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libtdevnc/x11vnc/README

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x11vnc README file Date: Sat Jan 15 23:37:28 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. 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
(e.g. via $PATH) 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 (because MIT-SHM shared memory is used to poll
the X11 framebuffer).
Step 2. In that far-away.east shell (with command prompt "far-away>"
in this example) run x11vnc directed at the far-away.east X session
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).
Desktop Sharing: The above more or less assumed nobody was sitting at
the workstation display "far-away.east:0". This is often the case: a
user wants to access her workstation remotely. Another usage pattern
has the user sitting at "far-away.east:0" and invites one or more
other people to view and interact with his desktop. Perhaps the user
gives a demo or presentation this way (using the telephone for vocal
communication). A "Remote Help Desk" mode would be similar: a
technician remotely connects to the user's desktop to interactively
solve a problem the user is having.
For these cases it should be obvious how it is done. The above steps
will work, but more easily the user sitting at far-away.east:0 simply
starts up x11vnc from a terminal window, after which the guests would
start their VNC viewers. For this usage mode the -accept popup option
discussed in the [15]FAQ below may be of use to allow the user at
far-away.east:0 to accept or reject incoming connections.
_________________________________________________________________
Tunnelling x11vnc via ssh:
The above example had no security or privacy at all. When logging into
remote machines (certainly when going over the internet) it is best to
use ssh, or use a VPN. For x11vnc one can tunnel the VNC protocol
through the encrypted ssh channel. It would look something like this:
sitting-here> ssh -L 5900:localhost:5900 far-away.east 'x11vnc -display :0'
(you will likely have to provide passwords/passphrases for the ssh
login) and then in another terminal window on sitting-here run the
command:
sitting-here> vncviewer -encodings "copyrect tight 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 [16]inetd(1)). See the 3rd
script example [17]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 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 [18]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 [19]-storepasswd
option can be used to create the password file. x11vnc also has the
slightly less secure [20]-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
[21]options and building x11vnc with [22]tcp_wrappers support to limit
host access.
_________________________________________________________________
Downloading x11vnc:
x11vnc is a contributed program to the [23]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 [24]x11vnc-0.7.tar.gz source package is
released (recommended download) . The [25]x11vnc 0.7 release notes.
The x11vnc package is the subset of the libvncserver package needed to
build the x11vnc program. (Please do not use the LibVNCServer-0.6
tarball: it contains an older, more buggy version of x11vnc (Oct 2003)
that you likely want to avoid). Also, you can get a copy of my latest,
bleeding edge [26]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 [27]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 [28]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:
* [29]http://www.tightvnc.com/download.html
* [30]http://www.realvnc.com/download-free.html
* [31]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:
* [32]rx11vnc wrapper script
* [33]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 $HOME/bin
Or do make install, it will probably install to /usr/local/bin (run
./configure --help for information on customizing your configuration).
You can now run it via typing "x11vnc", "x11vnc -help", "x11vnc -nap
-display :0", etc.
Note: Currently gcc is required to build libvncserver. In some cases
it will build with non-gcc compilers, but the resulting binary often
fails to run properly.
Building on Solaris: Depending on your version of Solaris (or other
Unix OS), the jpeg and/or zlib libraries may be in non-standard places
(e.g. /usr/local, /usr/sfw, /opt/sfw, etc).
Note: If configure cannot find these two libraries then TightVNC and
ZRLE encoding support will be disabled, and you don't want that! (the
TightVNC encoding gives very good compression and performance, it even
makes a noticeable difference over a fast LAN)
libjpeg is included in Solaris 9 and later (/usr/sfw/include and
/usr/sfw/lib), and zlib in Solaris 8 and later (/usr/include and
/usr/lib). To get the source for these libraries: libjpeg is available
at [34]ftp://ftp.uu.net/graphics/jpeg/ and zlib at
[35]http://www.gzip.org/zlib/. See also
[36]http://www.sunfreeware.com/ for Solaris binary packages of these
libraries.
