X11VNC(1) User Commands X11VNC(1)
x11vnc - allow VNC connections to real X11 displays
version: 0.9.16, lastmod: 2019-01-05
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
Once x11vnc establishes connections with the X11 server and starts lis‐
tening as a VNC server it will print out a string: PORT=XXXX where XXXX
is typically 5900 (the default VNC server port). One would next run
something like this on the local machine: "vncviewer hostname:N" where
"hostname" is the name of the machine running x11vnc and N is XXXX -
5900, i.e. usually "vncviewer hostname:0".
By default x11vnc will not allow the screen to be shared and it will
exit as soon as the client disconnects. See -shared and -forever below
to override these protections. See the FAQ for details how to tunnel
the VNC connection through an encrypted channel such as ssh(1). In
ssh -t -L 5900:localhost:5900 far-host 'x11vnc -localhost -dis‐
% vncviewer -encodings 'copyrect tight zrle hextile' localhost:0
Also, use of a VNC password (-rfbauth or -passwdfile) is strongly rec‐
For additional info see: http://www.karlrunge.com/x11vnc/ and
Config file support: if the file $HOME/.x11vncrc exists then each line
in it is treated as a single command line option. Disable with -norc.
For each option name, the leading character "-" is not required. E.g.
a line that is either "forever" or "-forever" may be used and are
equivalent. Likewise "wait 100" or "-wait 100" are acceptable and
equivalent lines. The "#" character comments out to the end of the
line in the usual way (backslash it for a literal). Leading and trail‐
ing whitespace is trimmed off. Lines may be continued with a "\" as
the last character of a line (it becomes a space character).
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.
See the description below of the "-display WAIT:..." exten‐
sions, where alias "-find" will find the user's display automat‐
ically, and "-create" will create a Xvfb session if no session
Set the X authority file to be file, equivalent to setting the
XAUTHORITY environment variable to file before startup. Same as
-xauth file. See Xsecurity(7) , xauth(1) man pages for more
Use '-auth guess' to have x11vnc use its -findauth mechanism
(described below) to try to guess the XAUTHORITY filename and
XDM/GDM/KDM: if you are running x11vnc as root and want to find
the XAUTHORITY before anyone has logged into an X session yet,
use: x11vnc -env FD_XDM=1 -auth guess ... (This will also find
the XAUTHORITY if a user is already logged into the X session.)
When running as root, FD_XDM=1 will be tried if the initial
-auth guess fails.
If the X display is :N, try to set the VNC display to also be :N
This just sets the -rfbport option to 5900+N The program will
exit immediately if that port is not available. The -N option
only works with normal -display usage, e.g. :0 or :8, -N is
ignored in the -display WAIT:..., -create, -find, -svc, -redi‐
rect, etc modes.
Automatically probe for a free VNC port starting at n. The
default is to start probing at 5900. Use this to stay away from
other VNC servers near 5900.
The VNC port to listen on (a LibVNCServer option), e.g. 5900,
5901, etc. If specified as "-rfbport PROMPT" then the x11vnc
-gui is used to prompt the user to enter the port number.
IPv6 listening support. In addition to IPv4, the IPv6 address
is listened on for incoming connections. The same port number
as IPv4 is used.
NOTE: This x11vnc binary was compiled to have the "-6" IPv6
listening mode ENABLED by default (CPPFLAGS -DX11VNC_LISTEN6=1).
So to disable IPv6 listening mode you MUST supply the "-no6"
option (see below.)
The "-6" mode works for both normal connections and -ssl
encrypted ones. Nearly everything is supported for the IPv6
case, but there are a few exceptions. See -stunnel for its IPv6
Currently, for absolutely everything to work correctly the
machine may need to have some IPv4 support, at the least for the
loopback interface. However, for nearly all usage modes no IPv4
support is required. See -noipv4.
If you have trouble compiling or running in IPv6 mode, set
-DX11VNC_IPV6=0 in CPPFLAGS when configuring to disable IPv6
Disable IPv6 listening support (only useful if the "-6" mode is
compiled in to be the default; see the X11VNC_LISTEN6 descrip‐
tion above under "-6".)
Do not try to use IPv6 for any listening or connecting sockets.
This includes both the listening service port(s) and outgoing
connections from -connect, -connect_or_exit, or -proxy. Use
this if you are having problems due to IPv6.
Do not try to use IPv4 for any listening or connecting sockets.
This is mainly for exploring the behavior of x11vnc on an
IPv6-only system, but may have other uses.
If the X server connection is disconnected, try to reopen the X
display (up to one time.) This is of use for display managers
like GDM (KillInitClients option) that kill x11vnc just after
the user logs into the X session. Note: the reopened state may
be unstable. Set X11VNC_REOPEN_DISPLAY=n to reopen n times and
set X11VNC_REOPEN_SLEEP_MAX to the number of seconds, default
10, to keep trying to reopen the display (once per second.)
Update: as of 0.9.9, x11vnc tries to automatically avoid being
killed by the display manager by delaying creating windows or
using XFIXES. So you shouldn't need to use KillInit‐
Clients=false as long as you log in quickly enough (within 45
seconds of connecting.) You can disable this by setting
X11VNC_AVOID_WINDOWS=never. You can also set it to the number
of seconds to delay.
Instead of connecting to and polling an X display, connect to
the remote VNC server host:N and be a reflector/repeater for it.
This is useful for trying to manage the case of many simultane‐
ous VNC viewers (e.g. classroom broadcasting) where, e.g. you
put a repeater on each network switch, etc, to improve perfor‐
mance by distributing the load and network traffic. Implies
-shared (use -noshared as a later option to disable). See the
discussion below under -rawfb vnc:host:N for more details.
Show the X window corresponding to windowid not the entire dis‐
play. 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 xwin‐
info(1) for you and extract the id. The -id option is useful
for exporting very simple applications (e.g. the current view on
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.
Simple application sharing based on the -id/-sid mechanism.
Every new toplevel window that the application creates induces a
new viewer window via a reverse connection. The -id/-sid and
-connect options are required. Run 'x11vnc -appshare -help' for
Only show the sub-region of the full display that corresponds to
the rectangle geometry with size WxH and offset +X+Y. The VNC
display has size WxH (i.e. smaller than the full display). This
also works for -id/-sid mode where the offset is relative to the
upper left corner of the selected window. An example use of
this option would be to split a large (e.g. Xinerama) display
into two parts to be accessed via separate viewers by running a
separate x11vnc on each part.
Use '-clip xinerama0' to clip to the first xinerama sub-screen
(if xinerama is active). xinerama1 for the 2nd sub-screen, etc.
This way you don't need to figure out the WxH+X+Y of the desired
xinerama sub-screen. screens are sorted in increasing distance
from the (0,0) origin (I.e. not the Xserver's order).
In 8bpp indexed color, let the installed colormap flash as the
pointer moves from window to window (slow). Also try the -8to24
option to avoid flash altogether.
Rare problem, but some 8bpp displays use less than 256 color‐
cells (e.g. 16-color grayscale, perhaps the other bits are used
for double buffering) *and* also need to shift the pixels values
away from 0, .., ncells. n indicates the shift to be applied to
the pixel values. To see the pixel values set DEBUG_CMAP=1 to
print out a colormap histogram. Example: -shiftcmap 240
For 8bpp displays, force indexed color (i.e. a colormap) even if
it looks like 8bpp TrueColor (rare problem).
If the X11 display is indexed color, lie to clients when they
first connect by telling them it is truecolor. To workaround
RealVNC: inPF has colourMap but not 8bpp Use '-advertise_true‐
color reset' to reset client fb too.
This 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 num‐
ber, 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" then for better or for worse the visual depth is
forced to be m. You may want to use -noshm when using this
option (so XGetImage may automatically translate the pixel
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 pass‐
ing the "-su" argument to Xsun (in /etc/dt/config/Xservers).
Use -overlay as a workaround for situations like these: Some
legacy applications require the default visual to be 8bpp
(8+24), or they will use 8bpp PseudoColor even when the default
visual is depth 24 TrueColor (24+8). In these cases colors in
some windows will be incorrect in x11vnc unless -overlay is
used. Another use of -overlay is to enable showing the exact
mouse cursor shape (details below).
Under -overlay, performance will be somewhat slower due to the
extra image transformations required. For optimal performance
do not use -overlay, but rather configure the X server so that
the default visual is depth 24 TrueColor and try to have all
apps use that visual (e.g. some apps have -use24 or -visual
Sets -overlay, but does not try to draw the exact mouse cursor
shape using the overlay mechanism.
Try this option if -overlay is not supported on your OS, and you
have a legacy 8bpp app that you want to view on a multi-depth
display with default depth 24 (and is 32 bpp) OR have a default
depth 8 display with depth 24 overlay windows for some apps.
This option may not work on all X servers and hardware (tested
on XFree86/Xorg mga driver and Xsun). The "opts" string is not
required and is described below.
This mode enables a hack where x11vnc monitors windows within 3
levels from the root window. If it finds any that are 8bpp it
extracts the indexed color pixel values using XGetImage() and
then applies a transformation using the colormap(s) to create
TrueColor RGB values that it in turn inserts into bits 1-24 of
the framebuffer. This creates a depth 24 "view" of the display
that is then exported via VNC.
Conversely, for default depth 8 displays, the depth 24 regions
are read by XGetImage() and everything is transformed and
inserted into a depth 24 TrueColor framebuffer.
Note that even if there are *no* depth 24 visuals or windows
(i.e. pure 8bpp), this mode is potentially an improvement over
-flashcmap because it avoids the flashing and shows each window
in the correct color.
This method works OK, but may still have bugs and it does hog
resources. If there are multiple 8bpp windows using different
colormaps, one may have to iconify all but one for the colors to
There may be painting errors for clipping and switching between
windows of depths 8 and 24. Heuristics are applied to try to
minimize the painting errors. One can also press 3 Alt_L's in a
row to refresh the screen if the error does not repair itself.
Also the option -fixscreen 8=3.0 or -fixscreen V=3.0 may be used
to periodically refresh the screen at the cost of bandwidth
(every 3 sec for this example).
The [opts] string can contain the following settings. Multiple
settings are separated by commas.
For for some X servers with default depth 24 a speedup may be
achieved via the option "nogetimage". This enables a scheme
were XGetImage() is not used to retrieve the 8bpp data.
Instead, it assumes that the 8bpp data is in bits 25-32 of the
32bit X pixels. There is no requirement that the X server
should put the data there for our poll requests, but some do and
so the extra steps to retrieve it can be skipped. Tested with
mga driver with XFree86/Xorg. For the default depth 8 case this
option is ignored.
To adjust how often XGetImage() is used to poll the non-default
visual regions for changes, use the option "poll=t" where "t" is
a floating point time. (default: 0.05)
Setting the option "level2" will limit the search for non-
default visual windows to two levels from the root window. Do
this on slow machines where you know the window manager only
imposes one extra window between the app window and the root
Also for very slow machines use "cachewin=t" where t is a float‐
ing point amount of time to cache XGetWindowAttributes results.
E.g. cachewin=5.0. This may lead to the windows being unnoticed
for this amount of time when deiconifying, painting errors, etc.
While testing on a very old SS20 these options gave tolerable
response: -8to24 poll=0.2,cachewin=5.0. For this machine -over‐
lay is supported and gives better response.
Debugging for this mode can be enabled by setting "dbg=1",
"dbg=2", or "dbg=3".
Very rare problem: if the framebuffer (X display or -rawfb) is
24bpp instead of the usual 32bpp, then dynamically transform the
pixels to 32bpp. This will be slower, but can be used to work
around problems where VNC viewers cannot handle 24bpp (e.g.
"main: setPF: not 8, 16 or 32 bpp?"). See the FAQ for more
In the case of -rawfb mode, the pixels are directly modified by
inserting a 0 byte to pad them out to 32bpp. For X displays, a
kludge is done that is equivalent to "-noshm -visual True‐
Color:32". (If better performance is needed for the latter,
feel free to ask).
Scale the framebuffer by factor fraction. Values less than 1
shrink the fb, larger ones expand it. Note: the image may not be
sharp and response may be slower. If fraction contains a deci‐
mal point "." it is taken as a floating point number, alterna‐
tively the notation "m/n" may be used to denote fractions
exactly, e.g. -scale 2/3
To scale asymmetrically in the horizontal and vertical direc‐
tions, specify a WxH geometry to stretch to: e.g. '-scale
1024x768', or also '-scale 0.9x0.75'
Scaling Options: can be added after fraction via ":", to supply
multiple ":" options use commas. If you just want a quick,
rough scaling without blending, append ":nb" to fraction (e.g.
-scale 1/3:nb). No blending is the default for 8bpp indexed
color, to force blending for this case use ":fb".
To disable -scrollcopyrect and -wirecopyrect under -scale use
":nocr". If you need to to enable them use ":cr" or specify
them explicitly on the command line. If a slow link is
detected, ":nocr" may be applied automatically. Default: :cr
More esoteric options: for compatibility with vncviewers the
scaled width is adjusted to be a multiple of 4: to disable this
use ":n4". ":in" use interpolation scheme even when shrinking,
":pad" pad scaled width and height to be multiples of scaling
denominator (e.g. 3 for 2/3).
Same as -scale WxH
By default if -scale is supplied the cursor shape is scaled by
the same factor. Depending on your usage, you may want to scale
the cursor independently of the screen or not at all. If you
specify -scale_cursor the cursor will be scaled by that factor.
When using -scale mode to keep the cursor at its "natural" size
use "-scale_cursor 1". Most of the ":" scaling options apply
here as well.
All VNC clients can only watch (default off).
VNC display is shared, i.e. more than one viewer can connect at
the same time (default off).
Exit after the first successfully connected viewer disconnects,
opposite of -forever. This is the Default.
Keep listening for more connections rather than exiting as soon
as the first client(s) disconnect. Same as -many
To get the standard non-shared VNC behavior where when a new VNC
client connects the existing VNC client is dropped use: -never‐
shared -forever This method can also be used to guard against
hung TCP connections that do not go away.
Create an outer loop restarting the x11vnc process whenever it
terminates. -bg and -inetd are ignored in this mode (however
see -loopbg below).
Useful for continuing even if the X server terminates and
restarts (at that moment the process will need permission to
reconnect to the new X server of course).
Use, e.g., -loop100 to sleep 100 millisecs between restarts,
etc. Default is 2000ms (i.e. 2 secs) Use, e.g. -loop300,5 to
sleep 300 ms and only loop 5 times.
If -loopbg (plus any numbers) is specified instead, the "-bg"
option is implied and the mode approximates inetd(8) usage to
some degree. In this case when it goes into the background any
listening sockets (i.e. ports 5900, 5800) are closed, so the
next one in the loop can use them. This mode will only be of
use if a VNC client (the only client for that process) is
already connected before the process goes into the background,
for example, usage of -display WAIT:.., -svc, and -connect can
make use of this "poor man's" inetd mode. The default wait time
is 500ms in this mode. This usage could use useful: -svc -bg
Exit unless a client connects within the first n seconds after
If there have been no connection attempts after n seconds x11vnc
exits immediately. If a client is trying to connect but has not
progressed to the normal operating state, x11vnc gives it a few
more seconds to finish and exits if it does not make it to the
For reverse connections via -connect or -connect_or_exit a time‐
out of n seconds will be set for all reverse connects. If the
connect timeout alarm goes off, x11vnc will exit immediately.
At startup sleep n seconds before proceeding (e.g. to allow
redirs and listening clients to start up)
If a range is given: '-sleepin min-max', a random value between
min and max is slept. E.g. '-sleepin 0-20' and ´-sleepin 10-30'.
Floats are allowed too.
Launched by inetd(8): stdio instead of listening socket. Note:
if you are not redirecting stderr to a log file (via shell 2> or
-o option) you MUST also specify the -q option, otherwise the
stderr goes to the viewer which will cause it to abort. Speci‐
fying both -inetd and -q and no -o will automatically close the
Enable the TightVNC file transfer extension. Note that that when
the -viewonly option is supplied all file transfers are dis‐
abled. Also clients that log in viewonly cannot transfer files.
However, if the remote control mechanism is used to change the
global or per-client viewonly state the filetransfer permissions
will NOT change.
IMPORTANT: please understand if -tightfilexfer is specified and
you run x11vnc as root for, say, inetd or display manager (gdm,
kdm, ...) access and you do not have it switch users via the
-users option, then VNC Viewers that connect are able to do
filetransfer reads and writes as *root*.
Also, tightfilexfer is disabled in -unixpw mode.
Note: to enable UltraVNC filetransfer and to get it to work you
probably need to supply these LibVNCServer options: "-rfbversion
3.6 -permitfiletransfer" "-ultrafilexfer" is an alias for this
IMPORTANT: please understand if -ultrafilexfer is specified and
you run x11vnc as root for, say, inetd or display manager (gdm,
kdm, ...) access and you do not have it switch users via the
-users option, then VNC Viewers that connect are able to do
filetransfer reads and writes as *root*.
Note that sadly you cannot do both -tightfilexfer and -ultra‐
filexfer at the same time because the latter requires setting
the version to 3.6 and tightvnc will not do filetransfer when it
sees that version number.
Instead of using -httpdir (see below) to specify where the Java
vncviewer applet is, have x11vnc try to *guess* where the direc‐
tory is by looking relative to the program location and in stan‐
dard locations (/usr/local/share/x11vnc/classes, etc). Under
-ssl or -stunnel the ssl classes subdirectory is sought.
As -http, but force lookup for ssl classes subdir.
Note that for HTTPS, single-port Java applet delivery you can
set X11VNC_HTTPS_DOWNLOAD_WAIT_TIME to the max number of seconds
to wait for the applet download to finish. The default is 15.
Use the Avahi/mDNS ZeroConf protocol to advertise this VNC
server to the local network. (Related terms: Rendezvous, Bon‐
jour). Depending on your setup, you may need to start avahi-
daemon and open udp port 5353 in your firewall.
You can set X11VNC_AVAHI_NAME, X11VNC_AVAHI_HOST, and/or
X11VNC_AVAHI_PORT environment variables to override the default
values. For example: -env X11VNC_AVAHI_NAME=wally
If the avahi API cannot be found at build time, a helper program
like avahi- publish(1) or dns- sd(1) will be tried
Same as -avahi.
Same as -avahi.
For use with "vncviewer -listen" reverse connections. If string
has the form "host" or "host:port" the connection is made once
Use commas for a list of host's and host:port's. E.g. -connect
host1,host2 or host1:0,host2:5678. Note that to reverse connect
to multiple hosts at the same time you will likely need to also
Note that unlike most vnc servers, x11vnc will require a pass‐
word for reverse as well as for forward connections. (provided
password auth has been enabled, -rfbauth, etc) If you do not
want to require a password for reverse connections set
X11VNC_REVERSE_CONNECTION_NO_AUTH=1 in your environment before
If string contains "/" it is instead interpreted as a file to
periodically check for new hosts. The first line is read and
then the file is truncated. Be careful about the location of
this file if x11vnc is running as root (e.g. via gdm(1) , etc).
Repeater mode: Some services provide an intermediate "vnc
repeater": http://www.uvnc.com/addons/repeater.html (and also
http://koti.mbnet.fi/jtko/ for linux port) that acts as a
proxy/gateway. Modes like these require an initial string to be
sent for the reverse connection before the VNC protocol is
started. Here are the ways to do this:
-connect pre=some_string+host:port -connect
pre128=some_string+host:port -connect repeater=ID:1234+host:port
SSVNC notation is also supported:
As with normal -connect usage, if the repeater port is not sup‐
plied 5500 is assumed.
The basic idea is between the special tag, e.g. "pre=" and "+"
is the pre-string to be sent. Note that in this case host:port
is the repeater server, NOT the vnc viewer. Somehow the pre-
string tells the repeater server how to find the vnc viewer and
connect you to it.
In the case pre=some_string+host:port, "some_string" is simply
sent. In the case preNNN=some_string+host:port "some_string" is
sent in a null padded buffer of length NNN. repeater= is the
same as pre250=, this is the ultravnc repeater buffer size.
Strings like "\n" and "\r", etc. are expanded to newline and
carriage return. "\c" is expanded to "," since the connect
string is comma separated.
See also the -proxy option below for additional ways to plumb
Reverse SSL: using -connect in -ssl mode makes x11vnc act as an
SSL client (initiates SSL connection) rather than an SSL server.
The idea is x11vnc might be connecting to stunnel on the viewer
side with the viewer in listening mode. If you do not want this
behavior, use -env X11VNC_DISABLE_SSL_CLIENT_MODE=1. With this
the viewer side can act as the SSL client as it normally does
for forward connections.
Reverse SSL Repeater mode: This will work, but note that if the
VNC Client does any sort of a 'Fetch Cert' action before con‐
necting, then the Repeater will likely drop the connection and
both sides will need to restart. Consider the use of -con‐
nect_or_exit and -loop300,2 to have x11vnc reconnect once to the
repeater after the fetch. You will probably also want to supply
-sslonly to avoid x11vnc thinking the delay in response means
the connection is VeNCrypt. The env var X11VNC_DIS‐
ABLE_SSL_CLIENT_MODE=1 discussed above may also be useful (i.e.
the viewer can do a forward connection as it normally does.)
IPv6: as of x11vnc 0.9.10 the -connect option should connect to
IPv6 hosts properly. If there are problems you can disable IPv6
by setting -DX11VNC_IPV6=0 in CPPFLAGS when configuring. If
there problems connecting to IPv6 hosts consider a relay like
the included inet6to4 script or the -proxy option.
As with -connect, except if none of the reverse connections suc‐
ceed, then x11vnc shuts down immediately
An easier to type alias for this option is '-coe'
By the way, if you do not want x11vnc to listen on ANY interface
use -rfbport 0 which is handy for the -connect_or_exit mode.
Use proxy in string (e.g. host:port) as a proxy for making
reverse connections (-connect or -connect_or_exit options).
Web proxies are supported, but note by default most of them only
support destination connections to ports 443 or 563, so this
might not be very useful (the viewer would need to listen on
that port or the router would have to do a port redirection).
A web proxy may be specified by either "host:port" or
"http://host:port" (the port is required even if it is the com‐
mon choices 80 or 8080)
SOCKS4, SOCKS4a, and SOCKS5 are also supported. SOCKS proxies
normally do not have restrictions on the destination port num‐
Use a format like this: socks://host:port or socks5://host:port.
Note that ssh -D does not support SOCKS4a, so use socks5://.
For socks:// SOCKS4 is used on a numerical IP and "localhost",
otherwise SOCKS4a is used (and so the proxy tries to do the DNS
An experimental mode is "-proxy http://host:port/..." Note the
"/" after the port that distinguishes it from a normal web
proxy. The port must be supplied even if it is the default 80.
For this mode a GET is done to the supplied URL with the string
host=H&port=P appended. H and P will be the -connect reverse
connect host and port. Use the string "__END__" to disable the
appending. The basic idea here is that maybe some cgi script
provides the actual viewer hookup and tunnelling. How to actu‐
ally achieve this within cgi, php, etc. is not clear... A cus‐
tom web server or apache module would be straight-forward.
Another experimental mode is "-proxy ssh://user@host" in which
case a SSH tunnel is used for the proxying. "user@" is not
needed unless your unix username is different on "host". For a
non-standard SSH port use ssh://user@host:port. If proxies are
chained (see next paragraph) then the ssh one must be the first
one. If ssh-agent is not active, then the ssh password needs to
be entered in the terminal where x11vnc is running. Examples:
-connect localhost:0 -proxy ssh://me@friends-pc:2222
-connect snoopy:0 -proxy ssh://ssh.company.com
Multiple proxies may be chained together in case one needs to
ricochet off of a number of hosts to finally reach the VNC
viewer. Up to 3 may be chained, separate them by commas in the
order they are to be connected to. E.g.:
http://host1:port1,socks5://host2:port2 or three like:
IPv6: as of x11vnc 0.9.10 the -proxy option should connect to
IPv6 hosts properly. If there are problems you can disable IPv6
by setting -DX11VNC_IPV6=0 in CPPFLAGS when configuring. If
there problems connecting to IPv6 hosts consider a relay like
the included inet6to4 script.
