SSVNC VNC viewer also supports the UltraVNC repeater.
• Support for the ZYWRLE encoding, this is the RealVNC ZRLE encoding extended to do motion video and photo regions more efficiently by way of a Wavelet based transformation.
• The -finddpy and -listdpy utilities help to debug and configure the -find, -create, and -display WAIT:... modes.
• Some automatic detection of screen resizes are handled even if the -xrandr option is not supplied.
• The -autoport options gives more control over the VNC port x11vnc chooses.
• The -ping secs can be used to help keep idle connections alive.
• Pasting of the selection/clipboard into remote applications (e.g. Java) has been improved.
• Fixed a bug if a client disconnects during the 'speed-estimation' phase.
• To unset Caps_Lock, Num_Lock and raise all keys in the X server use -clear_all.
• Usage with dvorak keyboards has been improved. See also: -xkb.

• Viewer-side pixmap caching. A large area of pixels (at least 2-3 times as big as the framebuffer itself; the bigger the better... default is 10X) is placed below the framebuffer to act as a buffer/cache area for pixel data. The VNC CopyRect encoding is used to move it around, so any viewer can take advantage of it. Until we start modifying viewers you will be able to see the cache area if you scroll down (this makes it easier to debug!). For testing the default is "-ncache 10". The unix Enhanced TightVNC Viewer ssvnc has a nice -ycrop option to help hide the pixel cache area from view.

• Building with no OpenSSL libssl available (or with --without-ssl) has been fixed.
• One can configure x11vnc via "./configure --with-system-libvncserver" to use a system installed libvncserver library instead of the one bundled in the release tarball.
• If UltraVNC file transfer or chat is detected, then VNC clients are "pinged" more often to prevent these side channels from becoming serviced too infrequently.
• In -unixpw mode in the username and password dialog no text will be echoed if the first character sent is "Escape". This enables a convenience feature in SSVNC to send the username and password automatically.

• The UltraVNC Java viewer has been enhanced to support SSL (as the TightVNC viewer had been previously). The UltraVNC Java supports ultravnc filetransfer, and so can be used as a VNC viewer on Unix that supports ultravnc filetransfer. It is in the classes/ssl/UltraViewerSSL.jar file (that is pointed to by ultra.vnc). The signed applet SignedUltraViewerSSL.jar version (pointed to by ultrasigned.vnc) will be needed to access the local drive if you are using it for file transfer via a Web browser. Some other bugs in the UltraVNC Java viewer were fixed and a few improvements to the UI made.
• A new Unix username login mode for VNC Viewers authenticated via a Client SSL Certificate: "-users sslpeer=". The emailAddress subject field is inspected for username@hostname and then acts as though "-users +username" has been supplied. This way the Unix username is identified by (i.e. simply extracted from) the Client SSL Certificate. This could be useful with -find, -create and -svc modes if you are also have set up and use VNC Client SSL Certificate authentication.
• For external display finding/creating programs (e.g. WAIT:cmd=...) if the VNC Viewer is authenticated via a Client SSL Certificate, then that Certificate is available in the environment variable RFB_SSL_CLIENT_CERT.

• VNC Service advertising via mDNS / ZeroConf / BonJour with the Avahi client library. Enable via "-avahi".
• Implementations of UltraVNC's TextChat, SingleWindow, and ServerInput extensions (requires ultravnc viewer or ssvnc Unix viewer). They toggle the selection of a single window (-id), and disable (friendly) user input and viewing (monitor blank) at the VNC server.
• Short aliases "-find", "-create", "-svc", and "-xdmsvc" for commonly used FINDCREATEDISPLAY usage modes.
• Reverse VNC connections (viewer listening) now work in SSL (-ssl) mode.
• New options to control the Monitor power state and keyboard/mouse grabbing: -forcedpms, -clientdpms, -noserverdpms, and -grabalways.
• A simple way to emulate inetd(8) to some degree via the "-loopbg" option.
• Monitor the accuracy of XDAMAGE and apply "-noxdamage" if it is not working well. OpenGL applications like like beryl and MythTv have been shown to make XDAMAGE not work properly.
• For Java SSL connections involving a router/firewall port redirection, an option -httpsredir to spare the user from needing to include &PORT=NNN in the browser URL.

