path: root/x11vnc/README

x11vnc README file                         Date: Mon Feb 21 22:41:53 EST 2005

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. The [4]FAQ contains a lot of information and solutions
   to problems, but please feel free to [5]contact me if you have
   problems or questions.

    Background:

   VNC (Virtual Network Computing) 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:
     * [6]http://www.uk.research.att.com/vnc/
     * [7]http://www.realvnc.com
     * [8]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 (the
   exception is cached pixmap data on the viewing-end). Also, with no
   state maintained the viewing-end can crash, be rebooted, or relocated
   and the applications and desktop continue running. Not so with X11.

   So the standard Xvnc 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 ([9]see below) and have it available to run on
   far-away.east. Similarly, have a VNC viewer (e.g. vncviewer) ready to
   run on sitting-here.west. We recommend [10]TightVNC Viewers.

   Step 1. By some means log in to far-away.east and get a command shell
   running there. You can use ssh, rlogin, telnet, or any other method to
   do this. x11vnc needs to be run on the same machine the X server
   process is running on (otherwise things would be extremely slow).

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

  far-away> x11vnc -display :0

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

   To get X11 permissions right, you may also need to set the XAUTHORITY
   environment variable (or use the -auth option) to point to the correct
   MIT-MAGIC-COOKIE file (e.g. /home/joe/.Xauthority). More on this
   [11]below.

   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 under "Background:" on how to obtain a
   viewer for your platform or [12]this FAQ. For Solaris, vncviewer is
   available in the [13]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 [14]option to have
   it wait for additional viewer connections).

   Shortcut: Of course if you left x11vnc running in a terminal window or
   as a [15]service on far-away.east:0, you'd only have to do Step 3 as
   you moved around. Be sure to use a VNC [16]password or [17]other
   measures if you do that.

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

   For these cases it should be obvious how it is done. The above steps
   will work, but more easily the user sitting at far-away.east:0 simply
   starts up x11vnc from a terminal window, after which the guests would
   start their VNC viewers. For this usage mode the "-connect
   host1,host2" option may be of use automatically connect to vncviewers
   in "-listen" mode on the list of hosts.
     _________________________________________________________________

    Tunnelling x11vnc via ssh:

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

   Some VNC viewers will do the ssh tunnelling for you automatically, the
   TightVNC vncviewer does this when the "-via far-away.east" option is
   supplied to it (this requires x11vnc to be already running on
   far-away.east or having it started by [18]inetd(1)). See the 3rd
   script example [19]below for more info.

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

   Scripts to automate ssh tunneling: As discussed below, there may be
   some problems with port 5900 being available. If that happens, the
   above port and display numbers may change a bit (e.g. -> 5901 and :1).
   However, if you "know" port 5900 will be free on the local and remote
   machines, you can easily automate the above two steps by using the
   x11vnc option -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 -localhost -rfbauth .vnc/passwd"
enc="copyrect tight zrle hextile zlib corre rre raw"

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

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

   See also rx11vnc.pl below.
     _________________________________________________________________

   Another method is to start the VNC viewer in listen mode "vncviewer
   -listen" and have x11vnc initiate a 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 -localhost -connect localhost"   # <-- note new opt
ion
enc="copyrect tight zrle hextile zlib corre rre raw"

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

   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 -localhost -rfbport 5900 -display :$d
isp; sleep 5"
export VNC_VIA_CMD

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

   Of course if you already have the x11vnc running waiting for
   connections (or have it started out of [20]inetd(1)), you can simply
   use the TightVNC "vncviewer -via gateway host:port" in its default
   mode to provide secure ssh tunnelling.


   VNC password file: Also note in the 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 [21]-storepasswd
   option can be used to create the password file. x11vnc also has the
   slightly less secure [22]-passwdfile and "-passwd XXXXX" options.

   Important: 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,
   stunnel, VPN, etc. Also look into the -allow and -localhost
   [23]options and building x11vnc with [24]tcp_wrappers support to limit
   host access.
     _________________________________________________________________

    Downloading x11vnc:

   x11vnc is a contributed program to the [25]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 Dec 2004, the [26]x11vnc-0.7.tar.gz source package is
   released (recommended download) . The [27]x11vnc 0.7 release notes.

   The x11vnc package is the subset of the libvncserver package needed to
   build the x11vnc program. Also, you can get a copy of my latest,
   bleeding edge [28]x11vnc.c file to replace the one in the above
   packages or the one in the CVS tree and then rebuild. You can also
   update the tcl/tk gui with the [29]tkx11vnc.h file. If you have an
   older libvncserver source tree, you may need to switch on the OLD_TREE
   variable near the top of the x11vnc.c file.

   See the [30]FAQ below for information about where you might obtain a
   precompiled x11vnc binary from 3rd parties.

   To obtain VNC viewers for the viewing side (Windows, Mac OS, or Unix)
   try here:
     * [31]http://www.tightvnc.com/download.html
     * [32]http://www.realvnc.com/download-free.html
     * [33]http://sourceforge.net/projects/cotvnc/

   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:
     * [34]rx11vnc wrapper script
     * [35]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 0.7 release of x11vnc: replace
   with the version you downloaded):
(un-tar the x11vnc+libvncserver tarball)
# gzip -dc x11vnc-0.7.tar.gz | tar -xvf -

(cd to the source directory)
# cd x11vnc-0.7

(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 and
   ZRLE encoding support will be disabled, and you don't want that! (the
   TightVNC encoding gives very good compression and performance, it even
   makes a noticeable difference over a fast LAN)

   Shortcut: On Solaris 10 you can pick up everything just by insuring
   that your PATH has /usr/sfw/bin (for gcc) and /usr/ccs/bin (for other
   build tools), e.g.:

  env PATH=/usr/sfw/bin:/usr/ccs/bin:$PATH sh -c './configure; make'

   libjpeg is included in Solaris 9 and later (/usr/sfw/include and
   /usr/sfw/lib), and zlib in Solaris 8 and later (/usr/include and
   /usr/lib).

   So on Solaris 9 you can pick up everything with something like this:
  env PATH=/usr/local/bin:/usr/ccs/bin:$PATH CPPFLAGS='-I /usr/sfw/include' LDF
LAGS='-L/usr/sfw/lib -R/usr/sfw/lib' sh -c './configure; make'

   assuming your gcc is in /usr/local/bin. That is getting pretty long,
   see those assignments split up in the build script below.

   If your system does not have these libraries you can get the source
   for these libraries to build them: libjpeg is available at
   [36]ftp://ftp.uu.net/graphics/jpeg/ and zlib at
   [37]http://www.gzip.org/zlib/. See also
   [38]http://www.sunfreeware.com/ for Solaris binary packages of these
   libraries as well as for gcc. Normally they will install into
   /usr/local.

   Here is a build script that indicates one way to pass the library
   locations information to the libvncserver configuration via the
   CPPFLAGS and LDFLAGS environmental variables:
#!/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 your gcc

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

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

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

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

# This only applies to Solaris 10 or later (XFIXES, DAMAGE, and RANDR)
CPPFLAGS="$CPPFLAGS -I /usr/X11/include"
LDFLAGS="$LDFLAGS -L /usr/X11/lib -R /usr/X11/lib"
LDFLAGS="$LDFLAGS -L /usr/openwin/sfw/lib -R /usr/openwin/sfw/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 utilities 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.

   If you need to build on Solaris 2.5.1 or earlier, see [39]this
   workaround FAQ.

   Building on HP-UX:   For jpeg and zlib you will need to do the same
   sort of thing as described above for Solaris. You set CPPFLAGS and
   LDFLAGS to find them. You do not need to do any of the above
   /usr/openwin stuff. Also, HP-UX does not seem to support -R, so get
   rid of the -R items in LDFLAGS. Because of this, at runtime you may
   need to set LD_LIBRARY_PATH to indicate the directory paths so the
   libraries can be found.

   Finally, there seems to be a bug with gcc on HP-UX 11.xx: something
   fails (in the gcc private header files?) and it thinks it cannot find
   gettimeofday(). As a workaround add this to CPPFLAGS:
   -DLIBVNCSERVER_HAVE_GETTIMEOFDAY=1. You may get some warnings but we
   have verified that this generates working x11vnc binaries on HP-UX
   hppa and ia64.
     _________________________________________________________________

    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. (This
   is one place where the X protocol has an advantage over the VNC
   protocol.) I suggest using xsetroot, dtstyle or similar utility to set
   a solid background while using x11vnc. You can turn the pretty
   background image back on when you are using the display directly.
   Update: As of Feb/2005 in the libvncserver CVS, x11vnc has the -solid
   [color] option that works on recent GNOME and KDE and also on classic
   X (background image is on the root window).

   I also find the [40]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 where NNNN is the desired port number.

   Options:   x11vnc has (far too) many features that may be activated
   via its [41]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 [42]-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. If available, the
   XFIXES extension is used to retrieve the current mouse cursor shape.

   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 [43]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)
   [44]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 #1:   Note that even though your SunRay X11 DISPLAY is
   something like :137, x11vnc still tries for port 5900 as its listening
   port if it can get it, in which case the VNC display (i.e. the
   information you supply to the VNC viewer) is something like
   sunray-server:0   (note the :0 corresponding to port 5900, it is not
   :137). If it cannot get 5900, it tries for 5901, and so on. You can
   also try to force the port (and thereby the VNC display) using the
   -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 10-200, 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 0.5-1 sec 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 (5-100 times) by using the Shadow
       Framebuffer (a copy of the framebuffer is kept in main memory and
       this can be read much more quickly). To do this one puts the line
       Option "ShadowFB" "true" (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 slower speed while sitting at the physical display was
       acceptable (this seems to be true for most video cards these
       days). Unfortunately it does not seem shadowfb can be turned on
       and off dynamically...
     * 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 "-cursor
       some", 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. A similar thing is done on IRIX as well when -overlay is
       supplied. As of Dec/2004 x11vnc supports the XFIXES extension (in
       Xorg and Solaris 10) to query the X server for the exact cursor
       shape, this works pretty well except that cursors with
       transparency (alpha channel) need to approximated to solid RGB
       values.
     * 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 [45]contact me if you have any questions,
   problems, or comments about x11vnc, etc.
     _________________________________________________________________

    x11vnc FAQ:


   [Building and Starting]

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

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

   [48]Q-3: Help, I need to run x11vnc on Solaris 2.5.1 and it doesn't
   compile! 

   [49]Q-4: Where can I get a precompiled x11vnc binary for my Operating
   System? 

   [50]Q-5: Where can I get a VNC Viewer binary (or source code) for the
   Operating System I will be viewing from? 

   [51]Q-6: How can I see all of x11vnc's command line options and
   documentation on how to use them? 

   [52]Q-7: I don't like typing arcane command line options every time I
   start x11vnc. What can I do? Is there a config file? Or a GUI? 

   [53]Q-8: Can I make x11vnc more quiet and also go into the background
   after starting up? 

   [54]Q-9: 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. 

   [Win2VNC Related]

   [55]Q-10: 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? 

   [56]Q-11: 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 

   [Color Issues]

   [57]Q-12: 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. 

   [58]Q-13: 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. 

   [59]Q-14: How do I figure out the window id to supply to the -id
   windowid option? 

   [60]Q-15: Why don't menus or other transient windows come up when I am
   using the -id windowid option to view a single application window? 

   [61]Q-16: My X display is depth 24 at 24bpp (instead of the normal
   depth 24 at 32bpp). I'm having lots of color and visual problems with
   x11vnc and vncviewer. 

   [Xterminals]

   [62]Q-17: 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? 

   [63]Q-18: How do I get my X permissions (MIT-MAGIC-COOKIE) correct for
   a Unix/Linux machine acting as an Xterminal? 

   [Remote Control]

   [64]Q-19: How do I stop x11vnc once it is running in the background? 

   [65]Q-20: Can I change settings in x11vnc without having to restart
   it? Is there a way to remote control it? 

   [Security and Permissions]

   [66]Q-21: 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? 

   [67]Q-22: Can I limit which machines incoming VNC clients can connect
   from? 

   [68]Q-23: How do I build x11vnc/libvncserver with libwrap
   (tcp_wrappers) support? 

   [69]Q-24: 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? 

   [70]Q-25: How do I create a VNC password for use with x11vnc? 

   [71]Q-26: How can I tunnel my connection to x11vnc via an encrypted
   SSH channel between two Unix machines? 

   [72]Q-27: How can I tunnel my connection to x11vnc via an encrypted
   SSH channel from Windows using an SSH client like Putty? 

   [73]Q-28: Does x11vnc support Unix usernames and passwords? Can I
   further limit the set of Unix usernames who can connect to the VNC
   desktop? 

   [74]Q-29: Can I have two passwords for VNC viewers, one for full
   access and the other for view-only access to the display? 

   [75]Q-30: 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? 

   [76]Q-31: Can I have x11vnc automatically lock the screen when I
   disconnect the VNC viewer? 

   [Display Managers and Services]

   [77]Q-32: How can I run x11vnc as a "service" that is always
   available? 

   [78]Q-33: How can I use x11vnc to connect to an X login screen like
   xdm, GNOME gdm, KDE kdm, or CDE dtlogin? (i.e. nobody is logged into
   an X session yet). 

   [79]Q-34: Can I run x11vnc out of inetd(1)? How about xinetd(1)? 