Monitor the VNC_CONNECT X property set by the standard VNC pro‐
gram vncconnect(1). When the property is set to "host" or
"host:port" establish a reverse connection. Using xprop(1)
instead of vncconnect may work (see the FAQ). The -remote con‐
trol mechanism uses X11VNC_REMOTE channel, and this option dis‐
ables/enables it as well. Default: -vncconnect
To use different names for these X11 properties (e.g. to have
separate communication channels for multiple x11vnc's on the
same display) set the VNC_CONNECT or X11VNC_REMOTE env. vars. to
the string you want, for example: -env
X11VNC_REMOTE=X11VNC_REMOTE_12345 Both sides of the channel must
use the same unique name. The same can be done for the internal
X11VNC_TICKER property (heartbeat and timestamp) if desired.
Only allow client connections from hosts matching the comma sep‐
arated list of hostnames or IP addresses. Can also be a numeri‐
cal 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 inter‐
preted 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.
-allow applies in -ssl mode, but not in -stunnel mode.
IPv6: as of x11vnc 0.9.10 a host can be specified in IPv6 numer‐
ical format, e.g. 2001:4860:b009::93.
Basically the same as "-allow 127.0.0.1".
Note: if you want to restrict which network interface x11vnc
listens on, see the -listen option below. E.g. "-listen local‐
host" or "-listen 192.168.3.21". As a special case, the option
"-localhost" implies "-listen localhost".
A rare case, but for non-localhost -listen usage, if you use the
remote control mechanism (-R) to change the -listen interface
you may need to manually adjust the -allow list (and vice versa)
to avoid situations where no connections (or too many) are
If you do not want x11vnc to listen on ANY interface (evidently
you are using -connect or -connect_or_exit, or plan to use
remote control: -R connect:host), use -rfbport 0
IPv6: if IPv6 is supported, this option automatically implies
the IPv6 loopback address '::1' as well.
Listen on the unix socket (AF_UNIX) 'str' for connections. This
mode is for either local connections or a tunnel endpoint where
one wants the file permission of the unix socket file to deter‐
mine what can connect to it. (This currently requires an edit
to libvnserver/rfbserver.c: comment out lines 310 and 311,
'close(sock)' and 'return NULL' in rfbserver.c after the set‐
sockopt() call.) Note that to disable all tcp listening ports
specify '-rfbport 0' and should be useful with this mode. Exam‐
ple: mkdir ~/s; chmod 700 ~/s; x11vnc -unixsock ~/s/mysock -rfb‐
port 0 ... The SSVNC unix vncviewer can connect to unix sock‐
When in IPv6 listen mode "-6", listen only on the network inter‐
face with address str. It also works for link scope addresses
(fe80::219:dbff:fee5:3f92%eth0) and IPv6 hostname strings (e.g.
ipv6.google.com.) Use LibVNCServer -listen option for the IPv4
Do not use gethostbyname() or gethostbyaddr() to look up host
names or IP numbers. Use this if name resolution is incorrectly
set up and leads to long pauses as name lookups time out, etc.
Fine tuning of allowed user input. If string does not contain a
comma "," the tuning applies only to normal clients. Otherwise
the part before "," is for normal clients and the part after for
view-only clients. "K" is for Keystroke input, "M" for Mouse-
motion input, "B" for Button-click input, "C" is for Clipboard
input, and "F" is for File transfer (ultravnc only). Their
presence in the string enables that type of input. E.g. "-input
M" means normal users can only move the mouse and "-input
KMBCF,M" lets normal users do anything and enables view-only
users to move the mouse. This option is ignored when a global
-viewonly is in effect (all input is discarded in that case).
When VNC viewers are connected, attempt to the grab the keyboard
so a (non-malicious) user sitting at the physical display is not
able to enter keystrokes. This method uses XGrabKeyboard(3X11)
and so it is not secure and does not rule out the person at the
physical display injecting keystrokes by flooding the server
with them, grabbing the keyboard himself, etc. Some degree of
cooperation from the person at the display is assumed. This is
intended for remote help-desk or educational usage modes.
Note: on some recent (12/2010) X servers and/or desktops,
-grabkbd no longer works: it prevents the window manager from
resizing windows and similar things. Try -ungrabboth below
(might not work.)
As -grabkbd, but for the mouse pointer using XGrabPointer(3X11).
Unfortunately due to the way the X server works, the mouse can
still be moved around by the user at the physical display, but
he will not be able to change window focus with it. Also some
window managers that call XGrabServer(3X11) for resizes, etc,
will act on the local user's input. Again, some degree of coop‐
eration from the person at the display is assumed.
Whenever there is any input (either keyboard or pointer), ungrab
*both* the keyboard and the pointer while injecting the syn‐
thetic input. This is to allow window managers, etc. a chance
Apply both -grabkbd and -grabptr even when no VNC viewers are
connected. If you only want one of them, use the -R remote con‐
trol to turn the other back on, e.g. -R nograbptr.
Supply a 2nd password for view-only logins. The -passwd (full-
access) password must also be supplied.
Specify the LibVNCServer password via the first line of the file
filename (instead of via -passwd on the command line where oth‐
ers might see it via ps(1) ).
See the descriptions below for how to supply multiple passwords,
view-only passwords, to specify external programs for the
authentication, and other features.
If the filename is prefixed with "rm:" it will be removed after
being read. Perhaps this is useful in limiting the readability
of the file. In general, the password file should not be read‐
able by untrusted users (BTW: neither should the VNC -rfbauth
file: it is NOT encrypted, only obscured with a fixed key).
If the filename is prefixed with "read:" it will periodically be
checked for changes and reread. It is guaranteed to be reread
just when a new client connects so that the latest passwords
will be used.
If filename is prefixed with "cmd:" then the string after the
":" is run as an external command: the output of the command
will be interpreted as if it were read from a password file (see
below). If the command does not exit with 0, then x11vnc termi‐
nates immediately. To specify more than 1000 passwords this way
set X11VNC_MAX_PASSWDS before starting x11vnc. The environment
variables are set as in -accept.
Note that due to the VNC protocol only the first 8 characters of
a password are used (DES key).
If filename is prefixed with "custom:" then a custom password
checker is supplied as an external command following the ":".
The command will be run when a client authenticates. If the
command exits with 0 the client is accepted, otherwise it is
rejected. The environment variables are set as in -accept.
The standard input to the custom command will be a decimal digit
"len" followed by a newline. "len" specifies the challenge size
and is usually 16 (the VNC spec). Then follows len bytes which
is the random challenge string that was sent to the client. This
is then followed by len more bytes holding the client's response
(i.e. the challenge string encrypted via DES with the user pass‐
word in the standard situation).
The "custom:" scheme can be useful to implement dynamic pass‐
words or to implement methods where longer passwords and/or dif‐
ferent encryption algorithms are used. The latter will require
customizing the VNC client as well. One could create an MD5SUM
based scheme for example.
File format for -passwdfile:
If multiple non-blank lines exist in the file they are all taken
as valid passwords. Blank lines are ignored. Password lines
may be "commented out" (ignored) if they begin with the charac‐
ter "#" or the line contains the string "__SKIP__". Lines may
be annotated by use of the "__COMM__" string: from it to the end
of the line is ignored. An empty password may be specified via
the "__EMPTY__" string on a line by itself (note your viewer
might not accept empty passwords).
If the string "__BEGIN_VIEWONLY__" appears on a line by itself,
the remaining passwords are used for viewonly access. For com‐
patibility, as a special case if the file contains only two
password lines the 2nd one is automatically taken as the
viewonly password. Otherwise the "__BEGIN_VIEWONLY__" token
must be used to have viewonly passwords. (tip: make the 3rd and
last line be "__BEGIN_VIEWONLY__" to have 2 full-access pass‐
Print to the screen the obscured VNC password kept in the
rfbauth file filename and then exit.
Use Unix username and password authentication. x11vnc will use
the su(1) program to verify the user's password. [list] is an
optional comma separated list of allowed Unix usernames. If the
[list] string begins with the character "!" then the entire list
is taken as an exclude list. See below for per-user options
that can be applied.
A familiar "login:" and "Password:" dialog is presented to the
user on a black screen inside the vncviewer. The connection is
dropped if the user fails to supply the correct password in 3
tries or does not send one before a 45 second timeout. Existing
clients are view-only during this period.
If the first character received is "Escape" then the unix user‐
name will not be displayed after "login:" as it is typed. This
could be of use for VNC viewers that automatically type the
username and password.
Since the detailed behavior of su(1) can vary from OS to OS and
for local configurations, test the mode before deployment to
make sure it is working properly. x11vnc will attempt to be
conservative and reject a login if anything abnormal occurs.
One case to note: FreeBSD and the other BSD's by default it is
impossible for the user running x11vnc to validate his *own*
password via su(1) (commenting out the pam_self.so entry in
/etc/pam.d/su eliminates this behavior). So the x11vnc login
will always *FAIL* for this case (even when the correct password
A possible workaround for this on *BSD would be to start x11vnc
as root with the "-users +nobody" option to immediately switch
to user nobody where the su'ing will proceed normally.
Another source of potential problems are PAM modules that prompt
for extra info, e.g. password aging modules. These logins will
fail as well even when the correct password is supplied.
**IMPORTANT**: to prevent the Unix password being sent in *clear
text* over the network, one of two schemes will be enforced: 1)
the -ssl builtin SSL mode, or 2) require both -localhost and
-stunnel be enabled.
Method 1) ensures the traffic is encrypted between viewer and
server. A PEM file will be required, see the discussion under
-ssl below (under some circumstances a temporary one can be
Method 2) requires the viewer connection to appear to come from
the same machine x11vnc is running on (e.g. from a ssh -L port
redirection). And that the -stunnel SSL mode be used for
encryption over the network. (see the description of -stunnel
Note: as a convenience, if you ssh(1) in and start x11vnc it
will check if the environment variable SSH_CONNECTION is set and
appears reasonable. If it does, then the -ssl or -stunnel
requirement will be dropped since it is assumed you are using
ssh for the encrypted tunnelling. -localhost is still enforced.
Use -ssl or -stunnel to force SSL usage even if SSH_CONNECTION
To override the above restrictions you can set environment vari‐
ables before starting x11vnc:
Set UNIXPW_DISABLE_SSL=1 to disable requiring either -ssl or
-stunnel (as under SSH_CONNECTION.) Evidently you will be using
a different method to encrypt the data between the vncviewer and
x11vnc: perhaps ssh(1) or an IPSEC VPN. -localhost is still
enforced (however, see the next paragraph.)
Set UNIXPW_DISABLE_LOCALHOST=1 to disable the -localhost
requirement in -unixpw modes. One should never do this (i.e.
allow the Unix passwords to be sniffed on the network.) This
also disables the localhost requirement for reverse connections
Note that use of -localhost with ssh(1) (and no -unixpw) is
roughly the same as requiring a Unix user login (since a Unix
password or the user's public key authentication is used by sshd
on the machine where x11vnc runs and only local connections from
that machine are accepted).
Regarding reverse connections (e.g. -R connect:host and -connect
host), when the -localhost constraint is in effect then reverse
connections can only be used to connect to the same machine
x11vnc is running on (default port 5500). Please use a ssh or
stunnel port redirection to the viewer machine to tunnel the
reverse connection over an encrypted channel.
In -inetd mode the Method 1) will be enforced (not Method 2).
With -ssl in effect reverse connections are disabled. If you
override this via env. var, be sure to also use encryption from
the viewer to inetd. Tip: you can also have your own stunnel
spawn x11vnc in -inetd mode (thereby bypassing inetd). See the
FAQ for details.
The user names in the comma separated [list] may have per-user
options after a ":", e.g. "fred:opts" where "opts" is a "+" sep‐
arated list of "viewonly", "fullaccess", "input=XXXX", or
"deny", e.g. "karl,wally:viewonly,boss:input=M". For "input="
it is the K,M,B,C described under -input.
If an item in the list is "*" that means those options apply to
all users. It ALSO implies all users are allowed to log in
after supplying a valid password. Use "deny" to explicitly deny
some users if you use "*" to set a global option. If [list]
begins with the "!" character then "*" is ignored for checking
if the user is allowed, but the option values associated with it
do apply as normal.
There are also some utilities for checking passwords if [list]
starts with the "%" character. See the quick_pw() function for
more details. Description: "%-" or "%stdin" means read one line
from stdin. "%env" means it is in $UNIXPW env var. A leading
"%/" or "%." means read the first line from the filename that
follows after the % character. % by itself means prompt for the
username and password. Otherwise: %user:pass E.g. -unixpw
%fred:swordfish For the other cases user:pass is read from the
indicated source. If the password is correct 'Y user' is
printed and the program exit code is 0. If the password is
incorrect it prints 'N user' and the exit code is 1. If there
is some other error the exit code is 2. This feature enables
x11vnc to be a general unix user password checking tool; it
could be used from scripts or other programs. These % password
checks also apply to the -unixpw_nis and -unixpw_cmd options.
For the % password check, if the env. var. UNIXPW_CMD is set to
a command then it is run as the user (assuming the password is
correct.) The output of the command is not printed, the program
or script must manage that by some other means. The exit code
of x11vnc will depend on the exit code of the command that is
Use -nounixpw to disable unixpw mode if it was enabled earlier
in the cmd line (e.g. -svc mode)
As -unixpw above, however do not use su(1) but rather use the
traditional getpwnam(3) + crypt(3) method to verify passwords.
All of the above -unixpw options and constraints apply.
This mode requires that the encrypted passwords be readable.
Encrypted passwords stored in /etc/shadow will be inaccessible
unless x11vnc is run as root.
This is called "NIS" mode simply because in most NIS setups user
encrypted passwords are accessible (e.g. "ypcat passwd") by an
ordinary user and so that user can authenticate ANY user.
NIS is not required for this mode to work (only that getpwnam(3)
return the encrypted password is required), but it is unlikely
it will work (as an ordinary user) for most modern environments
unless NIS is available. On the other hand, when x11vnc is run
as root it will be able to to access /etc/shadow even if NIS is
not available (note running as root is often done when running
x11vnc from inetd and xdm/gdm/kdm).
Looked at another way, if you do not want to use the su(1)
method provided by -unixpw (i.e. su_verify()), you can run
x11vnc as root and use -unixpw_nis. Any users with passwords in
/etc/shadow can then be authenticated.
In -unixpw_nis mode, under no circumstances is x11vnc's user
password verifying function based on su called (i.e. the func‐
tion su_verify() that runs /bin/su in a pseudoterminal to verify
passwords.) However, if -unixpw_nis is used in conjunction with
the -find and -create -display WAIT:... modes then, if x11vnc is
running as root, /bin/su may be called externally to run the
find or create commands.
As -unixpw above, however do not use su(1) but rather run the
externally supplied command cmd. The first line of its stdin
will be the username and the second line the received password.
If the command exits with status 0 (success) the VNC user will
be accepted. It will be rejected for any other return status.
Dynamic passwords and non-unix passwords, e.g. LDAP, can be
implemented this way by providing your own custom helper pro‐
gram. Note that the remote viewer is given 3 tries to enter the
correct password, and so the program may be called in a row that
many (or more) times.
If a list of allowed users is needed to limit who can log in,
use -unixpw [list] in addition to this option.
In FINDDISPLAY and FINDCREATEDISPLAY modes the cmd will also be
run with the RFB_UNIXPW_CMD_RUN env. var. non-empty and set to
the corresponding display find/create command. The first two
lines of input are the username and passwd as in the normal case
described above. To support FINDDISPLAY and FINDCREATEDISPLAY,
cmd should run the requested command as the user (and most
likely refusing to run it if the password is not correct.) Here
is an example script (note it has a hardwired bogus password
#!/bin/sh # Example x11vnc -unixpw_cmd script. # Read the first
two lines of stdin (user and passwd) read user read pass
debug=0 if [ $debug = 1 ]; then echo "user: $user" 1>&2 echo
"pass: $pass" 1>&2 env | egrep -i 'rfb|vnc' 1>&2 fi
# Check if the password is valid. # (A real example would use
ldap lookup, etc!) if [ "X$pass" != "Xabc" ]; then exit 1 #
incorrect password fi
if [ "X$RFB_UNIXPW_CMD_RUN" = "X" ]; then exit 0 # correct
password else # Run the requested command (finddisplay) if [
$debug = 1 ]; then echo "run: $RFB_UNIXPW_CMD_RUN" 1>&2 fi exec
/bin/su - "$user" -c "$RFB_UNIXPW_CMD_RUN" fi
In -unixpw_cmd mode, under no circumstances is x11vnc's user
password verifying function based on su called (i.e. the func‐
tion su_verify() that runs /bin/su in a pseudoterminal to verify
passwords.) It is up to the supplied unixpw_cmd to do user
switching if desired and if it has the permissions to do so.
Find the user's display using FINDDISPLAY. This is an alias for
Note: if a -display occurs later on the command line it will
override the -find setting.
For this and the next few options see -display WAIT:... below
for all of the details.
Run the FINDDISPLAY program, print out the found display (if
any) and exit. Output is like: DISPLAY=:0.0 DIS‐
PLAY=:0.0,XPID=12345 or DISPLAY=:0.0,VT=7. XPID is the process
ID of the found X server. VT is the Linux virtual terminal of
the X server.
Have the FINDDISPLAY program list all of your displays (i.e. all
the X displays on the local machine that you have access rights
to). x11vnc then exits.
Apply the -find/-finddpy heuristics to try to guess the XAUTHOR‐
ITY file for DISPLAY 'disp'. If 'disp' is not supplied, then
the value in the -display on the cmdline is used; failing that
$DISPLAY is used; and failing that ":0" is used. x11vnc then
If nothing is printed out, that means no XAUTHORITY was found
for 'disp'; i.e. failure. If "XAUTHORITY=" is printed out, that
means use the default (i.e. do not set XAUTHORITY). If "XAU‐
THORITY=/path/to/file" is printed out, then use that file.
XDM/GDM/KDM: if you are running x11vnc as root and want to find
the XAUTHORITY before anyone has logged into an X session yet,
use: x11vnc -env FD_XDM=1 -findauth ... (This will also find
the XAUTHORITY if a user is already logged into the X session.)
When running as root, FD_XDM=1 will be tried if the initial
First try to find the user's display using FINDDISPLAY, if that
doesn't succeed create an X session via the FINDCREATEDISPLAY
method. This is an alias for "-display WAIT:cmd=FINDCREATEDIS‐
Note: if a -display occurs later on the command line it will
override the -create setting.
SSH NOTE: for both -find and -create you can (should!) add the
"-localhost" option to force SSH tunnel access.
As in -create, except Xdummy instead of Xvfb.
As in -create, except Xvnc instead of Xvfb.
As in -create, except Xvnc.redirect instead of Xvfb.
Sets WAIT:cmd=FINDCREATEDISPLAY-<str> Can be on cmdline after
anything that sets WAIT:.. and other things (e.g. -svc, -xdmsvc)
to adjust the X server list. Example: -svc ... -create_xsrv
Terminal services mode based on SSL access. Alias for -display
WAIT:cmd=FINDCREATEDISPLAY-Xvfb -unixpw -users unixpw= -ssl SAVE
Note: if a -display, -unixpw, -users, or -ssl occurs later on
the command line it will override the -svc setting.
As -svc except Xdummy instead of Xvfb.
As -svc except Xvnc instead of Xvfb.
As -svc with Xdummy,Xvfb.
Display manager Terminal services mode based on SSL. Alias for
-display WAIT:cmd=FINDCREATEDISPLAY-Xvfb.xdmcp -unixpw -users
unixpw= -ssl SAVE Also "-xdm_service".
Note: if a -display, -unixpw, -users, or -ssl occurs later on
the command line it will override the -xdmsvc setting.
To create a session a user will have to first log in to the
-unixpw dialog and then log in again to the XDM/GDM/KDM prompt.
Subsequent re-connections will only require the -unixpw pass‐
word. See the discussion under -display WAIT:... for more
details about XDM, etc configuration.
Remember to enable XDMCP in the xdm-config, gdm.conf, or kdmrc
configuration file. See -display WAIT: for more info.
Display manager Terminal services mode based on SSH. Alias for
-display WAIT:cmd=FINDCREATEDISPLAY-Xvfb.xdmcp -localhost.
The -localhost option constrains connections to come in via a
SSH tunnel (which will require a login). To create a session a
user will also have to log into the XDM GDM KDM prompt. Subse‐
quent re-connections will only only require the SSH login. See
the discussion under -display WAIT:... for more details about
XDM, etc configuration.
Remember to enable XDMCP in the xdm-config, gdm.conf, or kdmrc
configuration file. See -display WAIT: for more info.
Present a "Press 'Escape' for System Greeter" option to the con‐
necting VNC client in combined -unixpw and xdmcp FINDCREATEDIS‐
PLAY modes (e.g. -xdmsvc).
Normally in a -unixpw mode the VNC client must supply a valid
username and password to gain access. However, if -unixpw_sys‐
tem_greeter is supplied AND the FINDCREATEDISPLAY command
matches 'xdmcp', then the user has the option to press Escape
and then get a XDM/GDM/KDM login/greeter panel instead. They
will then supply a username and password directly to the
Otherwise, in xdmcp FINDCREATEDISPLAY mode the user must supply
his username and password TWICE. First to the initial unixpw
login dialog, and second to the subsequent XDM/GDM/KDM greeter.
Note that if the user re-connects and supplies his username and
password in the unixpw dialog the xdmcp greeter is skipped and
he is connected directly to his existing X session. So the
-unixpw_system_greeter option avoids the extra password at X
session creation time.
Example: x11vnc -xdmsvc -unixpw_system_greeter See -unixpw and
-display WAIT:... for more info.
The special options after a colon at the end of the username
(e.g. user:solid) described under -display WAIT: are also
applied in this mode if they are typed in before the user hits
Escape. The username is ignored but the colon options are not.
The default message is 2 lines in a small font, set the env.
var. X11VNC_SYSTEM_GREETER1=true for a 1 line message in a
If the user pressed Escape the FINDCREATEDISPLAY command will be
run with the env. var. X11VNC_XDM_ONLY=1.
Remember to enable XDMCP in the xdm-config, gdm.conf, or kdmrc
configuration file. See -display WAIT: for more info.
As in FINDCREATEDISPLAY-Xvnc.redirect mode except redirect imme‐
diately (i.e. without X session finding or creation) to a VNC
server listening on port. You can also supply host:port to redi‐
rect to a different machine.
If 0 <= port < 200 it is taken as a VNC display (5900 is added
to get the actual port), if port < 0 then -port is used.
Probably the only reason to use the -redirect option is in con‐
junction with SSL support, e.g. -ssl SAVE. This provides an
easy way to add SSL encryption to a VNC server that does not
support SSL (e.g. Xvnc or vnc.so) In fact, the protocol does not
even need to be VNC, and so "-rfbport port1 -ssl SAVE -redirect
host:port2" can act as a replacement for stunnel(1).
This mode only allows one redirected connection. The -forever
option does not apply. Use -inetd or -loop for persistent ser‐
A special usage mode for the normal -display option. Useful
with -unixpw, but can be used independently of it. If the dis‐
play string begins with WAIT: then x11vnc waits until a VNC
client connects before opening the X display (or -rawfb device).
This could be useful for delaying opening the display for cer‐
tain usage modes (say if x11vnc is started at boot time and no X
server is running or users logged in yet).
If the string is, e.g. WAIT:0.0 or WAIT:1, i.e. "WAIT" in front
of a normal X display, then that indicated display is used.
One can also insert a geometry between colons, e.g.
WAIT:1280x1024:... to set the size of the display the VNC client
first attaches to since some VNC viewers will not automatically
adjust to a new framebuffer size.
A more interesting case is like this:
in which case the command after "cmd=" is run to dynamically
work out the DISPLAY and optionally the XAUTHORITY data. The
first line of the command output must be of the form DIS‐
PLAY=<xdisplay>. On Linux if the virtual terminal is known
append ",VT=n" to this string and the chvt(1) program will also
be run. Any remaining output is taken as XAUTHORITY data. It
can be either of the form XAUTHORITY=<file> or raw xauthority
data for the display. For example;
xauth extract - $DISPLAY"
NOTE: As specified in the previous paragraph, you can supply
your own WAIT:cmd=... program or script, BUT there are two very
useful *BUILT-IN* ones: FINDDISPLAY (alias -find above) and
FINDCREATEDISPLAY (alias -create above.) Most people use these
instead of creating their own script. Read the following (espe‐
cially the BUILT-IN modes sections) to see how to configure
these two useful builtin -display WAIT: modes.