Here is a build script that indicates one way to pass the library
locations information to the libvncserver configuration:
#!/bin/sh
# Build script for Solaris, etc, with gcc, libjpeg and libz in
# non-standard locations.
PATH=/path/to/gcc/bin:/usr/ccs/bin:$PATH # set to get gcc
JPEG=/path/to/jpeg # maybe "/usr/local", "/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="$LDFLAGS -L /usr/openwin/lib -R /usr/openwin/lib"
# This only applies to Solaris 10 or later (XFIXES and DAMAGE)
LDFLAGS="$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.
There is a build problem on Solaris 7 11/99 (update 4) where the
header file X11/extensions/XKBstr.h that X11/XKBlib.h uses was not
shipped. The x11vnc configure succeeds and sets
LIBVNCSERVER_HAVE_XKEYBOARD in rfb/rfbconfig.h but then the build of
x11vnc fails in the make. A workaround is to remove all lines
referring to LIBVNCSERVER_HAVE_XKEYBOARD in rfb/rfbconfig.h after
configure has been run. Alternatively, one could put #undef
LIBVNCSERVER_HAVE_XKEYBOARD after the rfb/rfb.h include in the
x11vnc/x11vnc.c file. (This problem has been fixed as of x11vnc 0.6.2
(Aug/2004))
If you need to build on Solaris 2.5.1 or earlier, see [37]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.
I also find the [38]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 [39]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 [40]-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 [41]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)
[42]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
if it can get it, in which case the VNC display (i.e. the information
you supply to the VNC viewer) is something like sunray-server:0
(note the :0 corresponding to port 5900, it is not :137). If it cannot
get 5900, it tries for 5901, and so on. You can also try to force the
port (and thereby the VNC display) using the -rfbport NNNN option.
Limitations:
* Due to the polling nature, some activities (opaque window moves,
scrolling), can be pretty choppy/ragged and others (exposures of
large areas) slow. Experiment with interacting a bit differently
than you normally do to minimize the effects (e.g. do fullpage
paging rather than line-by-line scrolling, and move windows in a
single, quick motion). Work is in progress to attempt to speed
things up using the copyrect encoding and other things, but they
will likely only speed up certain activities, not all.
* A rate limiting factor for x11vnc performance is that video
hardware is optimized for writing, not reading (x11vnc reads the
video framebuffer for the screen image data). The difference can
be a factor of 10-50, and it usually takes about 0.5-1 sec to read
in the whole video hardware framebuffer (5MB for 1280x1024 at
depth 24). So whenever activity changes most of the screen there
is a delay of 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 (5-50 times) by using the Shadow
Framebuffer (a copy of the framebuffer is kept in main memory and
this can be read much more quickly). To do this one puts the line
Option "ShadowFB" "true" (and depending on video card driver,
Option "NoAccel" "true" may be needed too) in the Device section
of the /etc/X11/XF86Config file. Note that this disables 2D
acceleration at the physical display and so likely defeats the
purpose. Nevertheless this could be handy in some circumstances,
e.g. if the 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 [43]contact me if you have any questions,
problems, or comments about x11vnc, etc.
_________________________________________________________________
x11vnc FAQ:
[Building and Starting]
[44]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?
[45]Q-2: I can't get x11vnc and/or libvncserver to compile.
[46]Q-3: Help, I need to run x11vnc on Solaris 2.5.1 and it doesn't
compile! If I try to run a binary built on Solaris 2.6 I get:
relocation error: file x11vnc: symbol XConvertCase: referenced symbol
not found
[47]Q-4: Where can I get a precompiled x11vnc binary for my Operating
System?
[48]Q-5: Where can I get a VNC Viewer binary (or source code) for the
Operating System I will be viewing from?
[49]Q-6: How can I see all of x11vnc's command line options and
documentation on how to use them?
[50]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?
[51]Q-8: Can I make x11vnc more quiet and also go into the background
after starting up?
[52]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]
[53]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?
[54]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]
[55]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.
[56]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.
[57]Q-14: How do I figure out the window id to supply to the -id
windowid option?
[58]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?
[59]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]
[60]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?
[61]Q-18: How do I get my X permissions (MIT-MAGIC-COOKIE) correct for
a Unix/Linux machine acting as an Xterminal?
