path: root/x11vnc/README

x11vnc README file                         Date: Tue Aug 31 22:39:00 EDT 2004

The following information is taken from these URLs:

	http://www.karlrunge.com/x11vnc/index.html
	http://www.karlrunge.com/x11vnc/x11vnc_opts.html

they contain the most up to date info.

=======================================================================
http://www.karlrunge.com/x11vnc/index.html:

     _________________________________________________________________

x11vnc: a VNC server for real X displays    (to [1]FAQ)    (to [2]downloads)
(to [3]building)

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

   I wrote x11vnc because x0rfbserver was basically impossible to build
   on Solaris and had poor performance. The primary x0rfbserver build
   problems centered around esoteric C++ toolkits. x11vnc is written in
   plain C and uses only standard libraries. I also added a few
   enhancements to improve the interactive response, add esoteric
   features, etc.

    Background:

   VNC is a very useful network graphics protocol in the spirit of X,
   however, unlike X, the viewing-end is very simple and maintains no
   state. It is a remote framebuffer (RFB) protocol .

   Some VNC links:
     * [4]http://www.uk.research.att.com/vnc/
     * [5]http://www.realvnc.com
     * [6]http://www.tightvnc.com

   For Unix, the VNC implementation includes a virtual X11 server Xvnc
   (usually launched via the vncserver command) that is not associated
   with a real display, but provides a "fake" one X11 clients (xterm,
   mozilla, etc.) can attach to. A remote user then connects to Xvnc via
   the VNC client vncviewer from anywhere on the network to view and
   interact with the whole virtual X11 desktop.

   The VNC protocol is in most cases better suited for remote connections
   with low bandwidth and high latency than is the X11 protocol. Also,
   with no state maintained the viewing-end can crash, be rebooted, or
   relocated and the applications and desktop continue running. Not so
   with X11.

   So the standard Xvnc program is very useful, I use it for things like:
     * desktop conferencing with other users (e.g. codereviews).
     * long running apps/tasks I want to be able to view from many
       places.
     * Motif, GNOME, and similar applications that would yield very poor
       performance over a high latency link.

   However, sometimes one wants to connect to a real X11 display (i.e.
   one attached to a physical monitor, keyboard, and mouse: a Workstation
   or a SunRay session) from far away. Maybe you want to close down an
   application cleanly rather than using kill, or want to work a bit in
   an already running application, or would like to help a distant
   colleague solve a problem with their desktop. This is where x11vnc is
   useful.
     _________________________________________________________________

    How to use x11vnc:

   In this example let's assume the remote machine with the X display you
   wish to view is far-away.east:0 and the workstation you are presently
   working at is sitting-here.west.

   Step 0. Download x11vnc ([7]see below) and have it available to run
   (e.g. via PATH) on far-away.east. Similarly, have a VNC viewer (e.g.
   vncviewer) ready to run on sitting-here.west.

   Step 1. By some means log in to far-away.east and get a command shell
   running there. You can use ssh, rlogin, telnet, or any other method to
   do this. x11vnc needs to be run on the same machine the X server
   process is running on (because MIT-SHM shared memory is used to poll
   the X11 framebuffer).

   Step 2. In that far-away.east shell (with command prompt "far-away>"
   in this example) run x11vnc directed at the far-away.east X session:

  far-away> x11vnc -display :0

   You could have also set the environment variable DISPLAY=:0 to achieve
   the same thing. This step attaches x11vnc to the far-away.east:0 X
   display (no viewer clients yet).

   There will then be much chatter printed out from x11vnc, until it
   finally says something like:
  .
  .
  13/05/2004 14:59:54 Autoprobing selected port 5900
  13/05/2004 14:59:54 screen setup finished.
  13/05/2004 14:59:54 The VNC desktop is far-away:0
  PORT=5900

   which means all is OK, and we are ready for the final step.

   Step 3. At the place where you are sitting (sitting-here.west in this
   example) you now want to run a VNC viewer program. There are VNC
   viewers for Unix, Windows, MacOS, Java-enabled web browsers, and even
   for PDA's like the Palm Pilot! You can use any of them to connect to
   x11vnc (see the above VNC links on how to obtain a viewer for your
   platform. For Solaris, vncviewer is available in the [8]Companion CD
   package SFWvnc ).

   In this example we'll use the Unix vncviewer program on sitting-here
   by typing the following command in a second terminal window:

  sitting-here> vncviewer far-away.east:0

   That should pop up a viewer window on sitting-here.west showing and
   allowing interaction with the far-away.east:0  X11 desktop. Pretty
   nifty! When finished, exit the viewer: the remote x11vnc process will
   shutdown automatically (or you can use the -forever [9]option to have
   it wait for additional viewer connections).

   Desktop Sharing: The above more or less assumed nobody was sitting at
   the workstation display far-away.east:0. This is often the case: a
   user wants to access her workstation remotely. Another usage pattern
   has the user sitting at far-away.east:0 and invites one or more other
   people to view and interact with his desktop. Perhaps the user gives a
   demo or presentation this way (using the telephone for vocal
   communication). A "Remote Help Desk" mode would be similar: a
   technician remotely connects to the user's desktop to interactively
   solve a problem the user is having.

   For these cases it should be obvious how it is done. The above steps
   will work, but more easily the user sitting at far-away.east:0 simply
   starts up x11vnc from a terminal window, after which the guests would
   start their VNC viewers. For this usage mode the -accept popup option
   discussed in the [10]FAQ below may be of use to allow the user at
   far-away.east:0 to accept or reject incoming connections.
     _________________________________________________________________

    Tunnelling x11vnc via ssh:

   The above example had no security or privacy at all. When logging into
   remote machines (certainly when going over the internet) it is best to
   use ssh, or use a VPN. For x11vnc one can tunnel the VNC protocol
   through the encrypted ssh channel. It would look something like this:
  sitting-here> ssh -L 5900:localhost:5900 far-away.east 'x11vnc -display :0'

   (you will likely have to provide passwords/passphrases for the ssh
   login) and then in another terminal window on sitting-here run the
   command:
  sitting-here> vncviewer -encodings "copyrect tight hextile" localhost:0

   The -encodings option is very important: vncviewer will default to
   "raw" encoding if it thinks the connection is to the local machine,
   and so vncviewer gets tricked this way by the ssh redirection. "raw"
   encoding will be extremely slow over a networked link, so you need to
   force the issue with -encodings "copyrect tight ...".

   If the machine you SSH into is not the same machine with the X display
   you wish to view (e.g. your company provides incoming SSH access to a
   gateway machine), then you need to change the above to, e.g.: -L
   5900:otherhost:5900. Once logged in, you'll need to do a second login
   (ssh or rsh) to the workstation machine 'otherhost' and then start up
   x11vnc on it.

   As discussed below, there may be some problems with port 5900 being
   available. If that happens, the above port and display numbers may
   change a bit. However, if you "know" port 5900 will be free on the
   local and remote machines, you can automate the above two steps by
   using the x11vnc option -bg (forks into background after connection to
   the display is set up) or using the -f option of ssh. A simple example
   script, assuming no problems with port 5900 being taken on the local
   or remote sides, looks like:
#!/bin/sh
# usage: x11vnc_ssh <host>:<xdisplay>
#  e.g.: x11vnc_ssh snoopy.peanuts.com:0

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

cmd="x11vnc -display :$disp -rfbauth .vnc/passwd"
enc="copyrect tight hextile zlib corre rre raw"

ssh -f -L 5900:localhost:5900 $host "$cmd"

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

   See also rx11vnc.pl below.

   Another method is to start the VNC viewer in listen mode "vncviewer
   -listen" and have x11vnc initiate the reverse connection using the
   -connect option:
#!/bin/sh
# usage: x11vnc_ssh <host>:<xdisplay>
#  e.g.: x11vnc_ssh snoopy.peanuts.com:0

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

cmd="x11vnc -display :$disp -connect localhost"   # <-- new option
enc="copyrect tight hextile zlib corre rre raw"

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

   A third way is specific to the TightVNC vncviewer special option -via
   for gateways. The only tricky part is we need to start up x11vnc and
   give it some time to start listening for connections (so we cannot use
   the TightVNC default setting for VNC_VIA_CMD):
#!/bin/sh
# usage: x11vnc_ssh <host>:<xdisplay>
#  e.g.: x11vnc_ssh snoopy.peanuts.com:0

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

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

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

   Of course if you already have the x11vnc running waiting for
   connections (or have it started out of inetd(1)), you can simply use
   the TightVNC vncviewer -via gateway host:port in its default mode to
   provide secure ssh tunneling.

   VNC password file: Also note in the first example script that the
   option "-rfbauth .vnc/passwd" provides additional protection by
   requiring a VNC password for every VNC viewer that connects. The
   vncpasswd or storepasswd programs, or the x11vnc [11]-storepasswd
   option can be used to create the password file. x11vnc also has the
   slightly less secure [12]-passwdfile and -passwd XXXXX options.

   It is up to you to tell x11vnc to use password protection, it will not
   do it for you automatically. The same goes for encrypting the channel
   between the viewer and x11vnc: it is up to you to use ssh, etc.
     _________________________________________________________________

    Downloading x11vnc:

   x11vnc is a contributed program to the [13]libvncserver project at
   SourceForge.net. I use libvncserver for all of the VNC aspects; I
   couldn't have done without it. The full source code may be found and
   downloaded (either file-release tarball or CVS tree) from the above
   link. As of Aug 2004, the [14]x11vnc 0.6.2 source package is released
   (recommended download) . The x11vnc package is the subset of the
   libvncserver package needed to build the x11vnc program. Also, you can
   get a copy of my latest, bleeding edge [15]x11vnc.c file to replace
   the one in the above packages or the one in the CVS tree and then
   rebuild.

   See the [16]FAQ below for information about where you might obtain a
   precompiled x11vnc binary from 3rd parties.

   More tools: Here is a rsh/ssh wrapper script rx11vnc that attempts to
   automatically do the above Steps 1-3 for you (provided you have
   rsh/ssh login permission on the machine x11vnc is to be run on). The
   above example would be: rx11vnc far-away.east:0 typed into a shell on
   sitting-here.west. Also included is an experimental script rx11vnc.pl
   that attempts to tunnel the vnc traffic through an ssh port
   redirection (and does not assume port 5900 is free). Have a look at
   them to see what they do and customize as needed:
     * [17]rx11vnc wrapper script
     * [18]rx11vnc.pl wrapper script to tunnel traffic thru ssh
     _________________________________________________________________

    Building x11vnc:

   If your OS has libjpeg.so and libz.so in standard locations you can
   build as follows (example given for the 0.6.2 release of x11vnc:
   replace with the version you downloaded):
(un-tar the x11vnc+libvncserver tarball)
# gzip -dc x11vnc-0.6.2.tar.gz | tar -xvf -

(cd to the source directory)
# cd x11vnc-0.6.2

(run configure and then run make)
# ./configure
# make

(if all went OK, copy x11vnc to the desired destination, e.g. $HOME/bin)
# cp ./x11vnc/x11vnc $HOME/bin

   Or do make install, it will probably install to /usr/local/bin (run
   ./configure --help for information on customizing your configuration).
   You can now run it via typing "x11vnc", "x11vnc -help", "x11vnc -nap
   -display :0", etc.

   Note: Currently gcc is required to build libvncserver. In some cases
   it will build with non-gcc compilers, but the resulting binary often
   fails to run properly.

   Building on Solaris:   Depending on your version of Solaris (or other
   Unix OS), the jpeg and/or zlib libraries may be in non-standard places
   (e.g. /usr/local, /usr/sfw, /opt/sfw, etc).

   Note: If configure cannot find these two libraries then TightVNC
   support will be disabled, and you don't want that! (the TightVNC
   encoding gives very good compression and performance, even makes a
   difference over a LAN)

   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). To get the source for these libraries: libjpeg is available
   at [19]ftp://ftp.uu.net/graphics/jpeg/ and zlib at
   [20]http://www.gzip.org/zlib/. See also
   [21]http://www.sunfreeware.com/ for Solaris binary packages of these
   libraries.

   Here is a build script that indicates one way to pass the library
   locations information to the libvncserver configuration:
#!/bin/sh

# Build script for Solaris, etc, with, gcc, libjpeg and libz in
# non-standard locations.

PATH=/path/to/gcc/bin:/usr/ccs/bin:$PATH        # set to get gcc

JPEG=/path/to/jpeg                      # maybe "/usr/local" or "/opt/sfw"
ZLIB=/path/to/zlib                      # maybe "/usr/local" or "/opt/sfw"

# Below we assume headers in $JPEG/include and $ZLIB/include and the
# shared libraries are in $JPEG/lib and $ZLIB/lib.  If your situation
# is different change the locations in the two lines below.

CPPFLAGS="-I $JPEG/include -I $ZLIB/include"
LDFLAGS="-L $JPEG/lib -R $JPEG/lib -L $ZLIB/lib -R $ZLIB/lib"

# These two lines may not be needed on more recent Solaris releases:
CPPFLAGS="$CPPFLAGS -I /usr/openwin/include"
LDFLAGS="$LDFLAGS -L /usr/openwin/lib -R /usr/openwin/lib"

# Everything needs to built with _REENTRANT for thread safe errno:
CPPFLAGS="$CPPFLAGS -D_REENTRANT"

export PATH CPPFLAGS LDFLAGS

./configure
make

ls -l ./x11vnc/x11vnc

   Then do make install or copy the binary to your desired destination.

   Note that on Solaris make is /usr/ccs/bin/make, so that is why the
   above puts /usr/ccs/bin in PATH. Other important build utililties are
   there too: ld, ar, etc. Also, it is probably a bad idea to have
   /usr/ucb in your PATH while building.

   One user had a problem where the above build script was failing
   because his work environment had the ENV variable set to a script that
   was resetting his PATH so that gcc could no longer be found. Make sure
   you do not have any ENV or BASH_ENV in your environment doing things
   like that.

   There is a build problem on Solaris 7 11/99 (update 4) where the
   header file X11/extensions/XKBstr.h that X11/XKBlib.h uses was not
   shipped. The x11vnc configure succeeds and sets
   LIBVNCSERVER_HAVE_XKEYBOARD in rfb/rfbconfig.h but then the build of
   x11vnc fails in the make. A workaround is to remove all lines
   referring to LIBVNCSERVER_HAVE_XKEYBOARD in rfb/rfbconfig.h after
   configure has been run. Alternatively, one could put #undef
   LIBVNCSERVER_HAVE_XKEYBOARD after the rfb/rfb.h include in the
   x11vnc/x11vnc.c file. (This problem has been fixed as of x11vnc 0.6.2
   (Aug/2004))
     _________________________________________________________________

    Some Notes:

   Network performance:   Whether you are using Xvnc or x11vnc it is
   always a good idea to have a solid background color instead of a
   pretty background image. Each and every re-exposure of the background
   must be resent over the network: better to have that background be a
   solid color that compresses very well compared to a photo image. I
   suggest using xsetroot, dtstyle or similar utility to set a solid
   background while using x11vnc.