In the case of -unixpw (and -unixpw_nis only if x11vnc is run‐
ning as root), then the cmd= command is run as the user who just
authenticated via the login and password prompt.
In the case of -unixpw_cmd, the commands will also be run as the
logged-in user, as long as the user-supplied helper program sup‐
ports RFB_UNIXPW_CMD_RUN (see the -unixpw_cmd option.)
Also in the case of -unixpw, the user logging in can place a
colon at the end of her username and supply a few options:
scale=, scale_cursor= (or sc=), solid (or so), id=, clear_mods
(or cm), clear_keys (or ck), clear_all (or ca), repeat, speeds=
(or sp=), readtimeout= (or rd=), viewonly (or vo), nodisplay=
(or nd=), rotate= (or ro=), or noncache (or nc), all separated
by commas if there is more than one. After the user logs in
successfully, these options will be applied to the VNC screen.
login: fred:scale=3/4,sc=1,repeat Password: ...
for convenience m/n implies scale= e.g. fred:3/4 If you type
and enter your password incorrectly, to retrieve your long
"login:" line press the Up arrow once (before typing anything
Most of these colon options only apply to the builtin FINDDIS‐
PLAY and FINDCREATEDISPLAY modes, but note that they are passed
to the extrenal command in the environment as well and so could
In the login panel, press F1 to get a list of the available
options that you can add after the username.
Another option is "geom=WxH" or "geom=WxHxD" (or ge=). This only
has an effect in FINDCREATEDISPLAY mode when a virtual X server
such as Xvfb is going to be created. It sets the width and
height of the new display, and optionally the color depth as
You can also supply "gnome", "kde", "twm", "fvwm", "mwm",
"dtwm", "wmaker", "xfce", "lxde", "enlightenment", "Xsession",
or "failsafe" (same as "xterm") to have the created display use
that mode for the user session.
Specify "tag=..." to set the unique FD_TAG desktop session tag
described below. Note: this option will be ignored if the
FD_TAG env. var. is already set or if the viewer-side supplied
value is not completely composed of alphanumeric or '_' or '-'
User preferences file: Instead of having the user type in
geom=WxH,... etc. every time he logs in to find or create his X
session, if you set FD_USERPREFS to a string that does not con‐
tain the "/" character, then the user's home directory is
prepended to that string and if the file exists its first line
is read and appended to any options he supplied at the login:
prompt. For example -env FD_USERPREFS=.x11vnc_create and the
user put "geom=1600x1200" in his ~/.x11vnc_create file.
To disable the option setting set the environment variable
X11VNC_NO_UNIXPW_OPTS=1 before starting x11vnc. To set any
other options, the user can use the gui (x11vnc -gui connect) or
the remote control method (x11vnc -R opt:val) during his VNC
So we see the combination of -display WAIT:cmd=... and -unixpw
allows automatic pairing of an unix authenticated VNC user with
his desktop. This could be very useful on SunRays and also any
system where multiple users share a given machine. The user
does not need to remember special ports or passwords set up for
his desktop and VNC.
A nice way to use WAIT:cmd=... is out of inetd(8) (it automati‐
cally forks a new x11vnc for each user). You can have the
x11vnc inetd spawned process run as, say, root or nobody. When
run as root (for either inetd or display manager), you can also
supply the option "-users unixpw=" to have the x11vnc process
switch to the user as well. Note: there will be a 2nd SSL
helper process that will not switch, but it is only encoding and
decoding the encrypted stream at that point.
-- Automatic Finding of User X Sessions --
As a special case, WAIT:cmd=FINDDISPLAY will run a script that
works on most Unixes to determine a user's DISPLAY variable and
xauthority data (see who(1) ).
NOTE: The option "-find" is an alias for this mode.
To have this default script printed to stdout (e.g. for cus‐
tomization) run with WAIT:cmd=FINDDISPLAY-print To have the
script run to print what display it would find use "-finddpy" or
The standard script runs xdpyinfo(1) run on potential displays.
If your X server(s) have a login greeter that exclusively grabs
the Xserver, then xdpyinfo blocks forever and this mode will not
work. See www.karlrunge.com/x11vnc/faq.html#faq-display-manager
for how to disable this for dtgreet on Solaris and possibly for
In -find/cmd=FINDDISPLAY mode, if you set FD_XDM=1, e.g. 'x11vnc
-env FD_XDM=1 -find ...' and x11vnc is running as root (e.g.
inetd) then it will try to find the XAUTHORITY file of a running
XDM/GDM/KDM login greeter (i.e. no user has logged into an X
As another special case, WAIT:cmd=HTTPONCE will allow x11vnc to
service one http request and then exit. This is usually done in
-inetd mode to run on, say, port 5800 and allow the Java
vncviewer to be downloaded by client web browsers. For example:
5815 stream tcp nowait root /usr/sbin/tcpd /.../x11vnc \ -inetd
-q -http_ssl -prog /.../x11vnc \ -display WAIT:cmd=HTTPONCE
Where /.../x11vnc is the full path to x11vnc. It is used in the
Apache SSL-portal example (see FAQ).
In this mode you can set X11VNC_SKIP_DISPLAY to a comma sepa‐
rated list of displays (e.g. ":0,:1") to ignore in the finding
process. The ":" is optional. Ranges n-m e.g. 0-20 can also be
supplied. This string can also be set by the connecting user via
"nd=" using "+" instead of "," If "nd=all" or you set
X11VNC_SKIP_DISPLAY=all then all display finding fails as if you
set X11VNC_FINDDISPLAY_ALWAYS_FAILS=1 (below.)
On some systems lsof(1) can be very slow. Set the env. var.
FIND_DISPLAY_NO_LSOF=1 to skip using lsof to try to find the
Linux VT the X server is running on. set FIND_DIS‐
PLAY_NO_VT_FIND=1 to avoid looking at all.
-- Automatic Creation of User X Sessions --
An interesting option is WAIT:cmd=FINDCREATEDISPLAY that is like
FINDDISPLAY in that is uses the same method to find an existing
display. However, if it does not find one it will try to
*start* up an X server session for the user. This is the only
time x11vnc tries to actually start up an X server.
NOTE: The option "-create" is an alias for this mode.
It will start looking for an open display number at :20 Override
via X11VNC_CREATE_STARTING_DISPLAY_NUMBER=n By default 80 X dis‐
plays are allowed (i.e. going to :99) Override via X11VNC_CRE‐
For its heuristics, the create display script sets LC_ALL=C so
that command output is uniform. By default it will try to
restore LC_ALL right before starting the user session. However,
if you don't mind it keeping LC_ALL=C set the env. var.:
By default FINDCREATEDISPLAY will try Xvfb and then Xdummy:
The Xdummy wrapper is part of the x11vnc source code
(x11vnc/misc/Xdummy) It should be available in PATH and have
run "Xdummy -install" once to create the shared library. Xdummy
only works on Linux. As of 12/2009 it no longer needs to be run
as root, and the default is to not run as root. In some circum‐
stances permissions may require running it as root, in these
cases specify FD_XDUMMY_RUN_AS_ROOT=1, this is the same as sup‐
plying -root to the Xdummy cmdline.
Xvfb is available on most platforms and does not require root.
An advantage of Xdummy over Xvfb is that Xdummy supports RANDR
dynamic screen resizing.
When x11vnc exits (i.e. user disconnects) the X server session
stays running in the background. The FINDDISPLAY will find it
directly next time. The user must exit the X session in the
usual way for it to terminate (or kill the X server process if
all else fails).
To troubleshoot the FINDCREATEDISPLAY mechanism, set the follow‐
ing env. var. to an output log file, e.g -env CREATE_DIS‐
So this is a somewhat odd mode for x11vnc in that it will start
up and poll virtual X servers! This can be used from, say,
inetd(8) to provide a means of definitely getting a desktop
(either real or virtual) on the machine. E.g. a desktop ser‐
5900 stream tcp nowait root /usr/sbin/tcpd /.../x11vnc -inetd -q
-http -ssl SAVE -unixpw -users unixpw=\ -passwd secret -prog
/.../x11vnc \ -display WAIT:cmd=FINDCREATEDISPLAY
Where /.../x11vnc is the full path to x11vnc.
See the -svc/-service option alias above.
If for some reason you do not want x11vnc to ever try to find an
existing display set the env. var X11VNC_FINDDIS‐
PLAY_ALWAYS_FAILS=1 (also -env ...) This is the same as setting
X11VNC_SKIP_DISPLAY=all or supplying "nd=all" after "username:"
Use WAIT:cmd=FINDCREATEDISPLAY-print to print out the script
that is used for this.
You can specify the preferred X server order via e.g.,
WAIT:cmd=FINDCREATEDISPLAY-Xdummy,Xvfb,X and/or leave out ones
you do not want. The the case "X" means try to start up a real,
hardware X server using xinit(1) or startx(1). If there is
already an X server running the X case may only work on Linux
(see startx(1) ).
"Xvnc" will start up a VNC X server (real- or tight-vnc, e.g.
use if Xvfb is not available). "Xsrv" will start up the server
program in the variable "FD_XSRV" if it is non-empty. You can
make this be a wrapper script if you like (it must handle :N,
-geometry, and -depth and other X server options).
You can set the environment variable FD_GEOM (or X11VNC_CRE‐
ATE_GEOM) to WxH or WxHxD to set the width and height and
optionally the color depth of the created display. You can also
set FD_SESS to be the session (short name of the windowmanager:
kde, gnome, twm, failsafe, etc.). FD_OPTS contains extra options
to pass to the X server. You can also set FD_PROG to be the full
path to the session/windowmanager program.
More FD tricks: FD_CUPS=port or FD_CUPS=host:port will set the
cups printing environment. Similarly for FD_ESD=port or
FD_ESD=host:port for esddsp sound redirection. Set FD_EXTRA to
a command to be run a few seconds after the X server starts up.
Set FD_TAG to be a unique name for the session, it is set as an
X property, that makes FINDDISPLAY only find sessions with that
Set FD_XDMCP_IF to the network interface that the display man‐
ager is running on; default is 'localhost' but you may need to
set it to '::1' on some IPv6 only systems or misconfigured dis‐
If you want the FINDCREATEDISPLAY session to contact an XDMCP
login manager (xdm/gdm/kdm) on the same machine, then use
"Xvfb.xdmcp" instead of "Xvfb", etc. The user will have to sup‐
ply his username and password one more time (but he gets to
select his desktop type so that can be useful). For this to
work, you will need to enable localhost XDMCP (udp port 177) for
the display manager. This seems to be:
for gdm in gdm.conf: Enable=true in section [xdmcp] for kdm in
kdmrc: Enable=true in section [Xdmcp] for xdm in xdm-con‐
fig: DisplayManager.requestPort: 177
See the shorthand options above "-svc", "-xdmsvc" and
"-sshxdmsvc" that specify the above options for some useful
If you set the env. var WAITBG=1 x11vnc will go into the back‐
ground once listening in wait mode.
Another special mode is FINDCREATEDISPLAY-Xvnc.redirect, (or
FINDDISPLAY-Xvnc.redirect). In this case it will start up Xvnc
as above if needed, but instead of polling it in its normal way,
it simply does a socket redirection of the connected VNC viewer
to the Xvnc.
So in Xvnc.redirect x11vnc does no VNC but merely transfers the
data back and forth. This should be faster then x11vnc's
polling method, but not as fast as connecting directly to the
Xvnc with the VNC Viewer. The idea here is to take advantage of
x11vnc's display finding/creating scheme, SSL, and perhaps a few
others. Most of x11vnc's options do not apply in this mode.
Xvnc.redirect should also work for the vnc.so X server module
for the h/w display however it will work only for finding the
display and the user must already be logged into the X console.
The VeNCrypt extension to the VNC protocol allows encrypted
SSL/TLS connections. If the -ssl mode is enabled, then VeNCrypt
is enabled as well BY DEFAULT (they both use a SSL/TLS tunnel,
only the protocol handshake is a little different.)
To control when and how VeNCrypt is used, specify the mode
string. If mode is "never", then VeNCrypt is not used. If mode
is "support" (the default) then VeNCrypt is supported. If mode
is "only", then the similar and older ANONTLS protocol is not
simultaneously supported. x11vnc's normal SSL mode (vncs://)
will be supported under -ssl unless you set mode to "force".
If mode is prefixed with "nodh:", then Diffie Hellman anonymous
key exchange is disabled. If mode is prefixed with "nox509:",
then X509 key exchange is disabled.
To disable all Anonymous Diffie-Hellman access (susceptible to
Man-In-The-Middle attack) you will need to supply "-vencrypt
nodh:support -anontls never" or "-vencrypt nodh:only"
If mode is prefixed with "newdh:", then new Diffie Hellman
parameters are generated for each connection (this can be time
consuming: 1-60 secs; see -dhparams below for a faster way)
rather than using the fixed values in the program. Using fixed,
publicly known values is not known to be a security problem.
This setting applies to ANONTLS as well.
Long example: -vencrypt newdh:nox509:support
Also, if mode is prefixed with "plain:", then if -unixpw mode is
active the VeNCrypt "*Plain" username+passwd method is enabled
for Unix logins. Otherwise in -unixpw mode the normal login
panel is provided.
You *MUST* supply the -ssl option for VeNCrypt to be active.
The -vencrypt option only fine-tunes its operation.
The ANONTLS extension to the VNC protocol allows encrypted
SSL/TLS connections. If the -ssl mode is enabled, then ANONTLS
is enabled as well BY DEFAULT (they both use a SSL/TLS tunnel,
only the protocol handshake is a little different.)
ANONTLS is an older SSL/TLS mode introduced by vino.
It is referred to as 'TLS' for its registered VNC security-type
name, but we use the more descriptive ´ANONTLS' here because it
provides only Anonymous Diffie-Hellman encrypted connections,
and hence no possibility for certificate authentication.
To control when and how ANONTLS is used, specify the mode
string. If mode is "never", then ANONTLS is not used. If mode
is "support" (the default) then ANONTLS is supported. If mode
is "only", then the similar VeNCrypt protocol is not simultane‐
ously supported. x11vnc's normal SSL mode (vncs://) will be
supported under -ssl unless you set mode to "force".
If mode is prefixed with "newdh:", then new Diffie Hellman
parameters are generated for each connection (this can be time
consuming: 1-60 secs; see -dhparams below for a faster way)
rather than using the fixed values in the program. Using fixed,
publicly known values is not known to be a security problem.
This setting applies to VeNCrypt as well. See the description
of "plain:" under -vencrypt.
Long example: -anontls newdh:plain:support
You *MUST* supply the -ssl option for ANONTLS to be active. The
-anontls option only fine-tunes its operation.
Same as: "-vencrypt never -anontls never" i.e. it disables the
VeNCrypt and ANONTLS encryption methods and only allows standard
SSL tunneling. You must also supply the -ssl ... option (see
For some operations a set of Diffie Hellman parameters (prime
and generator) is needed. If so, use the parameters in file. In
particular, the VeNCrypt and ANONTLS anonymous DH mode need
them. By default a fixed set is used. If you do not want to do
that you can specify "newdh:" to the -vencrypt and -anontls
options to generate a new set each session. If that is too slow
for you, use -dhparams file to a set you created manually via
"openssl dhparam -out file 1024"
Disable the -ssl option (see below). Since -ssl is off by
default -nossl would only be used on the commandline to unset
any *earlier* -ssl option (or -svc...)
Use the openssl library (www.openssl.org) to provide a built-in
encrypted SSL/TLS tunnel between VNC viewers and x11vnc. This
requires libssl support to be compiled into x11vnc at build
time. If x11vnc is not built with libssl support it will exit
immediately when -ssl is prescribed. See the -stunnel option
below for an alternative.
The VNC Viewer-side needs to support SSL/TLS as well. See this
URL and also the discussion below for ideas on how to enable SSL
support for the viewer: http://www.karl‐
runge.com/x11vnc/faq.html#faq-ssl-tun nel-viewers . x11vnc pro‐
vides an SSL enabled Java viewer applet in the classes/ssl
directory (-http or -httpdir options.) The SSVNC viewer package
supports SSL tunnels too.
If the VNC Viewer supports VeNCrypt or ANONTLS (vino's encryp‐
tion mode) they are also supported by the -ssl mode (see the
-vencrypt and -anontls options for more info; use -sslonly to
disable both of them.)
Use "-ssl /path/to/mycert.pem" to specify an SSL certificate
file in PEM format to use to identify and provide a key for this
server. See openssl(1) for more info about PEMs and the
-sslGenCert and "-ssl SAVE" options below for how to create
The connecting VNC viewer SSL tunnel can (at its option) authen‐
ticate this server if it has the public key part of the certifi‐
cate (or a common certificate authority, CA, is a more sophisti‐
cated way to verify this server's cert, see -sslGenCA below).
This authentication is done to prevent Man-In-The-Middle
attacks. Otherwise, if the VNC viewer simply accepts this
server's key WITHOUT verification, the traffic is protected from
passive sniffing on the network, but *NOT* from Man-In-The-Mid‐
dle attacks. There are hacker tools like dsniff/webmitm and cain
that implement SSL Man-In-The-Middle attacks.
If [pem] is empty or the string "SAVE" then the openssl(1) com‐
mand must be available to generate the certificate the first
time. A self-signed certificate is generated (see -sslGenCA and
-sslGenCert for use of a Certificate Authority.) It will be
saved to the file ~/.vnc/certs/server.pem. On subsequent calls
if that file already exists it will be used directly.
Use "SAVE_NOPROMPT" to avoid being prompted to protect the gen‐
erated key with a passphrase. However in -inetd and -bg modes
there will be no prompting for a passphrase in either case.
If [pem] is "SAVE_PROMPT" the server.pem certificate will be
created based on your answers to its prompts for all info such
as OrganizationalName, CommonName, etc.
Use "SAVE-<string>" and "SAVE_PROMPT-<string>" to refer to the
file ~/.vnc/certs/server-<string>.pem instead (it will be gener‐
ated if it does not already exist). E.g. "SAVE-charlie" will
store to the file ~/.vnc/certs/server-charlie.pem
Examples: x11vnc -ssl SAVE -display :0 ... x11vnc -ssl SAVE-
someother -display :0 ...
If [pem] is "TMP" and the openssl(1) utility command exists in
PATH, then a temporary, self-signed certificate will be gener‐
ated for this session. If openssl(1) cannot be used to generate
a temporary certificate x11vnc exits immediately. The temporary
cert will be discarded when x11vnc exits.
If successful in using openssl(1) to generate a temporary cer‐
tificate in "SAVE" or "TMP" creation modes, the public part of
it will be displayed to stderr (e.g. one could copy it to the
client-side to provide authentication of the server to VNC view‐
NOTE: In "TMP" mode, unless you safely copy the public part of
the temporary Cert to the viewer for authenticate *every time*
(unlikely...), then only passive sniffing attacks are prevented
and you are still open to Man-In-The-Middle attacks. This is
why the default "SAVE" mode is preferred (and more sophisticated
CA mode too). Only with saved keys AND the VNC viewer authenti‐
cating them (via the public certificate), are Man-In-The-Middle
If [pem] is "ANON" then the Diffie-Hellman anonymous key
exchange method is used. In this mode there are *no* SSL cer‐
tificates and so it is not possible to authenticate either the
VNC server or VNC client. Thus only passive network sniffing
attacks are avoided: the "ANON" method is susceptible to Man-In-
The-Middle attacks. "ANON" is not recommended; instead use a
SSL PEM you created or the default "SAVE" method.
See -ssldir below to use a directory besides the default
If your x11vnc binary was not compiled with OpenSSL library sup‐
port, use of the -ssl option will induce an immediate failure
and exit. For such binaries, consider using the -stunnel option
for SSL encrypted connections.
Misc Info: In temporary cert creation mode "TMP", set the env.
var. X11VNC_SHOW_TMP_PEM=1 to have x11vnc print out the entire
certificate, including the PRIVATE KEY part, to stderr. There
are better ways to get/save this info. See "SAVE" above and
Set SSL read timeout to n seconds. In some situations (i.e. an
iconified viewer in Windows) the viewer stops talking and the
connection is dropped after the default timeout (25s for about
the first minute, 43200s later). Set to zero to poll forever.
Set to a negative value to use the builtin setting.
Note that this value does NOT apply to the *initial* ssl init
connection. The default timeout for that is 20sec. Use -env
SSL_INIT_TIMEOUT=n to modify it.
Exit at the first SSL connection failure. Useful when scripting
SSL connections (e.g. x11vnc is started via ssh) and you do not
want x11vnc waiting around for more connections, tying up ports,
Use dir as an alternate ssl certificate and key management
toplevel directory. The default is ~/.vnc/certs
This directory is used to store server and other certificates
and keys and also other materials. E.g. in the simplest case,
"-ssl SAVE" will store the x11vnc server cert in dir/server.pem
Use of alternate directories via -ssldir allows you to manage
multiple VNC Certificate Authority (CA) keys. Another use is if
~/.vnc/cert is on an NFS share you might want your certificates
and keys to be on a local filesystem to prevent network snooping
(for example -ssldir /var/lib/x11vnc-certs).
-ssldir affects nearly all of the other -ssl* options, e.g. -ssl
SAVE, -sslGenCert, etc..
For either of the -ssl or -stunnel modes, use path to provide
certificates to authenticate incoming VNC *Client* connections
(normally only the server is authenticated in SSL.) This can be
used as a method to replace standard password authentication of
If path is a directory it contains the client (or CA) certifi‐
cates in separate files. If path is a file, it contains one or
more certificates. See special tokens below. These correspond
to the "CApath = dir" and "CAfile = file" stunnel options. See
the stunnel(8) manpage for details.
Examples: x11vnc -ssl -sslverify ~/my.crt x11vnc -ssl -sslverify
Note that if path is a directory, it must contain the certs in
separate files named like <HASH>.0, where the value of <HASH> is
found by running the command "openssl x509 -hash -noout -in
file.crt". Evidently one uses <HASH>.1 if there is a colli‐
The the key-management utility "-sslCertInfo HASHON" and
"-sslCertInfo HASHOFF" will create/delete these hashes for you
automatically (via symlink) in the HASH subdirs it manages.
Then you can point -sslverify to the HASH subdir.
Special tokens: in -ssl mode, if path is not a file or a direc‐
tory, it is taken as a comma separated list of tokens that are
interpreted as follows:
If a token is "CA" that means load the CA/cacert.pem file from
the ssl directory. If a token is "clients" then all the files
clients/*.crt in the ssl directory are loaded. Otherwise the
file clients/token.crt is attempted to be loaded. As a kludge,
use a token like ../server-foo to load a server cert if you find
Use -ssldir to use a directory different from the ~/.vnc/certs
Note that if the "CA" cert is loaded you do not need to load any
of the certs that have been signed by it. You will need to load
any additional self-signed certs however.
Examples: x11vnc -ssl -sslverify CA x11vnc -ssl -sslverify
self:fred,self:jim x11vnc -ssl -sslverify CA,clients
Usually "-sslverify CA" is the most effective. See the
-sslGenCA and -sslGenCert options below for how to set up and
manage the CA framework.
NOTE: the following utilities, -sslGenCA, -sslGenCert,
-sslEncKey, -sslCertInfo, and -sslCRL are provided for complete‐
ness, but for casual usage they are overkill.
They provide VNC Certificate Authority (CA) key creation and
server / client key generation and signing. So they provide a
basic Public Key management framework for VNC-ing with x11vnc.
(note that they require openssl(1) be installed on the system)
However, the simplest usage mode, "-ssl TMP" (where x11vnc auto‐
matically generates its own, self-signed, temporary key and the
VNC viewers always accept it, e.g. accepting via a dialog box)
is probably safe enough for most scenarios. CA management is
To protect against Man-In-The-Middle attacks the "TMP" mode can
be improved by using "-ssl SAVE" (same as "-ssl", i.e. the
default) to have x11vnc create a longer term self-signed cer‐
tificate, and then (safely) copy the corresponding public key
cert to the desired client machines (care must be taken the pri‐
vate key part is not stolen; you will be prompted for a
So keep in mind no CA key creation or management (-sslGenCA and
-sslGenCert) is needed for either of the above two common usage
One might want to use -sslGenCA and -sslGenCert if you had a
large number of VNC client and server workstations. That way
the administrator could generate a single CA key with -sslGenCA
and distribute its certificate part to all of the workstations.