[Remote Control]
[62]Q-19: How do I stop x11vnc once it is running in the background?
[63]Q-20: Can I change settings in x11vnc without having to restart
it? Is there a way to remote control it?
[Security and Permissions]
[64]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?
[65]Q-22: Can I limit which machines incoming VNC clients can connect
from?
[66]Q-23: How do I build x11vnc/libvncserver with libwrap
(tcp_wrappers) support?
[67]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?
[68]Q-25: How do I create a VNC password for use with x11vnc?
[69]Q-26: How can I tunnel my connection to x11vnc via an encrypted
SSH channel between two Unix machines?
[70]Q-27: How can I tunnel my connection to x11vnc via an encrypted
SSH channel from Windows using an SSH client like Putty?
[71]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?
[72]Q-29: Can I have two passwords for VNC viewers, one for full
access and the other for view-only access to the display?
[73]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?
[74]Q-31: Can I have x11vnc automatically lock the screen when I
disconnect the VNC viewer?
[Display Managers and Services]
[75]Q-32: How can I run x11vnc as a "service" that is always
available?
[76]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).
[77]Q-34: Can I run x11vnc out of inetd(1)? How about xinetd(1)?
[78]Q-35: How do I make x11vnc work with the Java VNC viewer applet in
a web browser?
[79]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]
[80]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)?
[81]Q-38: How can I make x11vnc use less system resources?
[82]Q-39: How can I make x11vnc use MORE system resources?
[83]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?
[84]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]
[85]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?
[86]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?
[87]Q-44: In XFIXES mode, are there any hacks to handle cursor
transparency ("alpha channel") exactly?
[Mouse Pointer]
[88]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?
[89]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)?
[90]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]
[91]Q-48: How can I get my AltGr and Shift modifiers to work between
keyboards for different languages?
[92]Q-49: When I try to type a "<" (i.e. less than) instead I get ">"
(i.e. greater than)! Strangely, typing ">" works OK!!
[93]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?
[94]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?
[95]Q-52: 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?
[96]Q-53: 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)
[97]Q-54: Can I map a keystroke to a mouse button click on the remote
machine?
[Screen Related Issues and Features]
[98]Q-55: 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?
[99]Q-56: Does x11vnc support server-side framebuffer scaling? (E.g.
to make the desktop smaller).
[100]Q-57: Does x11vnc work with Xinerama? (i.e. multiple monitors
joined together to form one big, single screen).
[101]Q-58: Can I use x11vnc on a multi-headed display that is not
Xinerama (i.e. separate screens :0.0, :0.1, ... for each monitor)?
[102]Q-59: Does x11vnc support the XRANDR (X Resize, Rotate and
Reflection) extension? Whenever I rotate or resize the screen x11vnc
just seems to crash.
[103]Q-60: Why is the view in my VNC viewer completely black? Or why
is everything flashing around randomly?
[104]Q-61: 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?
[105]Q-62: 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.]
[106]Q-63: Does the Clipboard/Selection get transferred between the
vncviewer and the X display?
[107]Q-64: 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.
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! If I try to run a binary built on Solaris 2.6 I get:
relocation error: file x11vnc: symbol XConvertCase: referenced symbol
not found
We apologize that x11vnc does not build cleanly on older versions of
Solaris, Linux, etc.: very few users are on these old releases. Here
is a workaround for Solaris 2.5.1 (and perhaps earlier):
First use the environment settings (CPPFLAGS, LDFLAGS, etc.) in the
above [108]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
#define SHUT_RDWR 2
typedef unsigned int in_addr_t;
#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.
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 [109]build steps above and [110]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) [111]http://packages.debian.org/x11vnc
Slackware: (.tgz) [112]http://www.linuxpackages.net/ Redhat/Fedora:
(.rpm) [113]http://dag.wieers.com/packages/x11vnc/ wwexptools: (.tgz)
[114]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 [115]build notes above for where to download libz and libjpeg, and
then build everything with gcc.