 
Here are some features that appeared in the 0.8.4 release:

• Native Mac OS X Aqua/Quartz support. (i.e. OSXvnc alternative; some activities are faster)
• A new login mode: "-display WAIT:cmd=FINDCREATEDISPLAY -unixpw ..." that will Create a new X session (either virtual or real and with or without a display manager, e.g. kdm) for the user if it cannot find the user's X session display via the FINDDISPLAY method. See the -svc and the -xdmsvc aliases.
• x11vnc can act as a VNC reflector/repeater using the "-reflect host:N" option. Instead of polling an X display, the remote VNC Server host:N is connected to and re-exported via VNC. This is intended for use in broadcasting a display to many (e.g. > 16; classroom or large demo) VNC viewers where bandwidth and other resources are conserved by spreading the load over a number of repeaters.
• Wireframe copyrect detection for local user activity (e.g. someone sitting at the physical display moving windows) Use -nowireframelocal to disable.
• The "-N" option couples the VNC Display number to the X Display number. E.g. if your X DISPLAY is :2 then the VNC display will be :2 (i.e. using port 5902). If that port is taken x11vnc will exit.
• Option -nodpms to avoid problems with programs like KDE's kdesktop_lock that keep restarting the screen saver every few seconds.
• To automatically fix the common mouse motion problem on XINERAMA (multi-headed) displays, the -xwarppointer option is enabled by default when XINERAMA is active.

 
Here are some features that appeared in the 0.8.3 release:

• The -ssl option provides SSL encryption and authentication natively via the www.openssl.org library. One can use from a simple self-signed certificate server certificate up to full CA and client certificate authentication schemes.
• Similar to -ssl, the -stunnel option starts up a SSL tunnel server stunnel (that must be installed separately on the system: www.stunnel.org stunnel.mirt.net ) to allow only encrypted SSL connections from the network.
• The -sslverify option allows for authenticating VNC clients via their certificates in either -ssl or -stunnel modes.
• Certificate creation and management tools are provide in the -sslGenCert, -sslGenCA, and related options.
• An SSL enabled Java applet VNC Viewer applet is provided in classes/ssl/VncViewer.jar. In addition to normal HTTP, the applet may be loaded into the web browser via HTTPS (HTTP over SSL). (one can use the VNC port, e.g. https://host:5900/, or also the separate -https port option). A wrapper shell script ss_vncviewer is also provided that sets up a stunnel client-side tunnel on Unix systems. See Enhanced TightVNC Viewer (SSVNC) for other SSL/SSH viewer possibilities.
• The -unixpw option supports Unix username and password authentication (a simpler variant is the -unixpw_nis option that works in environments where the encrypted passwords are readable, e.g. NIS). The -ssl or -localhost + -stunnel options are enforced in this mode to prevent password sniffing. As a convenience, these requirements are lifted if a SSH tunnel can be deduced (but -localhost still applies).
• Coupling -unixpw with "-display WAIT:cmd=FINDDISPLAY" or "-display WAIT:cmd=FINDCREATEDISPLAY" provides a way to allow a user to login with their UNIX password and have their display connected to automatically. See the -svc and the -xdmsvc aliases.
• Hooks are provided in the -unixpw_cmd and "-passwdfile cmd:,custom:..." options to allow you to supply your own authentication and password lookup programs.
• x11vnc can be configured and built to not depend on X11 libraries "./configure --without-x" for -rawfb only operation (e.g. embedded linux console devices).
• The -rotate option enables you to rotate or reflect the screen before exporting via VNC. This is intended for use on handhelds and other devices where the rotation orientation is not "natural".
• The "-ultrafilexfer" alias is provided and improved UltraVNC filetransfer rates have been achieved.
• Under the "-connect_or_exit host" option x11vnc will exit immediately unless the reverse connection to host succeeds. The "-rfbport 0" option disables TCP listening for connections (useful for this mode).
• The "-rawfb rand" and "-rawfb none" options are useful for testing automation scripts, etc., without requiring a full desktop.
• Reduced spewing of information at startup, use "-verbose" (also "-v") to turn it back on for debugging or if you are going to send me a problem report.

Here are some Previous Release Notes

Some Notes:

Both a client and a server:   It is sometimes confusing to people that x11vnc is both a client and a server at the same time. It is an X client because it connects to the running X server to do the screen polls. Think of it as a rather efficient "screenshot" program running continuously. It is a server in the sense that it is a VNC server that VNC viewers on the network can connect to and view the screen framebuffer it manages.

When trying to debug problems, remember to think of both roles. E.g. "how is x11vnc connecting to the X server?", "how is the vncviewer connecting to x11vnc?", "what permits/restricts the connection?". Both links may have reachability, permission, and other issues.