Next, he could create signed VNC server keys (-sslGenCert server
...) for each workstation or user that then x11vnc would use to
authenticate itself to any VNC client that has the CA cert.
Optionally, the admin could also make it so the VNC clients
themselves are authenticated to x11vnc (-sslGenCert client ...)
For this -sslverify would be pointed to the CA cert (and/or
x11vnc will be able to use all of these cert and key files. On
the VNC client side, they will need to be "imported" somehow.
Web browsers have "Manage Certificates" actions as does the Java
applet plugin Control Panel. stunnel can also use these files
(see the ss_vncviewer example script in the FAQ and SSVNC.)
Set the Certificate Revocation Lists (CRL) to path. This set‐
ting applies for both -ssl and -stunnel modes.
If path is a file, the file contains one or more CRLs in PEM
format. If path is a directory, it contains hash named files of
CRLs in the usual OpenSSL manner. See the OpenSSL and stun‐
nel(8) documentation for more info.
This option only applies if -sslverify has been supplied: it
checks for revocation along the certificate chain used to verify
the VNC client. The -sslCRL setting will be ignored when
-sslverify is not specified.
Note that if a CRL's expiration date has passed, all SSL connec‐
tions will fail regardless of if they are related to the subject
of the CRL or not.
Only rarely will one's x11vnc -ssl infrastructure be so large
that this option would be useful (since normally maintaining the
contents of the -sslverify file or directory should be enough.)
However, when using x11vnc with a Certificate Authority (see
-sslGenCA) to authenticate Clients via SSL/TLS, the -sslCRL
option can be useful to revoke users' certs whose private SSL
keys were lost or stolen (e.g. laptop.) This way a new CA
cert+key does not need to be created and new signed client keys
generated and distributed to all users.
To create a CRL file with revoked certificates the commands
'openssl ca -revoke ...' and 'openssl ca -gencrl ...' are use‐
ful. (Run them in ~/.vnc/certs)
Generate your own Certificate Authority private key, certifi‐
cate, and other files in directory [dir]. x11vnc then exits.
If [dir] is not supplied, a -ssldir setting is used, or other‐
wise ~/.vnc/certs is used.
This command also creates directories where server and client
certs and keys will be stored. The openssl(1) program must be
installed on the system and available in PATH.
After the CA files and directories are created the x11vnc com‐
mand exits; the VNC server is not run.
You will be prompted for information to put into the CA certifi‐
cate. The info does not have to be accurate just as long as
clients accept the cert for VNC connections. You will also need
to supply a passphrase of at least 4 characters for the CA pri‐
Once you have generated the CA you can distribute its certifi‐
cate part, [dir]/CA/cacert.pem, to other workstations where VNC
viewers will be run. One will need to "import" this certificate
in the applications, e.g. Web browser, Java applet plugin, stun‐
nel, etc. Next, you can create and sign keys using the CA with
the -sslGenCert option below.
Examples: x11vnc -sslGenCA x11vnc -sslGenCA ~/myCAdir x11vnc
-ssldir ~/myCAdir -sslGenCA
(the last two lines are equivalent)
-sslGenCert type name
Generate a VNC server or client certificate and private key pair
signed by the CA created previously with -sslGenCA. The
openssl(1) program must be installed on the system and available
After the Certificate is generated x11vnc exits; the VNC server
is not run.
The type of key to be generated is the string type. It is
either "server" (i.e. for use by x11vnc) or "client" (for a VNC
viewer). Note that typically only "server" is used: the VNC
clients authenticate themselves by a non-public-key method (e.g.
VNC or unix password). type is required.
An arbitrary default name you want to associate with the key is
supplied by the name string. You can change it at the various
prompts when creating the key. name is optional.
If name is left blank for clients keys then "nobody" is used.
If left blank for server keys, then the primary server key:
"server.pem" is created (this is the saved one referenced by
"-ssl SAVE" when the server is started)
If name begins with the string "self:" then a self-signed cer‐
tificate is created instead of one signed by your CA key.
If name begins with the string "req:" then only a key (.key) and
a certificate signing *request* (.req) are generated. You can
then send the .req file to an external CA (even a professional
one, e.g. Thawte) and then combine the .key and the received
cert into the .pem file with the same basename.
The distinction between "server" and "client" is simply the
choice of output filenames and sub-directory. This makes it so
the -ssl SAVE-name option can easily pick up the x11vnc PEM file
this option generates. And similarly makes it easy for the
-sslverify option to pick up your client certs.
There is nothing special about the filename or directory loca‐
tion of either the "server" and "client" certs. You can rename
the files or move them to wherever you like.
Precede this option with -ssldir [dir] to use a directory other
than the default ~/.vnc/certs You will need to run -sslGenCA on
that directory first before doing any -sslGenCert key creation.
Note you cannot recreate a cert with exactly the same distigu‐
ished name (DN) as an existing one. To do so, you will need to
edit the [dir]/CA/index.txt file to delete the line.
Similar to -sslGenCA, you will be prompted to fill in some
information that will be recorded in the certificate when it is
Tip: if you know the fully-qualified hostname other people will
be connecting to, you can use that as the CommonName "CN" to
avoid some applications (e.g. web browsers and java plugin) com‐
plaining that it does not match the hostname.
You will also need to supply the CA private key passphrase to
unlock the private key created from -sslGenCA. This private key
is used to sign the server or client certificate.
The "server" certs can be used by x11vnc directly by pointing to
them via the -ssl [pem] option. The default file will be
~/.vnc/certs/server.pem. This one would be used by simply typ‐
ing -ssl SAVE. The pem file contains both the certificate and
the private key. server.crt file contains the cert only.
The "client" cert + private key file will need to be copied and
imported into the VNC viewer side applications (Web browser,
Java plugin, stunnel, etc.) Once that is done you can delete
the "client" private key file on this machine since it is only
needed on the VNC viewer side. The, e.g.
~/.vnc/certs/clients/<name>.pem contains both the cert and pri‐
vate key. The <name>.crt contains the certificate only.
NOTE: It is very important to know one should generate new keys
with a passphrase. Otherwise if an untrusted user steals the
key file he could use it to masquerade as the x11vnc server (or
VNC viewer client). You will be prompted whether to encrypt the
key with a passphrase or not. It is recommended that you do.
One inconvenience to a passphrase is that it must be typed in
EVERY time x11vnc or the client app is started up.
x11vnc -sslGenCert server x11vnc -ssl SAVE -display :0 ...
and then on viewer using ss_vncviewer stunnel wrapper (see the
FAQ): ss_vncviewer -verify ./cacert.crt hostname:0
(this assumes the cacert.crt cert from -sslGenCA was safely
copied to the VNC viewer machine where ss_vncviewer is run)
Example using a name:
x11vnc -sslGenCert server charlie x11vnc -ssl SAVE-charlie -dis‐
play :0 ...
Example for a client certificate (rarely used):
x11vnc -sslGenCert client roger scp
~/.vnc/certs/clients/roger.pem somehost:. rm
x11vnc is then started with the option -sslverify
~/.vnc/certs/clients/roger.crt (or simply -sslverify roger), and
on the viewer user on somehost could do for example:
ss_vncviewer -mycert ./roger.pem hostname:0
If you set the env. var REQ_ARGS='...' it will be passed to
openssl req(1). A common use would be REQ_ARGS='-days 1095' to
bump up the expiration date (3 years in this case).
Utility to encrypt an existing PEM file with a passphrase you
supply when prompted. For that key to be used (e.g. by x11vnc)
the passphrase must be supplied each time.
The "SAVE" notation described under -ssl applies as well. (pre‐
cede this option with -ssldir [dir] to refer a directory besides
the default ~/.vnc/certs)
The openssl(1) program must be installed on the system and
available in PATH. After the Key file is encrypted the x11vnc
command exits; the VNC server is not run.
Examples: x11vnc -sslEncKey /path/to/foo.pem x11vnc -sslEncKey
SAVE x11vnc -sslEncKey SAVE-charlie
Prints out information about an existing PEM file. In addition
the public certificate is also printed. The openssl(1) program
must be in PATH. Basically the command "openssl x509 -text" is
run on the pem.
After the info is printed the x11vnc command exits; the VNC
server is not run.
The "SAVE" notation described under -ssl applies as well.
Using "LIST" will give a list of all certs being managed (in
the ~/.vnc/certs dir, use -ssldir to refer to another dir).
"ALL" will print out the info for every managed key (this can be
very long). Giving a client or server cert shortname will also
try a lookup (e.g. -sslCertInfo charlie). Use "LISTL" or "LL"
for a long (ls -l style) listing.
Using "HASHON" will create subdirs [dir]/HASH and [dir]/HASH
with OpenSSL hash filenames (e.g. 0d5fbbf1.0) symlinks pointing
up to the corresponding *.crt file. ([dir] is ~/.vnc/certs or
one given by -ssldir.) This is a useful way for other OpenSSL
applications (e.g. stunnel) to access all of the certs without
having to concatenate them. x11vnc will not use them unless you
specifically reference them. "HASHOFF" removes these HASH sub‐
The LIST, LISTL, LL, ALL, HASHON, HASHOFF words can also be low‐
ercase, e.g. "list".
Prompts you to delete all .crt .pem .key .req files associated
with [pem]. x11vnc then exits. "SAVE" and lookups as in
-sslCertInfo apply as well.
Prints out both the 'genCA' and 'genCert' x11vnc openssl wrapper
scripts for you to examine, modify, etc. The scripts are
printed to stdout and then the x11vnc program exits.
Use the stunnel(8) (stunnel.mirt.net) to provide an encrypted
SSL tunnel between viewers and x11vnc.
This external tunnel method was implemented prior to the inte‐
grated -ssl encryption described above. It still works well and
avoids the requirement of linking with the OpenSSL libraries.
This mode requires stunnel to be installed on the system and
available via PATH (n.b. stunnel is often installed in sbin
directories). Version 4.x of stunnel is assumed (but see -stun‐
[pem] is optional, use "-stunnel /path/to/stunnel.pem" to spec‐
ify a PEM certificate file to pass to stunnel. See the -ssl
option for more info on certificate files.
Whether or not your stunnel has its own certificate depends on
your stunnel configuration; stunnel often generates one at
install time. See your stunnel documentation for details. In
any event, if you want to use this certificate you must supply
the full path to it as [pem]. Note: the file may only be read‐
able by root.
[pem] may also be the special strings "TMP", "SAVE", and
"SAVE..." as described in the -ssl option. If [pem] is not sup‐
plied, "SAVE" is assumed.
Note that the VeNCrypt, ANONTLS, and "ANON" modes are not sup‐
ported in -stunnel mode.
stunnel is started up as a child process of x11vnc and any SSL
connections stunnel receives are decrypted and sent to x11vnc
over a local socket. The strings "The SSL VNC desktop is ..."
and "SSLPORT=..." are printed out at startup to indicate this.
The -localhost option is enforced by default to avoid people
routing around the SSL channel. Use -env STUNNEL_DISABLE_LOCAL‐
HOST=1 to disable this security requirement.
Set -env STUNNEL_DEBUG=1 for more debugging printout.
Set -env STUNNEL_PROG=xxx to the full path of stunnel program
you want to be used (e.g. /usr/bin/stunnel4).
Set -env STUNNEL_LISTEN=xxx to the address of the network inter‐
face to listen on (the default is to listen on all interfaces),
A simple way to add IPv6 support is STUNNEL_LISTEN=::
Your VNC viewer will also need to be able to connect via SSL.
Unfortunately not too many do this. See the information about
SSL viewers under the -ssl option. The x11vnc project's SSVNC
is an option.
Also, in the x11vnc distribution, patched TightVNC and UltraVNC
Java applet jar files are provided in the classes/ssl directory
that do SSL connections. Enable serving them with the -http,
-http_ssl, or -httpdir (see the option descriptions for more
Note that for the Java viewer applet usage the "?PORT=xxxx" in
the various URLs printed at startup will need to be supplied to
the web browser to connect properly.
Currently the automatic "single port" HTTPS mode of -ssl is not
fully supported in -stunnel mode. However, it can be emulated
% x11vnc -stunnel -http_ssl -http_oneport ...
In general, it is also not too difficult to set up an stunnel or
other SSL tunnel on the viewer side. A simple example on Unix
using stunnel 3.x is:
% stunnel -c -d localhost:5901 -r remotehost:5900 % vncviewer
For Windows, stunnel has been ported to it and there are proba‐
bly other such tools available. See the FAQ and SSVNC for more
Use version 3.x stunnel command line syntax instead of version
4.x. The -http/-httpdir Java applet serving is currently not
available in this mode.
Use symmetric encryption with cipher "cipher" and secret key
data in "keyfile". If keyfile is pw=<string> then "string" is
used as the key data.
NOTE: It is recommended that you use SSL via the -ssl option
instead of this option because SSL is well understood and takes
great care to establish unique session keys and is more compati‐
ble with other software. Use this option if you do not want to
deal with SSL certificates for authentication and do not want to
use SSH but want some encryption for your VNC session. Or if
you must interface with a symmetric key tunnel that you do not
have control over.
Note that this mode will NOT work with the UltraVNC DSM plugins
because they alter the RFB protocol in addition to tunnelling
with the symmetric cipher (an unfortunate choice of implementa‐
cipher can be one of: arc4, aesv2, aes-cfb, blowfish, aes256,
or 3des. See the OpenSSL documentation for more info. The key‐
size is 128 bits (except for aes256). Here is one way to make a
keyfile with that many bits:
dd if=/dev/random of=./my.key bs=16 count=1
you will need to securely share this key with the other side of
the VNC connection (See SSVNC for examples).
Example: -enc blowfish:./my.key Example: -enc blow‐
By default 16 bytes of random salt followed by 16 bytes of ran‐
dom initialization vector are sent at the very beginning of the
stream. The other side must read these and initialize their
cipher with them. These values make the session key unique
(without them the security is minimal). Similarly, the other
side must send us its random salt and IV with those same
The salt and key data are combined to create a session key using
an md5 hash as described in EVP_BytesToKey(3).
The exact call is: EVP_BytesToKey(Cipher, EVP_md5(), salt, key‐
data, len, 1, keystr, NULL); where salt is the random data as
described above, and keydata is the shared secret key data.
keystr is the resulting session key. The cipher is then seeded
with keystr and uses the random initialization vector as its
To modify the amount of random salt and initialization vector
use cipher@n,m where n is the salt length and m the initializa‐
tion vector length. E.g.
It is not a good idea to set either one to zero, although you
may be forced to if the other side of the tunnel is not under
To skip the salt and EVP_BytesToKey MD5 entirely (no hashing is
done: the keydata is directly inserted into the cipher) specify
"-1" for the salt, e.g.
The message digest can also be changed to something besides the
default MD5. Use cipher@md+n,m where "md" can be one of sha,
sha1, md5, or ripe. For example:
The SSVNC vnc viewer project supplies a symmetric encryption
tool named "ultravnc_dsm_helper" that can be used on the viewer
side. For example:
ssvncviewer exec='ultravnc_dsm_helper arc4 my.key 0 h:p'
where h:p is the hostname and port of the x11vnc server. ultra‐
vnc_dsm_helper may also be used standalone to provide a symmet‐
ric encryption tunnel for any viewer or server (VNC or other‐
wise.) The cipher (1st arg) is basically the same syntax as we
Also see the 'Non-Ultra DSM' SSVNC option for the ´UltraVNC DSM
Encryption Plugin' advanced option.
For both ways of using the viewer, you can specify the salt,ivec
sizes (in GUI or, e.g. arc4@8,16).
Use a special, separate HTTPS port (-ssl and -stunnel modes
only) for HTTPS Java viewer applet downloading. I.e. not 5900
and not 5800 (the defaults.)
BACKGROUND: In -ssl mode, it turns out you can use the single
VNC port (e.g. 5900) for both VNC and HTTPS connections. (HTTPS
is used to retrieve a SSL-aware VncViewer.jar applet that is
provided with x11vnc). Since both use SSL the implementation
was extended to detect if HTTP traffic (i.e. GET) is taking
place and handle it accordingly. The URL would be, e.g.:
This is convenient for firewalls, etc, because only one port
needs to be allowed in. However, this heuristic adds a few sec‐
onds delay to each connection and can be unreliable (especially
if the user takes much time to ponder the Certificate dialogs in
his browser, Java VM, or VNC Viewer applet. That's right 3 sep‐
arate "Are you sure you want to connect?" dialogs!)
END OF BACKGROUND.
USAGE: So use the -https option to provide a separate, more
reliable HTTPS port that x11vnc will listen on. If [port] is
not provided (or is 0), one is autoselected. The URL to use is
printed out at startup.
The SSL Java applet directory is specified via the -httpdir
option. If not supplied, -https will try to guess the directory
as though the -http option was supplied.
In -ssl mode with the Java applet retrieved via HTTPS, when the
HTML file containing applet parameters ('index.vnc' or
'proxy.vnc') is sent do NOT set the applet PORT parameter to the
actual VNC port but set it to "port" instead. If "port" is not
supplied, then the port number is guessed from the Host: HTTP
This is useful when an incoming TCP connection redirection is
performed by a router/gateway/firewall from one port to an
internal machine where x11vnc is listening on a different port.
The Java applet needs to connect to the firewall/router port,
not the VNC port on the internal workstation. For example, one
could redir from mygateway.com:443 to workstation:5900.
This spares the user from having to type in https://mygate‐
way.com/?PORT=443 into their web browser. Note that port 443 is
the default https port; other ports must be explicitly indi‐
cated, for example: https://mygateway.com:8000/?PORT=8000. To
avoid having to include the PORT= in the browser URL, simply
supply "-httpsredir" to x11vnc.
This option does not work in -stunnel mode.
More tricks: set the env var X11VNC_EXTRA_HTTPS_PARAMS to be
extra URL parameters to use. This way you do not need to spec‐
ify extra PARAMS in the index.vnc file. E.g. x11vnc -env
If you do not want to expose the non-SSL HTTP port to the net‐
work (i.e. you just want the single VNC/HTTPS port, e.g. 5900,
open for connections) then specify the option -env
X11VNC_HTTP_LISTEN_LOCALHOST=1 This way the connection to the
LibVNCServer httpd server will only be available on localhost
(note that in -ssl mode, HTTPS requests are redirected from SSL
to the non-SSL LibVNCServer HTTP server.)
For UN-encrypted connections mode (i.e. no -ssl, -stunnel, or
-enc options), allow the Java VNC Viewer applet to be downloaded
thru the VNC port via HTTP.
That is to say, you can use a single port for Java applet viewer
connections by using a URL in your web browser like this, for
The regular, two-port mode, URL http://hostname:5800 will con‐
tinue to work as well.
As mentioned above, this mode will NOT work with the -ssl,
-stunnel, or -enc encryption options. Note that is it equiva‐
lent to '-enc none' (i.e. it uses the same detection mechanism
as for HTTPS, but with no encryption.)
HTTPS single-port is on by default in -ssl encrypted mode (and
-enc too), so you only need -http_oneport when doing non-SSL
This mode could also be useful for SSH tunnels since it means
only one port needs to be redirected.
The -httpsredir option may also be useful for this mode when
using an SSH tunnel as well as for router port redirections.
Note that the -env X11VNC_HTTP_LISTEN_LOCALHOST=1 option
described above under -httpsredir applies for the LibVNCServer
httpd server in all cases (ssl or not.)
Create a remote listening port on machine "host" via a SSH tun‐
nel using the -R rport:localhost:lport method. lport will be the
local x11vnc listening port, so a connection to rport
(5900+disp) on "host" will reach x11vnc. E.g. email@example.com:0
This could be useful if a firewall/router prevents incoming con‐
nections to the x11vnc machine, but the ssh machine "host" can
be reached by the VNC viewer. "user@" is not needed unless the
remote unix username differs from the current one.
By default the remote sshd is usually configured to listen only
on localhost for rport, so the viewer may need to ssh -L redir
to "host" as well (See SSVNC to automate this). The sshd set‐
ting GatewayPorts enables listening on all interfaces for rport;
viewers can reach it more easily.
"disp" is the VNC display for the remote SSH side, e.g. 0 corre‐
sponds to port 5900, etc. If disp is greater than 200 the value
is used as the port. Use a negative value to force a low port,
e.g. host:-80 will use port 80.
If ssh-agent is not active, then the ssh password needs to be
entered in the terminal where x11vnc is running.
By default the remote ssh will issue a 'sleep 300' to wait for
the incoming connection for 5 mins. To modify this use
If the remote SSH server is on a non-standard port (i.e. not 22)
Note that the ssh process MAY NOT be killed when x11vnc exits.
It tries by looking at ps(1) output.
If no other password method was supplied on the command line,
first look for ~/.vnc/passwd and if found use it with -rfbauth;
next, look for ~/.vnc/passwdfile and use it with -passwdfile;
otherwise, prompt the user for a password to create
~/.vnc/passwd and use it with the -rfbauth option. If none of
these succeed x11vnc exits immediately.
-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
If called with no arguments, "x11vnc -storepasswd", the user is
prompted for a password and it is stored in the file
~/.vnc/passwd. Called with one argument, that will be the file
to store the prompted password in.
Disable the big warning message when you use x11vnc without some
sort of password.
Run a command (possibly to prompt the user at the X11 display)
to decide whether an incoming client should be allowed to con‐
nect 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 com‐
mand returns 0 the client is accepted, otherwise the client is
rejected. See below for an extension to accept a client view-
If x11vnc is running as root (say from inetd(8) or from display
managers xdm(1) , gdm(1) , etc), think about the security impli‐
cations carefully before supplying this option (likewise for the
Environment: The RFB_CLIENT_IP environment variable will be set
to the incoming client IP number and the port in RFB_CLIENT_PORT
(or -1 if unavailable). Similarly, RFB_SERVER_IP and
RFB_SERVER_PORT (the x11vnc side of the connection), are set to
allow identification of the tcp virtual circuit. The x11vnc
process id will be in RFB_X11VNC_PID, a client id number in
RFB_CLIENT_ID, and the number of other connected clients in
RFB_CLIENT_COUNT. RFB_MODE will be "accept". RFB_STATE will be
PROTOCOL_VERSION, SECURITY_TYPE, AUTHENTICATION, INITIALISATION,
NORMAL, or UNKNOWN indicating up to which state the client has
achieved. RFB_LOGIN_VIEWONLY will be 0, 1, or -1 (unknown).
RFB_USERNAME, RFB_LOGIN_TIME, and RFB_CURRENT_TIME may also be
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).
In the case of "popup" and when the -unixpw option is specified,
then a *second* window will be popped up after the user success‐
fully logs in via his UNIX password. This time the user will be
identified as UNIX:username@hostname, the "UNIX:" prefix indi‐
cates which user the viewer logged as via -unixpw. The first
popup is only for whether to allow him to even *try* to login
via unix password.
If string is "xmessage" then an xmessage(1) invocation is used
for the command. xmessage must be installed on the machine for
this to work.
Both "popup" and "xmessage" will present an option for accepting
the client "View-Only" (the client can only watch). This option
will not be presented if -viewonly has been specified, in which
case the entire display is view only.
If the user supplied command is prefixed with something like
"yes:0,no:*,view:3 mycommand ..." then this associates the
numerical command return code with the actions: accept, reject,
and accept-view-only, respectively. Use "*" instead of a number
to indicate the default action (in case the command returns an
unexpected value). E.g. "no:*" is a good choice.
Note that x11vnc blocks while the external command or popup is
running (other clients may see no updates during this period).
So a person sitting a the physical display is needed to respond
to an popup prompt. (use a 2nd x11vnc if you lock yourself out).
More -accept tricks: use "popupmouse" to only allow mouse clicks
in the builtin popup to be recognized. Similarly use "popupkey"
to only recognize keystroke responses. These are to help avoid
the user accidentally accepting a client by typing or clicking.
All 3 of the popup keywords can be followed by +N+M to supply a
position for the popup window. The default is to center the
As -accept, except to run a user supplied command after a client
has been accepted and authenticated. RFB_MODE will be set to
"afteraccept" and the other RFB_* variables are as in -accept.
Unlike -accept, the command return code is not interpreted by
x11vnc. Example: -afteraccept 'killall xlock &'
As -accept, except to run a user supplied command when a client
goes away (disconnects). RFB_MODE will be set to "gone" and the
other RFB_* variables are as in -accept. The "popup" actions
apply as well. Unlike -accept, the command return code is not
interpreted by x11vnc. Example: -gone 'xlock &'
If x11vnc is started as root (say from inetd(8) or from display
managers xdm(1) , gdm(1) , etc), then as soon as possible after
connections to the X display are established try to switch to
one of the users in the comma separated list. If x11vnc is not
running as root this option is ignored.