   [80]Q-35: How do I make x11vnc work with the Java VNC viewer applet in
   a web browser? 

   [81]Q-36: Are reverse connections (i.e. the VNC server connecting to
   the VNC viewer) using "vncviewer -listen" and vncconnect(1) supported?
   
   [Resource Usage and Performance]

   [82]Q-37: 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)? 

   [83]Q-38: How can I make x11vnc use less system resources? 

   [84]Q-39: How can I make x11vnc use MORE system resources? 

   [85]Q-40: I use x11vnc over a slow link with high latency (e.g. dialup
   modem), is there anything I can do to speed things up? 

   [86]Q-41: 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? 

   [Mouse Cursor Shapes]

   [87]Q-42: Why isn't the mouse cursor shape (the little icon shape
   where the mouse pointer is) correct as I move from window to window? 

   [88]Q-43: When using XFIXES cursorshape mode, some of the cursors look
   really bad with extra black borders around the cursor and other cruft.
   How can I improve their appearance? 

   [89]Q-44: In XFIXES mode, are there any hacks to handle cursor
   transparency ("alpha channel") exactly? 

   [Mouse Pointer]

   [90]Q-45: Why does the mouse arrow just stay in one corner in my
   vncviewer, whereas my cursor (that does move) is just a dot? 

   [91]Q-46: 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)? 

   [92]Q-47: Is it possible to swap the mouse buttons (e.g. left-handed
   operation), or arbitrarily remap them? How about mapping button clicks
   to keystrokes, e.g. to partially emulate Mouse wheel scrolling? 

   [Keyboard Issues]

   [93]Q-48: How can I get my AltGr and Shift modifiers to work between
   keyboards for different languages? 

   [94]Q-49: When I try to type a "<" (i.e. less than) instead I get ">"
   (i.e. greater than)! Strangely, typing ">" works OK!! 

   [95]Q-50: 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? 

   [96]Q-51: 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? 

   [97]Q-52: The x11vnc -norepeat mode is in effect, but I still get
   repeated keystrokes!! 

   [98]Q-53: 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? 

   [99]Q-54: 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) 

   [100]Q-55: Can I map a keystroke to a mouse button click on the remote
   machine? 

   [Screen Related Issues and Features]

   [101]Q-56: 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? 

   [102]Q-57: Does x11vnc support server-side framebuffer scaling? (E.g.
   to make the desktop smaller). 

   [103]Q-58: Does x11vnc work with Xinerama? (i.e. multiple monitors
   joined together to form one big, single screen). 

   [104]Q-59: Can I use x11vnc on a multi-headed display that is not
   Xinerama (i.e. separate screens :0.0, :0.1, ... for each monitor)? 

   [105]Q-60: Does x11vnc support the XRANDR (X Resize, Rotate and
   Reflection) extension? Whenever I rotate or resize the screen x11vnc
   just seems to crash. 

   [106]Q-61: Why is the view in my VNC viewer completely black? Or why
   is everything flashing around randomly? 

   [107]Q-62: 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? 

   [108]Q-63: I am using x11vnc where my local machine has "popup/hidden
   taskbars" (e.g. GNOME or MacOS X) and the remote display where x11vnc
   runs also has "popup/hidden taskbars" (e.g. GNOME). When I move the
   mouse to the edge of the screen where the popups happen, the taskbars
   interfere and fight with each other in strange ways. What can I do? 

   [Misc: Clipboard, Beeps, etc.]

   [109]Q-64: Does the Clipboard/Selection get transferred between the
   vncviewer and the X display? 

   [110]Q-65: Why don't I hear the "Beeps" in my X session (e.g. when
   typing tput bel in an xterm)? 
     _________________________________________________________________


   [Building and Starting]

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

   For the former error, you need to specify the X display to connect to
   (it also needs to be on the same machine 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
   correctly. See the xauth(1), Xsecurity(7), and xhost(1) man pages for
   much info. For example, you may need to set your XAUTHORITY
   environment variable or use the -auth option to point to the correct
   cookie file (e.g. /home/joe/.Xauthority or /var/gdm/:0.Xauth), or
   simply be sure you run x11vnc as the correct user (i.e. the user who
   owns the X session you wish to view). Running x11vnc as root is not
   enough: you need to know where the XAUTHORITY file for the desired X
   display is. Example:
  x11vnc -display :0 -auth /var/gdm/:0.Xauth

   Less safe, but to avoid figuring out where the XAUTHORITY file is, if
   the person sitting at the X session types "xhost +localhost" then one
   should be able to attach x11vnc to the session (from the same
   machine). The person could then type "xhost -localhost" after x11vnc
   has connected to go back to the default permissions. Also, for some
   situations the -users lurk= option may be of use (please read the
   documentation on the -users option).

   Some Linux distributions or display managers may set XAUTHORITY to a
   random local filename. You need to dig out where they have hidden the
   MIT-MAGIC-COOKIE file (and set XAUTHORITY to it or use the -auth
   option). This command is often useful to find non-standard settings
   for XAUTHORITY:
  ps wwwweaux | tr ' ' '\n' | grep XAUTHORITY | sort -u

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

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

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

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

   After running the libvncserver configure, carefully examine the output
   and the messages in the config.log file looking for missing
   components. 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: Help, I need to run x11vnc on Solaris 2.5.1 and it doesn't
   compile!

   We apologize that x11vnc does not build cleanly on older versions of
   Solaris, Linux, etc.: very few users are on these old releases.

   We have heard that since Dec/2004 a Solaris 2.6 built x11vnc will run
   on Solaris Solaris 2.5 and 2.5.1 (since a workaround for XConvertCase
   is provided).

   In any event, here is a workaround for Solaris 2.5.1 (and perhaps
   earlier and perhaps non-Solaris):

   First use the environment settings (CPPFLAGS, LDFLAGS, etc.) in the
   above [111]Solaris build script to run the configure command. That
   should succeed without failure. Then, you have to hand edit the
   autogenerated rfb/rfbconfig.h file in the source tree, and just before
   the last #endif at the bottom of that file insert these workaround
   lines:
#ifndef usleep
struct timeval _tmp_usleep_tv;
#define usleep(x) \
    _tmp_usleep_tv.tv_sec  = (x) / 1000000; \
    _tmp_usleep_tv.tv_usec = (x) % 1000000; \
    select(0, NULL, NULL, NULL, &_tmp_usleep_tv);
#endif
int gethostname(char *name, int namelen);
long random();
int srandom(unsigned int seed);
#undef LIBVNCSERVER_HAVE_LIBPTHREAD
#ifndef SHUT_RDWR
#define SHUT_RDWR 2
#endif
#ifndef in_addr_t
typedef unsigned int in_addr_t;
#endif
#ifndef snprintf
#define snprintf(a, n, args...) sprintf((a), ## args)
#endif

   Then run make with the Solaris build script environment, everything
   should compile without problems, and the resulting x11vnc binary
   should work OK (but note the workaround for XConvertCase in x11vnc.c
   only covers Latin 1). If some non-x11vnc related programs fail (e.g.
   test programs) and the x11vnc binary is not created try "make -k".
   Similar sorts of kludges can be done on other older OS (Solaris,
   Linux, ...) releases.

   Here are some notes for similar steps that need to be done to build on
   [112]SunOS 4.x

   Please let us know if you had to use the above workaround (and whether
   it worked or not). If there is enough demand we will try to push clean
   compilations back to earlier Solaris, Linux, etc, releases.

   Q-4: Where can I get a precompiled x11vnc binary for my Operating
   System?

   Hopefully the [113]build steps above and [114]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)  [115]http://packages.debian.org/x11vnc

   Slackware: (.tgz) [116]http://www.linuxpackages.net/ Redhat/Fedora:
   (.rpm) [117]http://dag.wieers.com/packages/x11vnc/ Solaris: (pkg)
   [118]http://www.sunfreeware.com/ wwexptools: (.tgz)
   [119]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 near the bottom of that page
   and select 'download info'.

   Note: it appears some of the wwexptools x11vnc binaries are not
   compiled with libz and libjpeg and so the fast compression encodings:
   "Tight", "ZRLE", etc are not supported by those binaries. You can see
   this by looking at the x11vnc output and if it says the encoding for a
   client is "hextile" then likely the fast compression encodings are
   missing. If you want optimal performance on your OS, you should see
   the [120]build notes above for where to download libz and libjpeg, and
   then build everything with gcc. For Solaris, the
   http://www.sunfreeware.com/ packages are built with libz and libjpeg.

   If the above binaries don't work and building x11vnc on your OS fails
   (and all else fails!) you can try one of my motley collection of
   [121]test binaries. Some may be old, some may have extra debugging
   output, etc. They may work on your OS, but please understand they are
   test/experimental binaries not intended for general usage like the
   above precompiled ones from 3rd parties.

   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-5: Where can I get a VNC Viewer binary (or source code) for the
   Operating System I will be viewing from?

   To obtain VNC viewers for the viewing side (Windows, Mac OS, or Unix)
   try here:
     * [122]http://www.tightvnc.com/download.html
     * [123]http://www.realvnc.com/download-free.html
     * [124]http://sourceforge.net/projects/cotvnc/

   Q-6: How can I see all of x11vnc's command line options and
   documentation on how to use them?

   Run:  x11vnc -opts   to list just the option names or run:  x11vnc
   -help   for long descriptions about each option. The output is listed
   [125]here as well.

   Q-7: I don't like typing arcane command line options every time I
   start x11vnc. What can I do? Is there a config file? Or a GUI?

   You could create a shell script that calls x11vnc with your options:
#!/bin/sh
#
# filename: X11vnc  (i.e. not "x11vnc")
# It resides in a directory in $PATH. "chmod 755 X11vnc" has been run on it.
#
x11vnc -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        # this is a 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.

   As of Dec/2004 in the libvncserver CVS there is now a simple tcl/tk
   GUI based on the remote-control functionality that was added. It's not
   particularly user-friendly, it just provides a point and click mode to
   set all the many x11vnc parameters and obtain help on them. See the
   -gui option for more info. Examples: "x11vnc ... -gui" and "x11vnc ...
   -gui other:0" in the latter case the gui is displayed on other:0, not
   the X display x11vnc is polling.

   Q-8: 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-9: 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.

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

   [Win2VNC Related]

   Q-10: 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 [127]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:
     * [128]Original Win2VNC
     * [129]Enhanced Win2VNC and [130]sourceforge link
     * [131]x2vnc
     * [132]x2x also [133]here
     * [134]zvnc (MorphOS)

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

   Q-11: 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,
   look in the "screen" section). There seems to be a bug in Win2VNC in
   that it cannot deal correctly with colormaps (PseudoColor is the most
   common example of a visual with a colormap).

   If so, there are a couple options. 1) Can you set the default visual
   on your display to be depth 24 TrueColor? Sun machines often have 8+24
   overlay/multi-depth visuals, and you can make the default visual depth
   24 TrueColor (see fbconfig(1) and Xsun(1)). 2) As of Feb/2004, 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.
   [Color Issues]

   Q-12: 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-13: 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 [135]previous question regarding 8 bpp
   PseudoColor.

   On some hardware (Sun/SPARC, Sgi), the -overlay option discussed a
   couple paragraphs down may solve this for you (you may want to skip to
   it directly).

   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.

   The -overlay mode: Another option is if the system with overlay
   visuals is a Sun system running Solaris or Sgi running IRIX you can
   use the -overlay x11vnc option (Aug/2004) to have x11vnc use the
   Solaris XReadScreen(3X11) function to poll the "true view" of the
   whole screen at depth 24 TrueColor. XReadDisplay(3X11) is used on
   IRIX. This is useful for Legacy applications (older versions of
   Cadence CAD apps are mentioned by x11vnc users) that require the
   default depth be 8bpp, or 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, on Solaris 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-14: 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
   [136]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 ....

   Also, as of Dec/2004 libvncserver CVS you can use "-id pick" to have
   x11vnc run xwininfo(1) for you and after you click the window it
   extracts the windowid. Besides "pick" there is also "id:root" to allow
   you to go back to root window when doing remote-control.

   Q-15: 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 you disable BackingStore and SaveUnders in the X server you should
   be able to see these transient windows.

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

   x11vnc is known to crash under both -id and -sid, so both modes are
   still experimental. Please report any reproducible bugs.

   Q-16: My X display is depth 24 at 24bpp (instead of the normal depth
   24 at 32bpp). I'm having lots of color and visual problems with x11vnc
   and vncviewer.

   First off, depth 24 at 24bpp (bpp=bits-per-pixel) is fairly uncommon
   and can cause problems in general. It also can be slower than depth 24
   at 32bpp. You might want to switch to 32bpp (for XFree86 see the
   "-fbbpp 32", DefaultFbBpp, FbBpp and related options). Perhaps you
   have 24bpp because the video memory of the machine is low and the
   screen wouldn't fit in video RAM at 32bpp. For this case depth 16 at
   16bpp might be an acceptable option.

   In any event x11vnc should handle depth 24 at 24bpp (although
   performance may be slower). There are some caveats involving the
   viewer however:

   The RealVNC Unix viewer cannot handle 24bpp from the server, it will
   say: "main: setPF: not 8, 16 or 32 bpp?" and exit. I have not checked
   the RealVNC Windows viewer.