Network performance:   Whether you are using Xvnc or x11vnc it is always a good idea to have a solid background color instead of a pretty background image. Each and every re-exposure of the background must be resent over the network: better to have that background be a solid color that compresses very well compared to a photo image. (This is one place where the X protocol has an advantage over the VNC protocol.) I suggest using xsetroot, dtstyle or similar utility to set a solid background while using x11vnc. You can turn the pretty background image back on when you are using the display directly. Update: As of Feb/2005 x11vnc has the -solid [color] option that works on recent GNOME, KDE, and CDE and also on classic X (background image is on the root window). Update: As of Oct/2007 x11vnc has the -ncache option that does a reasonable job caching the background (and other) pixmap data on the viewer side.

I also find the 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

Options:   x11vnc has (far too) many features that may be activated via its 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 -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 separated vertically by 32 pixels. 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 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) SunRay session. Here are some 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 -scrollcopyrect and -wireframe speedups using the CopyRect VNC encoding and other things, but they only speed up some activities, not all.
  
  
• A rate limiting factor for x11vnc performance is that graphics 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 of this 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. Update 2008: thankfully, these sped up drivers are becoming more common on Linux and *BSD systems and that makes x11vnc run somewhat more quickly.
  
  On XFree86/Xorg it is actually possible to increase the framebuffer read speed considerably (10-100 times) by using the Shadow Framebuffer (a copy of the framebuffer is kept in main memory and this can be read much more quickly). To do this one puts the line Option "ShadowFB" "true" in the Device section of the /etc/X11/XF86Config or /etc/X11/xorg.conf file. Note that this disables 2D acceleration at the physical display and so likely defeats the purpose. Nevertheless this could be handy in some circumstances, e.g. if the slower speed while sitting at the physical display was acceptable (this seems to be true for most video cards these days). Unfortunately it does not seem shadowfb can be turned on and off dynamically...
  
  Another amusing thing one can do is use Xvfb as the X server, e.g. "xinit $HOME/.xinitrc -- /usr/X11R6/bin/Xvfb :1 -screen 0 1024x768x16" x11vnc can poll Xvfb efficiently via main memory. It's not exactly clear why one would want to do this instead of using vncserver/Xvnc, (perhaps to take advantage of an x11vnc feature, such as framebuffer scaling or built-in SSL encryption), but we mention it because it may be of use for special purpose applications. You may need to use the "-cc 4" option to force Xvfb to use a TrueColor visual instead of DirectColor. See also the description of the -create option that does all of this automatically for you.
  
  Also, a faster and more accurate way is to use the "dummy" XFree86/Xorg device driver (or our Xdummy wrapper script). See 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" 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 -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, see the FAQ on this below.) The XBell() "beeps" will work if the X server supports the XKEYBOARD extension. (Note that on Solaris XKEYBOARD is disabled by default. Passing +kb to Xsun enables it).
  
  
• The scroll detection algorithm for the -scrollcopyrect option can give choppy or bunched up transient output and occasionally painting errors.
  
  
• Using -threads can expose some bugs/crashes in libvncserver.

Please feel free to contact me if you have any questions, problems, or comments about x11vnc, etc.
Also, some people ask if they can make a donation, see this link for that.

x11vnc FAQ:

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?

Q-2: I can't get x11vnc and/or libvncserver to compile.

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).

Q-4: Help, I need to run x11vnc on Solaris 2.5.1 (or other old Unix/Linux) and it doesn't compile!

Q-5: Where can I get a precompiled x11vnc binary for my Operating System?

Q-6: Where can I get a VNC Viewer binary (or source code) for the Operating System I will be viewing from?

Q-7: How can I see all of x11vnc's command line options and documentation on how to use them?

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?

Q-9: How can I get the GUI to run in the System Tray, or at least be a smaller, simpler icon?

Q-10: How can I get x11vnc to listen on a different port besides the default VNC port (5900)?

Q-11: My Firewall/Router doesn't allow VNC Viewers to connect to x11vnc.

Q-12: Is it possible for a VNC Viewer and a VNC Server to connect to each other even though both are behind Firewalls that block all incoming connections?

Q-13: Can I make x11vnc more quiet and also go into the background after starting up?

Q-14: 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.

Q-15: The Windows TightVNC 1.3.9 Viewer cannot connect to x11vnc.

Q-16: KDE's krdc VNC viewer cannot connect to x11vnc.

Q-17: Are there any build-time customizations possible, e.g. change defaults, create a smaller binary, etc?

Q-18: 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?

Q-19: 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

Q-20: Can I run "x11vnc -nofb" on a Mac OS X machine to redirect mouse and keyboard input to it from Windows and X11 machines via Win2VNC and x2vnc, respectively?

Q-21: 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.

Q-22: 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.

Q-23: I am on a high color system (depth ≥ 24) but I seem to have colormap problems. They either flash or everything is very dark.

Q-24: How do I figure out the window id to supply to the -id windowid option?