Why use this option? In general it is not needed since x11vnc
is already connected to the X display and can perform its pri‐
mary functions. The option was added to make some of the
*external* utility commands x11vnc occasionally runs work prop‐
erly. In particular under GNOME and KDE to implement the
"-solid color" feature external commands (gconftool-2 and dcop)
unfortunately must be run as the user owning the desktop ses‐
sion. Since this option switches userid it also affects the
userid used to run the processes for the -accept and -gone
options. It also affects the ability to read files for options
such as -connect, -allow, and -remap and also the ultra and
tight filetransfer feature if enabled. Note that the -connect
file is also sometimes written to.
So be careful with this option since in some situations its use
can decrease security.
In general the switch to a user will only take place if the dis‐
play can still be successfully opened as that user (this is pri‐
marily to try to guess the actual owner of the session). Exam‐
ple: "-users fred,wilma,betty". Note that a malicious local
user "barney" by quickly using "xhost +" when logging in may
possibly get the x11vnc process to switch to user "fred". What
Under display managers it may be a long time before the switch
succeeds (i.e. a user logs in). To instead make it switch imme‐
diately regardless if the display can be reopened prefix the
username with the "+" character. E.g. "-users +bob" or "-users
The latter (i.e. switching immediately to user "nobody") is the
only obvious use of the -users option that increases security.
Use the following notation to associate a group with a user:
user1.group1,user2.group2,... Note that initgroups(2) will
still be called first to try to switch to ALL of a user's groups
(primary and additional groups). Only if that fails or it is
not available then the single group specified as above (or the
user's primary group if not specified) is switched to with set‐
gid(2). Use -env X11VNC_SINGLE_GROUP=1 to prevent trying init‐
groups(2) and only switch to the single group. This sort of
setting is only really needed to make the ultra or tight file‐
transfer permissions work properly. This format applies to any
comma separated list of users, even the special "=" modes
In -unixpw mode, if "-users unixpw=" is supplied then after a
user authenticates himself via the -unixpw mechanism, x11vnc
will try to switch to that user as though "-users +username" had
been supplied. If you want to limit which users this will be
done for, provide them as a comma separated list after "unixpw="
Groups can also be specified as described above.
Similarly, in -ssl mode, if "-users sslpeer=" is supplied then
after an SSL client authenticates with his cert (the -sslverify
option is required for this) x11vnc will extract a UNIX username
from the "emailAddress" field (firstname.lastname@example.org) of the
"Subject" of the x509 SSL cert and then try to switch to that
user as though "-users +username" had been supplied. If you
want to limit which users this will be done for, provide them as
a comma separated list after "sslpeer=". Set the env. var
X11VNC_SSLPEER_CN to use the Common Name (normally a hostname)
instead of the Email field.
NOTE: for sslpeer= mode the x11vnc administrator must take care
that any client certs he adds to -sslverify have the intended
UNIX username in the "emailAddress" field of the cert. Other‐
wise a user may be able to log in as another. This command can
be of use in checking: "openssl x509 -text -in file.crt", see
the "Subject:" line. Also, along with the normal RFB_* env.
vars. (see -accept) passed to external cmd= commands,
RFB_SSL_CLIENT_CERT will be set to the client's x509 certificate
The sslpeer= mode can aid finding X sessions via the FINDDISPLAY
and FINDCREATEDISPLAY mechanisms.
To immediately switch to a user *before* connections to the X
display are made or any files opened use the "=" character:
"-users =bob". That user needs to be able to open the X display
and any files of course.
The special user "guess=" means to examine the utmpx database
(see who(1) ) looking for a user attached to the display number
(from DISPLAY or -display option) and try him/her. To limit the
list of guesses, use: "-users guess=bob,betty".
Even more sinister is the special user "lurk=" that means to try
to guess the DISPLAY from the utmpx login database as well. So
it "lurks" waiting for anyone to log into an X session and then
connects to it. Specify a list of users after the = to limit
which users will be tried. To enable a different searching
mode, if the first user in the list is something like ":0" or
":0-2" that indicates a range of DISPLAY numbers that will be
tried (regardless of whether they are in the utmpx database) for
all users that are logged in. Also see the "-display WAIT:..."
functionality. Examples: "-users lurk=" and also "-users
Be especially careful using the "guess=" and "lurk=" modes.
They are not recommended for use on machines with untrustworthy
Do not use the MIT-SHM extension for the polling. Remote dis‐
plays 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
Sometimes needed if remotely polled host has different endian‐
ness. Ignored unless -noshm is set.
Do not use the new copy_tiles() framebuffer mechanism, just use
1 shm tile for polling. Limits shm segments used to 3.
To disable any automatic shm reduction set the env. var.
To improve performance, when VNC clients are connected try to
change the desktop background to a solid color. The [color] is
optional: the default color is "cyan4". For a different one
specify the X color (rgb.txt name, e.g. "darkblue" or numerical
Currently this option only works on GNOME, KDE, CDE, XFCE, and
classic X (i.e. with the background image on the root window).
The "gconftool-2", "dcop" and "xfconf-query" external commands
are run for GNOME, KDE, and XFCE respectively. This also works
on native MacOSX. (There is no color selection for MacOSX or
XFCE.) Other desktops won't work, (send us the corresponding
commands if you find them). If x11vnc is running as root (
inetd(8) or gdm(1) ), the -users option may be needed for GNOME,
KDE, XFCE. If x11vnc guesses your desktop incorrectly, you can
force it by prefixing color with "gnome:", "kde:", "cde:",
"xfce:", or "root:".
Update: -solid no longer works on KDE4.
This mode works in a limited way on the Mac OS X Console with
one color ('kelp') using the screensaver writing to the back‐
ground. Look in "~/Library/Screen Savers" for VncSolidColor.png
to change the color.
Black out rectangles on the screen. string is a comma separated
list of WxH+X+Y type geometries for each rectangle. If one of
the items on the list is the string "noptr" the mouse pointer
will not be allowed to go into a blacked out region.
If your screen is composed of multiple monitors glued together
via XINERAMA, and that screen is not a rectangle this option
will try to guess the areas to black out (if your system has
libXinerama). default: -xinerama
In general, we have noticed on XINERAMA displays you may need to
use the "-xwarppointer" option if the mouse pointer misbehaves
and it is enabled by default. Use "-noxwarppointer" if you do
not want this.
Use the DEC-XTRAP extension for keystroke and mouse input inser‐
tion. For use on legacy systems, e.g. X11R5, running an incom‐
plete or missing XTEST extension. By default DEC-XTRAP will be
used if XTEST server grab control is missing, use -xtrap to do
the keystroke and mouse insertion via DEC-XTRAP as well.
If the display supports the XRANDR (X Resize, Rotate and Reflec‐
tion) 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
Since watching for XRANDR events and trapping errors increases
polling overhead, only use this option if XRANDR changes are
expected. For example on a rotatable screen PDA or laptop, or
using a XRANDR-aware Desktop where you resize often. It is best
to be viewing with a vncviewer that supports the NewFBSize
encoding, since it knows how to react to screen size changes.
Otherwise, LibVNCServer tries to do so something reasonable for
viewers that cannot do this (portions of the screen may be
clipped, unused, etc).
Note: the default now is to check for XRANDR events, but do not
trap every X call that may fail due to resize. If a resize
event is received, the full -xrandr mode is enabled. To disable
even checking for events supply: -noxrandr.
"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 sup‐
port the NewFBSize VNC encoding, and then resize the frame‐
buffer. "exit" means disconnect all viewer clients, and then
Rotate and/or flip the framebuffer view exported by VNC. This
transformation is independent of XRANDR and is done in software
in main memory and so may be slower. This mode could be useful
on a handheld with portrait or landscape modes that do not cor‐
respond to the scanline order of the actual framebuffer. string
x flip along x-axis y flip along y-axis xy flip
along x- and y-axes +90 rotate 90 degrees clockwise -90
rotate 90 degrees counter-clockwise +90x rotate 90 degrees
CW, then flip along x +90y rotate 90 degrees CW, then flip
these give all possible rotations and reflections.
Aliases: same as xy: yx, +180, -180, 180 same as -90: +270, 270
same as +90: 90, (ditto for 90x, 90y)
Like -scale, this transformation is applied at the very end of
any chain of framebuffer transformations and so any options with
geometries, e.g. -blackout, -clip, etc. are relative to the
original X (or -rawfb) framebuffer, not the final one sent to
If you do not want the cursor shape to be rotated prefix string
with "nc:", e.g. "nc:+90", "nc:xy", etc.
Whenever a new vncviewer connects, the framebuffer is replaced
with a fake, solid black one of geometry WxH. Shortly after‐
wards 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.)
In -unixpw mode this sets the size of the login screen. Use
"once:WxH" it ignore padgeom after the login screen is set up.
Write stderr messages to file logfile instead of to the termi‐
nal. Same as "-logfile file". To append to the file use "-oa
file" or "-logappend file". If logfile contains the string
"%VNCDISPLAY" it is expanded to the vnc display (the name may
need to be guessed at.) "%HOME" works too.
Write the "PORT=NNNN" (e.g. PORT=5900) string to file in addi‐
tion to stdout. This option could be useful by wrapper script
to detect when x11vnc is ready.
Remove file at exit to signal when x11vnc is done. The file is
created at startup if it does not already exist or if file is
prefixed with "create:". If the file is created, the x11vnc PID
is placed in the file. Otherwise the files contents is not
changed. Use prefix "nocreate:" to prevent creation.
Use filename instead of $HOME/.x11vncrc for rc file.
Do not process any .x11vncrc file for options.
Set the environment variable 'VAR' to value 'VALUE' at x11vnc
startup. This is a convenience utility to avoid shell script
wrappers, etc. to set the env. var. You may specify as many of
these as needed on the command line.
Set the full path to the x11vnc program for cases when it cannot
be determined from argv (e.g. tcpd/inetd)
Print this help text. -?, -opts Only list the
Print program version and last modification date.
Print out license information. Same as -copying and -warranty.
Instead of exiting after cleaning up, run a simple "debug crash
shell" when fatal errors are trapped.
Be quiet by printing less informational output to stderr. (use
-noquiet to undo an earlier -quiet.)
The -quiet option does not eliminate all informational output,
it only reduces it. It is ignored in most auxiliary usage
modes, e.g. -storepasswd. To eliminate all output use:
2>/dev/null 1>&2, etc.
Print out more information to stderr.
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 -t $host "x11vnc -display :0 -bg" | grep PORT`
port=`echo "$port" | sed -e 's/PORT=//'`
port=`expr $port - 5900`
Option -modtweak automatically tries to adjust the AltGr and
Shift modifiers for differing language keyboards between client
and host. Otherwise, only a single key press/release of a Key‐
code 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
If you are having trouble with with keys and -xkb or -noxkb, and
similar things don't help, try -nomodtweak.
On some HP-UX systems it is been noted that they have an odd
keymapping where a single keycode will have a keysym, e.g. "#",
up to three times. You can check via "xmodmap -pk" or the -dk
option. The failure is when you try to type "#" it yields "3".
If you see this problem try setting the environment variable
MODTWEAK_LOWEST=1 to see if it helps.
When in modtweak mode, use the XKEYBOARD extension (if the X
display supports it) to do the modifier tweaking. This is pow‐
erful and should be tried if there are still keymapping problems
when using -modtweak by itself. The default is to check whether
some common keysyms, e.g. !, @, [, are only accessible via -xkb
mode and if so then automatically enable the mode. To disable
this automatic detection use -noxkb.
When -xkb mode is active you can set these env. vars. They
apply only when there is ambiguity as to which key to choose
(i.e the mapping is not one-to-one). NOKEYHINTS=1: for up ascii
keystrokes do not use score hints saved when the key was pressed
down. NOANYDOWN=1: for up keystrokes do not resort to searching
through keys that are currently pressed down. KEYSDOWN=N:
remember the last N keys press down for tie-breaking when an up
keystroke comes in.
When in -modtweak (the default) or -xkb mode, if a keysym in the
range A-Z comes in check the X server to see if the Caps_Lock is
set. If it is do not artificially press Shift to generate the
keysym. This will enable the CapsLock key to behave correctly
in some circumstances: namely *both* the VNC viewer machine and
the x11vnc X server are in the CapsLock on state. If one side
has CapsLock on and the other off and the keyboard is not behav‐
ing as you think it should you should correct the CapsLock
states (hint: pressing CapsLock inside and outside of the viewer
can help toggle them both to the correct state). However, for
best results do not use this option, but rather *only* enable
CapsLock on the VNC viewer side (i.e. by pressing CapsLock out‐
side of the viewer window, also -skip_lockkeys below). Also try
-nomodtweak for a possible workaround.
Have x11vnc ignore all Caps_Lock, Shift_Lock, Num_Lock,
Scroll_Lock keysyms received from viewers. The idea is you
press Caps_Lock on the VNC Viewer side but that does not change
the lock state in the x11vnc-side X server. Nevertheless your
capitalized letters come in over the wire and are applied cor‐
rectly to the x11vnc-side X server. Note this mode probably
won't do what you want in -nomodtweak mode. Also, a kludge for
KP_n digits is always done in this mode: they are mapped to reg‐
ular digit keysyms. See also -capslock above. The default is
Ignore the comma separated list of decimal keycodes. Perhaps
these are keycodes not on your keyboard but your X server thinks
exist. Currently only applies to -xkb mode. Use this option to
help x11vnc in the reverse problem it tries to solve: Keysym ->
Keycode(s) when ambiguities exist (more than one Keycode per
Keysym). Run 'xmodmap -pk' to see your keymapping. Example:
Experimental option that tries to correct some "sloppy" key
behavior. E.g. if at the viewer you press Shift+Key but then
release the Shift before Key that could give rise to extra
unwanted characters (usually only between keyboards of different
languages). Only use this option if you observe problems with
Some VNC viewers send impossible repeated key events, e.g. key-
down, key-down, key-up, key-up all for the same key, or 20 downs
in a row for the same modifier key! Setting -skip_dups means to
skip these duplicates and just process the first event. Note:
some VNC viewers assume they can send down's without the corre‐
sponding up's and so you should not set this option for these
viewers (symptom: some keys do not autorepeat) Default:
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 on an unused key. Added Keysyms will be
removed periodically and also when x11vnc exits. Default:
At startup and exit clear the modifier keys by sending KeyRe‐
lease for each one. The Lock modifiers are skipped. Used to
clear the state if the display was accidentally left with any
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.
As -clear_keys, except try to release any CapsLock, NumLock,
etc. locks as well.
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 inter‐
preted as this form: key1-key2,key3-key4,... See
<X11/keysymdef.h> header file for a list of Keysym names, or use
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
I use these if the machine I am viewing from does not have a
scrollwheel or I don't like using the one it has:
-remap Super_R-Button4,Menu-Button5 -remap KP_Add-But‐
the former would be used on a PC, the latter on a MacBook. This
way those little used keys can be used to generate bigger hops
than the Up and Down arrows provide. One can scroll through
text or web pages more quickly this way (especially if x11vnc
scroll detection is active.)
Use Button44, Button12, etc. for multiple clicks.
To disable a keysym (i.e. make it so it will not be injected),
remap it to "NoSymbol" or "None".
Dead keys: "dead" (or silent, mute) keys are keys that do not
produce a character but must be followed by a 2nd keystroke.
This is often used for accenting characters, e.g. to put "`" on
top of "a" by pressing the dead key and then "a". Note that
this interpretation is not part of core X11, it is up to the
toolkit or application to decide how to react to the sequence.
The X11 names for these keysyms are "dead_grave", "dead_acute",
etc. However some VNC viewers send the keysyms "grave", "acute"
instead thereby disabling the accenting. To work around this
-remap can be used. For example "-remap grave-dead_grave,acute-
As a convenience, "-remap DEAD" applies these remaps:
If you just want a subset use the first letter label, e.g.
"-remap DEAD=ga" to get the first two. Additional remaps may
also be supplied via commas, e.g. "-remap DEAD=ga,Super_R-But‐
ton2". Finally, "DEAD=missing" means to apply all of the above
as long as the left hand member is not already in the X11
Option -norepeat disables X server key auto repeat when VNC
clients are connected and VNC keyboard input is not idle for
more than 5 minutes. This works around a repeating keystrokes
bug (triggered by long processing delays between key down and
key up client events: either from large screen changes or high
latency). Default: -norepeat
You can set the env. var. X11VNC_IDLE_TIMEOUT to the number of
idle seconds you want (5min = 300secs).
Note: your VNC viewer side will likely do autorepeating, so this
is no loss unless someone is simultaneously at the real X dis‐
Use "-norepeat N" to set how many times norepeat will be reset
if something else (e.g. X session manager) undoes it. The
default is 2. Use a negative value for unlimited resets.
Ignore video framebuffer: only process keyboard and pointer.
Intended for use with Win2VNC and x2vnc dual-monitor setups.
Do not watch for XBell events. (no beeps will be heard) Note:
XBell monitoring requires the XKEYBOARD extension.
Do not manage exchange of X selection/cutbuffer between VNC
viewers and the X server at all.
Do not poll the PRIMARY selection for changes to send back to
clients. (PRIMARY is still set on received changes, however).
Do not set the PRIMARY selection for changes received from VNC
Do not poll the CLIPBOARD selection for changes to send back to
clients. (CLIPBOARD is still set on received changes, however).
Do not set the CLIPBOARD selection for changes received from VNC
If direction string is "send", only send the selection to view‐
ers, and if it is "recv" only receive it from viewers. To work
around apps setting the selection too frequently and messing up
the other end. You can actually supply a comma separated list
of directions, including "debug" to turn on debugging output.
-cursor [mode], -nocursor
Sets how the pointer cursor shape (little icon at the 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 Cur‐
sorShapeUpdates 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 -nocursor‐
shape 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 informa‐
tion from the X server, then the default is to use that mode.
On Solaris this can be done with the SUN_OVL extension using
-overlay (see also the -overlay_nocursor option). A similar
overlay scheme is used on IRIX. Xorg (e.g. Linux) and recent
Solaris Xsun servers support the XFIXES extension to retrieve
the exact cursor shape from the X server. If XFIXES is present
it is preferred over Overlay and is used by default (see -nox‐
fixes below). This can be disabled with -nocursor, and also
some values of the "mode" option below.
Note that under XFIXES cursors with transparency (alpha channel)
will usually not be exactly represented and one may find Overlay
preferable. See also the -alphacut and -alphafrac options below
as fudge factors to try to improve the situation for cursors
with transparency for a given theme.
The "mode" string can be used to fine-tune the displaying of
cursor shapes. It can be used the following ways:
"-cursor arrow" - just show the standard arrow nothing more or
"-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 lit‐
tle 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
Show cursor shape changes even when the mouse is being dragged
with a mouse button down. This is useful if you want to be able
to see Drag-and-Drop cursor icons, etc.
Choose an alternate "arrow" cursor from a set of some common
ones. n can be 1 to 6. Default is: 1 Ignored when in XFIXES
Do not use the XFIXES extension to draw the exact cursor shape
even if it is available.
Note: To work around a crash in Xorg 1.5 and later some people
needed to use -noxfixes. The Xorg crash occurred right after a
Display Manager (e.g. GDM) login. Starting with x11vnc 0.9.9 it
tries to automatically avoid using XFIXES until it is sure a
window manager is running. See the -reopen option for more info
and how to use X11VNC_AVOID_WINDOWS=never to disable it.
When using the XFIXES extension for the cursor shape, cursors
with transparency will not usually be displayed exactly (but
opaque ones will). This option sets n as a cutoff for cursors
that have transparency ("alpha channel" with values ranging from
0 to 255) Any cursor pixel with alpha value less than n becomes
completely transparent. Otherwise the pixel is completely
opaque. Default 240
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.
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).
In XFIXES mode do not send cursor alpha channel data to LibVNC‐
Server. The default is to send it. The alphablend effect will
only be visible in -nocursorshape mode or for clients with cur‐
sorshapeupdates turned off. (However there is a hack for 32bpp
with depth 24, it uses the extra 8 bits to store cursor trans‐
parency for use with a hacked vncviewer that applies the trans‐
parency locally. See the FAQ for more info).
Do not use the TightVNC CursorShapeUpdates extension even if
clients support it. See -cursor above.
Option -cursorpos enables sending the X cursor position back to
all vnc clients that support the TightVNC CursorPosUpdates
extension. Other clients will be able to see the pointer
motions. Default: -cursorpos
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
It is also sometimes needed on XINERAMA displays and is enabled
by default if XINERAMA is found to be active. To prevent this,
Even if there is no displacement (dx = dy = 0) for a VNC mouse
event force the pointer to the indicated x,y position anyway.
Recent (2009) gui toolkits (gnome) have problems with x11vnc's
original mouse input injection method. So x11vnc's mouse input
injection method has been modified. To regain the OLD behavior
use this option: -always_inject. Then x11vnc will always force
positioning the mouse to the x,y position even if that position
has not changed since the previous VNC input event.
The first place this problem was noticed was in gnome terminal:
if you pressed and released mouse button 3, a menu was posted
and then its first element 'New Terminal Window' was activated.
This was because x11vnc injected the mouse position twice: once
on ButtonPress and again on ButtonRelease. The toolkit inter‐
preted the 2nd one as mouse motion even though the mouse hadn't
moved. So now by default x11vnc tries to avoid injecting the
Note that with the new default x11vnc will be oblivious to
applications moving the pointer (warping) or the user at the
physical display moving it. So it might, e.g., inject ButtonRe‐
lease at the wrong position. If this (or similar scenarios)
causes problems in your environment, specify -always_inject for
the old method.
String to remap mouse buttons. Format: IJK-LMN, this maps but‐
tons I -> L, etc., e.g. -buttonmap 13-31
Button presses can also be mapped to keystrokes: replace a but‐
ton 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:
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.
-buttonmap currently does not work on MacOSX console or in
Workaround: use -buttonmap IJ...-LM...=n to limit the number of
mouse buttons to n, e.g. 123-123=3. This will prevent x11vnc
from crashing if the X server reports there are 5 buttons (4/5
scroll wheel), but there are only really 3.
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.
Client-side caching scheme. Framebuffer memory n (an integer)
times that of the full display is allocated below the actual
framebuffer to cache screen contents for rapid retrieval. So a
W x H frambuffer is expanded to a W x (n+1)*H one. Use 0 to
The n is actually optional, the default is 10.
For this and the other -ncache* options below you can abbreviate
"-ncache" with "-nc". Also, "-nonc" is the same as "-ncache 0"
This is an experimental option, currently implemented in an awk‐
ward way in that in the VNC Viewer you can see the pixel cache
contents if you scroll down, etc. So you will have to set
things up so you can't see that region. If this method is suc‐
cessful, the changes required for clients to do this less awk‐
wardly will be investigated.
The SSVNC viewer does a good job at automatically hiding the
pixel cache region. Or use SSVNC's -ycrop option to explicitly
hide the region.
Note that this mode consumes a huge amount of memory, both on
the x11vnc server side and on the VNC Viewer side. If n=2 then
the amount of RAM used is roughly tripled for both x11vnc and
the VNC Viewer. As a rule of thumb, note that 1280x1024 at
depth 24 is about 5MB of pixel data.
For reasonable response when cycling through 4 to 6 large (e.g.
web browser) windows a value n of 6 to 12 is recommended.
(that's right: ~10X more memory...)
Because of the way window backingstore and saveunders are imple‐
mented, n must be even. It will be incremented by 1 if it is
This mode also works for native MacOS X, but may not be as
effective as the X version. This is due to a number of things,
one is the drop-shadow compositing that leaves extra areas that
need to be repaired (see -ncache_pad). Another is the window
iconification animations need to be avoided (see -macicontime).
It appears the that the 'Scale' animation mode gives better
results than the 'Genie' one. Also, window event detection not
as accurate as the X version.
In -ncache mode, try to do copyrect opaque window moves/drags
instead of wireframes (this can induce painting errors). The
wireframe will still be used when moving a window whose save-
unders has not yet been set or has been invalidated.