   So you need to use the TightVNC Unix viewer. However there are some
   problems with that too. It seems libvncserver does not do 24bpp
   correctly with the Tight encoding. The colors and screen ultimately
   get messed up. So you have to use a different encoding with the
   TightVNC vncviewer, try "zlib", "hextile", or one of the other
   encodings (e.g. vncviewer -encodings "zlib hextile" ...). I have not
   checked the TightVNC or UltraVNC Windows viewers.

   It appears the older RealVNC Unix viewers (e.g. 3.3.3 and 3.3.7) can
   handle 24bpp from the server, so you may want to use those. They
   evidently request 32 bpp and libvncserver obliges.

   Now coming the opposite direction if you are running the vncviewer on
   the 24bpp display, TightVNC will fail with "Can't cope with 24
   bits-per-pixel. Sorry." and RealVNC will fail with "main: Error:
   couldn't find suitable pixmap format" so evidently you cannot use
   24bpp for the vncviewers to work on that X display.
   [Xterminals]

   Q-17: 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-18: How do I get my X permissions (MIT-MAGIC-COOKIE) correct for a
   Unix/Linux machine acting as an Xterminal?

   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
   MIT-MAGIC-COOKIE auth files, are on the central server and not on the
   Xterminal where the X server and x11vnc processes are running. Somehow
   the MIT-MAGIC-COOKIE auth file data must be copied to the Xterminal.
   If $HOME/.Xauthority is exported via NFS (this is insecure of course),
   then x11vnc can simply pick it up via NFS (you may need to use the
   -auth option to point to the correct file). Other options include
   copying the auth file using scp, or something like:
central-server> xauth nextract - xterm123:0 | ssh xterm123 xauth nmerge -

   and then perhaps ssh from central-server to xterm123 to start x11vnc.
   You can use "xauth -f /path/to/cookie.file list" to examine the
   contents of the cookie in a file "/path/to/cookie.file". See the
   xauth(1) manpage for more details.

   If the display name needs to be changed between the two hosts, see
   [137]this note on the xauth add ... command.

   A less secure option is to run something like "xhost +127.0.0.1" to
   allow cookie-free local access for x11vnc.

   If the Xterminal is really stripped down and doesn't have any user
   accounts, NFS, etc. you'll need to contact your system administrator
   to set something up.

   Not recommended, but as a last resort, you could have x11vnc [138]poll
   the Xterminal over the network.

   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.

   [Remote Control]

   Q-19: How do I stop x11vnc once it is running in the background?

   As of Dec/2004 in the libvncserver CVS there is a remote control
   feature. It can change a huge amount of things on the fly: see the
   -remote and -query options. To shut down the running x11vnc server
   just type "x11vnc -R stop". To disconnect all clients do "x11vnc -R
   disconnect:all", etc.

   For older versions: If the -forever option has not been supplied,
   x11vnc will automatically exit after the first client disconnects. In
   general you will have to kill the x11vnc process This can be done via:
   "kill NNNNN" (where NNNNN is the x11vnc process id number found from
   ps(1)), or "pkill x11vnc", or "killall x11vnc" (Linux only).

   If you have not put x11vnc in the background via the -bg option or
   shell & operator, then simply press Ctrl-C in the shell where x11vnc
   is running to stop it. Potential Gotcha: If somehow your Keypress of
   Ctrl-C went through x11vnc to the Xserver that then delivered it to
   x11vnc it is possible one or both of the Ctrl or C keys will be left
   stuck in the pressed down state in the Xserver. Tapping the stuck key
   (either via x11vnc or at the physical console) will release it from
   the stuck state. If the keyboard seems to be acting strangely it is
   often fixed by tapping Ctrl, Shift, and Alt. Alternatively, the
   -clear_mods and -clear_keys options can be used to release pressed
   keys at startup and exit.

   Q-20: Can I change settings in x11vnc without having to restart it? Is
   there a way to remote control it?

   Look at the -remote (same as -R) and -query (same as -Q) options added
   in the Dec/2004 libvncserver CVS. They allow nearly everything to be
   changed dynamically and settings to be queried. Examples: "x11vnc -R
   shared", "x11vnc -R forever", "x11vnc -R scale:3/4", "x11vnc -Q
   modtweak", "x11vnc -R stop", "x11vnc -R disconnect:all", etc.. These
   commands do not start a x11vnc server, but rather communicate with one
   that is already running. The X display (VNC_CONNECT property) is used
   as the communication channel, so the X permissions and DISPLAY must be
   set up correctly for communication to be possible.

   There is also a simple tcl/tk gui based on this remote control
   mechanism. See the -gui option for more info.

   [Security and Permissions]

   Q-21: 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 ([139]see
   above), stunnel, or a VPN to authenticate and encrypt the viewer
   connections or to at least use the -rfbauth passwd-file [140]option to
   use VNC password protection (or [141]-passwdfile) It is up to you to
   apply these security measures, they will not be done for you
   automatically.

   Q-22: 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. For individual hosts you can use the hostname instead of
   the IP number, e.g.: "-allow snoopy", and "-allow darkstar,wombat".
   Note that -localhost is the same as "-allow 127.0.0.1"

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

   Q-23: How do I build x11vnc/libvncserver with libwrap (tcp_wrappers)
   support?

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

   then run make as usual. This requires libwrap and its development
   package (tcpd.h) to be installed on the build machine. If additional
   CPPFLAGS or LDFLAGS options are needed supply them as well.

   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 [142]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-24: 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. RFB_MODE will be "accept".

   As a special case, "-accept popup" will instruct x11vnc to create its
   own simple popup window. To accept the client press "y" or click mouse
   on the "Yes" button. To reject the client press "n" or click mouse on
   the "No" button. To accept the client View-only, press "v" or click
   mouse on the "View" button. If the -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 [143]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 [144]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" (except that RFB_MODE will
   be "gone").

   Q-25: How do I create a VNC password for use with x11vnc?

   You may already have one in $HOME/.vnc/passwd if you have used, say,
   the vncserver program from the regular RealVNC or TightVNC packages
   (i.e. launching the Xvnc server). Otherwise, you could use the
   vncpasswd(1) program from those packages. 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. Example:
  x11vnc -storepasswd 'sword*fish' $HOME/myvncpasswd

   You then use the password via the x11vnc option: -rfbauth
   $HOME/myvncpasswd

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

   Q-26: 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 [146]how to tunnel VNC via
   SSH from Unix to Unix. A number of ways are described along with some
   issues you may encounter.

   Other secure encrypted methods exists, e.g. stunnel, IPSEC, various
   VPNs, etc.

   Q-27: How can I tunnel my connection to x11vnc via an encrypted SSH
   channel from Windows using an SSH client like Putty?

   [147]Above we described how to tunnel VNC via SSH from Unix to Unix,
   you may want to review it. To do this from Windows using Putty it
   would go something like this:
     * In the Putty dialog window under 'Session' enter the hostname or
       IP number of the Unix machine with display to be viewed.
     * Make sure the SSH protocol is selected and the server port is
       correct.
     * Under 'Connections/SSH/Tunnels' Add a Local connection with
       'Source port:  5900' and 'Destination:  localhost:5900'
     * Log into the remote machine by pressing 'Open' and supplying
       username, password, etc.
     * In that SSH shell, start up x11vnc by typing the command: x11vnc
       -display :0 plus any other desired options.
     * 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 [148]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-28: 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
   [149]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-29: 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-30: 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 [150]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-31: 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 -forever -gone 'dtaction LockDisplay'

   Other possibilities are:
  x11vnc -display :0 -forever -gone 'xscreensaver-command -lock'
  x11vnc -display :0 -forever -gone 'kdesktop_lock'
  x11vnc -display :0 -forever -gone 'xlock &'


   [Display Managers and Services]

   Q-32: How can I run x11vnc as a "service" that is always available?

   There are a number of ways to do this. The primary thing you need to
   decide is whether you want x11vnc to connect to the X session on the
   machine 1) regardless of who (or if anyone) has the X session, or 2)
   only if a certain user has the X session. Because X sessions are
   protected by X permissions (XAUTHORITY and $HOME/.Xauthority) the
   automatically started x11vnc will of course need to have sufficient
   permissions.

   Here are some ideas:
     * Use the description under "Continuously" in the [151]FAQ on x11vnc
       and Display Managers
     * Use the description in the [152]FAQ on x11vnc and inetd(1)
     * Start x11vnc from $HOME/.xsession (or $HOME/.xinitrc)
     * Although less reliable, see the [153]x11vnc_loop rc.local hack
       below.

   The display manager scheme will not be specific to which user has the
   X session unless a test is specifically put into the display startup
   script (often Xsetup). The inetd(1) scheme may or may not be specific
   to which user has the X session (and it may not be able to do all
   users via the XAUTHORITY permission issues).

   The $HOME/.xsession scheme is obviously is specific to a particular
   user. If you do not know what a $HOME/.xsession script is or how to
   use one, perhaps your desktop has a "session startup commands"
   configuration option. The command to be run in the .xsession or
   .xinitrc file may look like this:
x11vnc -logfile $HOME/.x11vnc.log -rfbauth $HOME/.vnc/passwd -forever -bg

   plus any other options you desire.

   Q-33: How can I use x11vnc to connect to an X login screen like xdm,
   GNOME gdm, KDE kdm, or CDE dtlogin? (i.e. nobody is logged into an X
   session yet).

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

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

   (the -auth option sets XAUTHORITY). 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).

   Tricks: another place to look for the auth file is via ps(1) output
   for the X server process to find any -auth argument (e.g. ps wwwwaux |
   grep auth). Also, sometimes this command is useful: ps wwwweaux | tr '
   ' '\n' | grep XAUTHORITY | sort -u

   gdm seems to have an annoying setting that causes x11vnc (and any
   other X clients) to be killed after the user logs in. Setting
   KillInitClients=false in the [daemon] section of /etc/X11/gdm/gdm.conf
   avoids this. Otherwise, just restart x11vnc and then reconnect your
   viewer.

   For dtlogin in addition to the above sort of trick (BTW, the auth file
   should be in /var/dt), you'll also need to add something like
   Dtlogin*grabServer:False to the Xconfig file (/etc/dt/config/Xconfig
   or /usr/dt/config/Xconfig on Solaris). 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 a display manager startup script. The
   name of the script file depends on desktop used and seem to be:
        GNOME        /etc/X11/gdm/Init/Default  (or Init/:0)
        KDE          /etc/kde*/kdm/Xsetup
        XDM          /etc/X11/xdm/Xsetup        (or xdm/Xsetup_0)
        CDE          /etc/dt/config/Xsetup

   although the exact location can depend on operating system and
   distribution. See the documentation for your display manager:  gdm(1),
   kdm(1), xdm(1), dtlogin(1) for additional details. 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, you need to watch out for.

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

   where you should customize the exact command to your needs. Note that
   we do not need to specify -display or -auth because happily they are
   already set for us in the DISPLAY and XAUTHORITY environment
   variables.

   You may also want to force the VNC port with something like "-rfbport
   5900"

   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).

   Here is an example what we did on a vanilla install of Fedora-C3
   (seems to use gdm by default). Add a line like this to
   /etc/X11/gdm/Init/:0
  /usr/local/bin/x11vnc -rfbauth /etc/x11vnc.passwd -forever -bg -o /var/tmp/x1
1vnc.log

   And then add this line to /etc/X11/gdm/gdm.conf in the [daemon]
   section:
  KillInitClients=false

   Then restart: /usr/sbin/gdm-restart (or reboot). The
   KillInitClients=false setting is important: without it x11vnc will be
   killed immediately after the user logs in. Here are [154]full details
   on how to configure gdm

   Here is an example what we did on a vanilla install of Solaris:
   Make the directory /etc/dt/config:
  mkdir -p /etc/dt/config

   Copy over the Xconfig file for customization:
  cp /usr/dt/config/Xconfig /etc/dt/config/Xconfig

   Edit /etc/dt/config/Xconfig and uncomment the line:
  Dtlogin*grabServer:        False

   Next, copy over Xsetup for customization:
  cp /usr/dt/config/Xsetup /etc/dt/config/Xsetup

   Edit /etc/dt/config/Xsetup and at the bottom put a line like:
  /usr/local/bin/x11vnc -forever -o /var/tmp/x11vnc.log -bg

   (tweaked to your local setup and preferences, a password via -rfbauth,
   etc. would be a very good idea).

   Restart the X server and dtlogin:
  /etc/init.d/dtlogin stop
  /etc/init.d/dtlogin start

   (or reboot or maybe just restart the X session).

   If you do not want to deal with any display manager startup scripts,
   here is a kludgey script that can be run manually or out of a boot
   file like rc.local: [155]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.

   If the machine is a traditional Xterminal you may want to read
   [156]this FAQ.

   Q-34: Can I run x11vnc out of inetd(1)? How about xinetd(1)?

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

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

   where the shell script /usr/local/bin/x11vnc_sh looks something like
   (you'll need to customize to your settings).
#!/bin/sh
/usr/local/bin/x11vnc -inetd -display :0 -auth /home/fred/.Xauthority \
        -rfbauth /home/fred/.vnc/passwd 2>> /tmp/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 via -auth to point to the
   MIT-COOKIE auth file to get permission to connect to the X display
   (setting and exporting the XAUTHORITY variable accomplishes the same
   thing). See the x11vnc_loop file in the previous question for more
   ideas on what that auth file may be, etc.