   I also find the [22]tightvnc encoding gives the best response for my
   usage (Unix <-> Unix over cable modem). One needs a tightvnc-aware
   vncviewer to take advantage of this encoding.

   TCP port issues:   Notice the lines
  18/07/2003 14:36:31 Autoprobing selected port 5900
  PORT=5900

   in the output. 5900 is the default VNC listening port (just like 6000
   is X11's default listening port). Had port 5900 been taken by some
   other application, x11vnc would have next tried 5901. That would mean
   the viewer command above should be changed to vncviewer
   far-away.east:1. You can force the issue with the -rfbport NNNN
   option.

   Options:   x11vnc has (far too) many features that may be activated
   via its [23]command line options. Useful options are -nap to use fewer
   resources (it sleeps more between polls when activity is low) and
   -rfbauth passwd-file to use VNC password protection (the vncpasswd or
   storepasswd programs, or the x11vnc [24]-storepasswd option can be
   used to create the password file).

   Algorithm:   How does x11vnc do it? Rather brute-forcedly: it
   continuously polls the X11 framebuffer for changes using
   XShmGetImage(). When changes are discovered, it instructs libvncserver
   which rectangular regions of the framebuffer have changed, and
   libvncserver compresses the changes and sends them off to any
   connected VNC viewers. A number of applications do similar things,
   such as x0rfbserver, krfb, x0vncserver. x11vnc uses a 32 x 32 pixel
   tile model (the desktop is decomposed into ~1000 such tiles), where
   changed tiles are found by pseudo-randomly polling 1 pixel tall
   horizontal scanlines. This is a surprisingly effective algorithm for
   finding changed regions. For keyboard and mouse user input the XTEST
   extension is used to pass the input events to the X server. To detect
   XBell "beeps" the XKEYBOARD extension is used.

   Barbershop mirrors effect:   What if x11vnc is started up, and
   vncviewer is then started up on the same machine and displayed on the
   same display x11vnc is polling? One might "accidentally" do this when
   first testing out the programs. You get an interesting "feedback"
   effect where vncviewer images keep popping up each one contained in
   the previous one and slightly shifted a bit by the window manager
   decorations. There will be an even more interesting effect if -scale
   is used. Also, if the XKEYBOARD is supported and the XBell "beeps"
   once, you get an infinite loop of beeps going off. Although all of
   this is mildly exciting it is not much use: you will normally run and
   display the viewer on a different machine!

   SunRay notes:   You can run x11vnc on your (connected or disconnected)
   [25]SunRay session (Please remember to use -nap and maybe -wait 200 to
   avoid being a resource hog! It also helps a bit to have a solid
   background color). You have to know the name of the machine your
   SunRay session X server is running on. You also need to know the X11
   DISPLAY number for the session: on a SunRay it could be a large
   number, e.g. :137, since there are many people with X sessions (Xsun
   processes) on the same machine. If you don't know it, you can get it
   by running who(1) in a shell on the SunRay server and looking for the
   dtlocal entry with your username (and if you don't even know which
   server machine has your session, you could login to all possible ones
   looking at the who output for your username...).

   SunRay Gotcha:   Note that even though your SunRay X11 DISPLAY is
   something like :137, x11vnc still tries for port 5900 as its listening
   if it can get it, in which case the VNC display (i.e. the information
   you supply to the VNC viewer) is something like sunray-server:0
   (note the :0 corresponding to port 5900, it is not :137). If it cannot
   get 5900, it tries for 5901, and so on. You can also try to force the
   port (and thereby the VNC display) using the -rfbport NNNN option.

    Limitations:

     * Due to the polling nature, some activities (opaque window moves,
       scrolling), can be pretty choppy/ragged and others (exposures of
       large areas) slow. Experiment with interacting a bit differently
       than you normally do to minimize the effects (e.g. do fullpage
       paging rather than line-by-line scrolling, and move windows in a
       single, quick motion). Work is in progress to attempt to speed
       things up using the copyrect encoding and other things, but they
       will likely only speed up certain activities, not all.
     * A rate limiting factor for x11vnc performance is that video
       hardware is optimized for writing, not reading (x11vnc reads the
       video framebuffer for the screen image data). The difference can
       be a factor of 10-50, and it usually takes about 0.5-1 sec to read
       in the whole video hardware framebuffer (5MB for 1280x1024 at
       depth 24). So whenever activity changes most of the screen there
       is a delay of this length while x11vnc reads the changed regions
       in. To get a sense of the read and write speeds of your video
       card, you can run the benchmarks like: x11perf -getimage500,
       x11perf -putimage500,  x11perf -shmput500 and for XFree86 displays
       with direct graphics access the dga command (press "b" to run the
       benchmark and then after a few seconds press "q" to quit).
       On XFree86 it is actually possible to increase the framebuffer
       read speed considerably (5-50 times) by using the Shadow
       Framebuffer (a copy of the framebuffer is kept in main memory and
       this can be read much more quickly). To do this one puts the line
       Option "ShadowFB" "true" (and depending on video card driver,
       Option "NoAccel" "true" may be needed too) in the Device section
       of the /etc/X11/XF86Config file. Note that this disables 2D
       acceleration at the physical display and so likely defeats the
       purpose. Nevertheless this could be handy in some circumstances,
       e.g. if the speed at the physical display was tolerable.
       Unfortunately it does not seem shadowfb can be turned on and off
       dynamically...
     * Somewhat surprisingly, the X11 mouse (cursor) shape is write-only
       and cannot be queried from the X server. So in x11vnc the cursor
       shape stays fixed at an arrow. (see the "-cursor X" and other
       options, however, for a partial hack for the root window, etc.).
       Also, on Solaris using the SUN_OVL overlay extension, x11vnc can
       show the correct mouse cursor when the -overlay option is also
       supplied. For XFree86/Xorg, the XFIXES extension should help this
       as well.
     * Audio from applications is of course not redirected (separate
       redirectors do exist, e.g. esd). The XBell() "beeps" will work if
       the X server supports the XKEYBOARD extension. (Note that on
       Solaris XKEYBOARD is disabled by default. Passing +kb to Xsun
       enables it).
     * Occasionally a patch of tiles will not get updated correctly.
       Evidently a timing related bug and difficult to reproduce...
     * Using -threads can expose some bugs in libvncserver.

   Please feel free to [26]contact me if you have any questions,
   problems, or comments about x11vnc, etc.
     _________________________________________________________________

    x11vnc FAQ:

   [27]Q-1: I can't get x11vnc to start up. It says "XOpenDisplay failed
   ((null))" or "Xlib: connection to ":0.0" refused by server". What do I
   need to do? 

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

   [29]Q-3: Where can I get a precompiled x11vnc binary for my Operating
   System? 

   [30]Q-4: How can I see all of x11vnc's command line options and
   documentation on how to use them? 

   [31]Q-5: I don't like typing arcane command line options every time I
   start x11vnc. What can I do? Is there a config file? 

   [32]Q-6: Why does x11vnc exit as soon as the VNC viewer disconnects?
   And why doesn't it allow more than one VNC viewer to connect at the
   same time? 

   [33]Q-7: I have two separate machine displays in front of me, one
   Windows the other X11: can I use x11vnc in combination with Win2VNC in
   dual-screen mode to pass the keystrokes and mouse motions to the X11
   display? 

   [34]Q-8: I am running Win2VNC on my windows machine and trying to
   create a dual-screen mode with my second display by running x11vnc
   -nofb. Whenever I initiate the connection Win2VNC quickly disconnects
   and x11vnc says something like: rfbProcessClientNormalMessage: read:
   Connection reset by peer 

   [35]Q-9: 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 the colors are incorrect in certain
   windows. 

   [36]Q-10: Color problems: Why are the colors for some windows messed
   up in x11vnc? BTW, I have an X display that 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. 

   [37]Q-11: How do I figure out the window id to supply to the -id
   windowid option? 

   [38]Q-12: Why don't menus or other transient windows come up when I am
   using the -id windowid option to view a single application window? 

   [39]Q-13: Can I use x11vnc to view and interact with an Xterminal
   (e.g. NCD) that is not running UNIX and so x11vnc cannot be run on it
   directly? 

   [40]Q-14: Can I make x11vnc more quiet and also go into the background
   after starting up? 

   [41]Q-15: Can I limit which machines incoming VNC clients can connect
   from? 

   [42]Q-16: How do I build x11vnc/libvncserver with libwrap
   (tcp_wrappers) support? 

   [43]Q-17: Can I prompt the user at the local X display whether the
   incoming VNC client should be accepted or not? Can I decide to make
   some clients view-only? How about running an arbitrary program to make
   the decisions? 

   [44]Q-18: How do I create a VNC password for use with x11vnc? 

   [45]Q-19: How can I tunnel my connection to x11vnc via an encrypted
   SSH channel between two Unix machines? 

   [46]Q-20: How can I tunnel my connection to x11vnc via an encrypted
   SSH channel from Windows using an SSH client like Putty? 

   [47]Q-21: Does x11vnc support Unix usernames and passwords? Can I
   further limit the set of Unix usernames who can connect to the VNC
   desktop? 

   [48]Q-22: Can I have two passwords for VNC viewers, one for full
   access and the other for view-only access to the display? 

   [49]Q-23: I use a screen-lock when I leave my workstation (e.g.
   xscreensaver or xlock). When I remotely access my workstation desktop
   via x11vnc I can unlock the desktop fine, but I am worried people will
   see my activities on the physical monitor. What can I do to prevent
   this, or at least make it more difficult? 

   [50]Q-24: Can I have x11vnc automatically lock the screen when I
   disconnect the VNC viewer? 

   [51]Q-25: Are reverse connections (i.e. the VNC server connecting to
   the VNC viewer) using "vncviewer -listen" and vncconnect(1) supported?
   
   [52]Q-26: Sometimes when a VNC viewer dies abruptly, x11vnc also dies
   with the error message like: "Broken pipe". I'm using the -forever
   mode and I want x11vnc to keep running. 

   [53]Q-27: How can I use x11vnc to connect to an X login screen like
   xdm, GNOME gdm, KDE kdm, or CDE dtlogin? 

   [54]Q-28: Can I run x11vnc out of inetd(1)? 

   [55]Q-29: How do I make x11vnc work with the Java VNC viewer applet in
   a web browser? 

   [56]Q-30: Why isn't the mouse cursor shape (the little icon shape
   where the mouse pointer is) correct as I move from window to window? 

   [57]Q-31: Why does the mouse arrow just stay in one corner in my
   vncviewer, whereas my cursor (that does move) is just a dot? 

   [58]Q-32: Can I take advantage of the TightVNC extension to the VNC
   protocol where Cursor Positions Updates are sent back to all connected
   clients (i.e. passive viewers can see the mouse cursor being moved
   around by another viewer)? 

   [59]Q-33: Is it possible to swap the mouse buttons (e.g. left-handed
   operation), or arbitrarily remap them? How about mapping button clicks
   to keystrokes, e.g. to partially emulate Mouse wheel scrolling? 

   [60]Q-34: When I drag windows around with the mouse or scroll up and
   down things really bog down (unless I do the drag in a single, quick
   motion). Is there anything to do to improve things? 

   [61]Q-35: I have lots of memory, but why does x11vnc fail with
   shmget: No space left on device    or    Minor opcode of failed
   request: 1 (X_ShmAttach)? 

   [62]Q-36: How can I make x11vnc use less system resources? 

   [63]Q-37: How can I make x11vnc use MORE system resources? 

   [64]Q-38: I use x11vnc over a slow link with high latency (e.g. dialup
   modem), is there anything I can do to speed things up? 

   [65]Q-39: How can I get my AltGr and Shift modifiers to work between
   keyboards for different languages? 

   [66]Q-40: When I try to type a "<" (i.e. less than) instead I get ">"
   (i.e. greater than)! Strangely, typing ">" works OK!! 

   [67]Q-41: I'm using an "international" keyboard (e.g. German "de", or
   Danish "dk") and the -modtweak mode works well if the VNC viewer is
   run on a Unix/Linux machine with a similar keyboard. But if I run the
   VNC viewer on Unix/Linux with a different keyboard (e.g. "us") or
   Windows with any keyboard, I can't type some keys like: "@", "$", "<",
   ">", etc. How can I fix this? 

   [68]Q-42: When typing I sometimes get double, triple, or more of my
   keystrokes repeated. I'm sure I only typed them once, what can I do? 

   [69]Q-43: The machine where I run x11vnc has an AltGr key, but the
   local machine where I run the VNC viewer does not. Is there a way I
   can map a local unused key to send an AltGr? How about a Compose key
   as well? 

   [70]Q-44: I have a Sun machine I run x11vnc on. Its Sun keyboard has
   just one Alt key labelled "Alt" and two Meta keys labelled with little
   diamonds. The machine where I run the VNC viewer only has Alt keys.
   How can I send a Meta keypress? (e.g. emacs needs this) 

   [71]Q-45: Can I map a keystroke to a mouse button click on the remote
   machine? 

   [72]Q-46: The remote display is larger (in number of pixels) than the
   local display I am running the vncviewer on. I don't like the
   vncviewer scrollbars, what I can do? 

   [73]Q-47: Does x11vnc support server-side framebuffer scaling? (E.g.
   to make the desktop smaller). 

   [74]Q-48: Does x11vnc work with Xinerama? (i.e. multiple monitors
   joined together to form one big, single screen). 

   [75]Q-49: Can I use x11vnc on a multi-headed display that is not
   Xinerama (i.e. separate screens :0.0, :0.1, ... for each monitor)? 

   [76]Q-50: Why is the view in my VNC viewer completely black? Or why is
   everything flashing around randomly? 

   [77]Q-51: I use Linux Virtual Consoles (VC's) to implement 'Fast User
   Switching' between users' sessions (e.g. Betty is on Ctrl-Alt-F7,
   Bobby is on Ctrl-Alt-F8, and Sid is on Ctrl-Alt-F1: they use those
   keystrokes to switch between their sessions). How come the view in a
   VNC viewer connecting to x11vnc is either completely black or
   otherwise all messed up unless the X session x11vnc is attached to is
   in the active VC? 

   [78]Q-52: Does the Clipboard/Selection get transferred between the
   vncviewer and the X display? 

   [79]Q-53: Why don't I hear the "Beeps" in my X session (e.g. when
   typing tput bel in an xterm)? 

   [80]Q-54: I am using x11vnc where my local machine has "popup/hidden
   taskbars" (e.g. GNOME or MacOS X) and the remote display where x11vnc
   runs also has "popup/hidden taskbars" (e.g. GNOME). When I move the
   mouse to the edge of the screen where the popups happen, the taskbars
   interfere and fight with each other in strange ways. What can I do? 
     _________________________________________________________________

   Q-1: I can't get x11vnc to start up. It says "XOpenDisplay failed
   ((null))" or "Xlib: connection to ":0.0" refused by server". What do I
   need to do?