Some VNC Viewers provide better response than others with this
option. On Unix, realvnc viewer gives smoother drags than
tightvnc viewer. Response may also be choppy if the server side
machine is too slow.
Sometimes on very slow modem connections, this actually gives an
improvement because no pixel data at all (not even the box ani‐
mation) is sent during the drag.
In -ncache mode, do not assume that moving a window will cause
the window manager to raise it to the top of the stack. The
default is to assume it does, and so at the beginning of any
wireframe, etc, window moves the window will be pushed to top in
the VNC viewer.
In -ncache mode, do not try to guess when the desktop (viewport)
changes to another one (i.e. another workarea). The default is
to try to guess and when detected try to make the transistion
In -ncache mode, do not try to snapshot the desktop background
to use in guessing or reconstructing window save-unders.
In -ncache mode, do not try to disable window manager animations
and other effects (that usually degrade ncache performance or
cause painting errors). The default is to try to disable them
on KDE (but not GNOME) when VNC clients are connected.
For other window managers or desktops that provide animations,
effects, compositing, translucency, etc. that interfere with the
-ncache method you will have to disable them manually.
In -ncache mode, enable some heuristics for old style window
managers such as fvwm and twm.
In -ncache mode, pad each window with n pixels for the caching
rectangles. This can be used to try to improve the situation
with dropshadows or other compositing (e.g. MacOS X window man‐
ager), although it could make things worse. The default is 0 on
Unix and 24 on MacOS X.
Turn on debugging and profiling output under -ncache.
-wireframe [str], -nowireframe
Try to detect window moves or resizes when a mouse button is
held down and show a wireframe instead of the full opaque win‐
dow. This is based completely on heuristics and may not always
work: it depends on your window manager and even how you move
things around. See -pointer_mode below for discussion of the
"bogging down" problem this tries to avoid. Default: -wireframe
Shorter aliases: -wf [str] and -nowf
The value "str" is optional and, of course, is packed with many
tunable parameters for this scheme:
Format: shade,linewidth,percent,T+B+L+R,mod,t1+t2+t3+t4 Default:
If you leave nothing between commas: ",," the default value is
used. If you don't specify enough commas, the trailing parame‐
ters are set to their defaults.
"shade" indicate the "color" for the wireframe, usually a
greyscale: 0-255, however for 16 and 32bpp you can specify an
rgb.txt X color (e.g. "dodgerblue") or a value > 255 is treated
as RGB (e.g. red is 0xff0000). "linewidth" sets the width of
the wireframe in pixels. "percent" indicates to not apply the
wireframe scheme to windows with area less than this percent of
the full screen.
"T+B+L+R" indicates four integers for how close in pixels the
pointer has to be from the Top, Bottom, Left, or Right edges of
the window to consider wireframing. This is a speedup to
quickly exclude a window from being wireframed: set them all to
zero to not try the speedup (scrolling and selecting text will
likely be slower).
"mod" specifies if a button down event in the interior of the
window with a modifier key (Alt, Shift, etc.) down should indi‐
cate a wireframe opportunity. It can be "0" or "none" to skip
it, "1" or "all" to apply it to any modifier, or "Shift", "Alt",
"Control", "Meta", "Super", or "Hyper" to only apply for that
type of modifier key.
"t1+t2+t3+t4" specify four floating point times in seconds: t1
is how long to wait for the pointer to move, t2 is how long to
wait for the window to start moving or being resized (for some
window managers this can be rather long), t3 is how long to keep
a wireframe moving before repainting the window. t4 is the mini‐
mum time between sending wireframe "animations". If a slow link
is detected, these values may be automatically changed to some‐
thing better for a slow link.
By default, mouse motion and button presses of a user sitting at
the LOCAL display are monitored for wireframing opportunities
(so that the changes will be sent efficiently to the VNC
clients). Use this option to disable this behavior.
-wirecopyrect mode, -nowirecopyrect
Since the -wireframe mechanism evidently tracks moving windows
accurately, a speedup can be obtained by telling the VNC viewers
to locally copy the translated window region. This is the VNC
CopyRect encoding: the framebuffer update doesn't need to send
the actual new image data.
Shorter aliases: -wcr [mode] and -nowcr
"mode" can be "never" (same as -nowirecopyrect) to never try the
copyrect, "top" means only do it if the window was not covered
by any other windows, and "always" means to translate the
orginally unobscured region (this may look odd as the remaining
pieces come in, but helps on a slow link). Default: "always"
Note: there can be painting errors or slow response when using
-scale so you may want to disable CopyRect in this case "-wire‐
copyrect never" on the command line or by remote-control. Or
you can also use the "-scale xxx:nocr" scale option.
Turn on debugging info printout for the wireframe heuristics.
"-dwf" is an alias. Specify multiple times for more output.
-scrollcopyrect mode, -noscrollcopyrect
Like -wirecopyrect, but use heuristics to try to guess if a win‐
dow has scrolled its contents (either vertically or horizon‐
tally). This requires the RECORD X extension to "snoop" on X
applications (currently for certain XCopyArea and XConfigureWin‐
dow X protocol requests). Examples: Hitting <Return> in a ter‐
minal window when the cursor was at the bottom, the text scrolls
up one line. Hitting <Down> arrow in a web browser window, the
web page scrolls up a small amount. Or scrolling with a scroll‐
bar or mouse wheel.
Shorter aliases: -scr [mode] and -noscr
This scheme will not always detect scrolls, but when it does
there is a nice speedup from using the VNC CopyRect encoding
(see -wirecopyrect). The speedup is both in reduced network
traffic and reduced X framebuffer polling/copying. On the other
hand, it may induce undesired transients (e.g. a terminal cursor
being scrolled up when it should not be) or other painting
errors (window tearing, bunching-up, etc). These are automati‐
cally repaired in a short period of time. If this is unaccept‐
able disable the feature with -noscrollcopyrect.
Screen clearing kludges: for testing at least, there are some
"magic key sequences" (must be done in less than 1 second) to
aid repairing painting errors that may be seen when using this
3 Alt_L's in a row: resend whole screen, 4 Alt_L's in a row:
reread and resend whole screen, 3 Super_L's in a row: mark whole
screen for polling, 4 Super_L's in a row: reset RECORD context,
5 Super_L's in a row: try to push a black screen
note: Alt_L is the Left "Alt" key (a single key) Super_L is the
Left "Super" key (Windows flag). Both of these are modifier
keys, and so should not generate characters when pressed by
themselves. Also, your VNC viewer may have its own refresh hot-
key or button.
"mode" can be "never" (same as -noscrollcopyrect) to never try
the copyrect, "keys" means to try it in response to keystrokes
only, "mouse" means to try it in response to mouse events only,
"always" means to do both. Default: "always"
Note: there can be painting errors or slow response when using
-scale so you may want to disable CopyRect in this case
"-scrollcopyrect never" on the command line or by remote-con‐
trol. Or you can also use the "-scale xxx:nocr" scale option.
Set the minimum area in pixels for a rectangle to be considered
for the -scrollcopyrect detection scheme. This is to avoid
wasting the effort on small rectangles that would be quickly
updated the normal way. E.g. suppose an app updated the posi‐
tion of its skinny scrollbar first and then shifted the large
panel it controlled. We want to be sure to skip the small
scrollbar and get the large panel. Default: 60000
Skip scroll detection for applications matching the comma sepa‐
rated list of strings in list. Some applications implement
their scrolling in strange ways where the XCopyArea, etc, also
applies to invisible portions of the window: if we CopyRect
those areas it looks awful during the scroll and there may be
painting errors left after the scroll. Soffice.bin is the worst
Use "##" to denote the start of the application class (e.g.
"##XTerm") and "++" to denote the start of the application
instance name (e.g. "++xterm"). The string your list is matched
against is of the form "^^WM_NAME##Class++Instance<same-for-any-
subwindows>" The "xlsclients -la" command will provide this
If a pattern is prefixed with "KEY:" it only applies to Key‐
stroke generated scrolls (e.g. Up arrow). If it is prefixed
with "MOUSE:" it only applies to Mouse induced scrolls (e.g.
dragging on a scrollbar). Default: ##Soffice.bin,##StarOf‐
Opposite of -scr_skip: this list is consulted first and if there
is a match the window will be monitored via RECORD for scrolls
irrespective of -scr_skip. Use -scr_skip '*' to skip anything
that does not match your -scr_inc. Use -scr_inc '*' to include
For keystroke scroll detection, only apply the RECORD heuristics
to the comma separated list of keysyms in list. You may find
the RECORD overhead for every one of your keystrokes disrupts
typing too much, but you don't want to turn it off completely
with "-scr mouse" and -scr_parms does not work or is too confus‐
The listed keysyms can be numeric or the keysym names in the
<X11/keysymdef.h> header file or from the xev(1) program. Exam‐
ple: "-scr_keys Up,Down,Return". One probably wants to have
application specific lists (e.g. for terminals, etc) but that is
too icky to think about for now...
If list begins with the "-" character the list is taken as an
exclude list: all keysyms except those list will be considered.
The special string "builtin" expands to an internal list of
keysyms that are likely to cause scrolls. BTW, by default modi‐
fier keys, Shift_L, Control_R, etc, are skipped since they
almost never induce scrolling by themselves.
Yet another cosmetic kludge. Apply shell/terminal heuristics to
applications matching comma separated list (same as for
-scr_skip/-scr_inc). For example an annoying transient under
scroll detection is if you hit Enter in a terminal shell with
full text window, the solid text cursor block will be scrolled
up. So for a short time there are two (or more) block cursors
on the screen. There are similar scenarios, (e.g. an output
line is duplicated).
These transients are induced by the approximation of scroll
detection (e.g. it detects the scroll, but not the fact that the
block cursor was cleared just before the scroll). In nearly all
cases these transient errors are repaired when the true X frame‐
buffer is consulted by the normal polling. But they are dis‐
tracting, so what this option provides is extra "padding" near
the bottom of the terminal window: a few extra lines near the
bottom will not be scrolled, but rather updated from the actual
X framebuffer. This usually reduces the annoying artifacts.
Use "none" to disable. Default: "term"
If a key is held down (or otherwise repeats rapidly) and this
induces a rapid sequence of scrolls (e.g. holding down an Arrow
key) the "scrollcopyrect" detection and overhead may not be able
to keep up. A time per single scroll estimate is performed and
if that estimate predicts a sustainable scrollrate of keys per
second between "lo" and "hi" then repeated keys will be DIS‐
CARDED to maintain the scrollrate. For example your key autore‐
peat may be 25 keys/sec, but for a large window or slow link
only 8 scrolls per second can be sustained, then roughly 2 out
of every 3 repeated keys will be discarded during this period.
Set various parameters for the scrollcopyrect mode. The format
is similar to that for -wireframe and packed with lots of param‐
Format: T+B+L+R,t1+t2+t3,s1+s2+s3+s4+s5 Default:
If you leave nothing between commas: ",," the default value is
used. If you don't specify enough commas, the trailing parame‐
ters are set to their defaults.
"T+B+L+R" indicates four integers for how close in pixels the
pointer has to be from the Top, Bottom, Left, or Right edges of
the window to consider scrollcopyrect. If -wireframe overlaps
it takes precedence. This is a speedup to quickly exclude a
window from being watched for scrollcopyrect: set them all to
zero to not try the speedup (things like selecting text will
likely be slower).
"t1+t2+t3" specify three floating point times in seconds that
apply to scrollcopyrect detection with *Keystroke* input: t1 is
how long to wait after a key is pressed for the first scroll, t2
is how long to keep looking after a Keystroke scroll for more
scrolls. t3 is how frequently to try to update surrounding
scrollbars outside of the scrolling area (0.0 to disable)
"s1+s2+s3+s4+s5" specify five floating point times in seconds
that apply to scrollcopyrect detection with *Mouse* input: s1 is
how long to wait after a mouse button is pressed for the first
scroll, s2 is how long to keep waiting for additional scrolls
after the first Mouse scroll was detected. s3 is how frequently
to try to update surrounding scrollbars outside of the scrolling
area (0.0 to disable). s4 is how long to buffer pointer motion
(to try to get fewer, bigger mouse scrolls). s5 is the maximum
time to spend just updating the scroll window without updating
the rest of the screen.
Periodically "repair" the screen based on settings in string.
Hopefully you won't need this option, it is intended for cases
when the -scrollcopyrect or -wirecopyrect features leave too
many painting errors, but it can be used for any scenario. This
option periodically performs costly operations and so interac‐
tive response may be reduced when it is on. You can use 3
Alt_L's (the Left "Alt" key) taps in a row (as described under
-scrollcopyrect) instead to manually request a screen repaint
when it is needed.
string is a comma separated list of one or more of the follow‐
ing: "V=t", "C=t", "X=t", and "8=t". In these "t" stands for a
time in seconds (it is a floating point even though one should
usually use values > 2 to avoid wasting resources). V sets how
frequently the entire screen should be sent to viewers (it is
like the 3 Alt_L's). C sets how long to wait after a CopyRect
to repaint the full screen. X sets how frequently to reread the
full X11 framebuffer from the X server and push it out to con‐
nected viewers. Use of X should be rare, please report a bug if
you find you need it. 8= applies only for -8to24 mode: it sets
how often the non-default visual regions of the screen (e.g.
8bpp windows) are refreshed. Examples: -fixscreen V=10
Turn on debugging info printout for the scroll heuristics.
"-ds" is an alias. Specify it multiple times for more output.
Disable any use of the RECORD extension. This is currently used
by the -scrollcopyrect scheme and to monitor X server grabs.
Some of the use of the RECORD extension can leave a tiny window
for XGrabServer deadlock. This is only if the whole-server
grabbing application expects mouse or keyboard input before
releasing the grab. It is usually a window manager that does
this. x11vnc takes care to avoid the problem, but if caught
x11vnc will freeze. Without -grab_buster, the only solution is
to go the physical display and give it some input to satisfy the
grabbing app. Or manually kill and restart the window manager
if that is feasible. With -grab_buster, x11vnc will fork a
helper thread and if x11vnc appears to be stuck in a grab after
a period of time (20-30 sec) then it will inject some user
input: button clicks, Escape, mouse motion, etc to try to break
the grab. If you experience a lot of grab deadlock, please
report a bug.
Turn on debugging info printout with respect to XGrabServer()
deadlock for -scrollcopyrect__mode_.
Turn on debugging info printout with respect to PRIMARY, CLIP‐
BOARD, and CUTBUFFER0 selections.
Various pointer motion update schemes. "-pm" is an alias. The
problem is pointer motion can cause rapid changes on the screen:
consider the rapid changes when you drag a large window around
opaquely. Neither x11vnc's screen polling and vnc compression
routines nor the bandwidth to the vncviewers can keep up these
rapid screen changes: everything will bog down when dragging or
scrolling. So a scheme has to be used to "eat" much of that
pointer input before re-polling the screen and sending out
framebuffer updates. The mode number n can be 0 to 4 and selects
one of the schemes desribed below.
Note that the -wireframe and -scrollcopyrect__mode_s complement
-pointer_mode by detecting (and improving) certain periods of
"rapid screen change".
n=0: does the same as -nodragging. (all screen polling is sus‐
pended if a mouse button is pressed.)
n=1: was the original scheme used to about Jan 2004: it basi‐
cally 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
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 mecha‐
To try out the different pointer modes to see which one gives
the best response for your usage, it is convenient to use the
remote control function, for example "x11vnc -R pm:4" or the
tcl/tk gui (Tuning -> pointer_mode -> n).
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
Have x11vnc read and process all available client input before
Similar to -allinput but use the handleEventsEagerly mechanism
built into LibVNCServer.
Enable support for per-client input devices. Each client will
get its own cursor and keyboard focus.
x11vnc tries to estimate some speed parameters that are used to
optimize scheduling (e.g. -pointer_mode 4, -wireframe, -scroll‐
copyrect) 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 net‐
work latency to clients in milliseconds, respectively. If a
value is left blank, e.g. "-speeds ,100,15", then the internal
scheme is used to estimate the empty value(s).
Typical PC video cards have read rates of 5-10 MB/sec. If the
framebuffer is in main memory instead of video h/w (e.g. SunRay,
shadowfb, dummy driver, Xvfb), the read rate may be much faster.
"x11perf -getimage500" can be used to get a lower bound (remem‐
ber to factor in the bytes per pixel). It is up to you to esti‐
mate the network bandwith and latency to clients. For the
latency the ping(1) command can be used.
For convenience there are some aliases provided, e.g. "-speeds
modem". The aliases are: "modem" for 6,4,200; "dsl" for
6,100,50; and "lan" for 6,5000,1
For some features, e.g. -wireframe and -scrollcopyrect, x11vnc
has to work around issues for certain window managers or desk‐
tops (currently kde and xfce). By default it tries to guess
which one, but it can guess incorrectly. Use this option to
indicate which wm/dt. string can be "gnome", "kde", "cde",
"xfce", or "root" (classic X wm). Anything else is interpreted
Print debugging output for every pointer event.
Print debugging output for every keyboard event.
Same as -dp and -dk, respectively. Use multiple times for more output.
Time in ms to delay sending updates to connected clients (defer‐
UpdateTime) Default: 20
Time in ms to pause between screen polls. Used to cut down on
load. Default: 20
Perform extra FrameBufferUpdateRequests checks to try to be in
better sync with the client's requests. What this does is per‐
form extra polls of the client socket at critical times (before
'-defer' and '-wait' calls.) The default is n=1. Set to a
larger number to insert more checks or set to n=0 to disable. A
downside of these extra calls is that more mouse input may be
processed than desired.
Factor by which to cut the -wait time if there has been recent
user input (pointer or keyboard). Improves response, but
increases the load whenever you are moving the mouse or typing.
When the -wait_ui mechanism cuts down the wait time ms, set the
defer time to the same ms value. n=1 to enable, 0 to disable,
and -1 to set defer to 0 (no delay). Similarly, 2 and -2 indi‐
cate 'urgent_update' mode should be used to push the updates
even sooner. Default: 1
Do not detect if the screen polling is "bogging down" and sleep
more. Some activities with no user input can slow things down a
lot: consider a large terminal window with a long build running
in it continuously streaming text output. By default x11vnc
will try to detect this (3 screen polls in a row each longer
than 0.25 sec with no user input), and sleep up to 1.5 secs to
let things "catch up". Use this option to disable that detec‐
Floating point time in seconds to delay all screen polling. For
special purpose usage where a low frame rate is acceptable and
desirable, but you want the user input processed at the normal
rate so you cannot use -wait.
Floating point time in seconds to indicate how often to do the
equivalent of xrefresh(1) to force all windows (in the viewable
area if -id, -sid, or -clip is used) to repaint themselves. Use
this only if applications misbehave by not repainting themselves
properly. See also -noxdamage.
Monitor activity and if it is low take longer naps between
screen polls to really cut down load when idle. Default: take
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 Set the env. var. X11VNC_SB_FAC‐
TOR to scale it.
Set LibVNCServer rfbMaxClientWait to n seconds. On slow links
that take a long time to paint the first screen LibVNCServer may
hit the timeout and drop the connection. Default: 20 seconds.
Send a 1x1 framebuffer update to all clients every n seconds
(e.g. to try to keep a network connection alive)
If the system supports the FBPM (Frame Buffer Power Management)
extension (i.e. some Sun systems), then prevent the video h/w
from going into a reduced power state when VNC clients are con‐
FBPM capable video h/w save energy when the workstation is idle
by going into low power states (similar to DPMS for monitors).
This interferes with x11vnc's polling of the framebuffer data.
"-nofbpm" means prevent FBPM low power states whenever VNC
clients are connected, while "-fbpm" means to not monitor the
FBPM state at all. See the xset(1) manpage for details. -nof‐
bpm is basically the same as running "xset fbpm force on" peri‐
odically. Default: -fbpm
If the system supports the DPMS (Display Power Management Sig‐
naling) extension, then prevent the monitor from going into a
reduced power state when VNC clients are connected.
DPMS reduced power monitor states are a good thing and you nor‐
mally want the power down to take place (usually x11vnc has no
problem exporting the display in this state). You probably only
want to use "-nodpms" to work around problems with Screen Savers
kicking on in DPMS low power states. There is known problem
with kdesktop_lock on KDE where the screen saver keeps kicking
in every time user input stops for a second or two. Specifying
"-nodpms" works around it.
"-nodpms" means prevent DPMS low power states whenever VNC
clients are connected, while "-dpms" means to not monitor the
DPMS state at all. See the xset(1) manpage for details.
-nodpms is basically the same as running "xset dpms force on"
periodically. Default: -dpms
If the system supports the DPMS (Display Power Management Sig‐
naling) extension, then try to keep the monitor in a powered off
state. This is to prevent nosey people at the physical display
from viewing what is on the screen. Be sure to lock the screen
This method is far from bullet proof, e.g. suppose someone
attaches a non-DPMS monitor, or loads the machine so that there
is a gap of time before x11vnc restores the powered off state?
On many machines if he floods it with keyboard and mouse input
he can see flashes of what is on the screen before the DPMS off
state is reestablished. For this to work securely there would
need to be support in the X server to do this exactly rather
than approximately with DPMS.
As -forcedpms but only when VNC clients are connected.
The UltraVNC ServerInput extension is supported. This allows
the VNC viewer to click a button that will cause the server
(x11vnc) to try to disable keyboard and mouse input at the phys‐
ical display and put the monitor in dpms powered off state. Use
this option to skip powering off the monitor.
Disable the following UltraVNC extensions: SingleWindow and
ServerInput. The others managed by LibVNCServer (textchat, 1/n
scaling, rfbEncodingUltra) are not.
Place a local UltraVNC chat window on the X11 display that
x11vnc is polling. That way the person on the VNC viewer-side
can chat with the person at the physical X11 console. (e.g.
helpdesk w/o telephone)
For this to work the SSVNC package (version 1.0.21 or later)
MUST BE installed on the system where x11vnc runs and the
'ssvnc' command must be available in $PATH. The ssvncviewer is
used as a chat window helper. See http://www.karl‐
This option implies '-rfbversion 3.6' so as to trick UltraVNC
viewers, otherwise they assume chat is not available. To spec‐
ify a different rfbversion, place it after the -chatwindow
option on the cmdline.
See also the remote control 'chaton' and 'chatoff' actions.
These can also be set from the tkx11vnc GUI.
Do not use the X DAMAGE extension to detect framebuffer changes
even if it is available. Use -xdamage if your default is to
have it off.
x11vnc's use of the DAMAGE extension: 1) significantly reduces
the load when the screen is not changing much, and 2) detects
changed areas (small ones by default) more quickly.
Currently the DAMAGE extension is overly conservative and often
reports large areas (e.g. a whole terminal or browser window) as
damaged even though the actual changed region is much smaller
(sometimes just a few pixels). So heuristics were introduced to
skip large areas and use the damage rectangles only as "hints"
for the traditional scanline polling. The following tuning
parameters are introduced to adjust this behavior:
Set the largest DAMAGE rectangle area A (in pixels: width *
height) to trust as truly damaged: the rectangle will be copied
from the framebuffer (slow) no matter what. Set to zero to
trust *all* rectangles. Default: 20000
Set how long DAMAGE rectangles should be "remembered", f is a
floating point number and is in units of the scanline repeat
cycle time (32 iterations). The default (1.0) should give no
painting problems. Increase it if there are problems or decrease
it to live on the edge (perhaps useful on a slow machine).
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.
This option is not really needed since LibVNCServer is doing the
correct thing now for quite some time. However, for convenience
you can use it to ignore other signals, e.g. "-sigpipe
ignore:HUP,INT,TERM" in case that would be useful for some sort
of application. You can also put "exit:.." in the list to have
x11vnc cleanup on the listed signals. "-sig" is an alias for
this option if you don't like the 'pipe'. Example: -sig
Whether or not to use the threaded LibVNCServer algorithm
[rfbRunEventLoop] if libpthread is available. In this mode new
threads (one for input and one for output) are created to handle
each new client. Default: -nothreads.
Thread stability is much improved in version 0.9.8.
Multiple clients in threaded mode should be stable for the ZRLE
encoding on all platforms. The Tight and Zlib encodings are
currently only stable on Linux for multiple clients. Compile
with -DTLS=__thread if your OS and compiler and linker support
For resizes (randr, etc.) set this env. var. to the number of
milliseconds to sleep: X11VNC_THREADS_NEW_FB_SLEEP at various
places in the do_new_fb() action. This is to let various activ‐
ities settle. Default is about 500ms.