   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.

   For xinetd(1), one user reports he created the file
   /etc/xinetd.d/x11vncservice containing the following:
# default: off
# description:
service x11vncservice
{
        flags           = REUSE NAMEINARGS
        port            = 5900
        type            = UNLISTED
        socket_type     = stream
        protocol        = tcp
        wait            = no
        user            = root
        server          = /usr/sbin/tcpd
        server_args     = /usr/local/bin/x11vnc_sh
        disable         = no
}

   With the contents of /usr/local/bin/x11vnc_sh similar to the example
   given above.

   Q-35: 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-36: 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 starts 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 (Note: as of
   Dec/2004 -vncconnect is now the default). vncconnect(1) must be
   pointed to the same X11 DISPLAY as x11vnc (since it uses X properties
   to communicate with x11vnc). If you do not have or do not want to get
   the vncconnect(1) program, the following script (named "Vncconnect")
   may work if your xprop(1) supports the -set option:
#!/bin/sh
# usage: Vncconnect <host>
#        Vncconnect <host:port>
# note: not all xprop(1) support -set.
#
xprop -root -f VNC_CONNECT 8s -set VNC_CONNECT "$1"


   [Resource Usage and Performance]

   Q-37: 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 [157]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 [158]earlier question
   discussing -noshm).

   Q-38: 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-39: 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-40: 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). Consider using the -solid
       [color] option.
     * 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 [159]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)
     * 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 and -nocursorpos (repainting the remote cursor
       position and shape takes resources and round trips)

   Q-41: 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 -pointer_mode 1 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).

   As of Dec/2004 in the libvncserver CVS the -pointer_mode n option was
   introduced. n=1 is the original mose, n=2 and improvement, etc.. See
   the -pointer_mode n help for more info.

   [Mouse Cursor Shapes]

   Q-42: Why isn't the mouse cursor shape (the little icon shape where
   the mouse pointer is) correct as I move from window to window?

   On X servers supporting XFIXES or Overlay extensions this is possible.
   See the paragraphs below.

   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.

   Note that as of Aug/2004 in the libvncserver CVS, on Solaris using the
   SUN_OVL overlay extension and IRIX, x11vnc can show the correct mouse
   cursor when the -overlay is also supplied. (-overlay has some other
   problems however, and can be slower).

   Also as of Dec/2004 in the libvncserver CVS XFIXES X extension support
   has been added to allow exact extraction of the mouse cursor shape.
   The only issue is the handling of alpha channel transparency in
   cursors (they must be approximated). XFIXES is available on recent
   Linux Xorg based distros and Solaris 10 (on Solaris you will need to
   add "-L /usr/openwin/sfw/lib -R /usr/openwin/sfw/lib" to LDFLAGS for
   configure to enable it).

   Q-43: When using XFIXES cursorshape mode, some of the cursors look
   really bad with extra black borders around the cursor and other cruft.
   How can I improve their appearance?

   This happens for cursors with transparency ("alpha channel"); regular
   X cursors (bitmaps) should be correct. Unfortunately x11vnc 0.7 was
   released with a very poor algorithm for approximating the
   transparency, which led to the ugly black borders.

   The problem is as follows: XFIXES allows x11vnc to retrieve the
   current X server cursor shape, including the alpha channel for
   transparency. For traditional bitmap cursors the alpha value will be 0
   for completely transparent pixels and 255 for completely opaque
   pixels; whereas for modern, eye-candy cursors an alpha value between 0
   and 255 means to blend in the background colors to that degree with
   the cursor colors. The pixel color blending formula is something like
   this: Red = Red_cursor * a + Red_background * (1 - a), (where here 0
   =< a =< 1), with similar for Green and Blue. The VNC protocol does not
   currently support an alpha channel in cursors: it only supports
   regular X bitmap cursors and Rich Cursors that have RGB (Red, Green,
   Blue) color data, but no "A" = alpha data. So x11vnc has to
   approximate a cursor with transparency to create a Rich Cursor. This
   is easier said than done: some cursor themes have cursors with
   complicated drop shadows and other forms of translucency.

   Anyway, for the x11vnc 0.7.1 release the algorithm for approximating
   transparency is much improved and hopefully gives decent cursor shapes
   for most cursor themes.

   In case it still looks bad for your cursor theme, there are (of
   course!) some tunable parameters. The "-alphacut n" option lets you
   set the threshold "n" (between 0 and 255): cursor pixels with alpha
   values below n will be considered completely transparent while values
   equal to or above n will be completely opaque. The default is 240. The
   "-alphafrac f" option tries to correct individual cursors that did not
   fare well with the default -alphacut value: if a cursor has less than
   fraction f (between 0.0 and 1.0) of its pixels selected by the default
   -alphacut, the threshold is lowered until f of its pixels are
   selected. The default fraction is 0.33.

   Finally, there is an option -alpharemove that is useful for themes
   where many cursors are light colored (e.g. "whiteglass"). XFIXES
   returns the cursor data with the RGB values pre-multiplied by the
   alpha value. If the white cursors look too grey, specify -alpharemove
   to brighten them by dividing out the alpha value.

   Q-44: In XFIXES mode, are there any hacks to handle cursor
   transparency ("alpha channel") exactly?

   As of Jan/2005 in the libvncserver CVS, libvncserver has been modified
   to allow an alpha channel (i.e. RGBA data) for Rich Cursors. This only
   works if the screen pixel format has extra unused pixels where the
   alpha data can be stored. This effectively limits things to depth 24
   at 32bpp (bpp = bits per pixel, depth = the number of bits used to
   represent RGB color data and can be less than bpp); fortunately this
   is a common screen setup. This hack won't work for 16bpp. (well, it
   could work for depth 15 at 16bpp, but that only leaves one bit for the
   alpha data, which is not worth it).

   The -alphablend option instructs x11vnc to use RGBA for Rich Cursors
   (currently it is ignored except for depth 24 at 32bpp). So, in
   -nocursorshape mode, or for VNC clients that do not support
   CursorShapeUpdates (or have disabled them), x11vnc will draw the
   blended cursor with transparency into the x11vnc framebuffer for these
   clients, and the transparency should look correct for them.

   Now, if you want CursorShapeUpdates turned on for your viewer (e.g.
   because you do not like the lag between your pointer and the drawn
   cursor) it is possible to modify your VNC viewer to apply the alpha
   channel blending locally. This hack is outside of the VNC protocol.
   Not only does this require depth 24 at 32bpp (for the extra space to
   hide the alpha data), but it also currently requires the client and
   server to be of the same endianness (otherwise the hidden alpha data
   gets reset to zero by the translation function). As an example, for
   the TightVNC 1.3dev5 Unix vncviewer [160]this patch enables the
   TightVNC viewer to do the blending locally. You have to set the
   environment variable ALPHABLEND=1 before starting your modified
   viewer. The patch code should give an example on how to change the
   Windows TightVNC viewer to achieve the same thing (send me the patch
   if you get that working).

   [Mouse Pointer]

   Q-45: 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 [161]tightvnc extension
   (CursorShapeUpdates) that allows specifying a cursor image shape 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 (or ones that do not support
   CursorShapeUpdates) will be to draw the moving cursor into the x11vnc
   framebuffer. This can also be disabled via -nocursor.

   Q-46: 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 also -nocursorpos and
   -nocursorshape.

   Q-47: 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. Look in the include file
   <X11/keysymdef.h>, or use xev(1), or -debug_keyboard to fine the
   keysym names. Button clicks can also be included in the sequence via
   the fake keysyms Button1, etc.

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

   Exactly what keystroke "scrolling" events they should be bound to
   depends on one's taste. If this method is too approximate, one could
   consider not using -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).
   [Keyboard Issues]

   Q-48: 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 [162]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 [163]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-49: 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 [164]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-50: 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. See the -add_keysyms
       option below.
     * 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-51: 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.
   Update: as of Dec/2004 -norepeat is now the default. Use -repeat to
   disable it.

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

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

   Look at the output of "xset q" for the "auto repeat delay" setting. Is
   it low (e.g. < 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-52: The x11vnc -norepeat mode is in effect, but I still get repeated
   keystrokes!!

   Are you using x11vnc to log in to an X session? (as described
   [165]this FAQ) If so, x11vnc is starting before your session, and then
   your session startup could be resetting the autorepeat to be on. Or it
   could be something inside your desktop that decides to turn it back
   on. x11vnc in -norepeat mode will not battle with things turning
   autorepeat back on. (It will, however, turn it off whenever it goes
   from a state of zero clients to one client).

   Under these circumstances you will have to manually turn autorepeating
   off by typing "xset r off" or "x11vnc -R norepeat" or a desktop
   utility. If something in your desktop is automatically turning it back
   on you will have to disable that somehow.

   Q-53: 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-54: 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-55: 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
   X pasting a bit easier.

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

   [Screen Related Issues and Features]

   Q-56: 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 [166]this
   FAQ on x11vnc scaling.

   Q-57: 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). Note that if
   fraction is greater than one the display is expanded (not clear how
   useful this is).

   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 vncviewer option improves the readability of text when using
   -scale to shrink the display size. Also note that scaling may actually
   slow down the transfer of text regions because after being scaled they
   do not compress as well. (this can often be a significant slowdown,
   e.g. 10X).

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

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

   Q-58: 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-59: 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 [167]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-60: Does x11vnc support the XRANDR (X Resize, Rotate and Reflection)
   extension? Whenever I rotate or resize the screen x11vnc just seems to
   crash.

   As of Dec/2004 in the libvncserver CVS x11vnc supports XRANDR. You
   enable it with the -xrandr option to make x11vnc monitor XRANDR events
   and also trap X server errors if the screen change occurred in the
   middle of an X call like XGetImage. Once it traps the screen change it
   will create a new framebuffer using the new screen. If the connected
   vnc viewers support the NewFBSize VNC extension (Windows TightVNC
   viewer and RealVNC 4.0 windows and Unix viewers do) then the viewer
   will automatically resize. Otherwise, the new framebuffer is fit as
   best as possible into the original viewer size (portions of the screen
   may be clipped, unused, etc).

   If you specify "-xrandr newfbsize" then vnc viewers that do not
   support NewFBSize will be disconnected before the resize. If you
   specify "-xrandr exit" then all will be disconnected and x11vnc will
   terminate.

   Q-61: 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-62: 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-63: I am using x11vnc where my local machine has "popup/hidden
   taskbars" (e.g. GNOME or MacOS X) and the remote display where x11vnc
   runs also has "popup/hidden taskbars" (e.g. GNOME). When I move the
   mouse to the edge of the screen where the popups happen, the taskbars
   interfere and fight with each other in strange ways. What can I do?

   Is there a way to temporarily disable one or both of these magic
   desktop taskbars? One x11vnc user suggests: it should be
   straightforward to right mouse click on the task bar panel, and
   uncheck "enable auto-hide" from the panel properties dialog box. This
   will make the panel always visible.

   [Misc: Clipboard, Beeps, etc.]

   Q-64: 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.

   You may need to watch out for desktop utilities such as KDE's
   "Klipper" that do odd things with the selection, clipboard, and
   cutbuffers.

   Q-65: 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.
     _________________________________________________________________

   [PayPal]