Q-25: Why don't menus or other transient windows come up when I am using the -id windowid option to view a single application window?

Q-26: 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?

Q-27: 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?

Q-28: How do I get my X permissions (MIT-MAGIC-COOKIE file) correct for a Unix/Linux machine acting as an Xterminal?

Q-29: I'm having trouble using x11vnc with my Sun Ray session.

Q-30: How do I stop x11vnc once it is running in the background?

Q-31: Can I change settings in x11vnc without having to restart it? Can I remote control it?

Q-32: How do I create a VNC password for use with x11vnc?

Q-33: Can I make it so -storepasswd doesn't show my password on the screen?

Q-34: Can I have two passwords for VNC viewers, one for full access and the other for view-only access to the display?

Q-35: Can I have as many full-access and view-only passwords as I like?

Q-36: Does x11vnc support Unix usernames and passwords? Can I further limit the set of Unix usernames who can connect to the VNC desktop?

Q-37: Can I supply an external program to provide my own custom login method (e.g. Dynamic/One-time passwords or non-Unix (LDAP) usernames and passwords)?

Q-38: 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?

Q-39: Can I limit which machines incoming VNC clients can connect from?

Q-40: How do I build x11vnc/libvncserver with libwrap (tcp_wrappers) support?

Q-41: 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?

Q-42: 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?

Q-43: 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?

Q-44: 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?

Q-45: I start x11vnc as root because it is launched via inetd(8) or a display manager like gdm(1). Can I have x11vnc later switch to a different user?

Q-46: 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?

Q-47: Can I have x11vnc automatically lock the screen when I disconnect the VNC viewer?

Q-48: How can I tunnel my connection to x11vnc via an encrypted SSH channel between two Unix machines?

Q-49: How can I tunnel my connection to x11vnc via an encrypted SSH channel from Windows using an SSH client like Putty?

Q-50: How can I tunnel my connection to x11vnc via an encrypted SSL channel using an external tool like stunnel?

Q-51: Does x11vnc have built-in SSL tunneling?

Q-52: How do I use VNC Viewers with built-in SSL tunneling?

Q-53: How do I use the Java applet VNC Viewer with built-in SSL tunneling when going through a Web Proxy?

Q-54: 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?

Q-55: Can I create and use my own SSL Certificate Authority (CA) with x11vnc?

Q-56: How can I run x11vnc as a "service" that is always available?

Q-57: 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).

Q-58: Can I run x11vnc out of inetd(8)? How about xinetd(8)?

Q-59: Can I have x11vnc advertise its VNC service and port via mDNS / Zeroconf (e.g. Avahi) so VNC viewers on the local network can detect it automatically?

Q-60: Can I have x11vnc allow a user to log in with her UNIX username and password and then have it find her X session display on that machine and then connect to it? How about starting an X session if one cannot be found?

Q-61: Can I have x11vnc restart itself after it terminates?

Q-62: How do I make x11vnc work with the Java VNC viewer applet in a web browser?

Q-63: Are reverse connections (i.e. the VNC server connecting to the VNC viewer) using "vncviewer -listen" and vncconnect(1) supported?

Q-64: Can reverse connections be made to go through a Web or SOCKS proxy or SSH?

Q-65: Can I use x11vnc as a replacement for Xvnc? (i.e. not for a real display, but for a virtual one I keep around).

Q-66: How can I use x11vnc on "headless" machines? Why might I want to?

Q-67: 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)?

Q-68: How can I make x11vnc use less system resources?

Q-69: How can I make x11vnc use MORE system resources?

Q-70: I use x11vnc over a slow link with high latency (e.g. dialup modem or broadband), is there anything I can do to speed things up?

Q-71: Does x11vnc support the X DAMAGE Xserver extension to find modified regions of the screen quickly and efficiently?

Q-72: My OpenGL application shows no screen updates unless I supply the -noxdamage option to x11vnc.

Q-73: 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?

Q-74: Why not do something like wireframe animations to avoid the windows "lurching" when being moved or resized?

Q-75: Can x11vnc try to apply heuristics to detect when a window is scrolling its contents and use the CopyRect encoding for a speedup?

Q-76: Can x11vnc do client-side caching of pixel data? I.e. so when that pixel data is needed again it does not have to be retransmitted over the network.

Q-77: Why isn't the mouse cursor shape (the little icon shape where the mouse pointer is) correct as I move from window to window?

Q-78: 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?

Q-79: In XFIXES mode, are there any hacks to handle cursor transparency ("alpha channel") exactly?

Q-80: Why does the mouse arrow just stay in one corner in my vncviewer, whereas my cursor (that does move) is just a dot?