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
[116]test binaries. Some may be old, some may have extra debugging
output, etc. One 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:
* [117]http://www.tightvnc.com/download.html
* [118]http://www.realvnc.com/download-free.html
* [119]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 -help The output is listed [120]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
[121]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 [122]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:
* [123]Original Win2VNC
* [124]Enhanced Win2VNC and [125]sourceforge link
* [126]x2vnc
* [127]x2x also [128]here
* [129]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 [130]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 you can use the -overlay
x11vnc option (Aug/2004) to have x11vnc use the Solaris
XReadScreen(3X11) function to poll the "true view" of the whole screen
at depth 24 TrueColor.This is useful for Legacy applications (older
versions of Cadence CAD apps are mentioned by x11vnc users) that
require the default depth be 8bpp, or will use a 8bpp visual even if
depth 24 visuals are available, and so the default depth workaround
described in the previous paragraph is not sufficient for these apps.
The -overlay mode should also work on IRIX machines using
XReadDisplay(3X11).
Misc. notes on -overlay mode: An amusing by-product of -overlay mode
is that mouse cursor shape is correct. The -overlay mode may be
somewhat slower than normal mode due to the extra framebuffer
manipulations that must be performed. Also, there is a bug in that for
some popup menus, the windows they overlap will have painting problems
while the popup is up (a workaround is to disable SaveUnders by
passing -su to Xsun, e.g. in your /etc/dt/config/Xservers file).
Still not working? Run xwininfo on the application with the messed up
colors to verify that the depth of its visual is different from the
default visual depth (gotten from xdpyinfo). One possible workaround
in this case is to use the -id option to point x11vnc at the
application window itself. If the application is complicated (lots of
toplevel windows and popup menus) this may not be acceptable, and may
even crash x11vnc (but not the application).
It is theoretically possible to solve this problem in general (see
xwd(1) for example), but it does not seem trivial or sufficiently fast
for x11vnc to be able to do so in real time. Fortunately the -overlay
option works for Solaris machines with overlay visuals where most of
this problem occurs.
Q-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
[131]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
[132]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 [133]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 ([134]see
above), stunnel, or a VPN to authenticate and encrypt the viewer
connections or to at least use the -rfbauth passwd-file [135]option to
use VNC password protection (or [136]-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 [137]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 [138]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 [139]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.
You then use the password via the x11vnc option: -rfbauth filename
Compared to vncpasswd(1) the latter two methods are a somewhat unsafe
because the password is specified on the command line and so someone
may see it by using ps(1) or looking over your shoulder. Also watch
out for the command winding up in your shell's history file (history
-c is often a way to clear it).
x11vnc also has the [140]-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 [141]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?
[142]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 [143]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
[144]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 [145]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 :0.0 -forever -gone 'dtaction LockDisplay'
Other possibilities are:
x11vnc -display :0.0 -forever -gone 'xscreensaver-command -lock'
x11vnc -display :0.0 -forever -gone 'kdesktop_lock'
x11vnc -display :0.0 -forever -gone 'xlock &'
[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 [146]FAQ on x11vnc
and Display Managers
* Use the description in the [147]FAQ on x11vnc and inetd(1)
* Start x11vnc from $HOME/.xsession (or $HOME/.xinitrc)
* Although less reliable, see the [148]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 [149]full details
on how to configure gdm
If you do not want to deal with the display manager startup scripts,
here is a kludgey script that can be run manually or out of a boot
file like rc.local. [150]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
[151]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 [152]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 [153]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)
* 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 [154]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 express (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 [155]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 [156]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 [157]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 [158]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 [159]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. "<22>" by typing "a"
instead of space).
What to do? In general the VNC protocol has not really solved this
problem: what should be done if the VNC viewer sends a keysym not
recognized by the VNC server side? Workarounds can possibly be
created using the -remap x11vnc option:
-remap asciitilde-dead_tilde,asciicircum-dead_circumflex
etc. Use -remap filename if the list is long. Please send us your
workarounds for this problem on your keyboard. Perhaps we can have
x11vnc adjust automatically at some point. 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 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-53: 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-54: 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-55: 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 [160]this
FAQ on x11vnc scaling.