   For the former error, you need to specify the X display to connect to
   (it also needs to be on the same machine x11vnc is to run on). Set
   your DISPLAY environment variable or use the -display option to
   specify it. Nearly always the correct value will be ":0"

   For the latter error, you need to set up the X11 permissions. See the
   xauth(1), Xsecurity(7), and xhost(1) man pages. For example, you may
   need to set your XAUTHORITY environment variable to point to the
   correct cookie file (e.g. /home/joe/.Xauthority or
   /var/lib/xdm/authdir/authfiles/A:0-nRySEi), or simply be sure you run
   x11vnc as the correct user (i.e. the user who owns the X session you
   wish to view). Less safe, but if the owner of the X session runs xhost
   +localhost one should be able to attach x11vnc to the session (from
   the same machine).

   We have been informed that some recent Linux distribution display
   managers set XAUTHORITY to random local filenames, e.g.:
   /tmp/.gdmHaVtYy. So logging in as the correct user may not be
   enough... you need to dig out where they have hidden the
   MIT-MAGIC-COOKIE. The -e option to ps(1) may help, e.g.: ps wwwweaux |
   tr ' ' '\n' | grep XAUTHORITY | sort -u

   Note: use of Display Manager (gdm, kdm, ...) auth cookie files (i.e.
   from /var/...,  /tmp/..., or elsewhere) may require modification via
   xauth(1) to correctly include the display x11vnc refers to (e.g. xauth
   -f cookie.file add :0 . 45be51ae2ce9dfbacd882ab3ef8e96b1, where
   45be51... was found from an xauth -f /var/... list) or other reasons.
   See xauth(1) manpage for full details on how to transfer an
   MIT-MAGIC-COOKIE between machines and displays.

   To test out your X11 permissions, set DISPLAY and type xclock in the
   same place you will be typing (or otherwise running) x11vnc. If a
   little clock comes up on the display, that means the X11 permissions
   are OK. To test your X11 permissions when logged into the display
   machine remotely, use xdpyinfo (if you see the informational output
   about the display you know it connected to the X server successfully).
   Important: if you cannot get your X11 permissions so that the xclock
   or xdpyinfo tests work, x11vnc also will not work (all of these X
   clients must be able to connect to the X server to function).

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

   Make sure you have all of the required -devel packages installed.
   These include X11/XFree86, libjpeg, libz, ...

   After running the libvncserver configure, carefully examine the output
   and the messages in the config.log file looking for missing
   components. If the configure output looks like:
  checking how to run the C preprocessor... gcc -E
  checking for X... no
  checking for XkbSelectEvents in -lX11... no
  checking for XineramaQueryScreens in -lXinerama... no
  checking for XTestFakeKeyEvent in -lXtst... no

   there is quite a bit wrong with the build environment. Hopefully
   simply adding -devel packages will fix it.

   For Debian the list seems to be:
  gcc
  make
  libc6-dev
  libjpeg62-dev
  libx11-dev
  libxext-dev
  libxtst-dev
  x-dev
  xlibs-static-dev
  zlib1g-dev

   For Redhat the list seems to be:
  gcc
  make
  glibc-devel
  libjpeg-devel
  XFree86-devel
  zlib-devel

   Q-3: Where can I get a precompiled x11vnc binary for my Operating
   System?

   Hopefully the [81]build steps above and [82]FAQ provide enough info
   for a painless compile for most environments. Please report problems
   with the x11vnc configure, make, etc. on your system (if your system
   is known to compile other GNU packages successfully).

   There are precompiled x11vnc binaries made by other groups available
   at the following locations:
    Debian:         (.deb)  [83]http://packages.debian.org/x11vnc

   Slackware: (.tgz) [84]http://www.linuxpackages.net/ Redhat/Fedora:
   (.rpm) [85]http://dag.wieers.com/packages/x11vnc/ wwexptools: (.tgz)
   [86]http://www.bell-labs.com/project/wwexptools/packages.html The last
   one, wwexptools, provides a variety of Unix binaries (Linux, Solaris,
   HP-UX, Irix, ...) with the intent of being compatible on a wide range
   of OS releases. Find x11vnc at that link and select 'download info'.
   If any of the above binaries don't work and building x11vnc on your OS
   fails, and all else fails, you can contact me as I occasionally have a
   test binary I could give you.

   As a general note, the x11vnc program is simple enough you don't
   really need to install a package: the binary will in most cases work
   as is and from any location (as long as your system libraries are not
   too old, etc). So, for Linux distributions that are not one of the
   above, the x11vnc binary from the above packages has a good chance of
   working. You can "install" it by just copying the x11vnc binary to the
   desired directory in your PATH. Tip on extracting files from a Debian
   package: extract the archive via a command like: ar x
   x11vnc_0.6-2_i386.deb and then you can find the binary in the
   resulting data.tar.gz tar file. Also, rpm2cpio(1) is useful in
   extracting files from rpm packages.

   Q-4: How can I see all of x11vnc's command line options and
   documentation on how to use them?

   Run:  x11vnc -help    The output is listed [87]here as well.

   Q-5: I don't like typing arcane command line options every time I
   start x11vnc. What can I do? Is there a config file?

   You could create a shell script that calls x11vnc with your options:
#!/bin/sh
#
# filename: X11vnc  (i.e. not "x11vnc")
# It resides in a directory in $PATH. "chmod 755 X11vnc" has been run on it.
#
x11vnc -nap -wait 50 -localhost -rfbauth $HOME/.vnc/passwd -display :0 $*

   a similar thing can be via aliases in your shell (bash, tcsh, csh,
   etc..).

   Or as of Jun/2004 in the libvncserver CVS you can use the simple
   $HOME/.x11vncrc config file support. If that file exists, each line is
   taken as a command line option. E.g. the above would be:
# this is a comment in my ~/.x11vncrc file
nap
wait 50        # comment to the end of the line
-localhost     # note: the leading "-" is optional.
rfbauth  /home/fred/.vnc/passwd
display :0

   At some point this config file support will be expanded.

   Q-6: Why does x11vnc exit as soon as the VNC viewer disconnects? And
   why doesn't it allow more than one VNC viewer to connect at the same
   time?

   These defaults are simple safety measures to avoid someone unknowingly
   leaving his X11 desktop exposed (to the internet, say) for long
   periods of time. Use the -forever option (aka -many) to have x11vnc
   wait for more connections after the first client disconnects. Use the
   -shared option to have x11vnc allow multiple clients to connect
   simultaneously.

   Recommended additional safety measures include using ssh (see above)
   or a VPN to authenticate and encrypt the viewer connections or to at
   least use the -rfbauth passwd-file [88]option to use VNC password
   protection.

   Q-7: I have two separate machine displays in front of me, one Windows
   the other X11: can I use x11vnc in combination with Win2VNC in
   dual-screen mode to pass the keystrokes and mouse motions to the X11
   display?

   Yes, for best response start up x11vnc with the "-nofb" option
   (disables framebuffer polling, and does other optimizations) on the
   secondary display (X11). Then start up Win2VNC on the primary display
   (Windows) referring it to the secondary display.

   This will also work X11 to X11 using [89]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:
     * [90]Original Win2VNC
     * [91]Enhanced Win2VNC and [92]sourceforge link
     * [93]x2vnc
     * [94]x2x also [95]here
     * [96]zvnc (MorphOS)

   All of them (except x2x) will work with x11vnc.

   Q-8: I am running Win2VNC on my windows machine and trying to create a
   dual-screen mode with my second display by running x11vnc -nofb.
   Whenever I initiate the connection Win2VNC quickly disconnects and
   x11vnc says something like: rfbProcessClientNormalMessage: read:
   Connection reset by peer

   Is the default visual of the X display you run x11vnc on low color
   (e.g. 8 bit per pixel PseudoColor)? (you can run xdpyinfo to check).
   There seems to be a bug in Win2VNC in that it cannot deal correctly
   with colormaps (PseudoColor is the most common example of a visual
   with a colormap).

   If so, there are a couple options. 1) Can you set the default visual
   on your display to be depth 24 TrueColor? Sun machines often have 8+24
   overlay/multi-depth visuals, and you can make the default visual depth
   24 TrueColor (see fbconfig(1) and Xsun(1)). 2) As of Feb/2004, in the
   libvncserver CVS, x11vnc has the -visual option to allow you to force
   the framebuffer visual to whatever you want (this usually messes up
   the colors unless you are very careful). 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.

   Q-9: 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 the colors are incorrect in certain
   windows.

   Use the -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 that in some rare cases the -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-10: Color problems: Why are the colors for some windows messed up in
   x11vnc? BTW, I have an X display that 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 [97]previous question regarding 8 bpp
   PseudoColor.

   If that isn't the problem, 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? If it does, can you possibly
   re-configure your X server to make the depth 24 visual the default? If
   you can do it, this will save you a lot of grief WRT colors and x11vnc
   (and for general usage too!). 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 (see /usr/dt/config/Xservers). Also look at
   the fbconfig(1) and related manpages (e.g. ffbconfig, m64config,
   pgxconfig, SUNWjfb_config, etc ...) for hardware framebuffer settings
   that may achieve the same effect. In general for non-Sun machines,
   look at the "-cc class" and related options in your X server manpage
   (perhaps Xserver(1)), it may allow modifying the default visual (e.g.
   "-cc 4", see <X11/X.h> for the visual class numbers). On XFree86 some
   video card drivers (e.g. Matrox mga) have settings like Option
   "Overlay" "24,8" to support multi-depth overlays. For these, use the
   "-cc 4" X server command line option to get a depth 24 default visual.

   Another option is if the system with overlay visuals is a Sun system
   running Solaris you can use the -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. 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
   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.

   Misc. notes on -overlay mode: An amusing by-product of -overlay mode
   is that mouse cursor shape is correct. The -overlay mode may be
   somewhat slower than normal mode due to the extra framebuffer
   manipulations that must be performed. Also, there is a bug in that for
   some popup menus, the windows they overlap will have painting problems
   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).

   Still not working? Run xwininfo on the application with the messed up
   colors to verify that the depth of its visual is different from the
   default visual depth (gotten from xdpyinfo). One possible workaround
   in this case is to use the -id option to point x11vnc at the
   application window itself. If the application is complicated (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. Fortunately the -overlay
   option works for Solaris machines with overlay visuals where most of
   this problem occurs.

   Q-11: How do I figure out the window id to supply to the -id windowid
   option?

   Run the xwininfo program in a terminal. It will ask you to click on
   the desired application window. After clicking, it will print out much
   information, including the window id. Also, the visual and depth of
   the window printed out is often useful in debugging x11vnc
   [98]problems.

   When using -id windowid, note that some VNC viewers will have problems
   rendering screens that have a width that is not a multiple of 4. Try
   to manually adjust the window width before starting x11vnc -id ....

   Q-12: Why don't menus or other transient windows come up when I am
   using the -id windowid option to view a single application window?

   This is related to the behavior of the XGetImage(3X11) and
   XShmGetImage() interfaces regarding backingstore, saveunders, etc. The
   way the image is retrieved depends on some aspects of how the X server
   maintains the display image data and whether other windows are
   clipping or obscuring it. See the XGetImage man page for more details.

   If things are not working and you still want to do the single window
   polling, try the -sid windowid option ("shifted" windowid).

   x11vnc is known to crash under both -id and -sid, so both modes are
   still experimental.

   Q-13: Can I use x11vnc to view and interact with an Xterminal (e.g.
   NCD) that is not running UNIX and so x11vnc cannot be run on it
   directly?

   You can, but it will likely be very wasteful of network bandwidth
   since you will be polling the X display over the network as opposed to
   over the local hardware. To do this, run x11vnc on a UNIX machine as
   close as possible network-wise to the Xterminal machine. Use the
   -display to point the display to that of the Xterminal (you'll of
   course need basic X11 permission to do that) and also supply the
   -noshm option (this enables the polling over the network).

   The response will likely be sluggish. This mode is not recommended
   except for "quick checks" of hard to get to X servers. Use something
   like -wait 150 to cut down on the polling rate. You may also need
   -flipbyteorder if the colors get messed up due to endian byte order
   differences.

   Q-14: Can I make x11vnc more quiet and also go into the background
   after starting up?

   Use the -q and -bg options, respectively.  (also: -quiet is an alias
   for -q)

   Note that under -bg the stderr messages will be lost unless you use
   the "-o logfile" option.

   Q-15: Can I limit which machines incoming VNC clients can connect
   from?

   Yes, look at the -allow and -localhost options to limit connections by
   IP address. E.g.
  x11vnc -allow 192.168.0.1,192.168.0.2

   for those two hosts or
  x11vnc -allow 192.168.0.

   for a subnet. Note that -localhost is the same as "-allow 127.0.0.1"

   For more control, build libvncserver with libwrap support
   (tcp_wrappers) and then use /etc/hosts.allow.

   Q-16: How do I build x11vnc/libvncserver with libwrap (tcp_wrappers)
   support?

   Here is one way to pass this information to the configure script:
  env CPPFLAGS=-DUSE_LIBWRAP LDFLAGS=-lwrap ./configure

   then run make as usual. This requires libwrap and its development
   package (tcpd.h) to be installed on the build machine.

   The resulting x11vnc then uses libwrap/tcp_wrappers for connections.
   The service name you will use in /etc/hosts.allow and /etc/hosts.deny
   is "vnc", e.g.:
  vnc: 192.168.100.3 .example.com

   Note that if you run x11vnc out of [99]inetd you do not need to build
   x11vnc with libwrap support because the /usr/sbin/tcpd reference in
   /etc/inetd.conf handles the tcp_wrappers stuff.

   Q-17: Can I prompt the user at the local X display whether the
   incoming VNC client should be accepted or not? Can I decide to make
   some clients view-only? How about running an arbitrary program to make
   the decisions?

   Yes, look at the "-accept command" option, it allows you to specify an
   external command that is run for each new client. (use quotes around
   the command if it contains spaces, etc.). If the external command
   returns 0 the client is accepted, otherwise the client is rejected.
   See below how to also accept clients view-only.

   The external command will have the RFB_CLIENT_IP environment variable
   set to the client's numerical IP address, RFB_CLIENT_PORT its port
   number. Similarly for RFB_SERVER_IP and RFB_SERVER_PORT to allow
   identification of the tcp virtual circuit. DISPLAY will be set to that
   of the X11 display being polled. Also, RFB_X11VNC_PID is set to the
   x11vnc process id (e.g. in case you decided to kill it), RFB_CLIENT_ID
   will be an id number, and RFB_CLIENT_COUNT the number of other clients
   currently connected.

   As a special case, "-accept popup" will instruct x11vnc to create its
   own simple popup window. To accept the client press "y" or click mouse
   on the "Yes" button. To reject the client press "n" or click mouse on
   the "No" button. To accept the client View-only, press "v" or click
   mouse on the "View" button. If the -viewonly option has been supplied,
   the "View" action will not be present: the whole display is view only
   in that case.

   The popup window times out after 120 seconds, to change this behavior
   use "-accept popup:N" where N is the number of seconds (use 0 for no
   timeout). More tricks: "-accept popupmouse" will only take mouse click
   responses, while "-accept popupkey" will only take keystroke responses
   (popup takes both). After any of the 3 popup keywords you can supply a
   position of the window: +N+M, (the default is to center the window)
   e.g. -accept popupmouse+10+10.