Q-81: 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)?

Q-82: 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?

Q-83: How can I get my AltGr and Shift modifiers to work between keyboards for different languages?

Q-84: When I try to type a "<" (i.e. less than) instead I get ">" (i.e. greater than)! Strangely, typing ">" works OK!!

Q-85: When I try to type a "<" (i.e. less than) instead I get "<," (i.e. an extra comma).

Q-86: 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?

Q-87: 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?

Q-88: The x11vnc -norepeat mode is in effect, but I still get repeated keystrokes!!

Q-89: After using x11vnc for a while, I find that I cannot type some (or any) characters or my mouse clicks and drags no longer have any affect. What happened?

Q-90: 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?

Q-91: 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)

Q-92: Running x11vnc on HP-UX I cannot type "#" I just get a "3" instead.

Q-93: Can I map a keystroke to a mouse button click on the remote machine?

Q-94: How can I get Caps_Lock to work between my VNC viewer and x11vnc?

Q-95: 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?

Q-96: Does x11vnc support server-side framebuffer scaling? (E.g. to make the desktop smaller).

Q-97: Does x11vnc work with Xinerama? (i.e. multiple monitors joined together to form one big, single screen).

Q-98: Can I use x11vnc on a multi-headed display that is not Xinerama (i.e. separate screens :0.0, :0.1, ... for each monitor)?

Q-99: Can x11vnc show only a portion of the display? (E.g. for a special purpose application).

Q-100: Does x11vnc support the XRANDR (X Resize, Rotate and Reflection) extension? Whenever I rotate or resize the screen x11vnc just seems to crash.

Q-101: Independent of any XRANDR, can I have x11vnc rotate and/or reflect the screen that the VNC viewers see? (e.g. for a handheld whose screen is rotated 90 degrees).

Q-102: Why is the view in my VNC viewer completely black? Or why is everything flashing around randomly?

Q-103: 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?

Q-104: I am using x11vnc where my local machine has "popup/hidden taskbars" and the remote display where x11vnc runs also has "popup/hidden taskbars" and they interfere and fight with each other. What can I do?

Q-105: Help! x11vnc and my KDE screensaver keep switching each other on and off every few seconds.

Q-106: I am running the beryl 3D window manager (or MythTv, Google Earth, or some other OpenGL app) and I do not get screen updates in x11vnc.

Q-107: Can I use x11vnc to view my VMWare session remotely?

Q-108: Can non-X devices (e.g. a raw framebuffer) be viewed (and even controlled) via VNC with x11vnc?

Q-109: Can I export via VNC a Webcam or TV tuner framebuffer using x11vnc?

Q-110: Can I connect via VNC to a Qt-embedded/Qtopia application running on my handheld or PC using the Linux console framebuffer (i.e. not X11)?

Q-111: Now that non-X11 devices can be exported via VNC using x11vnc, can I build it with no dependencies on X11 header files and libraries?

Q-112: Does x11vnc support Mac OS X Aqua/Quartz displays natively (i.e. no X11 involved)?

Q-113: Can x11vnc be used as a VNC reflector/repeater to improve performance for the case of a large number of simultaneous VNC viewers (e.g. classroom broadcasting or a large demo)?

Q-114: Can x11vnc be used during a Linux, Solaris, etc. system Installation so the Installation can be done remotely?

Q-115: Does the Clipboard/Selection get transferred between the vncviewer and the X display?

Q-116: Can I use x11vnc to record a Shock Wave Flash (or other format) video of my desktop, e.g. to record a tutorial or demo?

Q-117: Can I transfer files back and forth with x11vnc?

Q-118: Which UltraVNC extensions are supported?

Q-119: Can x11vnc emulate UltraVNC's Single Click helpdesk mode for Unix? I.e. something very simple for a naive user to initiate a reverse vnc connection from their Unix desktop to a helpdesk operator's VNC Viewer.

Q-120: Can I (temporarily) mount my local (viewer-side) Windows/Samba File share on the machine where x11vnc is running?

Q-121: Can I redirect CUPS print jobs from the remote desktop where x11vnc is running to a printer on my local (viewer-side) machine?

Q-122: How can I hear the sound (audio) from the remote applications on the desktop I am viewing via x11vnc?

Q-123: Why don't I hear the "Beeps" in my X session (e.g. when typing tput bel in an xterm)?

Q-124: Does x11vnc work with IPv6?

Q-125: Thanks for your program and for your help! Can I make a donation?

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 -display option) to specify it. Nearly always the correct value will be ":0" (in fact, x11vnc will now assume :0 if given no other information).

 
For the latter error, you need to set up the X11 permissions correctly.