Q-56: 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-57: 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-58: 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 [161]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-59: 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-60: 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-61: 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-62: 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-63: Does the Clipboard/Selection get transferred between the
vncviewer and the X display?
As of Jan/2004 in the libvncserver CVS x11vnc supports the "CutText"
part of the rfb protocol. Furthermore, x11vnc is able to hold the
PRIMARY selection (Xvnc does not seem to do this). If you don't want
the Clipboard/Selection exchanged use the -nosel option. If you don't
want the PRIMARY selection to be polled for changes use the -noprimary
option.
Q-64: 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.
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#accept
16. http://www.karlrunge.com/x11vnc/index.html#inetd
17. http://www.karlrunge.com/x11vnc/index.html#tightvnc_via
18. http://www.karlrunge.com/x11vnc/index.html#inetd
19. http://www.karlrunge.com/x11vnc/index.html#passwd
20. http://www.karlrunge.com/x11vnc/index.html#passwdfile
21. http://www.karlrunge.com/x11vnc/index.html#allow_opt
22. http://www.karlrunge.com/x11vnc/index.html#tcp_wrappers
23. http://sourceforge.net/projects/libvncserver/
24. http://sourceforge.net/project/showfiles.php?group_id=32584&package_id=119006&release_id=292078
25. http://sourceforge.net/project/shownotes.php?group_id=32584&release_id=292078
26. http://www.karlrunge.com/x11vnc/x11vnc.c
27. http://www.karlrunge.com/x11vnc/tkx11vnc.h
28. http://www.karlrunge.com/x11vnc/index.html#binaries
29. http://www.tightvnc.com/download.html
30. http://www.realvnc.com/download-free.html
31. http://sourceforge.net/projects/cotvnc/
32. http://www.karlrunge.com/x11vnc/rx11vnc
33. http://www.karlrunge.com/x11vnc/rx11vnc.pl
34. ftp://ftp.uu.net/graphics/jpeg/
35. http://www.gzip.org/zlib/
36. http://www.sunfreeware.com/
37. http://www.karlrunge.com/x11vnc/index.html#solaris251build
38. http://www.tightvnc.com/
39. http://www.karlrunge.com/x11vnc/x11vnc_opts.html
40. http://www.karlrunge.com/x11vnc/index.html#passwd
41. http://www.karlrunge.com/x11vnc/recurse_x11vnc.jpg
42. http://wwws.sun.com/sunray/index.html
43. mailto:xvml@karlrunge.com
44. http://www.karlrunge.com/x11vnc/index.html#FAQ-1
45. http://www.karlrunge.com/x11vnc/index.html#FAQ-2
46. http://www.karlrunge.com/x11vnc/index.html#FAQ-3
47. http://www.karlrunge.com/x11vnc/index.html#FAQ-4
48. http://www.karlrunge.com/x11vnc/index.html#FAQ-5
49. http://www.karlrunge.com/x11vnc/index.html#FAQ-6
50. http://www.karlrunge.com/x11vnc/index.html#FAQ-7
51. http://www.karlrunge.com/x11vnc/index.html#FAQ-8
52. http://www.karlrunge.com/x11vnc/index.html#FAQ-9
53. http://www.karlrunge.com/x11vnc/index.html#FAQ-10
54. http://www.karlrunge.com/x11vnc/index.html#FAQ-11
55. http://www.karlrunge.com/x11vnc/index.html#FAQ-12
56. http://www.karlrunge.com/x11vnc/index.html#FAQ-13
57. http://www.karlrunge.com/x11vnc/index.html#FAQ-14
58. http://www.karlrunge.com/x11vnc/index.html#FAQ-15
59. http://www.karlrunge.com/x11vnc/index.html#FAQ-16
60. http://www.karlrunge.com/x11vnc/index.html#FAQ-17
61. http://www.karlrunge.com/x11vnc/index.html#FAQ-18