   Also as a special case "-accept xmessage" will run the xmessage(1)
   program to prompt the user whether the client should be accepted or
   not. This requires that you have xmessage installed and available via
   PATH. In case it is not already on your system, the xmessage program
   is available at [100]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 [101]dtVncPopup for use
   in CDE environments to do the same sort of thing. Information on how
   to use it is found at the top of the file. He encourages you to
   provide feedback to him to help improve the script.

   Note that in all cases x11vnc will block while the external command or
   popup is being run, so attached clients will not receive screen
   updates, etc during this period. (use of -threads may or may not alter
   this behavior).

   To run a command when a client disconnects, use the "-gone command"
   option. This is for the user's convenience only: the return code of
   the command is not interpreted by x11vnc. The same environment
   variables are set as in "-accept command"

   Q-18: How do I create a VNC password for use with x11vnc?

   You may already have one in $HOME/.vnc/passwd if you have used, say,
   the vncserver program from the regular RealVNC or TightVNC packages
   (i.e. launching the Xvnc server). Otherwise, you could use the
   vncpasswd(1) program from those packages. The libvncserver package
   also comes with a simple program: storepasswd in the examples
   directory. And as of Jun/2004 in the libvncserver CVS x11vnc supports
   the -storepasswd "pass" "file" option, which is the the same
   functionality of storepasswd. Be sure to quote the "pass" if it
   contains shell meta characters, spaces, etc.

   You then use the password via the x11vnc option: -rfbauth filename

   Compared to vncpasswd(1) the latter two methods are a somewhat unsafe
   because the password is specified on the command line and so someone
   may see it by using ps(1) or looking over your shoulder. Also watch
   out for the command winding up in your shell's history file (history
   -c is often a way to clear it).

   x11vnc also has the [102]-passwdfile and -passwd/-viewpasswd plain
   text (i.e. not obscured like the -rfbauth VNC passwords) password
   options.

   Q-19: How can I tunnel my connection to x11vnc via an encrypted SSH
   channel between two Unix machines?

   See the description earlier on this page on [103]how to tunnel VNC via
   SSH from Unix to Unix. A number of ways are described along with some
   issues you may encounter.

   Other secure encrypted methods exists, e.g. stunnel.

   Q-20: How can I tunnel my connection to x11vnc via an encrypted SSH
   channel from Windows using an SSH client like Putty?

   [104]Above we described how to tunnel VNC via SSH from Unix to Unix.
   To do this from Windows using Putty it would go something like this:
     * In the Putty dialog window under 'Session' enter the hostname or
       IP number of the Unix machine with display to be viewed.
     * Make sure the SSH protocol is selected and the server port is
       correct.
     * Under 'Connections/SSH/Tunnels' Add a Local connection with
       'Source port:  5900' and 'Destination:  localhost:5900'
     * Log into the remote machine by pressing 'Open' and supplying
       username, password, etc.
     * In that SSH shell, start up x11vnc by typing the command: x11vnc
       -display :0 plus any other desired options.
     * Finally, start up your VNC Viewer in Windows and enter
       'localhost:0' as the VNC server.

   You can keep all of the settings in a Putty 'Saved Session'. Also,
   once everything is working, you can consider putting x11vnc -display
   :0 (plus other cmdline options) in the 'Remote command' Putty setting
   under 'Connections/SSH'. It is likely possible to script the whole
   process in a BAT file including launching the VNC viewer by using the
   plink Putty utility. Send us the script if you get that working.

   For extra protection feel free to run x11vnc with the -localhost and
   -rfbauth/-passwdfile options.

   If the machine you SSH into via Putty is not the same machine with the
   X display you wish to view (e.g. your company provides incoming SSH
   access to a gateway machine), then you need to change the above Putty
   dialog setting to: 'Destination: otherhost:5900', Once logged in,
   you'll need to do a second login (ssh or rsh) to the workstation
   machine 'otherhost' and then start up x11vnc on it.

   As discussed [105]above another option is to first start the VNC
   viewer in "listen" mode, and then launch x11vnc with the "-connection
   localhost" option to establish the reverse connection. In this case a
   Remote port redirection (not Local) is needed for port 5500 instead of
   5900 (i.e. 'Source port:  5500' and 'Destination:  localhost:5500' for
   a Remote connection).

   Q-21: Does x11vnc support Unix usernames and passwords? Can I further
   limit the set of Unix usernames who can connect to the VNC desktop?

   Until the VNC protocol and libvncserver support this things will be
   approximate at best. Hopefully, it will not be too long to wait for
   such support.

   One approximate method involves starting x11vnc with the -localhost
   option. This basically requires the viewer user to log into the
   workstation where x11vnc is running via their Unix username and
   password, and then somehow set up a port redirection of his vncviewer
   connection to make it appear to emanate from the local machine. As
   discussed above, ssh is useful for this: ssh -l username -L
   5900:localhost:5900 hostname ... See the ssh wrapper scripts mentioned
   [106]elsewhere on this page. Of course a malicious user could allow
   other users to get in through his channel, but that is a problem with
   every method. Another thing to watch out for is a malicious user on
   the viewer side (where ssh is running) trying to sneak in through the
   ssh port redirection.

   Regarding limiting the set of Unix usernames who can connect, the
   traditional way would be to further require a VNC password to supplied
   (-rfbauth, -passwd, etc). A scheme that avoids a second password
   involves using the -accept option that runs a program to examine the
   connection information to determine which user is connecting from the
   local machine. For example, the program could use the ident service on
   the local machine (normally ident should not be trusted over the
   network, but on the local machine it should be accurate: otherwise
   root has been compromised and so there are more serious problems!). An
   example script passed in via -accept scriptname that deduces the Unix
   username and limits who can be accepted might look something like
   this:
#!/bin/sh
if [ "$RFB_CLIENT_IP" != "127.0.0.1" -o "$RFB_SERVER_IP" != "127.0.0.1" ]; then
        exit 1  # something fishy... reject it.
fi
user=`echo "$RFB_CLIENT_PORT, $RFB_SERVER_PORT" | nc -w 1 $RFB_CLIENT_IP 113 \
        | grep 'USERID.*UNIX' | head -1 | sed -e 's/[\r ]//g' | awk -F: '{print
 $4}'`

for okuser in fred barney wilma betty
do
        if [ "X$user" = "X$okuser" ]; then
                exit 0  # accept it
        fi
done
exit 1  # reject it

   For this to work with ssh port redirection, the ssh option
   UsePrivilegeSeparation must be enabled.

   Q-22: Can I have two passwords for VNC viewers, one for full access
   and the other for view-only access to the display?

   Yes, as of May/2004 in the libvncserver CVS there is the -viewpasswd
   option to supply the view-only password. Note the full-access password
   option -passwd must be supplied at the same time. E.g.: -passwd sword
   -viewpasswd fish.

   To avoid specifying the passwords on the command line (where they
   could be observed via the ps(1) command by any user) you can use the
   -passwdfile option to specify a file containing plain text passwords.
   Presumably this file is readable only by you, and ideally it is
   located on the machine x11vnc is run on (to avoid being snooped on
   over the network). The first line of this file is the full-access
   password. If there is a second line in the file and it is non-blank,
   it is taken as the view-only password.

   View-only passwords currently do not work for the -rfbauth password
   option (standard VNC password storing mechanism). FWIW, note that
   although the output (usually placed in $HOME/.vnc/passwd) by the
   vncpasswd or storepasswd programs (or from x11vnc -storepasswd) looks
   encrypted they are really just obscured to avoid "casual" password
   stealing. It takes almost no skill to figure out how to extract the
   plain text passwords from $HOME/.vnc/passwd since it is very
   straight-forward to work out what to do from the VNC source code.

   Q-23: I use a screen-lock when I leave my workstation (e.g.
   xscreensaver or xlock). When I remotely access my workstation desktop
   via x11vnc I can unlock the desktop fine, but I am worried people will
   see my activities on the physical monitor. What can I do to prevent
   this, or at least make it more difficult?

   Probably most work environments would respect your privacy if you
   powered off the monitor. Also remember if people have physical access
   to your workstation they basically can do anything they want with it
   (e.g. install a backdoor for later use, etc).

   In any event, as of Jun/2004 there is an experimental utility to make
   it more difficult for nosey people to see your x11vnc activities. The
   source for it is [107]blockdpy.c The idea behind it is simple (but
   obviously not bulletproof): when a VNC client attaches to x11vnc put
   the display monitor in the DPMS "off" state, if the DPMS state ever
   changes immediately start up the screen-lock program. The x11vnc user
   will notice something is happening and think about what to do next
   (while the screen is in a locked state).

   This works (or at least has a chance of working) because if the
   intruder moves the mouse or presses a key on the keyboard, the monitor
   wakes up out of the DPMS off state, and this induces the screen lock
   program to activate as soon as possible. Of course there are cracks in
   this, the eavesdropper could detach your monitor and insert a non-DPMS
   one, and there are race conditions. As mentioned above this is not
   bulletproof. A really robust solution would likely require X server
   and perhaps even video hardware support.

   The blockdpy utility is launched by the -accept option and told to
   exit via the -gone option (the vnc client user should obviously
   re-lock the screen before disconnecting!). Instructions can be found
   in the source code for the utility at the above link.

   Q-24: Can I have x11vnc automatically lock the screen when I
   disconnect the VNC viewer?

   Yes, a user mentions he uses the -gone option under CDE to run a
   screen lock program:
  x11vnc -display :0.0 -forever -gone 'dtaction LockDisplay'

   Other possibilities are:
  x11vnc -display :0.0 -forever -gone 'xscreensaver-command -lock'
  x11vnc -display :0.0 -forever -gone 'kdesktop_lock'
  x11vnc -display :0.0 -forever -gone 'xlock &'

   Q-25: Are reverse connections (i.e. the VNC server connecting to the
   VNC viewer) using "vncviewer -listen" and vncconnect(1) supported?

   As of Mar/2004 in the libvncserver CVS x11vnc supports reverse
   connections. On Unix one starts the VNC viewer in listen mode:
   vncviewer -listen, and then startus up x11vnc with the -connect
   option. To connect immediately at x11vnc startup time use the
   "-connect host:port" option (use commas for a list of hosts to connect
   to). The ":port" is optional (default is 5500). If a file is specified
   instead: -connect /path/to/some/file then that file is checked
   periodically (about once a second) for new hosts to connect to.

   To use the vncconnect(1) program (from the core VNC package at
   www.realvnc.com) specify the -vncconnect option to x11vnc.
   vncconnect(1) must be pointed to the same X11 DISPLAY as x11vnc (since
   it uses X properties to communicate with x11vnc). If you do not have
   or do not want to get the vncconnect(1) program, the following script
   (named "Vncconnect") may work if your xprop(1) supports the -set
   option:
#!/bin/sh
# usage: Vncconnect <host>
#        Vncconnect <host:port>
# note: not all xprop(1) support -set.
#
xprop -root -f VNC_CONNECT 8s -set VNC_CONNECT "$1"

   Q-26: Sometimes when a VNC viewer dies abruptly, x11vnc also dies with
   the error message like: "Broken pipe". I'm using the -forever mode and
   I want x11vnc to keep running.

   As of Jan/2004 in the libvncserver CVS the SIGPIPE signal is ignored.
   So if a viewer client terminates abruptly, libvncserver will notice on
   the next I/O operation and will close the connection and continue on.

   Currently (Apr/2004) the above fix only works for BSD signal systems
   (Linux, FreeBSD, ...) For SYSV systems there is a workaround in my
   [108]x11vnc.c file. It also has an option -sigpipe exit to have x11vnc
   clean up and exit upon receiving SIGPIPE.

   Q-27: How can I use x11vnc to connect to an X login screen like xdm,
   GNOME gdm, KDE kdm, or CDE dtlogin?

   One time only.   If the X login screen is running and you just want to
   connect to it once:

   On Linux it seems it is possible to do this by just adjusting the
   XAUTHORITY to point to the MIT-COOKIE auth file while running x11vnc
   as root, e.g. for the gnome display manager, gdm:
  env XAUTHORITY=/var/gdm/:0.Xauth x11vnc -display :0

   or equivalently with newer x11vnc:
  x11vnc -auth /var/gdm/:0.Xauth -display :0

   There will be a similar thing for xdm using however a different auth
   directory path (perhaps something like
   /var/lib/xdm/authdir/authfiles/A:0-XQvaJk for xdm or
   /var/lib/kdm/A:0-crWk72 for kdm, where the random characters in
   basename will vary a bit).

   Another place to look for the auth file is via ps(1) output for the X
   server process to find any -auth argument.

   gdm seems to have an annoying setting that causes x11vnc (and any
   other X clients) to be killed after the user logs in. Setting
   KillInitClients=false in /etc/X11/gdm/gdm.conf may avoid this.

   For dtlogin in addition to the above sort of trick (the auth file
   should be in /var/dt), you'll also need to add something like
   Dtlogin*grabServer:False to the Xconfig file (/etc/dt/config/Xconfig
   or /usr/dt/config/Xconfig on Solaris). Then restart dtlogin, e.g.:
   /etc/init.d/dtlogin stop; /etc/init.d/dtlogin start or reboot.

   Continuously.   Have x11vnc reattach each time the X server is
   restarted (i.e. after each logout):

   To make x11vnc always attached to the the X server (please consider
   the security implications of this!) including the login screen you
   will need to add a command to the display manager startup script. The
   name of the script file depends on desktop used and seem to be:
        GNOME        /etc/X11/gdm/PreSession/Default
        KDE          /etc/kde*/kdm/Xsetup
        XDM          /etc/X11/xdm/Xsetup
        CDE          /etc/dt/config/Xsetup

   although the exact location can depend on operating system and
   distribution. See the documentation for your display manager:  gdm(1),
   kdm(1), xdm(1), dtlogin(1) for additional details. The above
   Dtlogin*grabServer:False step will be needed for dtlogin here as well.
   There may also be display number specific scripts: e.g. Xsetup_0 vs.
   Xsetup.

   In any event, the line you will add to the script will look something
   like:
  /usr/local/bin/x11vnc -rfbauth /path/to/my/vnc/passwd -forever -bg

   where you should customize the exact command to your needs. You may
   want to redirect the x11vnc output to a separate log file for
   debugging. In that case replace the -bg above with something like:
        1>> /var/tmp/x11vnc.log 2>&1 &

   (or use the "-o logfile" option).

   If you do not want to deal with the display manager startup scripts,
   here is a kludgey script that can be run manually or out of a boot
   file like rc.local. [109]x11vnc_loop It will need some local
   customization before running. Because the XAUTHORITY auth file must be
   guessed by this script, use of the display manager script above is
   preferred.