References

   1. http://www.karlrunge.com/x11vnc/index.html#faq
   2. http://www.karlrunge.com/x11vnc/index.html#downloading
   3. http://www.karlrunge.com/x11vnc/index.html#building
   4. http://www.karlrunge.com/x11vnc/index.html#faq
   5. http://www.karlrunge.com/x11vnc/index.html#contact
   6. http://www.uk.research.att.com/vnc/
   7. http://www.realvnc.com/
   8. http://www.tightvnc.com/
   9. http://www.karlrunge.com/x11vnc/index.html#downloading
  10. http://www.tightvnc.com/download.html
  11. http://www.karlrunge.com/x11vnc/index.html#xperms
  12. http://www.karlrunge.com/x11vnc/index.html#viewer-download
  13. http://www.sun.com/software/solaris/freeware/
  14. http://www.karlrunge.com/x11vnc/x11vnc_opts.html
  15. http://www.karlrunge.com/x11vnc/index.html#service
  16. http://www.karlrunge.com/x11vnc/index.html#passwd
  17. http://www.karlrunge.com/x11vnc/index.html#vnc_password_file
  18. http://www.karlrunge.com/x11vnc/index.html#inetd
  19. http://www.karlrunge.com/x11vnc/index.html#tightvnc_via
  20. http://www.karlrunge.com/x11vnc/index.html#inetd
  21. http://www.karlrunge.com/x11vnc/index.html#passwd
  22. http://www.karlrunge.com/x11vnc/index.html#passwdfile
  23. http://www.karlrunge.com/x11vnc/index.html#allow_opt
  24. http://www.karlrunge.com/x11vnc/index.html#tcp_wrappers
  25. http://sourceforge.net/projects/libvncserver/
  26. http://sourceforge.net/project/showfiles.php?group_id=32584&package_id=119006&release_id=292078
  27. http://sourceforge.net/project/shownotes.php?group_id=32584&release_id=292078
  28. http://www.karlrunge.com/x11vnc/x11vnc.c
  29. http://www.karlrunge.com/x11vnc/tkx11vnc.h
  30. http://www.karlrunge.com/x11vnc/index.html#binaries
  31. http://www.tightvnc.com/download.html
  32. http://www.realvnc.com/download-free.html
  33. http://sourceforge.net/projects/cotvnc/
  34. http://www.karlrunge.com/x11vnc/rx11vnc
  35. http://www.karlrunge.com/x11vnc/rx11vnc.pl
  36. ftp://ftp.uu.net/graphics/jpeg/
  37. http://www.gzip.org/zlib/
  38. http://www.sunfreeware.com/
  39. http://www.karlrunge.com/x11vnc/index.html#solaris251build
  40. http://www.tightvnc.com/
  41. http://www.karlrunge.com/x11vnc/x11vnc_opts.html
  42. http://www.karlrunge.com/x11vnc/index.html#passwd
  43. http://www.karlrunge.com/x11vnc/recurse_x11vnc.jpg
  44. http://wwws.sun.com/sunray/index.html
  45. mailto:xvml@karlrunge.com
  46. http://www.karlrunge.com/x11vnc/index.html#FAQ-1
  47. http://www.karlrunge.com/x11vnc/index.html#FAQ-2
  48. http://www.karlrunge.com/x11vnc/index.html#FAQ-3
  49. http://www.karlrunge.com/x11vnc/index.html#FAQ-4
  50. http://www.karlrunge.com/x11vnc/index.html#FAQ-5
  51. http://www.karlrunge.com/x11vnc/index.html#FAQ-6
  52. http://www.karlrunge.com/x11vnc/index.html#FAQ-7
  53. http://www.karlrunge.com/x11vnc/index.html#FAQ-8
  54. http://www.karlrunge.com/x11vnc/index.html#FAQ-9
  55. http://www.karlrunge.com/x11vnc/index.html#FAQ-10
  56. http://www.karlrunge.com/x11vnc/index.html#FAQ-11
  57. http://www.karlrunge.com/x11vnc/index.html#FAQ-12
  58. http://www.karlrunge.com/x11vnc/index.html#FAQ-13
  59. http://www.karlrunge.com/x11vnc/index.html#FAQ-14
  60. http://www.karlrunge.com/x11vnc/index.html#FAQ-15
  61. http://www.karlrunge.com/x11vnc/index.html#FAQ-16
  62. http://www.karlrunge.com/x11vnc/index.html#FAQ-17
  63. http://www.karlrunge.com/x11vnc/index.html#FAQ-18
  64. http://www.karlrunge.com/x11vnc/index.html#FAQ-19
  65. http://www.karlrunge.com/x11vnc/index.html#FAQ-20
  66. http://www.karlrunge.com/x11vnc/index.html#FAQ-21
  67. http://www.karlrunge.com/x11vnc/index.html#FAQ-22
  68. http://www.karlrunge.com/x11vnc/index.html#FAQ-23
  69. http://www.karlrunge.com/x11vnc/index.html#FAQ-24
  70. http://www.karlrunge.com/x11vnc/index.html#FAQ-25
  71. http://www.karlrunge.com/x11vnc/index.html#FAQ-26
  72. http://www.karlrunge.com/x11vnc/index.html#FAQ-27
  73. http://www.karlrunge.com/x11vnc/index.html#FAQ-28
  74. http://www.karlrunge.com/x11vnc/index.html#FAQ-29
  75. http://www.karlrunge.com/x11vnc/index.html#FAQ-30
  76. http://www.karlrunge.com/x11vnc/index.html#FAQ-31
  77. http://www.karlrunge.com/x11vnc/index.html#FAQ-32
  78. http://www.karlrunge.com/x11vnc/index.html#FAQ-33
  79. http://www.karlrunge.com/x11vnc/index.html#FAQ-34
  80. http://www.karlrunge.com/x11vnc/index.html#FAQ-35
  81. http://www.karlrunge.com/x11vnc/index.html#FAQ-36
  82. http://www.karlrunge.com/x11vnc/index.html#FAQ-37
  83. http://www.karlrunge.com/x11vnc/index.html#FAQ-38
  84. http://www.karlrunge.com/x11vnc/index.html#FAQ-39
  85. http://www.karlrunge.com/x11vnc/index.html#FAQ-40
  86. http://www.karlrunge.com/x11vnc/index.html#FAQ-41
  87. http://www.karlrunge.com/x11vnc/index.html#FAQ-42
  88. http://www.karlrunge.com/x11vnc/index.html#FAQ-43
  89. http://www.karlrunge.com/x11vnc/index.html#FAQ-44
  90. http://www.karlrunge.com/x11vnc/index.html#FAQ-45
  91. http://www.karlrunge.com/x11vnc/index.html#FAQ-46
  92. http://www.karlrunge.com/x11vnc/index.html#FAQ-47
  93. http://www.karlrunge.com/x11vnc/index.html#FAQ-48
  94. http://www.karlrunge.com/x11vnc/index.html#FAQ-49
  95. http://www.karlrunge.com/x11vnc/index.html#FAQ-50
  96. http://www.karlrunge.com/x11vnc/index.html#FAQ-51
  97. http://www.karlrunge.com/x11vnc/index.html#FAQ-52
  98. http://www.karlrunge.com/x11vnc/index.html#FAQ-53
  99. http://www.karlrunge.com/x11vnc/index.html#FAQ-54
 100. http://www.karlrunge.com/x11vnc/index.html#FAQ-55
 101. http://www.karlrunge.com/x11vnc/index.html#FAQ-56
 102. http://www.karlrunge.com/x11vnc/index.html#FAQ-57
 103. http://www.karlrunge.com/x11vnc/index.html#FAQ-58
 104. http://www.karlrunge.com/x11vnc/index.html#FAQ-59
 105. http://www.karlrunge.com/x11vnc/index.html#FAQ-60
 106. http://www.karlrunge.com/x11vnc/index.html#FAQ-61
 107. http://www.karlrunge.com/x11vnc/index.html#FAQ-62
 108. http://www.karlrunge.com/x11vnc/index.html#FAQ-63
 109. http://www.karlrunge.com/x11vnc/index.html#FAQ-64
 110. http://www.karlrunge.com/x11vnc/index.html#FAQ-65
 111. http://www.karlrunge.com/x11vnc/index.html#solarisbuilding
 112. http://www.karlrunge.com/x11vnc/x11vnc_sunos4.html
 113. http://www.karlrunge.com/x11vnc/index.html#building
 114. http://www.karlrunge.com/x11vnc/index.html#buildfaq
 115. http://packages.debian.org/x11vnc
 116. http://www.linuxpackages.net/search_view.php?by=name&name=x11vnc
 117. http://dag.wieers.com/packages/x11vnc/
 118. http://www.sunfreeware.com/
 119. http://www.bell-labs.com/project/wwexptools/packages.html
 120. http://www.karlrunge.com/x11vnc/index.html#solarisbuilding
 121. http://www.karlrunge.com/x11vnc/bins
 122. http://www.tightvnc.com/download.html
 123. http://www.realvnc.com/download-free.html
 124. http://sourceforge.net/projects/cotvnc/
 125. http://www.karlrunge.com/x11vnc/x11vnc_opts.html
 126. http://www.karlrunge.com/x11vnc/x11vnc.c
 127. http://fredrik.hubbe.net/x2vnc.html
 128. http://www.hubbe.net/~hubbe/win2vnc.html
 129. http://www.deboer.gmxhome.de/
 130. http://sourceforge.net/projects/win2vnc/
 131. http://fredrik.hubbe.net/x2vnc.html
 132. http://freshmeat.net/projects/x2x/
 133. http://ftp.digital.com/pub/Digital/SRC/x2x/
 134. http://zapek.com/software/zvnc/
 135. http://www.karlrunge.com/x11vnc/index.html#8bpp
 136. http://www.karlrunge.com/x11vnc/index.html#overlays
 137. http://www.karlrunge.com/x11vnc/index.html#xauth_pain
 138. http://www.karlrunge.com/x11vnc/index.html#noshm
 139. http://www.karlrunge.com/x11vnc/index.html#tunnelling
 140. http://www.karlrunge.com/x11vnc/index.html#passwd
 141. http://www.karlrunge.com/x11vnc/index.html#passwdfile
 142. http://www.karlrunge.com/x11vnc/index.html#inetd
 143. ftp://ftp.x.org/
 144. http://www.karlrunge.com/x11vnc/dtVncPopup
 145. http://www.karlrunge.com/x11vnc/index.html#passwdfile
 146. http://www.karlrunge.com/x11vnc/index.html#tunnelling
 147. http://www.karlrunge.com/x11vnc/index.html#tunnelling
 148. http://www.karlrunge.com/x11vnc/index.html#tunnelling
 149. http://www.karlrunge.com/x11vnc/index.html#tunnelling
 150. http://www.karlrunge.com/x11vnc/blockdpy.c
 151. http://www.karlrunge.com/x11vnc/index.html#display_manager
 152. http://www.karlrunge.com/x11vnc/index.html#inetd
 153. http://www.karlrunge.com/x11vnc/index.html#x11vnc_loop
 154. http://www.jirka.org/gdm-documentation/x241.html
 155. http://www.karlrunge.com/x11vnc/x11vnc_loop
 156. http://www.karlrunge.com/x11vnc/index.html#xterminal_xauth
 157. http://www.karlrunge.com/x11vnc/shm_clear
 158. http://www.karlrunge.com/x11vnc/index.html#noshm
 159. http://www.tightvnc.com/
 160. http://www.karlrunge.com/x11vnc/tight-vncviewer-alphahack.patch
 161. http://www.tightvnc.com/
 162. http://www.karlrunge.com/x11vnc/index.html#greaterless
 163. http://www.karlrunge.com/x11vnc/index.html#xkbmodtweak
 164. http://www.karlrunge.com/x11vnc/index.html#xkbmodtweak
 165. http://www.karlrunge.com/x11vnc/index.html#display_manager
 166. http://www.karlrunge.com/x11vnc/index.html#scaling
 167. 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 -opts      (see below for -help long descriptions)

x11vnc: allow VNC connections to real X11 displays. 0.7.1 lastmod: 2005-02-22

x11vnc options:
  -display disp            -auth file             
  -id windowid             -sid windowid          
  -flashcmap               -notruecolor           
  -visual n                -overlay               
  -overlay_nocursor        -scale fraction        
  -viewonly                -shared                
  -once                    -forever               
  -timeout n               -inetd                 
  -connect string          -vncconnect            
  -novncconnect            -allow host1[,host2..] 
  -localhost               -input string          
  -viewpasswd string       -passwdfile filename   
  -storepasswd pass file   -accept string         
  -gone string             -users list            
  -noshm                   -flipbyteorder         
  -onetile                 -solid [color]         
  -blackout string         -xinerama              
  -xrandr [mode]           -padgeom WxH           
  -o logfile               -rc filename           
  -norc                    -h, -help              
  -?, -opts                -V, -version           
  -q                       -bg                    
  -modtweak                -nomodtweak            
  -xkb                     -skip_keycodes string  
  -add_keysyms             -clear_mods            
  -clear_keys              -remap string          
  -norepeat                -repeat                
  -nofb                    -nobell                
  -nosel                   -noprimary             
  -cursor [mode]           -nocursor              
  -noxfixes                -alphacut n            
  -alphafrac fraction      -alpharemove           
  -noalphablend            -nocursorshape         
  -cursorpos               -nocursorpos           
  -xwarppointer            -buttonmap string      
  -nodragging              -pointer_mode n        
  -input_skip n            -speeds rd,bw,lat      
  -debug_pointer           -debug_keyboard        
  -defer time              -wait time             
  -nap                     -nonap                 
  -sb time                 -sigpipe string        
  -threads                 -nothreads             
  -fs f                    -gaps n                
  -grow n                  -fuzz n                
  -snapfb                  -gui [gui-opts]        
  -remote command          -query variable        
  -sync                    -noremote              
  -unsafe                  -safer                 
  -deny_all              

libvncserver options:
-rfbport port          TCP port for RFB protocol
-rfbwait time          max time in ms to wait for RFB client
-rfbauth passwd-file   use authentication on RFB protocol
                       (use 'storepasswd' to create a password file)
-passwd plain-password use authentication 
                       (use plain-password as password, USE AT YOUR RISK)
-deferupdate time      time in ms to defer updates (default 40)
-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



% x11vnc -help

x11vnc: allow VNC connections to real X11 displays. 0.7.1 lastmod: 2005-02-22

Typical usage is:

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

       x11vnc -display :0

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

       vncviewer far-host:0

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

By default x11vnc will not allow the screen to be shared and it will exit
as soon as the client disconnects.  See -shared and -forever below to override
these protections.  See the FAQ on how to tunnel the VNC connection through
an encrypted channel such as ssh(1).