62. http://www.karlrunge.com/x11vnc/index.html#FAQ-19
63. http://www.karlrunge.com/x11vnc/index.html#FAQ-20
64. http://www.karlrunge.com/x11vnc/index.html#FAQ-21
65. http://www.karlrunge.com/x11vnc/index.html#FAQ-22
66. http://www.karlrunge.com/x11vnc/index.html#FAQ-23
67. http://www.karlrunge.com/x11vnc/index.html#FAQ-24
68. http://www.karlrunge.com/x11vnc/index.html#FAQ-25
69. http://www.karlrunge.com/x11vnc/index.html#FAQ-26
70. http://www.karlrunge.com/x11vnc/index.html#FAQ-27
71. http://www.karlrunge.com/x11vnc/index.html#FAQ-28
72. http://www.karlrunge.com/x11vnc/index.html#FAQ-29
73. http://www.karlrunge.com/x11vnc/index.html#FAQ-30
74. http://www.karlrunge.com/x11vnc/index.html#FAQ-31
75. http://www.karlrunge.com/x11vnc/index.html#FAQ-32
76. http://www.karlrunge.com/x11vnc/index.html#FAQ-33
77. http://www.karlrunge.com/x11vnc/index.html#FAQ-34
78. http://www.karlrunge.com/x11vnc/index.html#FAQ-35
79. http://www.karlrunge.com/x11vnc/index.html#FAQ-36
80. http://www.karlrunge.com/x11vnc/index.html#FAQ-37
81. http://www.karlrunge.com/x11vnc/index.html#FAQ-38
82. http://www.karlrunge.com/x11vnc/index.html#FAQ-39
83. http://www.karlrunge.com/x11vnc/index.html#FAQ-40
84. http://www.karlrunge.com/x11vnc/index.html#FAQ-41
85. http://www.karlrunge.com/x11vnc/index.html#FAQ-42
86. http://www.karlrunge.com/x11vnc/index.html#FAQ-43
87. http://www.karlrunge.com/x11vnc/index.html#FAQ-44
88. http://www.karlrunge.com/x11vnc/index.html#FAQ-45
89. http://www.karlrunge.com/x11vnc/index.html#FAQ-46
90. http://www.karlrunge.com/x11vnc/index.html#FAQ-47
91. http://www.karlrunge.com/x11vnc/index.html#FAQ-48
92. http://www.karlrunge.com/x11vnc/index.html#FAQ-49
93. http://www.karlrunge.com/x11vnc/index.html#FAQ-50
94. http://www.karlrunge.com/x11vnc/index.html#FAQ-51
95. http://www.karlrunge.com/x11vnc/index.html#FAQ-52
96. http://www.karlrunge.com/x11vnc/index.html#FAQ-53
97. http://www.karlrunge.com/x11vnc/index.html#FAQ-54
98. http://www.karlrunge.com/x11vnc/index.html#FAQ-55
99. http://www.karlrunge.com/x11vnc/index.html#FAQ-56
100. http://www.karlrunge.com/x11vnc/index.html#FAQ-57
101. http://www.karlrunge.com/x11vnc/index.html#FAQ-58
102. http://www.karlrunge.com/x11vnc/index.html#FAQ-59
103. http://www.karlrunge.com/x11vnc/index.html#FAQ-60
104. http://www.karlrunge.com/x11vnc/index.html#FAQ-61
105. http://www.karlrunge.com/x11vnc/index.html#FAQ-62
106. http://www.karlrunge.com/x11vnc/index.html#FAQ-63
107. http://www.karlrunge.com/x11vnc/index.html#FAQ-64
108. http://www.karlrunge.com/x11vnc/index.html#solarisbuilding
109. http://www.karlrunge.com/x11vnc/index.html#building
110. http://www.karlrunge.com/x11vnc/index.html#buildfaq
111. http://packages.debian.org/x11vnc
112. http://www.linuxpackages.net/search_view.php?by=name&name=x11vnc
113. http://dag.wieers.com/packages/x11vnc/
114. http://www.bell-labs.com/project/wwexptools/packages.html
115. http://www.karlrunge.com/x11vnc/index.html#solarisbuilding
116. http://www.karlrunge.com/x11vnc/bins
117. http://www.tightvnc.com/download.html
118. http://www.realvnc.com/download-free.html
119. http://sourceforge.net/projects/cotvnc/
120. http://www.karlrunge.com/x11vnc/x11vnc_opts.html
121. http://www.karlrunge.com/x11vnc/x11vnc.c
122. http://fredrik.hubbe.net/x2vnc.html
123. http://www.hubbe.net/~hubbe/win2vnc.html
124. http://www.deboer.gmxhome.de/
125. http://sourceforge.net/projects/win2vnc/