To make sure X11 permissions are the problem do this simple test: while sitting at the physical X display open a terminal window (gnome-terminal, xterm, etc). You should be able to run x11vnc successfully without any need for special steps or command line options in that terminal (i.e. just type "x11vnc"). If that works OK then you know X11 permissions are the only thing preventing it from working when you try to start x11vnc via, say, a remote shell.

How to Solve:  See the xauth(1), Xsecurity(7), and xhost(1) man pages or this Howto for much info on X11 permissions. For example, you may need to set your XAUTHORITY environment variable (or use the -auth option) to point to the correct MIT-MAGIC-COOKIE file (e.g. /home/joe/.Xauthority or /var/gdm/:0.Xauth or /var/lib/kdm/A:0-crWk72K or /tmp/.gdmzndVlR, etc.), or simply be sure you run x11vnc as the correct user (i.e. the user who is logged into the X session you wish to view).

Note: The MIT cookie file contains the secret key that allows x11vnc to connect to the desired X display.

If, say, sshd has set XAUTHORITY to point to a random file it has created for X forwarding that will cause problems. (Under some circumstances even su(1) and telnet(1) can set XAUTHORITY. See also the gdm parameter NeverPlaceCookiesOnNFS that sets XAUTHORITY to a random filename in /tmp for the whole X session).

Running x11vnc as root is often not enough: you need to know where the MIT-MAGIC-COOKIE file for the desired X display is.

Example solution:

  x11vnc -display :0 -auth /var/gdm/:0.Xauth

Note as of Feb/2007 you can also try the -find option instead of "-display ..." and see if that finds your display and Xauthority.

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 soon be of use (please read the documentation on the -users option).

To test out your X11 permissions from a remote shell, set DISPLAY and possibly XAUTHORITY (see your shell's man page, bash(1), tcsh(1), on how to set environment variables) and type xdpyinfo in the same place you will be typing (or otherwise running) x11vnc. If information is printed out about the X display (screen sizes, supported extensions, color visuals info) that means the X11 permissions are set up properly: xdpyinfo successfully connected to DISPLAY! You could also type xclock and make sure no errors are reported (a clock should appear on the X display, press Ctrl-C to stop it). If these work, then typing "x11vnc" in the same environment should also work.

Important: if you cannot get your X11 permissions so that the xdpyinfo or xclock tests work, x11vnc also will not work (all of these X clients must be allowed to connect to the X server to function properly).

Firewalls: Speaking of permissions, it should go without saying that the host-level firewall will need to be configured to allow connections in on a port. E.g. 5900 (default VNC port) or 22 (default SSH port for tunnelling VNC). Most systems these days have firewalls turned on by default, so you will actively have to do something to poke a hole in the firewall at the desired port number. See your system administration tool for Firewall settings (Yast, Firestarter, etc.).

Q-2: I can't get x11vnc and/or libvncserver to compile.

Make sure you have gcc (or other C compiler) and all of the required libraries and the corresponding -dev/-devel packages installed. These include Xorg/XFree86, libX11, libjpeg, libz, libssl, ... and don't forget the devs: libjpeg-dev, libssl-dev ...

The most common build problem that people encounter is that the necessary X11 libraries are installed on their system however it does not have the corresponding -dev/-devel packages installed. These dev packages include C header files and build-time .so symlink. It is a shame the current trend in distros is to not install the dev package by default when the the library runtime package is installed...

As of Nov/2006 here is a list of libraries that x11vnc usually likes to use:

libc.so        libX11.so       libXtst.so       libXext.so
libXfixes.so   libXdamage.so   libXinerama.so   libXrandr.so
libz.so        libjpeg.so      libpthread.so
libssl.so      libcrypto.so    libcrypt.so

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

  checking for C compiler default output file name... configure: error:
  C compiler cannot create executables
  See `config.log' for more details.

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
  libssl-dev

  gcc
  make
  glibc-devel
  libjpeg-devel
  xorg-x11-devel or XFree86-devel
  zlib-devel
  openssl097a

Have a look at Misc. Build Problems for additional fixes.

Note: there is growing trend in Linux and other distros to slice up core X11 software into more and smaller packages. So be prepared for more headaches compiling software...

libssl:  One user pointed out that if you use a precompiled binary (either one you downloaded or built on another machine) there is a chance it won't work because that x11vnc binary requires libssl0.9.7 but the system only has libssl0.9.8 (which evidently is incompatible with 0.9.7 and has a different SONAME). Your distro should allow you do have both runtimes installed on your system:

    % dpkg -l libssl0.9.7 libssl0.9.8
    ...
    ii  libssl0.9.7    0.9.7g-5ubuntu SSL shared libraries
    ii  libssl0.9.8    0.9.8a-7ubuntu SSL shared libraries

Q-3: I just built x11vnc successfully, but when I use it my keystrokes and mouse button clicks are ignored  (I am able to move the mouse though).