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


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

Options:

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

-id windowid           Show the window corresponding to "windowid" not
                       the entire display.  New windows like popup menus,
                       transient toplevels, etc, may not be seen or may be
                       clipped.  Disabling SaveUnders or BackingStore in the
                       X server may help show them.  x11vnc may crash if the
                       window is initially partially obscured, changes size,
                       is iconified, etc.  Some steps are taken to avoid this
                       and the -xrandr mechanism is used to track resizes.  Use
                       xwininfo(1) to get the window id, or use "-id pick"
                       to have x11vnc run xwininfo(1) for you and extract
                       the id.  The -id option is useful for exporting very
                       simple applications (e.g. the current view on a webcam).
-sid windowid          As -id, but instead of using the window directly it
                       shifts a root view to it: this shows SaveUnders menus,
                       etc, although they will be clipped if they extend beyond
                       the window.
-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).
-visual n              Experimental option: probably does not do what you
                       think.  It simply *forces* the visual used for the
                       framebuffer; this may be a bad thing... (e.g. messes
                       up colors or cause a crash). It is useful for testing
                       and for some workarounds.  n may be a decimal number,
                       or 0x hex.  Run xdpyinfo(1) for the values.  One may
                       also use "TrueColor", etc. see <X11/X.h> for a list.
                       If the string ends in ":m" the for better or for
                       worse the visual depth is forced to be m.
-overlay               Handle multiple depth visuals on one screen, e.g. 8+24
                       and 24+8 overlay visuals (the 32 bits per pixel are
                       packed with 8 for PseudoColor and 24 for TrueColor).

                       Currently -overlay only works on Solaris via
                       XReadScreen(3X11) and IRIX using XReadDisplay(3).
                       On Solaris there is a problem with image "bleeding"
                       around transient popup menus (but not for the menu
                       itself): a workaround is to disable SaveUnders
                       by passing the "-su" argument to Xsun (in
                       /etc/dt/config/Xservers).  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 to
                       be 8bpp (8+24), or they will use 8bpp PseudoColor even
                       when the default visual is depth 24 TrueColor (24+8).
                       In these cases colors in some windows will be messed
                       up in x11vnc unless -overlay is used.  Another use of
                       -overlay is to enable showing the exact mouse cursor
                       shape (details below).

                       Under -overlay, performance will be somewhat 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 (e.g. some apps have -use24 or -visual options).
-overlay_nocursor      Sets -overlay, but does not try to draw the exact mouse
                       cursor shape using the overlay mechanism.

-scale fraction        Scale the framebuffer by factor "fraction".  Values
                       less than 1 shrink the fb, larger ones expand it.
                       Note: image may not be sharp and response may be
                       slower.  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
-timeout n             Exit unless a client connects within the first n seconds
                       of startup.
-inetd                 Launched by inetd(1): stdio instead of listening socket.
                       Note: if you are not redirecting stderr to a log file
                       (via shell 2> or -o option) you must also specify the
                       -q option, otherwise the stderr goes to the viewer.
-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.
                       Be careful for this usage mode if x11vnc is running as
                       root (e.g. via inetd(1) or gdm(1)).
-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

-allow host1[,host2..] Only allow client connections from hosts matching
                       the comma separated list of hostnames or IP addresses.
                       Can also be a numerical IP prefix, e.g. "192.168.100."
                       to match a simple subnet, for more control build
                       libvncserver with libwrap support (See the FAQ).  If the
                       list contains a "/" it instead is a interpreted as a
                       file containing addresses or prefixes that is re-read
                       each time a new client connects.  Lines can be commented
                       out with the "#" character in the usual way.
-localhost             Same as -allow 127.0.0.1

-input string          Fine tuning of allowed user input.  If "string" does
                       not contain a comma "," the tuning applies only to
                       normal clients.  Otherwise the part before "," is
                       for normal clients and the part after for view-only
                       clients.  "K" is for Keystroke input, "M" for
                       Mouse-motion input, and "B" for Button-click input.
                       Their presence in the string enables that type of input.
                       E.g. "-input M" means normal users can only move
                       the mouse and  "-input KMB,M" lets normal users do
                       anything and enables view-only users to move the mouse.
                       This option is ignored when a global -viewonly is in
                       effect (all input is discarded).
-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 (where
                       others might see it via ps(1)).  If a second non blank
                       line exists in the file it is taken as a view-only
                       password (i.e. -viewpasswd) To supply an empty password
                       for either field the string "__EMPTY__" may be used.
                       Note: -passwdfile is a simple plaintext passwd, see
                       also -rfbauth and -storepasswd below for obfuscated
                       VNC password files.  Neither file should be readable
                       by others.
-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, shell characters, etc.  If the
                       external command returns 0 the client is accepted,
                       otherwise the client is rejected.  See below for an
                       extension to accept a client view-only.

                       If x11vnc is running as root (say from inetd(1) or from
                       display managers xdm(1), gdm(1), etc), think about the
                       security implications carefully before supplying this
                       option (likewise for the -gone option).

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

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

                       If "string" is "xmessage" then an xmessage(1)
                       invocation is used for the command.  xmessage must be
                       installed on the machine for this to work.

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

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

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

                       More -accept tricks: use "popupmouse" to only allow
                       mouse clicks in the builtin popup to be recognized.
                       Similarly use "popupkey" to only recognize
                       keystroke responses.  These are to help avoid the
                       user accidentally accepting a client by typing or
                       clicking. All 3 of the popup keywords can be followed
                       by +N+M to supply a position for the popup window.
                       The default is to center the popup window.
-gone string           As -accept, except to run a user supplied command when
                       a client goes away (disconnects).  RFB_MODE will be
                       set to "gone" and the other RFB_* variables are as
                       in -accept.  Unlike -accept, the command return code
                       is not interpreted by x11vnc.  Example: -gone 'xlock &'

-users list            If x11vnc is started as root (say from inetd(1) or from
                       display managers xdm(1), gdm(1), etc), then as soon
                       as possible after connections to the X display are
                       established try to switch to one of the users in the
                       comma separated "list".  If x11vnc is not running as
                       root this option is ignored.
                       
                       Why use this option?  In general it is not needed since
                       x11vnc is already connected to the X display and can
                       perform its primary functions.  The option was added
                       to make some of the *external* utility commands x11vnc
                       occasionally runs work properly.  In particular under
                       GNOME and KDE to implement the "-solid color" feature
                       external commands (gconftool-2 and dcop) must be run
                       as the user owning the desktop session.  Since this
                       option switches userid it also affects the userid used
                       to run the processes for the -accept and -gone options.
                       It also affects the ability to read files for options
                       such as -connect, -allow, and -remap.  Note that the
                       -connect file is also sometimes written to.
                       
                       So be careful with this option since in many situations
                       its use can decrease security.
                       
                       The switch to a user will only take place if the
                       display can still be successfully opened as that user
                       (this is primarily to try to guess the actual owner
                       of the session). Example: "-users fred,wilma,betty".
                       Note that a malicious user "barney" by quickly using
                       "xhost +" when logging in may get x11vnc to switch
                       to user "fred".  What happens next?
                       
                       Under display managers it may be a long time before
                       the switch succeeds (i.e. a user logs in).  To make
                       it switch immediately regardless if the display
                       can be reopened prefix the username with the "+"
                       character. E.g. "-users +bob" or "-users +nobody".
                       The latter (i.e. switching immediately to user
                       "nobody") is probably the only use of this option
                       that increases security.
                       
                       To immediately switch to a user *before* connections
                       to the X display are made or any files opened use the
                       "=" character: "-users =bob".  That user needs to
                       be able to open the X display of course.
                       
                       The special user "guess=" means to examine the utmpx
                       database (see who(1)) looking for a user attached to
                       the display number (from DISPLAY or -display option)
                       and try him/her.  To limit the list of guesses, use:
                       "-users guess=bob,betty".
                       
                       Even more sinister is the special user "lurk=" that
                       means to try to guess the DISPLAY from the utmpx login
                       database as well.  So it "lurks" waiting for anyone
                       to log into an X session and then connects to it.
                       Specify a list of users after the = to limit which
                       users will be tried.  To enable a difference searching
                       mode, if the first user in the list is something like
                       ":0" or ":0-2" that indicates a range of DISPLAY
                       numbers that will be tried (regardless of whether
                       they are in the utmpx database) for all users that
                       are logged in.  Examples: "-users lurk=" and also
                       "-users lurk=:0-1,bob,mary"
                       
                       Be especially careful using the "guess=" and "lurk="
                       modes.  They are not recommended for use on machines
                       with untrustworthy local users.
                       
-noshm                 Do not use the MIT-SHM extension for the polling.
                       Remote displays can be polled this way: be careful this
                       can use large amounts of network bandwidth.  This is
                       also of use if the local machine has a limited number
                       of shm segments and -onetile is not sufficient.
-flipbyteorder         Sometimes needed if remotely polled host has different
                       endianness.  Ignored unless -noshm is set.
-onetile               Do not use the new copy_tiles() framebuffer mechanism,
                       just use 1 shm tile for polling.  Limits shm segments
                       used to 3.

-solid [color]         To improve performance, when VNC clients are connected
                       try to change the desktop background to a solid color.
                       The [color] is optional: the default color is "cyan4".
                       For a different one specify the X color (rgb.txt name,
                       e.g. "darkblue" or numerical "#RRGGBB").

                       Currently this option only works on GNOME, KDE, CDE,
                       and classic X (i.e. with the background image on the
                       root window).  The "gconftool-2" and "dcop" external
                       commands are run for GNOME and KDE respectively.
                       Other desktops won't work, e.g. Xfce (send us the
                       corresponding commands if you find them).  If x11vnc is
                       running as root (inetd(1) or gdm(1)), the -users option
                       may be needed for GNOME and KDE.  If x11vnc guesses
                       your desktop incorrectly, you can force it by prefixing
                       color with "gnome:", "kde:", "cde:" or "root:".
-blackout string       Black out rectangles on the screen. "string" is a
                       comma separated list of WxH+X+Y type geometries for
                       each rectangle.
-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.

-xrandr [mode]         If the display supports the XRANDR (X Resize, Rotate
                       and Reflection) extension, and you expect XRANDR events
                       to occur to the display while x11vnc is running, this
                       options indicates x11vnc should try to respond to
                       them (as opposed to simply crashing by assuming the
                       old screen size).  See the xrandr(1) manpage and run
                       'xrandr -q' for more info.  [mode] is optional and
                       described below.

                       Since watching for XRANDR events and trapping errors
                       increases polling overhead, only use this option if
                       XRANDR changes are expected.  For example on a rotatable
                       screen PDA or laptop, or using a XRANDR-aware Desktop
                       where you resize often.  It is best to be viewing with a
                       vncviewer that supports the NewFBSize encoding, since it
                       knows how to react to screen size changes.  Otherwise,
                       libvncserver tries to do so something reasonable for
                       viewers that cannot do this (portions of the screen
                       may be clipped, unused, etc).

                       "mode" defaults to "resize", which means create a
                       new, resized, framebuffer and hope all viewers can cope
                       with the change.  "newfbsize" means first disconnect
                       all viewers that do not support the NewFBSize VNC
                       encoding, and then resize the framebuffer.  "exit"
                       means disconnect all viewer clients, and then terminate
                       x11vnc.
-padgeom WxH           Whenever a new vncviewer connects, the framebuffer is
                       replaced with a fake, solid black one of geometry WxH.
                       Shortly afterwards the framebuffer is replaced with the
                       real one.  This is intended for use with vncviewers
                       that do not support NewFBSize and one wants to make
                       sure the initial viewer geometry will be big enough
                       to handle all subsequent resizes (e.g. under -xrandr,
                       -remote id:windowid, rescaling, etc.)

-o logfile             Write stderr messages to file "logfile" instead of
                       to the terminal.  Same as "-logfile file".  To append
                       to the file use "-oa file" or "-logappend file".
-rc filename           Use "filename" instead of $HOME/.x11vncrc for rc file.
-norc                  Do not process any .x11vncrc file for options.
-h, -help              Print this help text.
-?, -opts              Only list the x11vnc options.
-V, -version           Print program version and last modification date.

-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
                       the X display supports it) to do the modifier tweaking.
                       This is powerful and should be tried if there are still
                       keymapping problems when using -modtweak by itself.
-skip_keycodes string  Ignore the comma separated list of decimal keycodes.
                       Perhaps these are keycodes not on your keyboard but
                       your X server thinks exist.  Currently only applies
                       to -xkb mode.  Use this option to help x11vnc in the
                       reverse problem it tries to solve: Keysym -> Keycode(s)
                       when ambiguities exist (more than one Keycode per
                       Keysym).  Run 'xmodmap -pk' to see your keymapping.
                       Example: "-skip_keycodes 94,114"
-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 x11vnc exits.
-clear_mods            At startup and exit clear the modifier keys by sending
                       KeyRelease for each one. The Lock modifiers are skipped.
                       Used to clear the state if the display was accidentally
                       left with any pressed down.
-clear_keys            As -clear_mods, except try to release any pressed key.
                       Note that this option and -clear_mods can interfere
                       with a person typing at the physical keyboard.
-remap string          Read Keysym remappings from file named "string".
                       Format is one pair of Keysyms per line (can be name
                       or hex value) separated by a space.  If no file named
                       "string" exists, it is instead interpreted as this
                       form: key1-key2,key3-key4,...  See <X11/keysymdef.h>
                       header file for a list of Keysym names, or use xev(1).
                       To map a key to a button click, use the fake Keysyms
                       "Button1", ..., etc. E.g: "-remap Super_R-Button2"
                       (useful for pasting on a laptop)
-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: -norepeat

-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 to disable).  For other viewers the cursor shape
                       is written directly to the framebuffer every time the
                       pointer is moved or changed and gets sent along with
                       the other framebuffer updates.  In this case, there
                       will be some lag between the vnc viewer pointer and
                       the remote cursor position.