126. http://fredrik.hubbe.net/x2vnc.html
127. http://freshmeat.net/projects/x2x/
128. http://ftp.digital.com/pub/Digital/SRC/x2x/
129. http://zapek.com/software/zvnc/
130. http://www.karlrunge.com/x11vnc/index.html#8bpp
131. http://www.karlrunge.com/x11vnc/index.html#overlays
132. http://www.karlrunge.com/x11vnc/index.html#xauth_pain
133. http://www.karlrunge.com/x11vnc/index.html#noshm
134. http://www.karlrunge.com/x11vnc/index.html#tunnelling
135. http://www.karlrunge.com/x11vnc/index.html#passwd
136. http://www.karlrunge.com/x11vnc/index.html#passwdfile
137. http://www.karlrunge.com/x11vnc/index.html#inetd
138. ftp://ftp.x.org/
139. http://www.karlrunge.com/x11vnc/dtVncPopup
140. http://www.karlrunge.com/x11vnc/index.html#passwdfile
141. http://www.karlrunge.com/x11vnc/index.html#tunnelling
142. http://www.karlrunge.com/x11vnc/index.html#tunnelling
143. http://www.karlrunge.com/x11vnc/index.html#tunnelling
144. http://www.karlrunge.com/x11vnc/index.html#tunnelling
145. http://www.karlrunge.com/x11vnc/blockdpy.c
146. http://www.karlrunge.com/x11vnc/index.html#display_manager
147. http://www.karlrunge.com/x11vnc/index.html#inetd
148. http://www.karlrunge.com/x11vnc/index.html#x11vnc_loop
149. http://www.jirka.org/gdm-documentation/x241.html
150. http://www.karlrunge.com/x11vnc/x11vnc_loop
151. http://www.karlrunge.com/x11vnc/index.html#xterminal_xauth
152. http://www.karlrunge.com/x11vnc/shm_clear
153. http://www.karlrunge.com/x11vnc/index.html#noshm
154. http://www.tightvnc.com/
155. http://www.karlrunge.com/x11vnc/tight-vncviewer-alphahack.patch
156. http://www.tightvnc.com/
157. http://www.karlrunge.com/x11vnc/index.html#greaterless
158. http://www.karlrunge.com/x11vnc/index.html#xkbmodtweak
159. http://www.karlrunge.com/x11vnc/index.html#xkbmodtweak
160. http://www.karlrunge.com/x11vnc/index.html#scaling
161. http://www.karlrunge.com/x11vnc/index.html#solshm
=======================================================================
http://www.karlrunge.com/x11vnc/x11vnc_opts.html:
_________________________________________________________________
x11vnc: a VNC server for real X displays
Here are all of x11vnc command line options:
% x11vnc -help
x11vnc: allow VNC connections to real X11 displays. 0.7.1pre lastmod: 2005-01-1
6
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 a 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 "nap" or "-nap" may be used and are equivalent.
Likewise "wait 100" or "-wait 100" are acceptable and equivalent lines.
The "#" character comments out to the end of the line in the usual way.
Leading and trailing whitespace is trimmed off. Lines may be continued with
a "\" as the last character of a line (it becomes a space character).
Options:
-display disp X11 server display to connect to, usually :0. The X
server process must be running on same machine and
support MIT-SHM. Equivalent to setting the DISPLAY
environment variable to "disp".
-auth file Set the X authority file to be "file", equivalent to
setting the XAUTHORITY environment variable to "file"
before startup. See Xsecurity(7), xauth(1) man pages.
-id windowid Show the window corresponding to "windowid" not
the entire display. New windows like popup menus,
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" 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 (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
-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.