   Xterminals:   Note that if the display machine is a traditional
   Xterminal (where the X server runs on the Xterminal box, but all of
   the X client applications run on a central server), the login display
   manager, and hence the auth files, are on the central server and not
   on the Xterminal where the X server and x11vnc processes are running.
   Somehow the MIT-COOKIE auth file data must be copied to the Xterminal
   (e.g. via ssh, possibly using xauth nextract). You can use xauth -f
   cookie.file list to test the contents of the cookie in a file
   "cookie.file"

   Note: use of Display Manager (gdm, kdm, ...) auth cookie files (i.e.
   from /var/...,  /tmp/..., or elsewhere) may require modification via
   xauth(1) to correctly include the display x11vnc refers to (e.g. xauth
   -f cookie.file add :0 . 45be51ae2ce9dfbacd882ab3ef8e96b1, where
   45be51... was found from an xauth -f /var/... list) or other reasons.
   See xauth(1) manpage for full details on how to transfer an
   MIT-MAGIC-COOKIE between machines and displays.

   Q-28: Can I run x11vnc out of inetd(1)?

   Yes, perhaps a line something like this in /etc/inetd.conf will do it
   for you:

  5900 stream tcp nowait root /usr/sbin/tcpd /usr/local/bin/x11vnc_sh

   where the shell script /usr/local/bin/x11vnc_sh looks something like
   (you'll need to customize to your settings).
#!/bin/sh
XAUTHORITY=/home/fred/.Xauthority; export XAUTHORITY
/usr/local/bin/x11vnc -inetd -display :0 -rfbauth /home/fred/.vnc/passwd 2>> /t
mp/x11vnc_sh.log

   Note that you must redirect the standard error output to a log file or
   /dev/null for proper operation via inetd (otherwise the standard error
   also goes to the VNC vncviewer, and that confuses it greatly). If you
   do not use a wrapper script as above but rather call x11vnc directly
   in /etc/inetd.conf and do not redirect stderr, then you must specify
   the -q (aka -quiet) option: /usr/local/bin/x11vnc -q -inetd ... or use
   the -o logfile to collect the output in a file. The wrapper script
   with stderr redirection to a log file is the recommended method
   because the errors and warnings printed out are very useful in
   troubleshooting problems.

   Note also the need to set XAUTHORITY to point to the MIT-COOKIE auth
   file to get permission to connect to the X display (the x11vnc -auth
   option could also have been used). See the x11vnc_loop file in the
   previous question for more ideas on what that auth file may be, etc.

   On Solaris you cannot have the bare number 5900 in /etc/inetd.conf,
   you'll need to replace it with a word like x11vnc an then put
   something like "x11vnc 5900/tcp" in /etc/services.

   Be sure to look at your /etc/hosts.allow and /etc/hosts.deny settings
   to limit the machines that can connect to this service (your
   desktop!). For the above example with /etc/hosts.allow:
  x11vnc_sh : 123.45.67.89

   A really safe way to do things is to limit the above inetd to
   localhost only (via /etc/hosts.allow) and use ssh to tunnel the
   incoming connection. Using inetd for this prevents there being a tiny
   window of opportunity between x11vnc starting up and your vncviewer
   connecting to it. Always use a VNC password to further protect against
   unwanted access.

   Q-29: How do I make x11vnc work with the Java VNC viewer applet in a
   web browser?

   To have x11vnc serve up a Java VNC viewer applet to any web browsers
   that connect to it, run x11vnc with this option:
  -httpdir /path/to/the/java/classes/dir

   (this directory will contain the files index.vnc and, for example,
   VncViewer.jar) Note that libvncserver contains the TightVNC Java
   classes jar file for your convenience. (it is the file
   classes/VncViewer.jar in the source tree).

   You will see output something like this:
  14/05/2004 11:13:56 Autoprobing selected port 5900
  14/05/2004 11:13:56 Listening for HTTP connections on TCP port 5800
  14/05/2004 11:13:56   URL http://walnut:5800
  14/05/2004 11:13:56 screen setup finished.
  14/05/2004 11:13:56 The VNC desktop is walnut:0
  PORT=5900

   then you can connect to that URL with any Java enabled browser. Feel
   free to customize the default index.vnc file in the classes directory.

   Note that if you wanted to, you could also start the Java viewer
   entirely from the viewer-side by having the jar file there and using
   either the java or appletviewer commands to run the program.

   Q-30: Why isn't the mouse cursor shape (the little icon shape where
   the mouse pointer is) correct as I move from window to window?

   As mentioned above, the X11 mouse cursor shape (i.e. little picture:
   an arrow, X, I-beam, resizer, etc) is one of the few write-only
   objects in X11. That is, an application can tell the X server what the
   cursor shape should be when the pointer is in a given window, but a
   program (like x11vnc) unfortunately cannot read this information. I
   believe this is because the cursor shape is often downloaded to the
   graphics hardware (video card), but I could be mistaken.

   A simple kludge is provided by the "-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 "-cursor some" option for additional kludges.

   It should be possible to apply some heuristics where x11vnc tries to
   build up a table of cursors for the windows it sees, perhaps using a
   user supplied hints file, but that has not been explored yet.

   Also note that as of Aug/2004 in the libvncserver CVS, on Solaris
   using the SUN_OVL overlay extension, x11vnc can show the correct mouse
   cursor when the -overlay is also supplied. (-overlay has some other
   problems however, and can be slower). Plans are in the works to use
   XFIXES for this on XFree86, Xorg, and Xsun.

   Q-31: Why does the mouse arrow just stay in one corner in my
   vncviewer, whereas my cursor (that does move) is just a dot?

   This default takes advantage of a [110]tightvnc extension that allows
   specifying a cursor image for the local VNC viewer. You may disable it
   with the -nocursor option to x11vnc if your viewer does not have this
   extension.

   Note: as of Aug/2004 in the libvncserver CVS this should be fixed: the
   default for non-tightvnc viewers will be to draw the moving cursor
   into the framebuffer. This can also be disabled via -nocursor.

   Q-32: Can I take advantage of the TightVNC extension to the VNC
   protocol where Cursor Positions Updates are sent back to all connected
   clients (i.e. passive viewers can see the mouse cursor being moved
   around by another viewer)?

   Use the -cursorpos option when starting x11vnc. A VNC viewer must
   support the Cursor Positions Updates for the user to see the mouse
   motions (the TightVNC viewers support this). As of Aug/2004 in the
   libvncserver CVS -cursorpos is the default. See -nocursorpos and
   -nocursorshape.

   Q-33: Is it possible to swap the mouse buttons (e.g. left-handed
   operation), or arbitrarily remap them? How about mapping button clicks
   to keystrokes, e.g. to partially emulate Mouse wheel scrolling?

   You can remap the mouse buttons via something like: -buttonmap 13-31
   (or perhaps 12-21). Also, note that xmodmap(1) lets you directly
   adjust the X server's button mappings, but in some circumstances it
   might be more desirable to have x11vnc do it.

   One user had an X server with only one mouse button(!) and was able to
   map all of the VNC client mouse buttons to it via: -buttonmap 123-111.

   Note that the -debug_pointer option prints out much info for every
   mouse/pointer event.

   To map mouse button clicks to keystrokes you can use the alternate
   format where the keystrokes are enclosed between colons like this
   :<KeySym>: in place of the mouse button digit. For a sequence of
   keysyms separate them with "+" signs. Button clicks can also be
   included in the sequence via the fake keysyms Button1, etc.

   As an example, suppose the VNC viewer machine has a mouse wheel (these
   generate button 4 and 5 events), but the machine that x11vnc is run on
   only has the 3 regular buttons. In normal operation x11vnc will
   discard the button 4 and 5 events. However, either of the following
   button maps could possibly be of use emulating the mouse wheel events
   in this case:
  -buttonmap 12345-123:Prior::Next:
  -buttonmap 12345-123:Up+Up+Up::Down+Down+Down:

   Exactly what keystroke "scrolling" events they should be bound to
   depends on one's taste. If this method is too approximate, one could
   consider not using -buttonmap but rather configuring the X server to
   think it has a mouse with 5 buttons even though the physical mouse
   does not.

   Note that when a keysym-mapped mouse button is clicked down this
   immediately generates the key-press and key-release events (for each
   keysym in turn if the mapping has a sequence of keysyms). When the
   mouse button goes back up nothing is generated.

   If you include modifier keys like Shift_L instead of key-press
   immediately followed by key-release the state of the modifier key is
   toggled (however the initial state of the modifier key is ignored). So
   to map the right button to type my name 'Karl Runge' I could use this:
  -buttonmap 3-:Shift_L+k+Shift_L+a+r+l+space+Shift_L+r+Shift_L+u+n+g+e:

   (yes, this is getting a little silly).

   Q-34: When I drag windows around with the mouse or scroll up and down
   things really bog down (unless I do the drag in a single, quick
   motion). Is there anything to do to improve things?

   As of Jan/2004 there are some improvements in the libvncserver CVS
   tree. The default should now be much better than before and dragging
   small windows around should no longer be a huge pain. If for some
   reason these changes make matters worse, you can go back to the old
   way via the -old_pointer option.

   Also added was the -nodragging option that disables all screen updates
   while dragging with the mouse (i.e. mouse motion with a button held
   down). This gives the snappiest response, but might be undesired in
   some circumstances when you want to see the visual feedback while
   dragging (e.g. menu traversal or text selection).

   Q-35: I have lots of memory, but why does x11vnc fail with    shmget:
   No space left on device    or    Minor opcode of failed request: 1
   (X_ShmAttach)?

   It is not a matter of free memory, but rather free shared memory (shm)
   slots, also known as shm segments. This often occurs on a public
   Solaris machine using the default of only 100 slots. You (or the owner
   or root) can clean them out with ipcrm(1). x11vnc tries hard to
   release its slots, but it, and other programs, are not always able to
   (e.g. if kill -9'd).

   Sometimes x11vnc will notice the problem with shm segments and tries
   to get by with fewer, only giving a warning like this:
  19/03/2004 10:10:58 shmat(tile_row) failed.
  shmat: Too many open files
  19/03/2004 10:10:58 error creating tile-row shm for len=4
  19/03/2004 10:10:58 reverting to single_copytile mode

   Here is a shell script [111]shm_clear to list and prompt for removal
   of your unattached shm segments (attached ones are skipped). I use it
   while debugging x11vnc (I use shm_clear -y to assume "yes" for each
   prompt). If x11vnc is regularly not cleaning up its shm segments,
   please contact me so we can work to improve the situation.

   Longer term, on Solaris you can put something like this in
   /etc/system:
  set shmsys:shminfo_shmmax = 0x2000000
  set shmsys:shminfo_shmmni = 0x1000

   to sweep the problem under the rug (4096 slots). On Linux, examine
   /proc/sys/kernel/shmmni; you can modify the value by writing to that
   file.

   Things are even more tight on Solaris 8 and earlier, there is a
   default maximum number of shm segments per process of 6. The error is
   the X server (not x11vnc) being unable to attach to the segments, and
   looks something like this:
  30/04/2004 14:04:26 Got connection from client 192.168.1.23
  30/04/2004 14:04:26   other clients:
  X Error of failed request:  BadAccess (attempt to access private resource den
ied)
     Major opcode of failed request:  131 (MIT-SHM)
     Minor opcode of failed request:  1 (X_ShmAttach)
     Serial number of failed request:  14
     Current serial number in output stream:  17

   This tight limit on Solaris 8 can be increased via:
  set shmsys:shminfo_shmseg = 100

   in /etc/system. See the next paragraph for more workarounds.

   To minimize the number of shm segments used by x11vnc try using the
   -onetile option (corresponds to only 3 shm segments used, and adding
   -fs 1.0 knocks it down to 2). If you are having much trouble with shm
   segments, consider disabling shm completely via the -noshm option.
   Performance will be somewhat degraded but when done over local machine
   sockets it should be acceptable (see an [112]earlier question
   discussing -noshm).

   Q-36: How can I make x11vnc use less system resources?

   The -nap and "-wait n" (where n is the sleep between polls in
   milliseconds, the default is 30 or so) option are good places to
   start. Reducing the X server bits per pixel depth (e.g. to 16bpp or
   even 8bpp) will further decrease memory I/O and network I/O. Using the
   -onetile option will use less memory and use fewer shared memory slots
   (add -fs 1.0 for one less slot).

   Q-37: How can I make x11vnc use MORE system resources?

   You can try -threads and dial down the wait time (e.g. -wait 1) and
   possibly dial down -defer as well. Note that if you try to increase
   the "frame rate" too much you can bog down the server end with the
   extra work it needs to do compressing the framebuffer data, etc.

   That said, it is possible to "stream" video via x11vnc if the video
   window is small enough. E.g. a 256x192 xawtv TV capture window (using
   the x11vnc -id option) can be streamed over a LAN or wireless at a
   reasonable frame rate.

   Q-38: I use x11vnc over a slow link with high latency (e.g. dialup
   modem), is there anything I can do to speed things up?

   Some things you might want to experiment with (most of which will help
   performance on faster links as well):

     X server/session parameters:
     * Configure the X server bits per pixel to 16bpp or even 8bpp.
       (reduces amount of data needed to be sent)
     * Use a smaller desktop size (e.g. 1024x768 instead of 1280x1024)
     * Make sure the desktop background is a solid color (the background
       is resent every time it is re-exposed)
     * Configure your window manager or desktop "theme" to not use fancy
       images, shading, and gradients for the window decorations, etc.
       Disable Opaque moves, resizes, and animations.
     * Avoid small scrolls of large windows using the Arrow keys or
       scrollbar. Try to use PageUp/PageDown instead.
     * On XFree86 turn on the Shadow Framebuffer to speed up reading.
       (Option "ShadowFB" "true", and possibly Option "NoAccel" "true" as
       well, in the Device section of /etc/X11/XF86Config) This disables
       2D acceleration on the physical display and so is probably not
       worth it, but could be of use in some situations.

     VNC viewer parameters:
     * Use a [113]TightVNC enabled viewer!
     * Make sure the tight encoding is being used (look at vncviewer and
       x11vnc outputs)
     * Request 8 bits per pixel using -bgr233 (up to 4X speedup over
       depth 24 TrueColor (32bpp), but colors will be off)
     * The -depth option is similar to -bgr233 in reducing the requested
       number of bits per pixel.
     * Try increasing the TightVNC -compresslevel (compresses more on
       server side before sending, but uses more CPU)
     * Try reducing the TightVNC -quality (increases JPEG compression,
       but is lossy)
     * Try other VNC encodings via -encodings (tight is probably fastest,
       but you should check)
     * On the machine where vncviewer is run, make sure Backing Store is
       enabled (XFree86 disables it by default causing re-exposures of
       vncviewer to be very slow)

     x11vnc parameters:
     * Try using -nodragging (no screen updates when dragging mouse, but
       sometimes you miss visual feedback)
     * Try the -progressive pixelheight mode with the block pixelheight
       100 or so (delays sending vertical blocks since they may change
       while viewer is receiving earlier ones)
     * Set -fs 1.0 (disables fullscreen updates)
     * Enable server-side scaling via -scale m/n to make the VNC
       frambuffer smaller. (less data needs to be sent, but image may not
       be sharp and requires extra resources on the server end, may
       actually slow down transfers of text due to poorer compression)
     * Try increasing -wait or -defer (reduces the maximum "frame rate",
       but won't help much for large screen changes)
     * If you just want to watch one (simple) window use -id (cuts down
       extraneous polling and updates, but can be buggy or insufficient)
     * Set -nosel (disables all clipboard selection exchange)
     * Use -nocursor (repainting the remote cursor position and shape
       takes resources and round trips)

   Q-39: How can I get my AltGr and Shift modifiers to work between
   keyboards for different languages?