                       If the X display supports retrieving the cursor shape
                       information from the X server, then the default is
                       to use that mode.  On Solaris this can be done with
                       the SUN_OVL extension using -overlay (see also the
                       -overlay_nomouse option).  A similar overlay scheme
                       is used on IRIX.  Xorg (e.g. Linux) and recent Solaris
                       Xsun servers support the XFIXES extension to retrieve
                       the exact cursor shape from the X server.  If XFIXES
                       is present it is preferred over Overlay and is used by
                       default (see -noxfixes below).  This can be disabled
                       with -nocursor, and also some values of the "mode"
                       option below.
                       
                       Note that under XFIXES cursors with transparency (alpha
                       channel) will not be exactly represented and one may
                       find Overlay preferable.  See also the -alphacut and
                       -alphafrac options below as fudge factors to try to
                       improve the situation for cursors with transparency
                       for a given theme.

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

                       "-cursor arrow" - just show the standard arrow
                       nothing more or nothing less.

                       "-cursor none" - same as "-nocursor"

                       "-cursor X" - when the cursor appears to be on the
                       root window, draw the familiar X shape.  Some desktops
                       such as GNOME cover up the root window completely,
                       and so this will not work, try "X1", etc, to try to
                       shift the tree depth.  On high latency links or slow
                       machines there will be a time lag between expected and
                       the actual cursor shape.

                       "-cursor some" - like "X" but use additional
                       heuristics to try to guess if the window should have
                       a windowmanager-like resizer cursor or a text input
                       I-beam cursor.  This is a complete hack, but may be
                       useful in some situations because it provides a little
                       more feedback about the cursor shape.

                       "-cursor most" - try to show as many cursors as
                       possible.  Often this will only be the same as "some"
                       unless the display has overlay visuals or XFIXES
                       extensions available.  On Solaris and IRIX if XFIXES
                       is not available, -overlay mode will be attempted.

-noxfixes              Do not use the XFIXES extension to draw the exact cursor
                       shape even if it is available.
-alphacut n            When using the XFIXES extension for the cursor shape,
                       cursors with transparency will not be displayed exactly
                       (but opaque ones will).  This option sets n as a cutoff
                       for cursors that have transparency ("alpha channel"
                       with values ranging from 0 to 255) Any cursor pixel with
                       alpha value less than n becomes completely transparent.
                       Otherwise the pixel is completely opaque.  Default 240
                       
                       Note: the options -alphacut, -alphafrac, and -alphafrac
                       may be removed if a more accurate internal method for
                       handling cursor transparency is implemented.
-alphafrac fraction    With the threshold in -alphacut some cursors will become
                       almost completely transparent because their alpha values
                       are not high enough.  For those cursors adjust the
                       alpha threshold until fraction of the non-zero alpha
                       channel pixels become opaque.  Default 0.33
-alpharemove           By default, XFIXES cursors pixels with transparency have
                       the alpha factor multiplied into the RGB color values
                       (i.e. that corresponding to blending the cursor with a
                       black background).  Specify this option to remove the
                       alpha factor. (useful for light colored semi-transparent
                       cursors).
-noalphablend          In XFIXES mode do not send cursor alpha channel data
                       to libvncserver.  The default is to send it.  The
                       alphablend effect will only be visible in -nocursorshape
                       mode or for clients with cursorshapeupdates turned
                       off. (However there is a hack for 32bpp with depth 24,
                       it uses the extra 8 bits to store cursor transparency
                       for use with a hacked vncviewer that applies the
                       transparency locally.  See the FAQ for more info).

-nocursorshape         Do not use the TightVNC CursorShapeUpdates extension
                       even if clients support it.  See -cursor above.
-cursorpos             Option -cursorpos enables sending the X cursor position
-nocursorpos           back to all vnc clients that support the TightVNC
                       CursorPosUpdates extension.  Other clients will be able
                       to see the pointer motions. Default: -cursorpos
-xwarppointer          Move the pointer with XWarpPointer(3X) instead of
                       the XTEST extension.  Use this as a workaround
                       if the pointer motion behaves incorrectly, e.g.
                       on touchscreens or other non-standard setups.
                       Also sometimes needed on XINERAMA displays.

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

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

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

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

-nodragging            Do not update the display during mouse dragging events
                       (mouse button held down).  Greatly improves response on
                       slow setups, but you lose all visual feedback for drags,
                       text selection, and some menu traversals.  It overrides
                       any -pointer_mode setting
-pointer_mode n        Various pointer motion update schemes. "-pm" is
                       an alias.  The problem is pointer motion can cause
                       rapid changes on the screen: consider the rapid changes
                       when you drag a large window around.  Neither x11vnc's
                       screen polling and vnc compression routines nor the
                       bandwidth to the vncviewers can keep up these rapid
                       screen changes: everything will bog down when dragging
                       or scrolling.  So a scheme has to be used to "eat"
                       much of that pointer input before re-polling the screen
                       and sending out framebuffer updates. The mode number
                       "n" can be 0 to 4 and selects one of the schemes
                       desribed below.

                       n=0: does the same as -nodragging. (all screen polling
                       is suspended if a mouse button is pressed.)

                       n=1: was the original scheme used to about Jan 2004:
                       it basically just skips -input_skip keyboard or pointer
                       events before repolling the screen.

                       n=2 is an improved scheme: by watching the current rate
                       of input events it tries to detect if it should try to
                       "eat" additional pointer events before continuing.

                       n=3 is basically a dynamic -nodragging mode: it detects
                       when the mouse motion has paused and then refreshes
                       the display.

                       n=4: attempts to measures network rates and latency,
                       the video card read rate, and how many tiles have been
                       changed on the screen.  From this, it aggressively tries
                       to push screen "frames" when it decides it has enough
                       resources to do so.  NOT FINISHED.

                       The default n is 2. Note that modes 2, 3, 4 will skip
                       -input_skip keyboard events (but it will not count
                       pointer events).  Also note that these modes are not
                       available in -threads mode which has its own pointer
                       event handling mechanism.

                       To try out the different pointer modes to see which
                       one gives the best response for your usage, it is
                       convenient to use the remote control function, for
                       example "x11vnc -R pm:4" or the tcl/tk gui (Tuning ->
                       pointer_mode -> n).

-input_skip n          For the pointer handling when non-threaded: try to
                       read n user input events before scanning display. n < 0
                       means to act as though there is always user input.
                       Default: 10

-speeds rd,bw,lat      x11vnc tries to estimate some speed parameters that
                       are used to optimize scheduling (e.g. -pointer_mode
                       4) and other things.  Use the -speeds option to set
                       these manually.  The triple "rd,bw,lat" corresponds
                       to video h/w read rate in MB/sec, network bandwidth to
                       clients in KB/sec, and network latency to clients in
                       milliseconds, respectively.  If a value is left blank,
                       e.g. "-speeds ,100,15", then the internal scheme is
                       used to estimate the empty value(s).

                       Typical PC video cards have read rates of 5-10 MB/sec.
                       If the framebuffer is in main memory instead of video
                       h/w (e.g. SunRay, shadowfb, Xvfb), the read rate may
                       be much faster.  "x11perf -getimage500" can be used
                       to get a lower bound (remember to factor in the bytes
                       per pixel).  It is up to you to estimate the network
                       bandwith to clients.  For the latency the ping(1)
                       command can be used.

                       For convenience there are some aliases provided,
                       e.g. "-speeds modem".  The aliases are: "modem" for
                       6,4,200; "dsl" for 6,100,50; and "lan" for 6,5000,1

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

-defer time            Time in ms to wait for updates before sending to client
                       (deferUpdateTime)  Default: 30
-wait time             Time in ms to pause between screen polls.  Used to cut
                       down on load.  Default: 30
-nap                   Monitor activity and if it is low take longer naps
-nonap                 between screen polls to really cut down load when idle.
                       Default: take naps
-sb time               Time in seconds after NO activity (e.g. screen blank)
                       to really throttle down the screen polls (i.e. sleep
                       for about 1.5 secs). Use 0 to disable.  Default: 60

-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
-snapfb                Instead of polling the X display framebuffer (fb) for
                       changes, periodically copy all of X display fb into main
                       memory and examine that copy for changes.  Under some
                       circumstances this will improve interactive response,
                       or at least make things look smoother, but in others
                       (many) it will make the response worse.  If the video
                       h/w fb is such that reading small tiles is very slow
                       this mode could help.  To keep the "framerate" up
                       the screen size x bpp cannot be too large.  Note that
                       this mode is very wasteful of memory I/O resources
                       (it makes full screen copies even if nothing changes).
                       It may be of use in video capture-like applications,
                       or where window tearing is a problem.

-gui [gui-opts]        Start up a simple tcl/tk gui based on the the remote
                       control options -remote/-query described below.
                       Requires the "wish" program to be installed on the
                       machine.  "gui-opts" is not required: the default is
                       to start up both the gui and x11vnc with the gui showing
                       up on the X display in the environment variable DISPLAY.

                       "gui-opts" can be a comma separated list of items.
                       Currently there are these types of items: 1) a gui mode,
                       a 2) gui "simplicity", and 3) the X display the gui
                       should display on.

                       1) The gui mode can be "start", "conn", or "wait"
                       "start" is the default mode above and is not required.
                       "conn" means do not automatically start up x11vnc,
                       but instead just try to connect to an existing x11vnc
                       process.  "wait" means just start the gui and nothing
                       else (you will later instruct the gui to start x11vnc
                       or connect to an existing one.)

                       2) The gui simplicity is off by default (a power-user
                       gui with all options is presented) To start with
                       something less daunting supply the string "simple"
                       ("ez" is an alias for this).  Once the gui is
                       started you can toggle between the two with "Misc ->
                       simple_gui".

                       3) Note the possible confusion regarding the potentially
                       two different X displays: x11vnc polls one, but you
                       may want the gui to appear on another.  For example, if
                       you ssh in and x11vnc is not running yet you may want
                       the gui to come back to you via your ssh redirected X
                       display (e.g. localhost:10).

                       Examples: "x11vnc -gui", "x11vnc -gui ez"
                       "x11vnc -gui localhost:10", "x11vnc -gui conn,host:0"

                       If you do not specify a gui X display in "gui-opts"
                       then the DISPLAY environment variable and -display
                       option are tried (in that order).  Regarding the x11vnc
                       X display the gui will try to connect to, it first
                       tries -display and then DISPLAY.  For example, "x11vnc
                       -display :0 -gui otherhost:0", will remote control an
                       x11vnc polling :0 and display the gui on otherhost:0

                       If you do not intend to start x11vnc from the gui
                       (i.e. just remote control an existing one), then the
                       gui process can run on a different machine from the
                       x11vnc server as long as X permissions, etc. permit
                       communication between the two.

-remote command        Remotely control some aspects of an already running
                       x11vnc server.  "-R" and "-r" are aliases for
                       "-remote".  After the remote control command is
                       sent to the running server the 'x11vnc -remote ...'
                       command exits.  You can often use the -query command
                       (see below) to see if the x11vnc server processed your
                       -remote command.

                       The default communication channel is that of X
                       properties (specifically VNC_CONNECT), and so this
                       command must be run with correct settings for DISPLAY
                       and possibly XAUTHORITY to connect to the X server
                       and set the property.  Alternatively, use the -display
                       and -auth options to set them to the correct values.
                       The running server cannot use the -novncconnect option
                       because that disables the communication channel.
                       See below for alternate channels.

                       For example: 'x11vnc -remote stop' (which is the same as
                       'x11vnc -R stop') will close down the x11vnc server.
                       'x11vnc -R shared' will enable shared connections, and
                       'x11vnc -R scale:3/4' will rescale the desktop.

                       Note: the more drastic the change induced by the -remote
                       command, the bigger the chance for bugs or crashes.
                       Please report reproducible bugs.