Multiple clients in threaded mode could yield better performance
for 'class-room' broadcasting usage; also in -appshare broadcast
mode. See also the -reflect option.
If the fraction of changed tiles in a poll is greater than f,
the whole screen is updated. Default: 0.75
Heuristic to fill in gaps in rows or cols of n or less tiles.
Used to improve text paging. Default: 4
Heuristic to grow islands of changed tiles n or wider by check‐
ing the tile near the boundary. Default: 3
Tolerance in pixels to mark a tiles edges as changed. Default:
Print debugging output for tiles, fb updates, etc.
Instead of polling the X display framebuffer (fb) for changes,
periodically copy all of X display fb into main memory and exam‐
ine that copy for changes. (This setting also applies for non-X
-rawfb modes). Under some circumstances this will improve
interactive response, or at least make things look smoother, but
in others (most!) it will make the response worse. If the video
h/w fb is such that reading small tiles is very slow this mode
could help. To keep the "framerate" up the screen size x bpp
cannot be too large. Note that this mode is very wasteful of
memory I/O resources (it makes full screen copies even if noth‐
ing changes). It may be of use in video capture-like applica‐
tions, webcams, or where window tearing is a problem.
Instead of polling X, poll the memory object specified in
For file polling, to memory map mmap(2) a file use:
"map:/path/to/a/file@WxHxB", with framebuffer Width, Height, and
Bits per pixel. "mmap:..." is the same.
If there is trouble with mmap, use "file:/..." for slower
lseek(2) based reading.
Use "snap:..." to imply -snapfb mode and the "file:" access
(this is for unseekable devices that only provide the fb all at
once, e.g. a video camera provides the whole frame).
For shared memory segments string is of the form: "shm:N@WxHxB"
which specifies a shmid N and with WxHxB as above. See shmat(1)
If you do not supply a type "map" is assumed if the file exists
(see the next paragraphs for some exceptions to this.)
If string is "setup:cmd", then the command "cmd" is run and the
first line from it is read and used as string. This allows ini‐
tializing the device, determining WxHxB, etc. These are often
done as root so take care.
If the string begins with "video", see the VIDEO4LINUX discus‐
sion below where the device may be queried for (and possibly
set) the framebuffer parameters.
If the string begins with "console", "/dev/fb", "fb", or "vt",
see the LINUX CONSOLE discussion below where the framebuffer
device is opened and keystrokes (and possibly mouse events) are
inserted into the console.
If the string begins with "vnc", see the VNC HOST discussion
below where the framebuffer is taken as that of another remote
Optional suffixes are ":R/G/B" and "+O" to specify red, green,
and blue masks (in hex) and an offset into the memory object.
If the masks are not provided x11vnc guesses them based on the
bpp (if the colors look wrong, you need to provide the masks.)
Another optional suffix is the Bytes Per Line which in some
cases is not WxB/8. Specify it as WxHxB-BPL e.g.
800x600x16-2048. This could be a normal width 1024 at 16bpp fb,
but only width 800 shows up.
So the full format is: mode:file@WxHxB:R/G/B+O-BPL
-rawfb file:/dev/urandom@128x128x8 -rawfb
snap:/dev/video0@320x240x24 -24to32 -rawfb video0 -rawfb video
-pipeinput VID -rawfb console -rawfb vt2 -rawfb vnc:somehost:0
(see ipcs(1) and fbset(1) for the first two examples)
In general all user input is discarded by default (see the
-pipeinput option for how to use a helper program to insert).
Most of the X11 (screen, keyboard, mouse) options do not make
sense and many will cause this mode to crash, so please think
twice before setting or changing them in a running x11vnc.
If you DO NOT want x11vnc to close the X DISPLAY in rawfb mode,
prepend a "+" e.g. +file:/dev/fb0... Keeping the display open
enables the default remote-control channel, which could be use‐
ful. Alternatively, if you specify -noviewonly, then the mouse
and keyboard input are STILL sent to the X display, this usage
should be very rare, i.e. doing something strange with /dev/fb0.
If the device is not "seekable" (e.g. webcam) try reading it all
at once in full snaps via the "snap:" mode (note: this is a
resource hog). If you are using file: or map: AND the device
needs to be reopened for *every* snapfb snapshot, set the envi‐
ronment variable: SNAPFB_RAWFB_RESET=1 as well.
If you want x11vnc to dynamically transform a 24bpp rawfb to
32bpp (note that this will be slower) also supply the -24to32
option. This would be useful for, say, a video camera that
delivers the pixel data as 24bpp packed RGB. This is the
default under "video" mode if the bpp is 24.
Normally the bits per pixel, B, is 8, 16, or 32 (or rarely 24),
however there is also some support for B < 8 (e.g. old graphics
displays 4 bpp or 1 bpp). In this case you certainly must sup‐
ply the masks as well: WxHxB:R/G/B. The pixels will be padded
out to 8 bpp using depth 8 truecolor. The scheme currently does
not work with snap fb (ask if interested.) B=1 monochrome exam‐
ple: file:/dev/urandom@128x128x1:1/1/1 Some other like this are
For B < 8 framebuffers you can also set the env. var RAWFB_CGA=1
to try a CGA mapping for B=4 (e.g. linux vga16fb driver.) Note
with low bpp and/or resolution VGA and VGA16 modes on the Linux
console one's attempt to export them via x11vnc can often be
thwarted due to special color palettes, pixel packings, and even
video painting buffering. OTOH, often experimenting with the
RGB masks can yield something recognizable.
VIDEO4LINUX: on Linux some attempt is made to handle video
devices (webcams or TV tuners) automatically. The idea is the
WxHxB will be extracted from the device itself. So if you do
not supply "@WxHxB... parameters x11vnc will try to determine
them. It first tries the v4l API if that support has been com‐
piled in. Otherwise it will run the v4l- info(1) external pro‐
gram if it is available.
The simplest examples are "-rawfb video" and "-rawfb video1"
which imply the device file /dev/video and /dev/video1, respec‐
tively. You can also supply the /dev if you like, e.g. "-rawfb
Since the video capture device framebuffer usually changes con‐
tinuously (e.g. brightness fluctuations), you may want to use
the -wait, -slow_fb, or -defer options to lower the "framerate"
to cut down on network VNC traffic.
A more sophisticated video device scheme allows initializing the
device's settings using:
The prefix could also be, as above, e.g. "video1:" to specify
the device file. The v4l API must be available for this to
work. Otherwise, you will need to try to initialize the device
with an external program, e.g. xawtv, spcaview, and hope they
persist when x11vnc re-opens the device.
<settings> is a comma separated list of key=value pairs. The
device's brightness, color, contrast, and hue can be set to per‐
centages, e.g. br=80,co=50,cn=44,hu=60.
The device filename can be set too if needed (if it does not
start with "video"), e.g. fn=/dev/qcam.
The width, height and bpp of the framebuffer can be set via,
Related to the bpp above, the pixel format can be set via the
fmt=XXX, where XXX can be one of: GREY, HI240, RGB555, RGB565,
RGB24, and RGB32 (with bpp 8, 8, 16, 16, 24, and 32 respec‐
tively). See http://www.linuxtv.org for more info (V4L api).
For TV/rf tuner cards one can set the tuning mode via tun=XXX
where XXX can be one of PAL, NTSC, SECAM, or AUTO.
One can switch the input channel by the inp=XXX setting, where
XXX is the name of the input channel (Television, Composite1, S-
Video, etc). Use the name that is in the information about the
device that is printed at startup.
For input channels with tuners (e.g. Television) one can change
which station is selected by the sta=XXX setting. XXX is the
station number. Currently only the ntsc-cable-us (US cable)
channels are built into x11vnc. See the -freqtab option below
to supply one from xawtv. If XXX is greater than 500, then it is
interpreted as a raw frequency in KHz.
one might need to add inp=Television too for the input channel
to be TV if the card doesn't come up by default in that one.
Note that not all video capture devices will support all of the
See the -pipeinput VID option below for a way to control the
settings through the VNC Viewer via keystrokes. As a shortcut,
if the string begins "Video.." instead of "video.." then
-pipeinput VID is implied.
As above, if you specify a "@WxHxB..." after the <settings>
string they are used verbatim: the device is not queried for the
current values. Otherwise the device will be queried.
LINUX CONSOLE: The following describes some ways to view and
possibly interact with the Linux text/graphics console (i.e. not
Note: If the LibVNCServer LinuxVNC program is on your system you
may want to use that instead of the following method because it
will be faster and more accurate for the Linux text console and
includes mouse support. There is, however, the basic LinuxVNC
functionality in x11vnc if you replace "console" with "vt" in
the examples below.
If the rawfb string begins with "console" the framebuffer device
/dev/fb0 is opened and /dev/tty0 is opened too. The latter is
used to inject keystrokes (not all are supported, but the basic
ones are). You will need to be root to inject keystrokes, but
not necessarily to open /dev/fb0. /dev/tty0 refers to the
active VT, to indicate one explicitly, use, e.g., "console2" for
/dev/tty2, etc. by indicating the specific VT number.
For the Linux framebuffer device, /dev/fb0, (fb1, etc) to be
enabled the appropriate kernel drivers must be loaded. E.g.
vesafb or vga16fb and also by setting the boot parameter
vga=0x301 (or 0x314, 0x317, etc.) (The vga=... method is the
preferred way; set your machines up that way.) Otherwise there
will be a ´No such device' error. You can also load a Linux
framebuffer driver specific to your make of video card for more
functionality. Once the machine is booted one can often 'mod‐
probe' the fb driver as root to obtain a framebuffer device.
If you cannot get /dev/fb0 working on Linux, try using the Lin‐
uxVNC emulation mode by "-rawfb vtN" where N = 1, ... 6 is the
Linux Virtual Terminal (aka virtual console) you wish to view,
e.g. "-rawfb vt2". Unlike /dev/fb mode, it need not be the
active Virtual Terminal. Note that this mode can only show text
and not graphics. x11vnc polls the text in /dev/vcsaN
Set the env. var. RAWFB_VCSA_BW=1 to disable colors in the "vtN"
mode (i.e. black and white only.) If you do not prefer the
default 16bpp set RAWFB_VCSA_BPP to 8 or 32. If you need to
tweak the rawfb parameters by using the 'console_guess' string
printed at startup, be sure to indicate the snap: method.
uinput: If the Linux version appears to be 2.6 or later and the
"uinput" module appears to be present (modprobe uinput), then
the uinput method will be used instead of /dev/ttyN. uinput
allows insertion of BOTH keystrokes and mouse input and so it
preferred when accessing graphical (e.g. QT-embedded) linux con‐
sole apps. It also provides more accurate keystroke insertion.
See -pipeinput UINPUT below for more information on this mode;
you will have to use -pipeinput if you want to tweak any UINPUT
parameters. You may also want to also use the -nodragging and
-cursor none options. Use "console0", etc or -pipeinput CON‐
SOLE to force the /dev/ttyN method.
Note you can change the Linux VT remotely using the chvt(1) com‐
mand to make the one you want be the active one (e.g. 'chvt 3').
Sometimes switching out and back corrects the framebuffer's
graphics state. For the "-rawfb vtN" mode there is no need to
switch the VT's.
To skip input injecting entirely use "consolex" or "vtx".
The string "/dev/fb0" (1, etc.) can be used instead of "con‐
sole". This can be used to specify a different framebuffer
device, e.g. /dev/fb1. As a shortcut the "/dev/" can be
dropped. If the name is something nonstandard, use "con‐
If you do not want x11vnc to guess the framebuffer's WxHxB and
masks automatically (sometimes the kernel gives incorrect infor‐
mation), specify them with a @WxHxB (and optional :R/G/B masks)
at the end of the string.
Examples: -rawfb console -rawfb /dev/fb0 (same) -rawfb
console3 (force /dev/tty3) -rawfb consolex
(no keystrokes or mouse) -rawfb console:/dev/nonstd -rawfb con‐
sole -pipeinput UINPUT:accel=4.0 -rawfb vt3
(/dev/tty3 w/o /dev/fb0)
VNC HOST: if the -rawfb string is of the form "vnc:host:N" then
the VNC display "N" on the remote VNC server "host" is connected
to (i.e. x11vnc acts as a VNC client itself) and that frame‐
buffer is exported.
This mode is really only of use if you are trying to improve
performance in the case of many (e.g. > 10) simultaneous VNC
viewers, and you try a divide and conquer scheme to reduce band‐
width and improve responsiveness. (However, another user found
this mode useful to export a demo display through a slow link:
then multiple demo viewers connected to the reflecting x11vnc on
the fast side of the link, and so avoided all of the demo view‐
ers going through the slow link.)
For example, if there will be 64 simultaneous VNC viewers this
can lead to a lot of redundant VNC traffic to and from the
server host:N, extra CPU usage, and all viewers response can be
reduced by having to wait for writes to the slowest client to
finish. However, if you set up 8 reflectors/repeaters started
with option -rawfb vnc:host:N, then there are only 8 connections
to host:N. Each repeater then handles 8 vnc viewer connections
thereby spreading the load around. In classroom broadcast
usage, try to put the repeaters on different switches. This
mode is the same as -reflect host:N. Replace "host:N" by "lis‐
ten" or "listen:port" for a reverse connection.
Overall performance will not be as good as a single direct con‐
nection because, among other things, there is an additional
level of framebuffer polling and pointer motion can still induce
many changes per second that must be propagated. Tip: if the
remote VNC is x11vnc doing wireframing, or an X display that
does wireframing that gives much better response than opaque
window dragging. Consider the -nodragging option if the problem
The env. var. X11VNC_REFLECT_PASSWORD can be set to the password
needed to log into the vnc host server, or to
"file:path_to_file" to indicate a file containing the password
as its first line.
To set the pixel format that x11vnc requests as a VNC CLIENT set
the env. vars: X11VNC_REFLECT_bitsPerSample X11VNC_REFLECT_sam‐
plesPerPixel, and X11VNC_REFLECT_bytesPerPixel; the defaults are
8, 3, 4. 2, 3, 1 would give a low color mode. See the function
rfbGetClient() in libvncclient for more info.
The VNC HOST mode implies -shared. Use -noshared as a subse‐
quent cmdline option to disable sharing.
For use with "-rawfb video" for TV tuner devices to specify sta‐
tion frequencies. Instead of using the built in ntsc-cable-us
mapping of station number to frequency, use the data in file.
For stations that are not numeric, e.g. SE20, they are placed
above the highest numbered station in the order they are found.
Example: "-freqtab /usr/X11R6/share/xawtv/europe-west.list" You
can make your own freqtab by copying the xawtv format.
This option lets you supply an external command in cmd that
x11vnc will pipe all of the user input events to in a simple
format. In -pipeinput mode by default x11vnc will not process
any of the user input events. If you prefix cmd with "tee:" it
will both send them to the pipe command and process them. For a
description of the format run "-pipeinput tee:/bin/cat".
Another prefix is "reopen" which means to reopen pipe if it
exits. Separate multiple prefixes with commas.
In combination with -rawfb one might be able to do amusing
things (e.g. control non-X devices). To facilitate this, if
-rawfb is in effect then the value is stored in X11VNC_RAWFB_STR
for the pipe command to use if it wants. Do 'env | grep X11VNC'
Built-in pipeinput modes (no external program required):
If cmd is "VID" and you are using the -rawfb for a video capture
device, then an internal list of keyboard mappings is used to
set parameters of the video. The mappings are:
"B" and "b" adjust the brightness up and down. "H" and "h"
adjust the hue. "C" and "c" adjust the colour. "N" and "n"
adjust the contrast. "S" and "s" adjust the size of the capture
screen. "I" and "i" cycle through input channels. Up and Down
arrows adjust the station (if a tuner) F1, F2, ..., F6 will
switch the video capture pixel format to HI240, RGB565, RGB24,
RGB32, RGB555, and GREY respectively. See -rawfb video for
If cmd is "CONSOLE" or "CONSOLEn" where n is a Linux console
number, then the linux console keystroke insertion to /dev/ttyN
(see -rawfb console) is performed.
If cmd begins with "UINPUT" then the Linux uinput module is used
to insert both keystroke and mouse events to the Linux console
(see -rawfb above). This usually is the /dev/input/uinput
device file (you may need to create it with "mknod
/dev/input/uinput c 10 223" and insert the module with "modprobe
The UINPUT mode currently only does US keyboards (a scan code
option may be added), and not all keysyms are supported. But it
is probably more accurate than the "CONSOLE" method.
You may want to use the options -cursor none and -nodragging in
Additional tuning options may be supplied via: UIN‐
PUT:opt1,opt2,... (a comma separated list). If an option begins
with "/" it is taken as the uinput device file.
Which uinput is injected can be controlled by an option string
made of the characters "K", "M", and "B" (see the -input
option), e.g. "KM" allows keystroke and motion but not button
A UINPUT option of the form: accel=f, or accel=fx+fy sets the
mouse motion "acceleration". This is used to correct raw mouse
relative motion into how much the application cursor moves
(x11vnc has no control over, or knowledge of how the windowing
application interprets the raw mouse motions). Typically the
acceleration for an X display is 2 (see xset "m" option). "f"
is a floating point number, e.g. 3.0. Use "fx+fy" if you need
to supply different corrections for x and y.
Note: the default acceleration is 2.0 since it seems both X and
qt-embedded often (but not always) use this value.
Even with a correct accel setting the mouse position will get
out of sync (probably due to a mouse "threshold" setting where
the acceleration doe not apply, set xset(1) ). The option
reset=N sets the number of ms (default 150) after which the cur‐
sor is attempted to be reset (by forcing the mouse to (0, 0) via
small increments and then back out to (x, y) in 1 jump), This
correction seems to be needed but can cause jerkiness or unex‐
pected behavior with menus, etc. Use reset=0 to disable.
If you set the env. var X11VNC_UINPUT_THRESHOLDS then the
thresh=n mode will be enabled. It is currently not working
well. If |dx| <= thresh and |dy| < thresh no acceleration is
applied. Use "thresh=+n" |dx| + |dy| < thresh to be used
Example: -pipeinput UINPUT:accel=4.0 -cursor none
If the uinput device has an absolute pointer (as opposed to a
normal mouse that is a relative pointer) you can specify the
option "abs". Note that a touchpad on a laptop is an absolute
device to some degree. This (usually) avoids all the problems
with mouse acceleration. If x11vnc has trouble deducing the
size of the device, use "abs=WxH". Furthermore, if the device
is a touchscreen (assumed to have an absolute pointer) use
"touch" or "touch=WxH". For touchscreens, when a mouse button
is pressed, a pressure increase is injected, and when the button
is released a pressure of zero is injected.
If touch has been set, use "touch_always=1" to indicate whenever
the mouse moves with no button pressed, a touch event of zero
pressure should be sent anyway. Also use "btn_touch=1" to indi‐
cate a BTN_TOUCH keystroke press or release should be sent
instead of a pressure change. Set "dragskip=n" to skip n
dragged mouse touches (with pressure applied) before injecting
one. To indicate the pressure that should be sent when there is
a button click for a touchscreen device, specify pressure=n,
e.g. n=5. The default is n=1.
If a touch screen is being used ("touch" above) and it is having
its input processed by tslib, you can specify the tslib calibra‐
tion file via tslib_cal=<file>. For example,
tslib_cal=/etc/pointercal. To get accurate or even usable posi‐
tioning this is required when tslib is in use.
The Linux uinput mechanism can be bypassed and one can write
input events DIRECTLY to the devices instead. To do this, spec‐
ify one or more of the following for the input classes:
direct_rel=<device> direct_abs=<device> direct_btn=<device> or
direct_key=<device>. The <device> file is usually something
like /dev/input/event1 but you can specify any device file or
pipe. You must specify each one of the above classes even if
they correspond to the same device file (rel/abs and btn are
often the same.) Look at the file /proc/bus/input/devices to
get an idea what is available and the device filenames. Note:
The /dev/input/mouse* devices do not seem to work, use the cor‐
responding /dev/input/event* file instead. Any input class not
directly specified as above will be handled via the uinput mech‐
anism. To disable creating a uinput device (and thereby dis‐
carding unhandled input), specify "nouinput".
this was used on a qtmoko Neo freerunner (armel):
(where the long line has been split into two.)
You can set the env. var X11VNC_UINPUT_DEBUG=1 or higher to get
debugging output for UINPUT mode.
For the native MacOSX server, disable dimming.
For the native MacOSX server, disable display sleep.
For the native MacOSX server, disable screensaver.
For the native MacOSX server, do not wait for the user to switch
back to his display.
For the native MacOSX server, set the mouse wheel speed to n
For the native MacOSX server, do not swap mouse buttons 2 and 3.
For the native MacOSX server, do not resize or reset the frame‐
buffer even if it is detected that the screen resolution or
depth has changed.
For the native MacOSX server, set n to the number of millisec‐
onds that the window iconify/deiconify animation takes. In
-ncache mode this value will be used to skip the animation if
possible. (default 400)
For the native MacOSX server, in -ncache client-side caching
mode, try to cache pull down menus (not perfect because they
have animated fades, etc.)
For the native MacOSX server, use the original keystroke inser‐
tion code based on a US keyboard.
For the native MacOSX server, do not use OpenGL for screen cap‐
ture, but rather use the original, deprecated raw memory access
method: addr = CGDisplayBaseAddress().
For the native MacOSX server, disable the raw memory address
screen capture method.
MACOSX NOTE: There are some deprecated MacOSX interfaces to
inject keyboard and mouse events and the raw memory access
method is deprecated as well (however, OpenGL will be preferred
if available because it is faster.) One can force not using any
deprecated interfaces at compile time by setting
-DX11VNC_MACOSX_NO_DEPRECATED=1 in CPPFLAGS. Or to turn them
off one by one: -DX11VNC_MACOSX_NO_DEPRECATED_LOCALEVENTS=1,
-DX11VNC_MACOSX_NO_DEPRECATED_FRAMEBUFFER=1 At run time, for
testing and workarounds, one can disable them by using: -env
X11VNC_MACOSX_NO_DEPRECATED=1 -env X11VNC_MACOSX_NO_DEPRE‐
CATED_LOCALEVENTS=1 -env X11VNC_MACOSX_NO_DEPRE‐
CATED_POSTEVENTS=1 or -env X11VNC_MACOSX_NO_DEPRECATED_FRAME‐
BUFFER=1 Note: When doing either of these for the mouse input
not everything works currently, e.g. double clicks and wirefram‐
ing. Also, screen resolution and pixel depth changes will not
be automatically detected unless the deprecated framebuffer
interfaces are allowed.
Conversely, if you are compiling on an older machine that does
not have some of the newer interfaces, you may need to specify
-DX11VNC_MACOSX_USE_GETMAINDEVICE to regain the very old Quick‐
Draw GetMainDevice() interface (rare...)
Start up a simple tcl/tk gui based on the remote control options
-remote/-query described below. Requires the "wish" program to
be installed on the machine. "gui-opts" is not required: the
default is to start up both the full gui and x11vnc with the gui
showing up on the X display in the environment variable DISPLAY.
"gui-opts" can be a comma separated list of items. Currently
there are these types of items: 1) a gui mode, a 2) gui "sim‐
plicity", 3) the X display the gui should display on, 4) a
"tray" or "icon" mode, and 5) a gui geometry.
1) The gui mode can be "start", "conn", or "wait" "start" is the
default mode above and is not required. "conn" means do not
automatically start up x11vnc, but instead just try to connect
to an existing x11vnc process. "wait" means just start the gui
and nothing else (you will later instruct the gui to start
x11vnc or connect to an existing one.)
2) The gui simplicity is off by default (a power-user gui with
all options is presented) To start with something less daunting
supply the string "simple" ("ez" is an alias for this). Once
the gui is started you can toggle between the two with "Misc ->
3) Note the possible confusion regarding the potentially two
different X displays: x11vnc polls one, but you may want the gui
to appear on another. For example, if you ssh in and x11vnc is
not running yet you may want the gui to come back to you via
your ssh redirected X display (e.g. localhost:10).
If you do not specify a gui X display in "gui-opts" then the
DISPLAY environment variable and -display option are tried (in
that order). Regarding the x11vnc X display the gui will try to
communication with, it first tries -display and then DISPLAY.
For example, "x11vnc -display :0 -gui otherhost:0", will remote
control an x11vnc polling :0 and display the gui on otherhost:0
The "tray/icon" mode below reverses this preference, preferring
to display on the x11vnc display.