   The option -modtweak should be of some use for this. It is a mode that
   monitors the state of the Shift and AltGr Modifiers and tries to
   deduce the correct keycode to send, possibly by sending fake modifier
   key presses and releases in addition to the actual keystroke.

   Update:  As of Jul/2004 in the libvncserver CVS, -modtweak is now the
   default (use -nomodtweak to get the old behavior). This was done
   because it was noticed on newer XFree86 setups even on bland "us"
   keyboards like "pc104 us" XFree86 included a "ghost" key with both "<"
   and ">" it. This key does not exist on the keyboard (see [114]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 [115]FAQ about the -xkb option for a more powerful method
   of modifier tweaking for use on X servers with the XKEYBOARD
   extension.

   When trying to resolve keyboard mapping problems, that the
   -debug_keyboard option prints out much info for every keystroke and so
   can be useful debugging things.

   Q-40: When I try to type a "<" (i.e. less than) instead I get ">"
   (i.e. greater than)! Strangely, typing ">" works OK!!

   Does your keyboard have a single key with both "<" and ">" on it? Even
   if it doesn't, your X server may think your keyboard has such a key
   (e.g. pc105 in the XF86Config file when it should be something else,
   say pc104).

   The problem here is that on the Xserver where x11vnc is run there are
   two keycodes that correspond to the "<" keysym. Run something like
   this to see:

  xmodmap -pk | egrep -i 'KeyCode|less|greater'
  There are 4 KeySyms per KeyCode; KeyCodes range from 8 to 255.
      KeyCode     Keysym (Keysym) ...
       59         0x002c (comma)  0x003c (less)
       60         0x002e (period) 0x003e (greater)
       94         0x003c (less)   0x003e (greater)

   That keycode 94 is the special key with both "<" and ">". When x11vnc
   receives the "<" keysym over the wire from the remote VNC client, it
   unfortunately maps it to keycode 94 instead of 59, and sends 94 to the
   X server. Since Shift is down (i.e. you are Shifting the comma key),
   the X server interprets this as Shifted-94, which is ">".

   A workaround in the X server configuration is to "deaden" that special
   key:

  xmodmap -e "keycode 94 = "

   However, one user said he had to do this:

  xmodmap -e "keycode 94 = 0x002c 0x003c"

   (If the numerical values are different for your setup, substitute the
   ones that correspond to your display. The above xmodmap scheme can
   often be used to work around other ambiguous keysym to keycode
   mappings).

   Alternatively, here are some x11vnc options to try to work around the
   problem:
   -modtweak

   and
   -remap less-comma

   These are convenient in that they do not modify the actual X server
   settings. The former is a mode that monitors the state of the Shift
   and AltGr modifiers and tries to deduce the correct keycode sequence
   to send. The latter is an immediate remapping of the keysym less to
   the keysym comma when it comes in from a client (so when Shift is down
   the comma press will yield "<").

   See also the [116]FAQ about the -xkb option as a possible workaround
   using the XKEYBOARD extension. Note that of Jul/2004 in the
   libvncserver CVS the -modtweak option is now that default.

   Note that the -debug_keyboard option prints out much info for every
   keystroke to aid debugging keyboard problems.

   Q-41: I'm using an "international" keyboard (e.g. German "de", or
   Danish "dk") and the -modtweak mode works well if the VNC viewer is
   run on a Unix/Linux machine with a similar keyboard. But if I run the
   VNC viewer on Unix/Linux with a different keyboard (e.g. "us") or
   Windows with any keyboard, I can't type some keys like: "@", "$", "<",
   ">", etc. How can I fix this?

   The problem with Windows is it does not seem to handle AltGr well. It
   seems to fake it up by sending Control_L+Alt_R to applications. The
   Windows VNC viewer sends those two down keystrokes out on the wire to
   the VNC server, but when the user types the next key to get, e.g., "@"
   the Windows VNC viewer sends events bringing the up the
   Control_L+Alt_R keys, and then sends the "@" keysym by itself.

   The Unix/Linux VNC viewer on a "us" keyboard does a similar thing
   since "@" is the Shift of the "2" key. The keysyms Shift and "@" are
   sent to the VNC server.

   In both cases no AltGr is sent to the VNC server, but we know AltGr is
   needed on the physical international keyboard to type a "@".

   This all worked fine with x11vnc running with the -modtweak option (it
   figures out how to adjust the Modifier keys (Shift or AltGr) to get
   the "@"). However it fails under recent versions of XFree86 (and the
   X.org fork). These run the XKEYBOARD extension by default and make
   heavy use of it to handle international keyboards.

   To make a long story short, on these newer XFree86 setups the
   traditional X keymap lookup x11vnc uses is no longer accurate. x11vnc
   can't find the keysym "@" anywhere in the keymapping! (even though it
   is in the XKEYBOARD extended keymapping).

   How to Solve: As of Jul/2004 in the libvncserver CVS x11vnc has two
   changes:
     * -modtweak (tweak Modifier keys) is now the default (use
       -nomodtweak to go back to the old way)
     * there is a new option -xkb to use the XKEYBOARD extension API to
       do the Modifier key tweaking.

   The -xkb option seems to fix all of the missing keys: "@", "<", ">",
   etc.: it is recommended that you try it if you have this sort of
   problem. Let us know if there are any remaining problems (see the next
   paragraph for some known problems). If you specify the -debug_keyboard
   (aka -dk) option twice you will get a huge amount of keystroke
   debugging output (send it along with any problems you report).

   Known problems:
     * One user had to disable a "ghost" Mode_switch key that was causing
       problems under -xkb. His physical AltGr key was bound to
       ISO_Level3_Shift (which seems to be the XKEYBOARD way of doing
       things), while there was a ghost key Mode_switch (which seems to
       be obsolete) in the mapping as well. Both of these keysyms were
       bound to Mod5 and x11vnc was unfortunately choosing Mode_switch.
       From the x11vnc -xkb -dk -dk output it was noted that Mode_switch
       was attached to keycode 93 (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:
       -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 -remap x11vnc option:
  -remap asciitilde-dead_tilde,asciicircum-dead_circumflex
       etc. Use -remap filename if the list is long. Please send us your
       workarounds for this problem on your keyboard. Perhaps we can have
       x11vnc adjust automatically at some point.
     * To complement the above workaround using the -remap, an option
       -add_keysyms was added. This option instructs x11vnc to bind any
       unknown Keysyms coming in from VNC viewers to unused Keycodes in
       the X server. This modifies the global state of the X server. When
       x11vnc exits it removes the extra keymappings it created. Note
       that the -remap mappings are applied first, right when the Keysym
       is received from a VNC viewer, and only after that would
       -add_keysyms, or anything else, come into play.

   Q-42: When typing I sometimes get double, triple, or more of my
   keystrokes repeated. I'm sure I only typed them once, what can I do?

   This may be due to an interplay between your X server's key autorepeat
   delay and the extra time delays caused by x11vnc processing.

   Short answer: disable key autorepeating by running the command "xset r
   off" on the Xserver where x11vnc is run (restore via "xset r on") or
   use the new (Jul/2004) -norepeat x11vnc option. You will still have
   autorepeating because that is taken care of on your VNC viewer side.

   Details: suppose you press a key DOWN and it generates changes in
   large regions of the screen. The CPU and I/O work x11vnc does for the
   large screen change could be longer than your X server's key
   autorepeat delay. x11vnc may not get to processing the key UP event
   until after the screen work is completed. The X server believes the
   key has been held down all this time, and applies its autorepeat
   rules.

   Even without inducing changes in large regions of the screen, this
   problem could arise when accessing x11vnc via a dialup modem or
   otherwise high latency link (e.g. > 250 ms latency).

   Look at the output of "xset q" for the "auto repeat delay" setting. Is
   it low (e.g. < 500 ms)? If you increase it to a very large delay, e.g.
   "xset r rate 1500" or turn off autorepeat completely: "xset r off",
   does the problem go away?

   We are looking into a good way to fix this, but in the meantime as a
   workaround try to use xset r rate N for large enough delay N or xset r
   off to get rid of the problem. Also, as of Jul/2004 in the
   libvncserver CVS there is the -norepeat option to automatically
   disable autorepeating in the X server whenever VNC viewers are
   attached. Note that the VNC viewer side of the connection will (nearly
   always) do its own autorepeating so there is no big loss here, unless
   someone is also working at the physical display and misses his
   autorepeating.

   Q-43: The machine where I run x11vnc has an AltGr key, but the local
   machine where I run the VNC viewer does not. Is there a way I can map
   a local unused key to send an AltGr? How about a Compose key as well?

   Something like "-remap Super_R-Mode_switch" x11vnc option may work.
   Note that Super_R is the "Right Windoze(tm) Flaggie" key; you may want
   to choose another. The -debug_keyboard option comes in handy in
   finding keysym names (so does xev(1)).

   For Compose how about "-remap Menu-Multi_key" (note that Multi_key is
   the official name for Compose) To do both at the same time: "-remap
   Super_R-Mode_switch,Menu-Multi_key" or use "-remap filename" to
   specify remappings from a file.

   Q-44: I have a Sun machine I run x11vnc on. Its Sun keyboard has just
   one Alt key labelled "Alt" and two Meta keys labelled with little
   diamonds. The machine where I run the VNC viewer only has Alt keys.
   How can I send a Meta keypress? (e.g. emacs needs this)

   Here are a couple ideas. The first one is to simply use xmodmap(1) to
   adjust the Sun X server. Perhaps xmodmap -e "keysym Alt_L = Meta_L
   Alt_L" will do the trick. (there are other ways to do it, one user
   used: xmodmap -e "keycode 26 = Meta_L" for his setup).

   Since xmodmap(1) modifies the X server mappings you may not want to do
   this (because it affects local work on that machine). Something like
   the -remap Alt_L-Meta_L to x11vnc may be sufficient for ones needs,
   and does not modify the X server environment. Note that you cannot
   send Alt_L in this case, maybe -remap Super_L-Meta_L would be a better
   choice.

   Q-45: Can I map a keystroke to a mouse button click on the remote
   machine?

   This can be done directly in some X servers using AccessX and
   Pointer_EnableKeys, but is a bit awkward. It may be more convenient to
   have x11vnc do the remapping. This can be done via the -remap option
   using the fake "keysyms" Button1, Button2, etc. as the "to" keys (i.e.
   the ones after the "-")

   As an example, consider a laptop that has a touchpad with only two
   buttons. It is difficult to do a middle button "paste" because (using
   XFree86 Emulate3Buttons) you have to click both buttons on the touch
   pad at the same time. This remapping:
  -remap Super_R-Button2

   maps the Super_R "flag" key press to the Button2 click, thereby making
   pasting a bit easier.

   Note that once the key goes down, the button down and button up events
   are generated immediately on the x11vnc side. When the key is released
   (i.e. goes up) no events are generated.

   Q-46: The remote display is larger (in number of pixels) than the
   local display I am running the vncviewer on. I don't like the
   vncviewer scrollbars, what I can do?

   vncviewer has a option (usually accessible via F8 key or -fullscreen
   option) for vncviewer to run in full screen, where it will
   automatically scroll when the mouse is near the edge of the current
   view. For quick scrolling, also make sure Backing Store is enabled on
   the machine vncviewer is run on. (XFree86 disables it by default for
   some reason, add Option "backingstore" to XF86Config on the vncviewer
   side).

   BTW, contact me if you are having problems with vncviewer in
   fullscreen mode with your window manager (i.e. no keyboard response).
   I have a workaround for vncviewer using XGrabServer().

   There may also be scaling viewers out there (e.g. TightVNC on Windows)
   that automatically shrink or expand the remote framebuffer to fit the
   local display. Especially for hand-held devices. See also [117]this
   FAQ

   Q-47: Does x11vnc support server-side framebuffer scaling? (E.g. to
   make the desktop smaller).

   As of Jun/2004 in the libvncserver CVS x11vnc provides basic
   server-side scaling. It is a global scaling of the desktop, not a
   per-client setting. To enable it use the "-scale fraction" option.
   "fraction" can either be a floating point number (e.g. -scale 0.5) or
   the alternative m/n fraction notation (e.g. -scale 2/3).

   The current implementation is experimental in that it still needs to
   be optimized. 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).

   In general for a scaled display if you are using a TightVNC viewer you
   may want to turn off jpeg encoding (e.g. vncviewer -nojpeg host:0).
   There appears to be a noise enhancement effect, especially for regions
   containing font/text: the scaling can introduce some pixel artifacts
   that evidently causes the TightVNC to incorrectly detect the regions
   as image data and thereby introduce additional pixel artifacts due to
   the lossiness of the jpeg compression algorithm. Experiment to see if
   -nojpeg improves the readability of text when using -scale to shrink
   the display size. Also note that scaling may actually slow down the
   transfer of text regions because after being scaled they do not
   compress as well.

   Another issue is that it appears VNC viewers require the screen width
   to be a multiple of 4. When scaling x11vnc will round the width to the
   nearest multiple of 4. To disable this use the ":n4" sub option (like
   ":nb" in the previous paragraph; to specify both use a comma:
   ":nb,n4", etc.)

   If one desires per-client scaling for something like 1:1 from a
   workstation and 1:2 from a smaller device (e.g. handheld), currently
   the only option is to run two (or more) x11vnc processes with
   different scalings listening on separate ports (-rfbport option,
   etc.).

   Q-48: Does x11vnc work with Xinerama? (i.e. multiple monitors joined
   together to form one big, single screen).

   Yes, it should generally work because it simply polls the big
   effective screen. If the viewing-end monitor is not as big as the
   remote Xinerama display, then the vncviewer scrollbars, etc, will have
   to be used to pan across the large area.

   There are a couple potential issues however. If the screen is not
   rectangular (e.g. 1280x1024 and 1024x768 monitors joined together),
   then there will be "non-existent" areas on the screen. The X server
   will return "garbage" image data for these areas and so they may be
   distracting to the viewer. The -blackout x11vnc option allows you to
   blacken-out rectangles by specifying their WxH+X+Y geometries. If your
   system has the libXinerama library, the -xinerama x11vnc option can be
   used to have it automatically determine the rectangles to be blackened
   out. (Note on 8bpp PseudoColor displays the fill color may not be
   black).

   Some users have reported that the mouse does not behave properly for
   their Xinerama display: i.e. the mouse cannot be moved to all regions
   of the large display. If this happens try using the -xwarppointer
   option. This instructs x11vnc to fake mouse pointer motions using the
   XWarpPointer function instead of the XTestFakeMotionEvent XTEST
   function. (This may be due to a bug in the X server for XTEST when
   Xinerama is enabled).