This is most likely due to you not having a working build environment for the XTEST client library libXtst.so. The library is probably present on your system, but the package installing the development header file is missing.

If you were watching carefully while configure was running you would have seen:

  checking for XTestFakeKeyEvent in -lXtst... no

The solution is to add the necessary build environment package (and the library package if that is missing too). On Debian the build package is libxtst-dev. Other distros/OS's may have it in another package.

x11vnc will build without support for this library (e.g. perhaps one wants a view-only x11vnc on a stripped down or embedded system...). And at runtime it will also continue to run even if the X server it connects to does not support XTEST. In both cases it cannot inject keystrokes or button clicks since XTEST is needed for that (it can still move the mouse pointer using the X API XWarpPointer()).

You will see a warning message something like this at run time:

  20/03/2005 22:33:09 WARNING: XTEST extension not available (either missing from
  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 DISCARDED.
  20/03/2005 22:33:09   If display does have XTEST, be sure to build x11vnc with
  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.

Also, as of Nov/2006 there will be a configure build time warning as well:

  ...
  checking for XFixesGetCursorImage in -lXfixes... yes
  checking for XDamageQueryExtension in -lXdamage... yes
  configure: WARNING:
  ==========================================================================
  A working build environment for the XTEST extension was not found (libXtst).
  An x11vnc built this way will be only barely usable.  You will be able to
  move the mouse but not click or type.  There can also be deadlocks if an
  application grabs the X server.
  
  It is recommended that you install the necessary development packages
  for XTEST (perhaps it is named something like libxtst-dev) and run
  configure again.
  ==========================================================================

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 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 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 build steps above and 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:

    Slackware:      (.tgz)  http://www.linuxpackages.net/
    Redhat/Fedora:  (.rpm)  http://dag.wieers.com/packages/x11vnc/
                            http://dries.ulyssis.org/rpm/packages/x11vnc
    SuSE:           (.rpm)  http://linux01.gwdg.de/~pbleser/
    Gentoo:         (info)  http://gentoo-wiki.com/ and http://gentoo-portage.com/
    FreeBSD:        (.tbz)  http://www.freebsd.org/
                            http://www.freshports.org/net/x11vnc
    NetBSD:         (src)   http://pkgsrc.se/x11/x11vnc
    Arch Linux:     (.tgz)  http://www.archlinux.org/
    Nokia 770       (.deb)  http://mike.saunby.googlepages.com/x11vncfornokia7702
    Sharp Zaurus            http://www.focv.com/
    Debian:         (.deb)  http://packages.debian.org/x11vnc (N.B: often unmaintained; might be better to compile from source)
    Solaris:        (pkg)   http://www.sunfreeware.com/       (N.B: very old; better to compile from source)
    OpenBSD:        (.tgz)  http://www.openbsd.org/           (N.B: very old and unmaintained; better to compile from source)

If the above binaries don't work and building x11vnc on your OS fails (and all else fails!) you can try one of My Collection of x11vnc 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.

If you use a standalone binary like this and also want x11vnc to serve up the Java VNC Viewer jar file (either SSL enabled or regular one), then you will need to extract the classes subdirectory from the source tarball and point x11vnc to it via the -httpdir option. E.g.:

    x11vnc -httpdir /path/to/x11vnc-0.8.3/classes/ssl ...

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:

• http://www.tightvnc.com/download.html
• http://www.realvnc.com/download-free.html
• http://sourceforge.net/projects/cotvnc/
• http://www.ultravnc.com/
• Our Enhanced TightVNC Viewer (SSVNC)
   
  

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 here as well. Yes, x11vnc does have a lot of options, doesn't it...

Q-8: I don't like typing arcane command line options every time I start x11vnc. What can I do? Is there a config file? Or a GUI?

You could create a shell script that calls x11vnc with your options:

#!/bin/sh
#
# filename: X11vnc  (i.e. not "x11vnc")
# It resides in a directory in $PATH. "chmod 755 X11vnc" has been run on it.
#
x11vnc -wait 50 -localhost -rfbauth $HOME/.vnc/passwd -display :0 $*

Or as of Jun/2004 you can use the simple $HOME/.x11vncrc config file support. If that file exists, each line is taken as a command line option. E.g. the above would be:

# this is a comment in my ~/.x11vncrc file
wait 50        # this is a comment to the end of the line.
-localhost     # note: the leading "-" is optional.
rfbauth  /home/fred/.vnc/passwd
display :0

As of Dec/2004 there is now a simple Tcl/Tk GUI based on the remote-control functionality ("-R") that was added. The /usr/bin/wish program is needed for operation. The gui is not particularly user-friendly, it just provides a point and click mode to set all the many x11vnc parameters and obtain help on them. It is also very useful for testing. See the -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 "-gui tray" system tray mode.