                       The following -remote/-R commands are supported:

                       stop            terminate the server, same as "quit"
                                       "exit" or "shutdown".
                       ping            see if the x11vnc server responds.
                                       Return is: ans=ping:<xdisplay>
                       blacken         try to push a black fb update to all
                                       clients (due to timings a client
                                       could miss it). Same as "zero", also
                                       "zero:x1,y1,x2,y2" for a rectangle.
                       refresh         send the entire fb to all clients.
                       reset           recreate the fb, polling memory, etc.
                       id:windowid     set -id window to "windowid". empty
                                       or "root" to go back to root window
                       sid:windowid    set -sid window to "windowid"
                       flashcmap       enable  -flashcmap mode.
                       noflashcmap     disable -flashcmap mode.
                       notruecolor     enable  -notruecolor mode.
                       truecolor       disable -notruecolor mode.
                       overlay         enable  -overlay mode (if applicable).
                       nooverlay       disable -overlay mode.
                       overlay_cursor  in -overlay mode, enable cursor drawing.
                       overlay_nocursor disable cursor drawing. same as
                                        nooverlay_cursor.
                       visual:vis      set -visual to "vis"
                       scale:frac      set -scale to "frac"
                       viewonly        enable  -viewonly mode.
                       noviewonly      disable -viewonly mode.
                       shared          enable  -shared mode.
                       noshared        disable -shared mode.
                       forever         enable  -forever mode.
                       noforever       disable -forever mode.
                       timeout:n       reset -timeout to n, if there are
                                       currently no clients, exit unless one
                                       connects in the next n secs.
                       deny            deny any new connections, same as "lock"
                       nodeny          allow new connections, same as "unlock"
                       connect:host    do reverse connection to host, "host"
                                       may be a comma separated list of hosts
                                       or host:ports.  See -connect.
                       disconnect:host disconnect any clients from "host"
                                       same as "close:host".  Use host
                                       "all" to close all current clients.
                                       If you know the client internal hex ID,
                                       e.g. 0x3 (returned by -query clients and
                                       RFB_CLIENT_ID), you can use that too.
                       allowonce:host  For the next connection only, allow
                                       connection from "host".
                       allow:hostlist  set -allow list to (comma separated)
                                       "hostlist". See -allow and -localhost.
                                       Do not use with -allow /path/to/file
                                       Use "+host" to add a single host, and
                                       use "-host" to delete a single host
                       localhost       enable  -localhost mode
                       nolocalhost     disable -localhost mode
                       input:str       set -input to "str", empty to disable.
                       client_input:str set the K, M, B -input on a per-client
                                       basis.  select which client as for
                                       disconnect, e.g. client_input:host:MB
                                       or client_input:0x2:K
                       accept:cmd      set -accept "cmd" (empty to disable).
                       gone:cmd        set -gone "cmd" (empty to disable).
                       noshm           enable  -noshm mode.
                       shm             disable -noshm mode (i.e. use shm).
                       flipbyteorder   enable -flipbyteorder mode, you may need
                                       to set noshm for this to do something.
                       noflipbyteorder disable -flipbyteorder mode.
                       onetile         enable  -onetile mode. (you may need to
                                       set shm for this to do something)
                       noonetile       disable -onetile mode.
                       solid           enable  -solid mode
                       nosolid         disable -solid mode.
                       solid_color:color set -solid color (and apply it).
                       blackout:str    set -blackout "str" (empty to disable).
                                       See -blackout for the form of "str"
                                       (basically: WxH+X+Y,...)
                                       Use "+WxH+X+Y" to append a single
                                       rectangle use "-WxH+X+Y" to delete one
                       xinerama        enable  -xinerama mode. (if applicable)
                       noxinerama      disable -xinerama mode.
                       xrandr          enable  -xrandr mode. (if applicable)
                       noxrandr        disable -xrandr mode.
                       xrandr_mode:mode set the -xrandr mode to "mode".
                       padgeom:WxH     set -padgeom to WxH (empty to disable)
                                       If WxH is "force" or "do" the padded
                                       geometry fb is immediately applied.
                       quiet           enable  -quiet mode.
                       noquiet         disable -quiet mode.
                       modtweak        enable  -modtweak mode.
                       nomodtweak      enable  -nomodtweak mode.
                       xkb             enable  -xkb modtweak mode.
                       noxkb           disable -xkb modtweak mode.
                       skip_keycodes:str enable -xkb -skip_keycodes "str".
                       add_keysyms     enable -add_keysyms mode.
                       noadd_keysyms   stop adding keysyms. those added will
                                       still be removed at exit.
                       clear_mods      enable  -clear_mods mode and clear them.
                       noclear_mods    disable -clear_mods mode.
                       clear_keys      enable  -clear_keys mode and clear them.
                       noclear_keys    disable -clear_keys mode.
                       remap:str       set -remap "str" (empty to disable).
                                       See -remap for the form of "str"
                                       (basically: key1-key2,key3-key4,...)
                                       Use "+key1-key2" to append a single
                                       keymapping, use "-key1-key2" to delete.
                       norepeat        enable  -norepeat mode.
                       repeat          disable -norepeat mode.
                       nofb            enable  -nofb mode.
                       fb              disable -nofb mode.
                       bell            enable  bell (if supported).
                       nobell          disable bell.
                       nosel           enable  -nosel mode.
                       sel             disable -nosel mode.
                       noprimary       enable  -noprimary mode.
                       primary         disable -noprimary mode.
                       cursor:mode     enable  -cursor "mode".
                       show_cursor     enable  showing a cursor.
                       noshow_cursor   disable showing a cursor. (same as
                                       "nocursor")
                       xfixes          enable  xfixes cursor shape mode.
                       noxfixes        disable xfixes cursor shape mode.
                       alphacut:n      set -alphacut to n.
                       alphafrac:f     set -alphafrac to f.
                       alpharemove     enable  -alpharemove mode.
                       noalpharemove   disable -alpharemove mode.
                       alphablend      disable -noalphablend mode.
                       noalphablend    enable  -noalphablend mode.
                       cursorshape     disable -nocursorshape mode.
                       nocursorshape   enable  -nocursorshape mode.
                       cursorpos       disable -nocursorpos mode.
                       nocursorpos     enable  -nocursorpos mode.
                       xwarp           enable  -xwarppointer mode.
                       noxwarp         disable -xwarppointer mode.
                       buttonmap:str   set -buttonmap "str", empty to disable
                       dragging        disable -nodragging mode.
                       nodragging      enable  -nodragging mode.
                       pointer_mode:n  set -pointer_mode to n. same as "pm"
                       input_skip:n    set -input_skip to n.
                       speeds:str      set -speeds to str.
                       debug_pointer   enable  -debug_pointer, same as "dp"
                       nodebug_pointer disable -debug_pointer, same as "nodp"
                       debug_keyboard   enable  -debug_keyboard, same as "dk"
                       nodebug_keyboard disable -debug_keyboard, same as "nodk"
                       defer:n         set -defer to n ms,same as deferupdate:n
                       wait:n          set -wait to n ms.
                       rfbwait:n       set -rfbwait (rfbMaxClientWait) to n ms.
                       nap             enable  -nap mode.
                       nonap           disable -nap mode.
                       sb:n            set -sb to n s, same as screen_blank:n
                       fs:frac         set -fs fraction to "frac", e.g. 0.5
                       gaps:n          set -gaps to n.
                       grow:n          set -grow to n.
                       fuzz:n          set -fuzz to n.
                       snapfb          enable  -snapfb mode.
                       nosnapfb        disable -snapfb mode.
                       progressive:n   set libvncserver -progressive slice
                                       height parameter to n.
                       desktop:str     set -desktop name to str for new clients
.
                       rfbport:n       set -rfbport to n.
                       http            enable  http client connections.
                       nohttp          disable http client connections.
                       httpport:n      set -httpport to n.
                       httpdir:dir     set -httpdir to dir (and enable http).
                       enablehttpproxy   enable  -enablehttpproxy mode.
                       noenablehttpproxy disable -enablehttpproxy mode.
                       alwaysshared     enable  -alwaysshared mode.
                       noalwaysshared   disable -alwaysshared mode.
                                        (may interfere with other options)
                       nevershared      enable  -nevershared mode.
                       nonevershared    disable -nevershared mode.
                                        (may interfere with other options)
                       dontdisconnect   enable  -dontdisconnect mode.
                       nodontdisconnect disable -dontdisconnect mode.
                                        (may interfere with other options)
                       noremote        disable the -remote command processing,
                                       it cannot be turned back on.

                       The vncconnect(1) command from standard VNC
                       distributions may also be used if string is prefixed
                       with "cmd=" E.g. 'vncconnect cmd=stop'.  Under some
                       circumstances xprop(1) can used if it supports -set
                       (see the FAQ).

                       If "-connect /path/to/file" has been supplied to the
                       running x11vnc server then that file can be used as a
                       communication channel (this is the only way to remote
                       control one of many x11vnc's polling the same X display)
                       Simply run: 'x11vnc -connect /path/to/file -remote ...'
                       or you can directly write to the file via something
                       like: "echo cmd=stop > /path/to/file", etc.

-query variable        Like -remote, except just query the value of
                       "variable".  "-Q" is an alias for "-query".
                       Multiple queries can be done by separating variables
                       by commas, e.g. -query var1,var2. The results come
                       back in the form ans=var1:value1,ans=var2:value2,...
                       to the standard output.  If a variable is read-only,
                       it comes back with prefix "aro=" instead of "ans=".

                       Some -remote commands are pure actions that do not make
                       sense as variables, e.g. "stop" or "disconnect",
                       in these cases the value returned is "N/A".  To direct
                       a query straight to the VNC_CONNECT property or connect
                       file use "qry=..." instead of "cmd=..."

                       Here is the current list of "variables" that can
                       be supplied to the -query command. This includes the
                       "N/A" ones that return no useful info.  For variables
                       names that do not correspond to an x11vnc option or
                       remote command, we hope the name makes it obvious what
                       the returned value corresponds to (hint: the ext_*
                       variables correspond to the presence of X extensions):

                       ans= stop quit exit shutdown ping blacken zero
                       refresh reset close disconnect id sid waitmapped
                       nowaitmapped flashcmap noflashcmap truecolor notruecolor
                       overlay nooverlay overlay_cursor overlay_yescursor
                       nooverlay_nocursor nooverlay_cursor nooverlay_yescursor
                       overlay_nocursor visual scale viewonly noviewonly
                       shared noshared forever noforever once timeout deny
                       lock nodeny unlock connect allowonce allow localhost
                       nolocalhost accept gone shm noshm flipbyteorder
                       noflipbyteorder onetile noonetile solid_color solid
                       nosolid blackout xinerama noxinerama xrandr noxrandr
                       xrandr_mode padgeom quiet q noquiet modtweak nomodtweak
                       xkb noxkb skip_keycodes add_keysyms noadd_keysyms
                       clear_mods noclear_mods clear_keys noclear_keys
                       remap repeat norepeat fb nofb bell nobell sel
                       nosel primary noprimary cursorshape nocursorshape
                       cursorpos nocursorpos cursor show_cursor noshow_cursor
                       nocursor xfixes noxfixes alphacut alphafrac alpharemove
                       noalpharemove alphablend noalphablend xwarp xwarppointer
                       noxwarp noxwarppointer buttonmap dragging nodragging
                       pointer_mode pm input_skip input client_input speeds
                       debug_pointer dp nodebug_pointer nodp debug_keyboard dk
                       nodebug_keyboard nodk deferupdate defer wait rfbwait
                       nap nonap sb screen_blank fs gaps grow fuzz snapfb
                       nosnapfb progressive rfbport http nohttp httpport
                       httpdir enablehttpproxy noenablehttpproxy alwaysshared
                       noalwaysshared nevershared noalwaysshared dontdisconnect
                       nodontdisconnect desktop noremote

                       aro=  display vncdisplay desktopname http_url auth
                       users rootshift scale_str scaled_x scaled_y scale_numer
                       scale_denom scale_fac scaling_noblend scaling_nomult4
                       scaling_pad scaling_interpolate inetd safer unsafe
                       passwdfile using_shm logfile o rc norc h help V version
                       lastmod bg sigpipe threads clients client_count pid
                       ext_xtest ext_xkb ext_xshm ext_xinerama ext_overlay
                       ext_xfixes ext_xdamage ext_xrandr rootwin num_buttons
                       button_mask mouse_x mouse_y bpp depth indexed_color
                       dpy_x dpy_y rfbauth passwd

-sync                  By default -remote commands are run asynchronously, that
                       is, the request is posted and the program immediately
                       exits.  Use -sync to have the program wait for an
                       acknowledgement from the x11vnc server that command
                       was processed.  On the other hand -query requests are
                       always processed synchronously because they have wait
                       for the result.

                       Also note that if both -remote and -query requests are
                       supplied on the command line, the -remote is processed
                       first (synchronously: no need for -sync), and then
                       the -query request is processed in the normal way.
                       This allows for a reliable way to see if the -remote
                       command was processed by querying for any new settings.
                       Note however that there is timeout of a few seconds so
                       if the x11vnc takes longer than that to process the
                       requests the requestor will think that a failure has
                       taken place.

-noremote              Do not process any remote control commands or queries.

                       A note about security wrt remote control commands.
                       If someone can connect to the X display and change the
                       property VNC_CONNECT, then they can remotely control
                       x11vnc.  Normally access to the X display is protected.
                       Note that if they can modify VNC_CONNECT, they could
                       also run their own x11vnc and have complete control
                       of the desktop.  If the  "-connect /path/to/file"
                       channel is being used, obviously anyone who can
                       write to /path/to/file can remotely control x11vnc.
                       So be sure to protect the X display and that file's
                       write permissions.

                       To disable the VNC_CONNECT property channel completely
                       use -novncconnect.

-unsafe                If x11vnc is running as root (e.g. inetd or Xsetup for
                       a display manager) a few remote commands are disabled
                       (currently: id:pick, accept:<cmd>, and gone:<cmd>)
                       because they are associated with running external
                       programs.  If you specify -unsafe, then these remote
                       control commands are allowed when running as root.
                       When running as non-root all commands are allowed.
                       See -safer below.
-safer                 Even if not running as root, disable the above unsafe
                       remote control commands.

-deny_all              For use with -remote nodeny: start out denying all
                       incoming clients until "-remote nodeny" is used to
                       let them in.


These options are passed to libvncserver:

-rfbport port          TCP port for RFB protocol
-rfbwait time          max time in ms to wait for RFB client
-rfbauth passwd-file   use authentication on RFB protocol
                       (use 'storepasswd' to create a password file)
-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 -add_keysyms

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

References

   1. mailto:xvml@karlrunge.com