   Q-49: Can I use x11vnc on a multi-headed display that is not Xinerama
   (i.e. separate screens :0.0, :0.1, ... for each monitor)?

   You can, but it is a little bit awkward: you must start separate
   x11vnc processes for each screen, and on the viewing end start up
   separate VNC viewer processes connecting to them. e.g. on the remote
   end:
  x11vnc -display :0.0 -bg -q -rfbport 5900
  x11vnc -display :0.1 -bg -q -rfbport 5901

   (this could be automated in the display manager Xsetup for example)
   and then on the local machine where you are sitting:
  vncviewer somehost:0 &
  vncviewer somehost:1 &

   Note: if you are running on Solaris 8 or earlier you can easily hit up
   against the maximum of 6 shm segments per process (for Xsun in this
   case) from running multiple x11vnc processes. You should modify
   /etc/system as mentioned in another [118]FAQ to increase the limit. It
   is probably also a good idea to run with the -onetile option in this
   case (to limit each x11vnc to 3 shm segments), or even -noshm to use
   no shm segments.

   Q-50: Why is the view in my VNC viewer completely black? Or why is
   everything flashing around randomly?

   See the next FAQ for a possible explanation.

   Q-51: I use Linux Virtual Consoles (VC's) to implement 'Fast User
   Switching' between users' sessions (e.g. Betty is on Ctrl-Alt-F7,
   Bobby is on Ctrl-Alt-F8, and Sid is on Ctrl-Alt-F1: they use those
   keystrokes to switch between their sessions). How come the view in a
   VNC viewer connecting to x11vnc is either completely black or
   otherwise all messed up unless the X session x11vnc is attached to is
   in the active VC?

   This seems to have to do with how applications (the X server processes
   in this case) must "play nicely" if they are not on the active VC.
   That is, they should not read from the keyboard or mouse or manage the
   video display unless they have the active VC. Given that it appears
   the XGetImage() call must ultimately retrieve the framebuffer data
   from the video hardware itself, it would make sense x11vnc's polling
   wouldn't work unless the X session had active control of the VC.

   There does not seem to be an easy way to work around this. Even xwd(1)
   doesn't work in this case (try it). Something would need to be done at
   a lower level, say in the XFree86 X server. Also, using the XFree86
   Shadow Framebuffer (a copy of the video framebuffer is kept in main
   memory) does not appear to fix the problem.

   If no one is sitting at the workstation and you just want to remotely
   switch the VC over to the one associated with your X session (so
   x11vnc can poll it), one can use the switchto(1) command, e.g.
   "switchto 7" for VC #7.

   Q-52: Does the Clipboard/Selection get transferred between the
   vncviewer and the X display?

   As of Jan/2004 in the libvncserver CVS x11vnc supports the "CutText"
   part of the rfb protocol. Furthermore, x11vnc is able to hold the
   PRIMARY selection (Xvnc does not seem to do this). If you don't want
   the Clipboard/Selection exchanged use the -nosel option. If you don't
   want the PRIMARY selection to be polled for changes use the -noprimary
   option.

   Q-53: Why don't I hear the "Beeps" in my X session (e.g. when typing
   tput bel in an xterm)?

   As of Dec/2003 in the libvncserver CVS "Beep" XBell events are tracked
   by default. The X server must support the XKEYBOARD extension (this is
   not on by default in Solaris, see Xserver(1) for how to turn it on),
   and so you won't hear them if the extension is not present.

   If you don't want to hear the beeps use the -nobell option. If you
   want to hear the audio from the remote applications, consider trying a
   redirector such as esd.

   Q-54: I am using x11vnc where my local machine has "popup/hidden
   taskbars" (e.g. GNOME or MacOS X) and the remote display where x11vnc
   runs also has "popup/hidden taskbars" (e.g. GNOME). When I move the
   mouse to the edge of the screen where the popups happen, the taskbars
   interfere and fight with each other in strange ways. What can I do?

   No useful answer so far. Is there a way to temporarily disable one or
   both of these magic desktop taskbars?

References

   1. http://www.karlrunge.com/x11vnc/index.html#faq
   2. http://www.karlrunge.com/x11vnc/index.html#downloading
   3. http://www.karlrunge.com/x11vnc/index.html#building
   4. http://www.uk.research.att.com/vnc/
   5. http://www.realvnc.com/
   6. http://www.tightvnc.com/
   7. http://www.karlrunge.com/x11vnc/index.html#downloading
   8. http://www.sun.com/software/solaris/freeware/
   9. http://www.karlrunge.com/x11vnc/x11vnc_opts.html
  10. http://www.karlrunge.com/x11vnc/index.html#accept
  11. http://www.karlrunge.com/x11vnc/index.html#passwd
  12. http://www.karlrunge.com/x11vnc/index.html#passwdfile
  13. http://sourceforge.net/projects/libvncserver/
  14. http://sourceforge.net/project/showfiles.php?group_id=32584&package_id=119006&release_id=257442
  15. http://www.karlrunge.com/x11vnc/x11vnc.c
  16. http://www.karlrunge.com/x11vnc/index.html#binaries
  17. http://www.karlrunge.com/x11vnc/rx11vnc
  18. http://www.karlrunge.com/x11vnc/rx11vnc.pl
  19. ftp://ftp.uu.net/graphics/jpeg/
  20. http://www.gzip.org/zlib/
  21. http://www.sunfreeware.com/
  22. http://www.tightvnc.com/
  23. http://www.karlrunge.com/x11vnc/x11vnc_opts.html
  24. http://www.karlrunge.com/x11vnc/index.html#passwd
  25. http://wwws.sun.com/sunray/index.html
  26. mailto:xvml@karlrunge.com
  27. http://www.karlrunge.com/x11vnc/index.html#FAQ-1
  28. http://www.karlrunge.com/x11vnc/index.html#FAQ-2
  29. http://www.karlrunge.com/x11vnc/index.html#FAQ-3
  30. http://www.karlrunge.com/x11vnc/index.html#FAQ-4
  31. http://www.karlrunge.com/x11vnc/index.html#FAQ-5
  32. http://www.karlrunge.com/x11vnc/index.html#FAQ-6
  33. http://www.karlrunge.com/x11vnc/index.html#FAQ-7
  34. http://www.karlrunge.com/x11vnc/index.html#FAQ-8
  35. http://www.karlrunge.com/x11vnc/index.html#FAQ-9
  36. http://www.karlrunge.com/x11vnc/index.html#FAQ-10
  37. http://www.karlrunge.com/x11vnc/index.html#FAQ-11
  38. http://www.karlrunge.com/x11vnc/index.html#FAQ-12
  39. http://www.karlrunge.com/x11vnc/index.html#FAQ-13
  40. http://www.karlrunge.com/x11vnc/index.html#FAQ-14
  41. http://www.karlrunge.com/x11vnc/index.html#FAQ-15
  42. http://www.karlrunge.com/x11vnc/index.html#FAQ-16
  43. http://www.karlrunge.com/x11vnc/index.html#FAQ-17
  44. http://www.karlrunge.com/x11vnc/index.html#FAQ-18
  45. http://www.karlrunge.com/x11vnc/index.html#FAQ-19
  46. http://www.karlrunge.com/x11vnc/index.html#FAQ-20
  47. http://www.karlrunge.com/x11vnc/index.html#FAQ-21
  48. http://www.karlrunge.com/x11vnc/index.html#FAQ-22
  49. http://www.karlrunge.com/x11vnc/index.html#FAQ-23
  50. http://www.karlrunge.com/x11vnc/index.html#FAQ-24
  51. http://www.karlrunge.com/x11vnc/index.html#FAQ-25
  52. http://www.karlrunge.com/x11vnc/index.html#FAQ-26
  53. http://www.karlrunge.com/x11vnc/index.html#FAQ-27
  54. http://www.karlrunge.com/x11vnc/index.html#FAQ-28
  55. http://www.karlrunge.com/x11vnc/index.html#FAQ-29
  56. http://www.karlrunge.com/x11vnc/index.html#FAQ-30
  57. http://www.karlrunge.com/x11vnc/index.html#FAQ-31
  58. http://www.karlrunge.com/x11vnc/index.html#FAQ-32
  59. http://www.karlrunge.com/x11vnc/index.html#FAQ-33
  60. http://www.karlrunge.com/x11vnc/index.html#FAQ-34
  61. http://www.karlrunge.com/x11vnc/index.html#FAQ-35
  62. http://www.karlrunge.com/x11vnc/index.html#FAQ-36
  63. http://www.karlrunge.com/x11vnc/index.html#FAQ-37
  64. http://www.karlrunge.com/x11vnc/index.html#FAQ-38
  65. http://www.karlrunge.com/x11vnc/index.html#FAQ-39
  66. http://www.karlrunge.com/x11vnc/index.html#FAQ-40
  67. http://www.karlrunge.com/x11vnc/index.html#FAQ-41
  68. http://www.karlrunge.com/x11vnc/index.html#FAQ-42
  69. http://www.karlrunge.com/x11vnc/index.html#FAQ-43
  70. http://www.karlrunge.com/x11vnc/index.html#FAQ-44
  71. http://www.karlrunge.com/x11vnc/index.html#FAQ-45
  72. http://www.karlrunge.com/x11vnc/index.html#FAQ-46
  73. http://www.karlrunge.com/x11vnc/index.html#FAQ-47
  74. http://www.karlrunge.com/x11vnc/index.html#FAQ-48
  75. http://www.karlrunge.com/x11vnc/index.html#FAQ-49
  76. http://www.karlrunge.com/x11vnc/index.html#FAQ-50
  77. http://www.karlrunge.com/x11vnc/index.html#FAQ-51
  78. http://www.karlrunge.com/x11vnc/index.html#FAQ-52
  79. http://www.karlrunge.com/x11vnc/index.html#FAQ-53
  80. http://www.karlrunge.com/x11vnc/index.html#FAQ-54
  81. http://www.karlrunge.com/x11vnc/index.html#building
  82. http://www.karlrunge.com/x11vnc/index.html#buildfaq
  83. http://packages.debian.org/x11vnc
  84. http://www.linuxpackages.net/search_view.php?by=name&name=x11vnc
  85. http://dag.wieers.com/packages/x11vnc/
  86. http://www.bell-labs.com/project/wwexptools/packages.html
  87. http://www.karlrunge.com/x11vnc/x11vnc_opts.html
  88. http://www.karlrunge.com/x11vnc/index.html#passwd
  89. http://fredrik.hubbe.net/x2vnc.html
  90. http://www.hubbe.net/~hubbe/win2vnc.html
  91. http://www.deboer.gmxhome.de/
  92. http://sourceforge.net/projects/win2vnc/
  93. http://fredrik.hubbe.net/x2vnc.html
  94. http://freshmeat.net/projects/x2x/
  95. http://ftp.digital.com/pub/Digital/SRC/x2x/
  96. http://zapek.com/software/zvnc/
  97. http://www.karlrunge.com/x11vnc/index.html#8bpp
  98. http://www.karlrunge.com/x11vnc/overlays
  99. http://www.karlrunge.com/x11vnc/index.html#inetd
 100. ftp://ftp.x.org/
 101. http://www.karlrunge.com/x11vnc/dtVncPopup
 102. http://www.karlrunge.com/x11vnc/index.html#passwdfile
 103. http://www.karlrunge.com/x11vnc/index.html#tunnelling
 104. http://www.karlrunge.com/x11vnc/index.html#tunnelling
 105. http://www.karlrunge.com/x11vnc/index.html#tunnelling
 106. http://www.karlrunge.com/x11vnc/index.html#tunnelling
 107. http://www.karlrunge.com/x11vnc/blockdpy.c
 108. http://www.karlrunge.com/x11vnc/x11vnc.c
 109. http://www.karlrunge.com/x11vnc/x11vnc_loop
 110. http://www.tightvnc.com/
 111. http://www.karlrunge.com/x11vnc/shm_clear
 112. http://www.karlrunge.com/x11vnc/index.html#noshm
 113. http://www.tightvnc.com/
 114. http://www.karlrunge.com/x11vnc/index.html#greaterless
 115. http://www.karlrunge.com/x11vnc/index.html#xkbmodtweak
 116. http://www.karlrunge.com/x11vnc/index.html#xkbmodtweak
 117. http://www.karlrunge.com/x11vnc/index.html#scaling
 118. http://www.karlrunge.com/x11vnc/index.html#solshm


=======================================================================
http://www.karlrunge.com/x11vnc/x11vnc_opts.html:

     _________________________________________________________________

x11vnc: a VNC server for real X displays

   Here are all of x11vnc command line options:
% x11vnc -help

x11vnc: allow VNC connections to real X11 displays. 0.6.3pre lastmod: 2004-08-2
9

Typical usage is:

   Run this command in a shell on the remote machine "far-host"
   with X session you wish to view:

       x11vnc -display :0

   Then run this in another window on the machine you are sitting at:

       vncviewer far-host:0

Once x11vnc establishes connections with the X11 server and starts
listening as a VNC server it will print out a string: PORT=XXXX where
XXXX is typically 5900 (the default VNC port).  One would next run something
like this on the local machine: "vncviewer host:N" where N is XXXX - 5900,
i.e. usually "vncviewer host:0"

By default x11vnc will not allow the screen to be shared and it will
exit as soon as a client disconnects.  See -shared and -forever below
to override these protections.

For additional info see: http://www.karlrunge.com/x11vnc/
                    and  http://www.karlrunge.com/x11vnc/#faq


Rudimentary config file support: if the file $HOME/.x11vncrc exists then each
line in it is treated as a single command line option.  Disable with -norc.
For each option name, the leading character "-" is not required.  E.g. a
line that is either "nap" or "-nap" may be used and are equivalent.
Likewise "wait 100" or "-wait 100" are acceptable and equivalent lines.
The "#" character comments out to the end of the line in the usual way.
Leading and trailing whitespace is trimmed off.  Lines may be continued with
a "\" as the last character of a line (it becomes a space character).

Options:

-display disp          X11 server display to connect to, usually :0.  The X
                       server process must be running on same machine and
                       support MIT-SHM.  Equivalent to setting the DISPLAY
                       environment variable to "disp".
-auth file             Set the X authority file to be "file", equivalent to
                       setting the XAUTHORITY environment varirable to "file"
                       before startup.  See Xsecurity(7), xauth(1) man pages.

-id windowid           Show the window corresponding to "windowid" not
                       the entire display.  New windows like popup menus,
                       etc may not be seen, or will be clipped.  x11vnc may
                       crash if the window changes size, is iconified, etc.
                       Use xwininfo(1) to get the window id.  Primarily useful
                       for exporting very simple applications.
-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.
-flashcmap             In 8bpp indexed color, let the installed colormap flash
                       as the pointer moves from window to window (slow).
-notruecolor           For 8bpp displays, force indexed color (i.e. a colormap)
                       even if it looks like 8bpp TrueColor. (rare problem)
-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 (it uses
                       XReadScreen(3X11)).  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, say).  Also note that,
                       the mouse cursor shape is exactly correct in this mode.