-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
-viewpasswd string Supply a 2nd password for view-only logins. The -passwd
(full-access) password must also be supplied.
-passwdfile filename Specify libvncserver -passwd via the first line of
the file "filename" instead of via command line.
If a second non blank line exists in the file it is
taken as a view-only password (i.e. -viewpasswd) Note:
this is a simple plaintext passwd, see also -rfbauth
and -storepasswd below for obfuscated passwords.
-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.
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 &'
-noshm Do not use the MIT-SHM extension for the polling.
Remote displays can be polled this way: be careful this
can use large amounts of network bandwidth. This is
also of use if the local machine has a limited number
of shm segments and -onetile is not sufficient.
-flipbyteorder Sometimes needed if remotely polled host has different
endianness. Ignored unless -noshm is set.
-onetile Do not use the new copy_tiles() framebuffer mechanism,
just use 1 shm tile for polling. Limits shm segments
used to 3.
-blackout string Black out rectangles on the screen. "string" is a
comma separated list of WxH+X+Y type geometries for
each rectangle.
-xinerama If your screen is composed of multiple monitors
glued together via XINERAMA, and that screen is
non-rectangular this option will try to guess the
areas to black out (if your system has libXinerama).
In general on XINERAMA displays you may need to use the
-xwarppointer option if the mouse pointer misbehaves.
-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 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.
-V, -version Print program version (last modification date).
-q Be quiet by printing less informational output to
stderr. Same as -quiet.
-bg Go into the background after screen setup. Messages to
stderr are lost unless -o logfile is used. Something
like this could be useful in a script:
port=`ssh $host "x11vnc -display :0 -bg" | grep PORT`
port=`echo "$port" | sed -e 's/PORT=//'`
port=`expr $port - 5900`
vncviewer $host:$port
-modtweak Option -modtweak automatically tries to adjust the AltGr
-nomodtweak and Shift modifiers for differing language keyboards
between client and host. Otherwise, only a single key
press/release of a Keycode is simulated (i.e. ignoring
the state of the modifiers: this usually works for
identical keyboards). Also useful in resolving cases
where a Keysym is bound to multiple keys (e.g. "<" + ">"
and "," + "<" keys). Default: -modtweak
-xkb When in modtweak mode, use the XKEYBOARD extension (if
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.
E.g. "-skip_keycodes 94,114"
-add_keysyms If a Keysym is received from a VNC viewer and
that Keysym does not exist in the X server, then
add the Keysym to the X server's keyboard mapping.
Added Keysyms will be removed when exiting.
-clear_mods At startup and exit clear the modifier keys by sending
KeyRelease for each one. The Lock modifiers are skipped.
Used to clear the state if the display was accidentally
left with any pressed down.
-clear_keys As -clear_mods, except try to release any pressed key.
Note that this option and -clear_mods can interfere
with a person typing at the physical keyboard.
-remap string Read Keysym remappings from file named "string".
Format is one pair of Keysyms per line (can be name
or hex value) separated by a space. If no file named
"string" exists, it is instead interpreted as this
form: key1-key2,key3-key4,... See <X11/keysymdef.h>
header file for a list of Keysym names, or use
xev(1). To map a key to a button click, use the
fake Keysyms "Button1", ..., etc. E.g. "-remap
Super_R-Button2" (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
so Overlay may be preferred. 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).
-alphablend In XFIXES mode send cursor alpha channel data to
libvncserver. The blending 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,
e.g. "x11vnc -R pointer_mode: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 low take longer naps between
polls to really cut down load when idle. Default: off
-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 only two types of items: 1) a gui
mode and 2) the X display the gui should display on.
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.)
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 localhost:10",
"x11vnc -gui :10", "x11vnc -gui wait,:10",
"x11vnc -gui <x11vnc-opts...>"
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.
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
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.
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.
bell enable bell (if supported).
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 enable -alphablend mode.
noalphablend disable -alphablend 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 deny lock nodeny
unlock connect allowonce allow localhost nolocalhost
accept gone shm noshm flipbyteorder noflipbyteorder
onetile noonetile 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 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 auth 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.
-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
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