Q-9: How can I get the GUI to run in the System Tray, or at least be a smaller, simpler icon?

As of Jul/2005 the gui can run in a more friendly small icon mode "-gui icon" or in the system tray: "-gui tray". It has balloon status, a simple menu, and a Properities dialog. The full, complicated, gui is only available under "Advanced". Other improvements were added as well. Try "Misc -> simple_gui" for a gui with fewer esoteric menu items.

If the gui fails to embed itself in the system tray, do a retry via "Window View -> icon" followed by "Window View -> tray" with the popup menu.

For inexperienced users starting up x11vnc and the GUI while sitting at the physical X display (not remotely), using something like "x11vnc -display :0 -gui tray=setpass" might be something for them that they are accustomed to in a Desktop environment (it prompts for an initial password, etc). This is a basic "Share My Desktop" usage mode.

Q-10: How can I get x11vnc to listen on a different port besides the default VNC port (5900)?

Use something like, e.g., "x11vnc -rfbport 5901" to force it to use port 5901 (this is VNC display :1). If something else is using that port x11vnc will exit immediately. If you do not supply the -rfbport option, it will autoprobe starting at 5900 and work its way up to 5999 looking for a free port to listen on. In that case, watch for the PORT=59xx line to see which port it found, then subtract 5900 from it for the VNC display number to enter into the VNC Viewer(s).

The "-N" option will try to match the VNC display number to the X display (e.g. X11 DISPLAY of :5 (port 6005) will have VNC display :5 (port 5905)).

Also see the "-autoport n" option to indicated at which value the auto probing should start at.

Q-11: My Firewall/Router doesn't allow VNC Viewers to connect to x11vnc.

See the Firewalls/Routers discussion.

Q-12: Is it possible for a VNC Viewer and a VNC Server to connect to each other even though both are behind Firewalls that block all incoming connections?

This is very difficult or impossible to do unless a third machine, reachable by both, is used as a relay. So we assume a third machine is somehow being used as a relay.

In the following discussion, we will suppose port 5950 is being used on the relay machine as the VNC port for the rendezvous.

A way to rendezvous is to have the VNC Server start a reverse connection to the relay machine:

   x11vnc -connect third-machine.net:5950 ...

   vncviewer third-machine.net:50

What software to run on third-machine? A TCP relay of some sort could be used... Try a google search on "tcp relay" or "ip relay". However, note that this isn't a simple redirection because it hooks up two incoming connections.

Also, if you are not the admin of third-machine you'd have to convince the owner to allow you to install this software (and he would likely need to open his server's firewall to allow the port through).

It is recommended that SSL is used for encryption (e.g. "-ssl SAVE") when going over the internet.

We have a prototype for performing a rendezvous via a Web Server acting as the relay machine. Download the vncxfer CGI script and see the instructions at the top.

Once that CGI script is set up on the website, both users go to, say, http://somesite.com/vncxfer (or maybe a "/cgi-bin" directory or ".cgi" suffix must be used). Previously, both have agreed on the same session name (say by phone or email) , e.g. "5cows", and put that into the entry form on the vncxfer starting page (hopefully separated by a few seconds, so the relay helper can fully start up at the first request).

The page returned tells them the hostname and port number and possible command to use for forward (VNC Viewer) and reverse (VNC Server, i.e. x11vnc) connections as described above.

Also since Oct/2007, x11vnc can connect directly (no web browser), like this:

   x11vnc ... -connect localhost:0 -proxy 'http://somesite.com/vncxfer?session=5cows&'

Unfortunately the prototype requires that the Web server's firewall allow in the port (e.g. 5950) used for the rendezvous. Most web servers are not configured to do this, so you would need to ask the admin to do this for you. Nearly all free webspace sites, e.g. www.zendurl.com, will not allow your CGI script to be an open relay like this. (If you find one that does allow this, let me know!).

Maybe someday a clever trick will be thought up to relax the listening port requirement (e.g. use HTTP/CGI itself for the transfer... it is difficult to emulate a full-duplex TCP connection with them.)

See also the Firewalls/Routers discussion and Reverse Connection Proxy discussion.

Instead of assuming port 5900 is free on the SSH machine, we will assume both users agreed to use 5933. This will illustrate