                       Use -overlay as a workaround for situations like these:
                       Some legacy applications require the default visual
                       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 messed
                       up in x11vnc unless -overlay is used.

                       Under -overlay, performance will be somewhat degraded
                       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 (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.
-visual n              Experimental option: probably does not do what you
                       think.  It simply *forces* the visual used for the
                       framebuffer; this may be a bad thing... It is useful for
                       testing and for some workarounds.  n may be a decimal
                       number, or 0x hex.  Run xdpyinfo(1) for the values.
                       One may also use "TrueColor", etc. see <X11/X.h>
                       for a list.  If the string ends in ":m" for better
                       or for worse the visual depth is forced to be m.

-scale fraction        Scale the framebuffer by factor "fraction".
                       Values less than 1 shrink the fb.  Note: image may not
                       be sharp and response may be slower.  Currently the
                       cursor shape is not scaled.  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).  For compatibility with vncviewers the scaled
                       width is adjusted to be a multiple of 4: to disable
                       this use ":n4".  More esoteric options: ":in" use
                       interpolation scheme even when shrinking, ":pad",
                       pad scaled width and height to be multiples of scaling
                       denominator (e.g. 3 for 2/3).

-viewonly              All VNC clients can only watch (default off).
-shared                VNC display is shared (default off).
-once                  Exit after the first successfully connected viewer
                       disconnects, opposite of -forever. This is the Default.
-forever               Keep listening for more connections rather than exiting
                       as soon as the first client(s) disconnect. Same as -many
-connect string        For use with "vncviewer -listen" reverse connections.
                       If "string" has the form "host" or "host:port"
                       the connection is made once at startup.  Use commas
                       for a list of host's and host:port's.  If "string"
                       contains "/" it is instead interpreted as a file to
                       periodically check for new hosts.  The first line is
                       read and then the file is truncated.
-vncconnect            Monitor the VNC_CONNECT X property set by the standard
-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.  Default: -vncconnect
-inetd                 Launched by inetd(1): stdio instead of listening socket.
                       Note: if you are not redirecting stderr to a log file
                       (via shell 2> or -o option) you must also specify the
                       -q option.

-allow addr1[,addr2..] Only allow client connections from IP addresses matching
                       the comma separated list of numerical addresses.
                       Can be a prefix, e.g. "192.168.100." to match a
                       simple subnet, for more control build libvncserver
                       with libwrap support.  If the list contains a "/"
                       it instead is a interpreted as a file containing
                       addresses or prefixes that is re-read each time a new
                       client connects.  Lines can be commented out with the
                       "#" character in the usual way.
-localhost             Same as -allow 127.0.0.1
-viewpasswd string     Supply a 2nd password for view-only logins.  The -passwd
                       (full-access) password must also be supplied.
-passwdfile filename   Specify libvncserver -passwd via the first line of
                       the file "filename" instead of via command line.
                       If a second non blank line exists in the file it is
                       taken as a view-only password (i.e. -viewpasswd) Note:
                       this is a simple plaintext passwd, see also -rfbauth
                       and -storepasswd below.
-storepasswd pass file Store password "pass" as the VNC password in the
                       file "file".  Once the password is stored the
                       program exits.  Use the password via "-rfbauth file"
-accept string         Run a command (possibly to prompt the user at the
                       X11 display) to decide whether an incoming client
                       should be allowed to connect or not.  "string" is
                       an external command run via system(3) or some special
                       cases described below.  Be sure to quote "string"
                       if it contains spaces, etc.  If the external command
                       returns 0 the client is accepted, otherwise the client
                       is rejected.  See below for an extension to accept a
                       client view-only.

                       Environment: The RFB_CLIENT_IP environment variable will
                       be set to the incoming client IP number and the port
                       in RFB_CLIENT_PORT (or -1 if unavailable).  Similarly,
                       RFB_SERVER_IP and RFB_SERVER_PORT (the x11vnc side
                       of the connection), are set to allow identification
                       of the tcp virtual circuit.  The x11vnc process
                       id will be in RFB_X11VNC_PID, a client id number in
                       RFB_CLIENT_ID, and the number of other connected clients
                       in RFB_CLIENT_COUNT.

                       If "string" is "popup" then a builtin popup window
                       is used.  The popup will time out after 120 seconds,
                       use "popup:N" to modify the timeout to N seconds
                       (use 0 for no timeout)

                       If "string" is "xmessage" then an xmessage(1)
                       invocation is used for the command.

                       Both "popup" and "xmessage" will present an option
                       for accepting the client "View-Only" (the client
                       can only watch).  This option will not be presented if
                       -viewonly has been specified, in which case the entire
                       display is view only.

                       If the user supplied command is prefixed with something
                       like "yes:0,no:*,view:3 mycommand ..." then this
                       associates the numerical command return code with
                       the actions: accept, reject, and accept-view-only,
                       respectively.  Use "*" instead of a number to indicate
                       the default action (in case the command returns an
                       unexpected value).  E.g. "no:*" is a good choice.

                       Note that x11vnc blocks while the external command or
                       or popup is running (other clients may see no updates
                       during this period).

                       More -accept tricks: use "popupmouse" to only allow
                       mouse clicks in the builtin popup to be recognized.
                       Similarly use "popupkey" to only recognize keystroke
                       responses.  All 3 of the popup keywords can be followed
                       by +N+M to supply a position for the popup window.
                       The default is to center the popup window.
-gone string           As -accept, except to run a user supplied command when
                       a client goes away (disconnects).  Unlike -accept,
                       the command return code is not interpreted by x11vnc.

-noshm                 Do not use the MIT-SHM extension for the polling.
                       Remote displays can be polled this way: be careful this
                       can use large amounts of network bandwidth.  This is
                       also of use if the local machine has a limited number
                       of shm segments and -onetile is not sufficient.
-flipbyteorder         Sometimes needed if remotely polled host has different
                       endianness.  Ignored unless -noshm is set.
-onetile               Do not use the new copy_tiles() framebuffer mechanism,
                       just use 1 shm tile for polling.  Limits shm segments
                       used to 3.

-blackout string       Black out rectangles on the screen. "string" is a
                       comma separated list of WxH+X+Y type geometries for
                       each rectangle.
-xinerama              If your screen is composed of multiple monitors
                       glued together via XINERAMA, and that screen is
                       non-rectangular this option will try to guess the
                       areas to black out (if your system has libXinerama).
                       In general on XINERAMA displays you may need to use the
                       -xwarppointer option if the mouse pointer misbehaves.

-o logfile             Write stderr messages to file "logfile" instead of
                       to the terminal.  Same as -logfile "file".
-rc filename           Use "filename" instead of $HOME/.x11vncrc for rc file.
-norc                  Do not process any .x11vncrc file for options.
-h, -help              Print this help text.
-V, -version           Print program version (last modification date).

-q                     Be quiet by printing less informational output to
                       stderr.  Same as -quiet.
-bg                    Go into the background after screen setup.  Messages to
                       stderr are lost unless -o logfile is used.  Something
                       like this could be useful in a script:
                         port=`ssh $host "x11vnc -display :0 -bg" | grep PORT`
                         port=`echo "$port" | sed -e 's/PORT=//'`
                         port=`expr $port - 5900`
                         vncviewer $host:$port

-modtweak              Option -modtweak automatically tries to adjust the AltGr
-nomodtweak            and Shift modifiers for differing language keyboards
                       between client and host.  Otherwise, only a single key
                       press/release of a Keycode is simulated (i.e. ignoring
                       the state of the modifiers: this usually works for
                       identical keyboards).  Also useful in resolving cases
                       where a Keysym is bound to multiple keys (e.g. "<" + ">"
                       and "," + "<" keys).  Default: -modtweak
-xkb                   When in modtweak mode, use the XKEYBOARD extension
                       (if it exists) to do the modifier tweaking.  This is
                       powerful and should be tried if there are still
                       keymapping problems when using the simpler -modtweak.
-skip_keycodes string  Skip keycodes not on your keyboard but your X server
                       thinks exist.  Currently only applies to -xkb mode.
                       "string" is a comma separated list of decimal
                       keycodes.  Use this option to help x11vnc in the reverse
                       problem it tries to solve: Keysym -> Keycode(s) when
                       ambiguities exist.  E.g. -skip_keycodes 94,114
-add_keysyms           If a Keysym is received from a VNC viewer and
                       that Keysym does not exist in the X server, then
                       add the Keysym to the X server's keyboard mapping.
                       Added Keysyms will be removed when exiting.
-clear_mods            At startup and exit clear the modifier keys by sending
                       KeyRelease for each one. The Lock modifiers are skipped.
                       Used to clear the state if the display was accidentally
                       left with any pressed down.
-clear_keys            As -clear_mods, except try to release any pressed key.
                       Note that this option and -clear_mods can interfere
                       with a person typing at the physical keyboard.
-remap string          Read Keysym remappings from file named "string".
                       Format is one pair of Keysyms per line (can be name
                       or hex value) separated by a space.  If no file named
                       "string" exists, it is instead interpreted as this
                       form: key1-key2,key3-key4,...  See <X11/keysymdef.h>
                       header file for a list of Keysym names, or use
                       xev(1). To map a key to a button click, use the
                       fake Keysyms "Button1", ..., etc.
                       E.g. -remap Super_R-Button2
-norepeat              Option -norepeat disables X server key auto repeat
-repeat                when VNC clients are connected.  This works around a
                       repeating keystrokes bug (triggered by long processing
                       delays between key down and key up client events:
                       either from large screen changes or high latency).
                       Note: your VNC viewer side will likely do autorepeating,
                       so this is no loss unless someone is simultaneously at
                       the real X display.  Default: -repeat

-nofb                  Ignore video framebuffer: only process keyboard and
                       pointer.  Intended for use with Win2VNC and x2vnc
                       dual-monitor setups.
-nobell                Do not watch for XBell events. (no beeps will be heard)
                       Note: XBell monitoring requires the XKEYBOARD extension.
-nosel                 Do not manage exchange of X selection/cutbuffer between
                       VNC viewers and the X server.
-noprimary             Do not poll the PRIMARY selection for changes to send
                       back to clients.  (PRIMARY is still set on received
                       changes, however).

-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).  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 requires
                       the SUN_OVL extension and the -overlay option to be
                       supplied. (see also the -overlay_nomouse option). (Soon)
                       on XFree86/Xorg the XFIXES extension is required.
                       Either can be disabled with -nocursor, and also some
                       values of the "mode" option below.

                       The "mode" string can be used to fine-tune the
                       displaying of cursor shapes.  It can be used the
                       following ways:

                       "-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".
                       On Solaris if XFIXES is not available, -overlay mode
                       will be used.

-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 XTEST
                       extension.  Use this as a workaround if the pointer
                       motion behaves incorrectly, e.g.  on touchscreens or
                       other non-standard setups.  Also sometimes needed on
                       XINERAMA displays.

-buttonmap string      String to remap mouse buttons.  Format: IJK-LMN, this
                       maps buttons I -> L, etc., e.g.  -buttonmap 13-31

                       Button presses can also be mapped to keystrokes: replace
                       a button digit on the right of the dash with :<sym>:
                       or :<sym1>+<sym2>: etc. for multiple keys. For example,
                       if the viewing machine has a mouse-wheel (buttons 4 5)
                       but the x11vnc side does not, these will do scrolls:
                              -buttonmap 12345-123:Prior::Next:
                              -buttonmap 12345-123:Up+Up+Up::Down+Down+Down:

                       See <X11/keysymdef.h> header file for a list of Keysyms,
                       or use the xev(1) program.  Note: mapping of button
                       clicks to Keysyms may not work if -modtweak or -xkb is
                       needed for the Keysym.

                       If you include a modifier like "Shift_L" the
                       modifier's up/down state is toggled, e.g. to send
                       "The" use :Shift_L+t+Shift_L+h+e: (the 1st one is
                       shift down and the 2nd one is shift up). (note: the
                       initial state of the modifier is ignored and not reset)
                       To include button events use "Button1", ... etc.

-nodragging            Do not update the display during mouse dragging events
                       (mouse motion with a button held down).  Greatly
                       improves response on slow setups, but you lose all
                       visual feedback for drags, text selection, and some
                       menu traversals.
-old_pointer           Do not use the new pointer input handling mechanisms.
                       See check_input() and pointer() in source file for
                       details.
-input_skip n          For the old pointer handling when non-threaded: try to
                       read n user input events before scanning display. n < 0
                       means to act as though there is always user input.

-debug_pointer         Print debugging output for every pointer event.
-debug_keyboard        Print debugging output for every keyboard event.
                       Same as -dp and -dk, respectively.  Use multiple
                       times for more output.

-defer time            Time in ms to wait for updates before sending to client
                       [rfbDeferUpdateTime]  Default: 30
-wait time             Time in ms to pause between screen polls.  Used to cut
                       down on load.  Default: 30
-nap                   Monitor activity and if low take longer naps between
                       polls to really cut down load when idle.  Default: off

-sigpipe string        Broken pipe (SIGPIPE) handling.  "string" can be
                       "ignore" or "exit".  For "ignore" libvncserver
                       will handle the abrupt loss of a client and continue,
                       for "exit" x11vnc will cleanup and exit at the 1st
                       broken connection.  Default: "ignore".
-threads               Whether or not to use the threaded libvncserver
-nothreads             algorithm [rfbRunEventLoop] if libpthread is available
                       Default: -nothreads

-fs f                  If the fraction of changed tiles in a poll is greater
                       than f, the whole screen is updated.  Default: 0.75
-gaps n                Heuristic to fill in gaps in rows or cols of n or
                       less tiles.  Used to improve text paging.  Default: 4
-grow n                Heuristic to grow islands of changed tiles n or wider
                       by checking the tile near the boundary.  Default: 3
-fuzz n                Tolerance in pixels to mark a tiles edges as changed.
                       Default: 2


These options are passed to libvncserver:

-rfbport port          TCP port for RFB protocol
-rfbwait time          max time in ms to wait for RFB client
-rfbauth passwd-file   use authentication on RFB protocol
                       (use 'storepasswd' to create a password file)
-passwd plain-password use authentication 
                       (use plain-password as password, USE AT YOUR RISK)
-deferupdate time      time in ms to defer updates (default 40)
-desktop name          VNC desktop name (default "LibVNCServer")
-alwaysshared          always treat new clients as shared
-nevershared           never treat new clients as shared
-dontdisconnect        don't disconnect existing clients when a new non-shared
                       connection comes in (refuse new connection instead)
-httpdir dir-path      enable http server using dir-path home
-httpport portnum      use portnum for http connection
-enablehttpproxy       enable http proxy support
-progressive height    enable progressive updating for slow links

   Pretty wild huh? [1]Contact me if you have any questions or problems.

   Personally, I use:
x11vnc -rfbauth $HOME/.vnc/passwd -nap -flashcmap -cursor X -norepeat -add_keys
yms

   (the -flashcmap only matters on old 8-bit X displays)

   [2]Back to main x11vnc page

References

   1. mailto:xvml@karlrunge.com
   2. http://www.karlrunge.com/x11vnc/index.html