4) When "tray" or "icon" is specified, the gui presents itself
as a small icon with behavior typical of a "system tray" or
"dock applet". The color of the icon indicates status (con‐
nected clients) and there is also a balloon status. Clicking on
the icon gives a menu from which properties, etc, can be set and
the full gui is available under "Advanced". To be fully func‐
tional, the gui mode should be "start" (the default).
Note that tray or icon mode will imply the -forever x11vnc
option (if the x11vnc server is started along with the gui)
unless -connect or -connect_or_exit has been specified. So
x11vnc (and the tray/icon gui) will wait for more connections
after the first client disconnects. If you want only one viewer
connection include the -once option.
For "icon" the gui just a small standalone window. For "tray"
it will attempt to embed itself in the "system tray" if possi‐
ble. If "=setpass" is appended then at startup the X11 user will
be prompted to set the VNC session password. If =<hexnumber> is
appended that icon will attempt to embed itself in the window
given by hexnumber. Use =noadvanced to disable the full gui.
(To supply more than one, use "+" sign). E.g. -gui tray=setpass
and -gui icon=0x3600028
Other modes: "full", the default and need not be specified.
"-gui none", do not show a gui, useful to override a ~/.x11vncrc
5) When "geom=+X+Y" is specified, that geometry is passed to the
gui toplevel. This is the icon in icon/tray mode, or the full
gui otherwise. You can also specify width and height, i.e.
WxH+X+Y, but it is not recommended. In "tray" mode the geometry
is ignored unless the system tray manager does not seem to be
running. One could imagine using something like "-gui
tray,geom=+4000+4000" with a display manager to keep the gui
invisible until someone logs in...
More icon tricks, "icon=minimal" gives an icon just with the VNC
display number. You can also set the font with "iconfont=...".
The following could be useful: "-gui icon=minimal,icon‐
General examples of the -gui option: "x11vnc -gui", "x11vnc -gui
ez" "x11vnc -gui localhost:10", "x11vnc -gui conn,host:0",
"x11vnc -gui tray,ez" "x11vnc -gui tray=setpass"
If you do not intend to start x11vnc from the gui (i.e. just
remote control an existing one), then the gui process can run on
a different machine from the x11vnc server as long as X permis‐
sions, etc. permit communication between the two.
FONTS: On some systems the tk fonts can be too small, jagged, or
otherwise unreadable. There are 4 env vars you can set to be
the tk font you prefer:
X11VNC_FONT_BOLD main font for menus and buttons.
X11VNC_FONT_FIXED font for fixed width text.
X11VNC_FONT_BOLD_SMALL tray icon font. X11VNC_FONT_REG_SMALL
tray icon menu font.
The last two only apply for the tray icon mode.
Here are some examples:
-env X11VNC_FONT_BOLD='Helvetica -16 bold' -env
X11VNC_FONT_FIXED='Courier -14' -env X11VNC_FONT_REG_SMALL='Hel‐
You can put the lines like the above (without the quotes) in
your ~/.x11vncrc file to avoid having to specify them on the
x11vnc command line.
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 ...' x11vnc command exits. You can often use the
-query command (see below) to see if the x11vnc server processed
your -remote command.
The default communication channel is that of X properties
(specifically X11VNC_REMOTE), and so this command must be run
with correct settings for DISPLAY and possibly XAUTHORITY to
connect to the X server and set the property. Alternatively,
use the -display and -auth options to set them to the correct
values. The running server cannot use the -novncconnect option
because that disables the communication channel. See below for
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.
To use a different name for the X11 property (e.g. to have sepa‐
rate communication channels for multiple x11vnc's on the same
display) set the X11VNC_REMOTE environment variable to the
string you want, for example: -env
X11VNC_REMOTE=X11VNC_REMOTE_12345 Both sides of the channel must
use the same unique name.
To run a bunch of commands in a sequence use something like:
x11vnc -R 'script:firstcmd;secondcmd;...'
Use x11vnc -R script:file=/path/to/file to read commands from a
file (can be multi-line and use the comment '#' character in the
normal way. The ';' separator must still be used to separate
To not try to contact another x11vnc process and instead just
run the command (or query) directly, prefix the command with the
The following -remote/-R commands are supported:
stop terminate the server, same as "quit" "exit" or
ping see if the x11vnc server responds. return is:
ping:mystring as above, but use your own unique string.
return is: ans=ping:mystring:<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"
id_cmd:cmd cmds: raise, lower, map, unmap, iconify,
move:dXdY, resize:dWdH, geom:WxH+X+Y. dX dY, dW, and dH must
have a leading "+" or "-" e.g.: move:-30+10 resize:+20+35 also:
wm_delete, wm_name:string and icon_name:string. Also
waitmapped wait until subwin is mapped.
nowaitmapped do not wait until subwin is mapped.
clip:WxH+X+Y set -clip mode to "WxH+X+Y"
flashcmap enable -flashcmap mode.
noflashcmap disable -flashcmap mode.
shiftcmap:n set -shiftcmap to n.
notruecolor enable -notruecolor mode.
truecolor disable -notruecolor mode.
overlay enable -overlay mode (if applicable).
nooverlay disable -overlay mode.
overlay_cursor in -overlay mode, enable cursor drawing.
overlay_nocursor disable cursor drawing. same as nooverlay_cur‐
8to24 enable -8to24 mode (if applicable).
no8to24 disable -8to24 mode.
8to24_opts:str set the -8to24 opts to "str".
24to32 enable -24to32 mode (if applicable).
no24to32 disable -24to32 mode.
visual:vis set -visual to "vis"
scale:frac set -scale to "frac"
scale_cursor:f set -scale_cursor to "f"
viewonly enable -viewonly mode.
noviewonly disable -viewonly mode.
shared enable -shared mode.
noshared disable -shared mode.
forever enable -forever mode.
noforever disable -forever mode.
timeout:n reset -timeout to n, if there are currently no
clients, exit unless one connects in the next n secs.
tightfilexfer enable filetransfer for NEW clients.
notightfilexfer disable filetransfer for NEW clients.
ultrafilexfer enable filetransfer for clients.
noultrafilexfer disable filetransfer for clients.
rfbversion:n.m set -rfbversion for new clients.
http enable http client connections.
nohttp disable http client connections.
deny deny any new connections, same as "lock"
nodeny allow new connections, same as "unlock"
avahi enable avahi service advertising.
noavahi disable avahi service advertising.
mdns enable avahi service advertising.
nomdns disable avahi service advertising.
zeroconf enable avahi service advertising.
nozeroconf disable avahi service advertising.
connect:host do reverse connection to host, "host" may be a
comma separated list of hosts or host:ports. See -connect.
Passwords required as with fwd connections. See
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.
proxy:host:port set reverse connection proxy (empty to disable).
allowonce:host For the next connection only, allow connection
from "host". In -ssl mode two connections are allowed (i.e.
Fetch Cert) unless X11VNC_NO_SSL_ALLOW_TWICE=1
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
localhost enable -localhost mode
nolocalhost disable -localhost mode
listen:str set -listen to str, empty to disable.
noipv6 enable -noipv6 mode.
ipv6 disable -noipv6 mode.
noipv4 enable -noipv4 mode.
ipv4 disable -noipv4 mode.
6 enable -6 IPv6 listening mode.
no6 disable -6 IPv6 listening mode.
lookup disable -nolookup mode.
nolookup enable -nolookup mode.
lookup disable -nolookup mode.
input:str set -input to "str", empty to disable.
grabkbd enable -grabkbd mode.
nograbkbd disable -grabkbd mode.
grabptr enable -grabptr mode.
nograbptr disable -grabptr mode.
grabalways enable -grabalways mode.
nograbalways disable -grabalways mode.
grablocal:n set -grablocal to n.
client_input:str set the K, M, B -input on a per-client basis.
select which client as for disconnect, e.g. client_input:host:MB
accept:cmd set -accept "cmd" (empty to disable).
afteraccept:cmd set -afteraccept (empty to disable).
gone:cmd set -gone "cmd" (empty to disable).
noshm enable -noshm mode.
shm disable -noshm mode (i.e. use shm).
flipbyteorder enable -flipbyteorder mode, you may need to set
noshm for this to do something.
noflipbyteorder disable -flipbyteorder mode.
onetile enable -onetile mode. (you may need to set shm
for this to do something)
noonetile disable -onetile mode.
solid enable -solid mode
nosolid disable -solid mode.
solid_color:color set -solid color (and apply it).
blackout:str set -blackout "str" (empty to disable). See
-blackout for the form of "str" (basically: WxH+X+Y,...) Use
"+WxH+X+Y" to append a single rectangle use "-WxH+X+Y" to delete
xinerama enable -xinerama mode. (if applicable)
noxinerama disable -xinerama mode.
xtrap enable -xtrap input mode(if applicable)
noxtrap disable -xtrap input mode.
xrandr enable -xrandr mode. (if applicable)
noxrandr disable -xrandr mode.
xrandr_mode:mode set the -xrandr mode to "mode".
rotate:mode set the -rotate 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.
capslock enable -capslock mode.
nocapslock disable -capslock mode.
skip_lockkeys enable -skip_lockkeys mode.
noskip_lockkeys disable -skip_lockkeys mode.
skip_keycodes:str enable -xkb -skip_keycodes "str".
sloppy_keys enable -sloppy_keys mode.
nosloppy_keys disable -sloppy_keys mode.
skip_dups enable -skip_dups mode.
noskip_dups disable -skip_dups mode.
add_keysyms enable -add_keysyms mode.
noadd_keysyms stop adding keysyms. those added will still be
removed at exit.
clear_mods enable -clear_mods mode and clear them.
noclear_mods disable -clear_mods mode.
clear_keys enable -clear_keys mode and clear them.
noclear_keys disable -clear_keys mode.
clear_locks do the clear_locks action.
clear_all do the clear_all action.
keystate have x11vnc print current keystate.
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
norepeat enable -norepeat mode.
repeat disable -norepeat mode.
nofb enable -nofb mode.
fb disable -nofb mode.
bell enable bell (if supported).
nobell disable bell.
sendbell ring the bell now.
nosel enable -nosel mode.
sel disable -nosel mode.
noprimary enable -noprimary mode.
primary disable -noprimary mode.
nosetprimary enable -nosetprimary mode.
setprimary disable -nosetprimary mode.
noclipboard enable -noclipboard mode.
clipboard disable -noclipboard mode.
nosetclipboard enable -nosetclipboard mode.
setclipboard disable -nosetclipboard mode.
seldir:str set -seldir to "str"
resend_cutbuffer resend the most recent CUTBUFFER0 copy
resend_clipboard resend the most recent CLIPBOARD copy
resend_primary resend the most recent PRIMARY copy
cursor:mode enable -cursor "mode".
show_cursor enable showing a cursor.
noshow_cursor disable showing a cursor. (same as "nocursor")
cursor_drag enable cursor changes during drag.
nocursor_drag disable cursor changes during drag.
arrow:n set -arrow to alternate n.
xfixes enable xfixes cursor shape mode.
noxfixes disable xfixes cursor shape mode.
alphacut:n set -alphacut to n.
alphafrac:f set -alphafrac to f.
alpharemove enable -alpharemove mode.
noalpharemove disable -alpharemove mode.
alphablend disable -noalphablend mode.
noalphablend enable -noalphablend mode.
cursorshape disable -nocursorshape mode.
nocursorshape enable -nocursorshape mode.
cursorpos disable -nocursorpos mode.
nocursorpos enable -nocursorpos mode.
xwarp enable -xwarppointer mode.
noxwarp disable -xwarppointer mode.
always_inject enable -always_inject mode.
noalways_inject disable -always_inject mode.
buttonmap:str set -buttonmap "str", empty to disable
dragging disable -nodragging mode.
nodragging enable -nodragging mode.
ncache reenable -ncache mode.
noncache disable -ncache mode.
ncache_size:n set -ncache size to n.
ncache_cr enable -ncache_cr mode.
noncache_cr disable -ncache_cr mode.
ncache_no_moveraise enable no_moveraise mode.
noncache_no_moveraise disable no_moveraise mode.
ncache_no_dtchange enable ncache_no_dtchange mode.
noncache_no_dtchange disable ncache_no_dtchange mode.
ncache_old_wm enable ncache_old_wm mode.
noncache_old_wm disable ncache_old_wm mode.
ncache_no_rootpixmap enable ncache_no_rootpixmap.
noncache_no_rootpixmap disable ncache_no_rootpixmap.
ncache_reset_rootpixmap recheck the root pixmap, ncrp
ncache_keep_anims enable ncache_keep_anims.
noncache_keep_anims disable ncache_keep_anims.
ncache_pad:n set -ncache_pad to n.
wireframe enable -wireframe mode. same as "wf"
nowireframe disable -wireframe mode. same as "nowf"
wireframe:str enable -wireframe mode string.
wireframe_mode:str enable -wireframe mode string.
wireframelocal enable wireframelocal. same as "wfl"
nowireframe disable wireframelocal. same as "nowfl"
wirecopyrect:str set -wirecopyrect string. same as "wcr:"
scrollcopyrect:str set -scrollcopyrect string. same "scr"
noscrollcopyrect disable -scrollcopyrect__mode_. "noscr"
scr_area:n set -scr_area to n
scr_skip:list set -scr_skip to "list"
scr_inc:list set -scr_inc to "list"
scr_keys:list set -scr_keys to "list"
scr_term:list set -scr_term to "list"
scr_keyrepeat:str set -scr_keyrepeat to "str"
scr_parms:str set -scr_parms parameters.
fixscreen:str set -fixscreen to "str".
noxrecord disable all use of RECORD extension.
xrecord enable use of RECORD extension.
reset_record reset RECORD extension (if avail.)
pointer_mode:n set -pointer_mode to n. same as "pm"
input_skip:n set -input_skip to n.
allinput enable use of -allinput mode.
noallinput disable use of -allinput mode.
input_eagerly enable use of -input_eagerly mode.
noinput_eagerly disable use of -input_eagerly mode.
ssltimeout:n set -ssltimeout to n.
speeds:str set -speeds to str.
wmdt:str set -wmdt to str.
debug_pointer enable -debug_pointer, same as "dp"
nodebug_pointer disable -debug_pointer, same as "nodp"
debug_keyboard enable -debug_keyboard, same as "dk"
nodebug_keyboard disable -debug_keyboard, same as "nodk"
keycode:n inject keystroke 'keycode' (xmodmap -pk)
keycode:n,down inject 'keycode' (down=0,1)
keysym:str inject keystroke 'keysym' (number/name)
keysym:str,down inject 'keysym' (down=0,1)
ptr:x,y,mask inject pointer event x, y, button-mask
fakebuttonevent:button,down direct XTestFakeButtonEvent.
sleep:t sleep floating point time t.
get_xprop:p get X property named 'p'.
set_xprop:p:val set X property named 'p' to 'val'. p ->
id=NNN:p for hex/dec window id.
wininfo:id get info about X window id. use 'root' for root
window, use +id for children.
grab_state get state of pointer and keyboard grab.
pointer_pos print XQueryPointer x,y cursor position.
pointer_x print XQueryPointer x cursor position.
pointer_y print XQueryPointer y cursor position.
pointer_same print XQueryPointer ptr on same screen.
pointer_root print XQueryPointer curr ptr rootwin.
pointer_mask print XQueryPointer button and mods mask
mouse_x print x11vnc's idea of cursor position.
mouse_y print x11vnc's idea of cursor position.
noop do nothing.
defer:n set -defer to n ms,same as deferupdate:n
wait:n set -wait to n ms.
extra_fbur:n set -extra_fbur to n.
wait_ui:f set -wait_ui factor to f.
setdefer:n set -setdefer to -2,-1,0,1, or 2.
wait_bog disable -nowait_bog mode.
nowait_bog enable -nowait_bog mode.
slow_fb:f set -slow_fb to f seconds.
xrefresh:f set -xrefresh to f seconds.
readtimeout:n set read timeout to n seconds.
nap enable -nap mode.
nonap disable -nap mode.
sb:n set -sb to n s, same as screen_blank:n
fbpm disable -nofbpm mode.
nofbpm enable -nofbpm mode.
dpms disable -nodpms mode.
nodpms enable -nodpms mode.
forcedpms enable -forcedpms mode.
noforcedpms disable -forcedpms mode.
clientdpms enable -clientdpms mode.
noclientdpms disable -clientdpms mode.
noserverdpms enable -noserverdpms mode.
serverdpms disable -noserverdpms mode.
noultraext enable -noultraext mode.
ultraext disable -noultraext mode.
chatwindow enable local chatwindow mode.
nochatwindow disable local chatwindow mode.
chaton begin chat using local window.
chatoff end chat using local window.
xdamage enable xdamage polling hints.
noxdamage disable xdamage polling hints.
xd_area:A set -xd_area max pixel area to "A"
xd_mem:f set -xd_mem remembrance to "f"
fs:frac set -fs fraction to "frac", e.g. 0.5
gaps:n set -gaps to n.
grow:n set -grow to n.
fuzz:n set -fuzz to n.
snapfb enable -snapfb mode.
nosnapfb disable -snapfb mode.
rawfb:str set -rawfb mode to "str".
uinput_accel:f set uinput_accel to f.
uinput_thresh:n set uinput_thresh to n.
uinput_reset:n set uinput_reset to n ms.
uinput_always:n set uinput_always to 1/0.
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.
macnosaver enable -macnosaver mode.
macsaver disable -macnosaver mode.
macnowait enable -macnowait mode.
macwait disable -macnowait mode.
macwheel:n set -macwheel to n.
macnoswap enable -macnoswap mouse button mode.
macswap disable -macnoswap mouse button mode.
macnoresize enable -macnoresize mode.
macresize disable -macnoresize mode.
maciconanim:n set -maciconanim to n.
macmenu enable -macmenu mode.
macnomenu disable -macmenu mode.
macuskbd enable -macuskbd mode.
macnouskbd disable -macuskbd mode.
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
dontdisconnect enable -dontdisconnect mode.
nodontdisconnect disable -dontdisconnect mode. (may interfere
with other options)
debug_xevents enable debugging X events.
nodebug_xevents disable debugging X events.
debug_xdamage enable debugging X DAMAGE mechanism.
nodebug_xdamage disable debugging X DAMAGE mechanism.
debug_wireframe enable debugging wireframe mechanism.
nodebug_wireframe disable debugging wireframe mechanism.
debug_scroll enable debugging scrollcopy mechanism.
nodebug_scroll disable debugging scrollcopy mechanism.
debug_tiles enable -debug_tiles
nodebug_tiles disable -debug_tiles
debug_grabs enable -debug_grabs
nodebug_grabs disable -debug_grabs
debug_sel enable -debug_sel
nodebug_sel disable -debug_sel
debug_ncache enable -debug_ncache
nodebug_ncache disable -debug_ncache
dbg enable -dbg crash shell
nodbg disable -dbg crash shell
noremote disable the -remote command processing, it can‐
not be turned back on.
bcx_xattach:str This remote control command is for use with the
BARCO xattach program or the x2x program. Both of these pro‐
grams are for 'pointer and keyboard' sharing between separate X
displays. In general the two displays are usually nearby, e.g.
on the same desk, and this allows the user to share a single
pointer and keyboard between them. The user moves the mouse to
an edge and then the mouse pointer appears to 'jump' to the
other display screen. Thus it emulates what a single X server
would do for two screens (e.g. :0.0 and :0.1) The illusion of a
single Xserver with multiple screens is achieved by forwarding
events to the 2nd one via the XTEST extension.
What the x11vnc bcx_xattach command does is to perform some
pointer movements to try to INDUCE xattach/x2x to 'jump' to the
other display. In what follows the ´master' display refers to
the one that when it has ´focus' it is basically doing nothing
besides watching for the mouse to go over an edge. The 'slave'
display refers to the one to which the mouse and keyboard is
redirected to once an edge in the master has been crossed. Note
that the x11vnc executing the bcx_xattach command MUST be the
one connected to the *master* display.
Also note that when input is being redirected (via XTEST) from
the master display to the slave display, the master display's
pointer and keyboard are *grabbed* by xattach/x2x. x11vnc can
use this info to verify that the master/slave mode change has
taken place correctly. If you specify the "ifneeded" option
(see below) and the initial grab state is that of the desired
final state, then no pointer movements are injected and
"DONE,GRAB_OK" is returned.
"str" must contain one of "up", "down", "left", or "right" to
indicate the direction of the 'jump'. "str" must also contain
one of "master_to_slave" or "slave_to_master" to indicate the
type of mode change induced by the jump. Use "M2S" and "S2M" as
"str" may be a "+" separated list of additional tuning options.
The "shift=n" option indicates an offset shift position away
from (0,0) (default 20). "final=x+y" specifies the final posi‐
tion of the cursor at the end of the normal move sequence;
default 30+30. "extra_move=x+y" means to do one more pointer
move after "final" to x+y. "dt=n" sets the sleep time in mil‐
liseconds between pointer moves (default: 40ms) "retry=n" speci‐
fies the maximum number of retries if the grab state change
fails. "ifneeded" means to not apply the pointer movements if
the initial grab state is that of the desired final state.
"nograbcheck" means to not check if the grab state changed as
expected and only apply the pointer movements (default is to
check the grab states.)
If you do not specify "up", etc., to bcx_xattach nothing will be
attempted and the command returns the string FAIL,NO_DIREC‐
TION_SPECIFIED. If you do not specify "master_to_slave" or
"M2S", etc., to bcx_xattach nothing will be attempted and the
command returns the string FAIL,NO_MODE_CHANGE_SPECIFIED.
Otherwise, the returned string will contain "DONE". It will be
"DONE,GRAB_OK" if the grab state changed as expected (or if
"ifneeded" was supplied and the initial grab state was already
the desired one.) If the initial grab state was incorrect, but
the final grab state was correct then it is
"DONE,GRAB_FAIL_INIT". If the initial grab state was correct,
but the final grab state was incorrect then it is
"DONE,GRAB_FAIL_FINAL". If both are incorrect it will be
"DONE,GRAB_FAIL". Under grab failure the string will be fol‐
lowed by ":p1,k1-p2,k2" where p1,k1 indicates the initial
pointer and keyboard grab states and p2,k2 the final ones. If
GRAB_FAIL or GRAB_FAIL_FINAL occurs, the action will be retried
up to 3 times; trying to reset the state and sleeping a bit
between each try. Set retry=n to adjust the number of retries,
zero to disable retries.
Examples: -R bcx_xattach:down+M2S -R bcx_xattach:up+S2M -R
bcx_xattach:up+S2M+nograbcheck+dt=30 -R bcx_xat‐
or use -Q instead of -R to retrieve the result text.
End of the bcx_xattach:str description.
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 -con‐
nect /path/to/file -remote ...' or you can directly write to
the file via something like: "echo cmd=stop > /path/to/file",
Like -remote, except just query the value of variable. "-Q" is
an alias for "-query". Multiple queries can be done by separat‐
ing variables by commas, e.g. -query var1,var2. The results come
back in the form ans=var1:value1,ans=var2:value2,... to the
standard output. If a variable is read-only, it comes back with
prefix "aro=" instead of "ans=".
Some -remote commands are pure actions that do not make sense as
variables, e.g. "stop" or "disconnect", in these cases the value
returned is "N/A". To direct a query straight to the
X11VNC_REMOTE property or connect file use "qry=..." instead of
ans= stop quit exit shutdown ping resend_cutbuffer resend_clip‐
board resend_primary blacken zero refresh reset close disconnect
id_cmd id sid waitmapped nowaitmapped clip flashcmap noflashcmap
shiftcmap truecolor notruecolor overlay nooverlay overlay_cursor
overlay_yescursor nooverlay_nocursor nooverlay_cursor noover‐
lay_yescursor overlay_nocursor 8to24 no8to24 8to24_opts 24to32
no24to32 visual scale scale_cursor viewonly noviewonly shared
noshared forever noforever once timeout tightfilexfer notight‐
filexfer ultrafilexfer noultrafilexfer rfbversion deny lock
nodeny unlock avahi mdns zeroconf noavahi nomdns nozeroconf con‐
nect proxy allowonce allow noipv6 ipv6 noipv4 ipv4 no6 6 local‐
host nolocalhost listen lookup nolookup accept afteraccept gone
shm noshm flipbyteorder noflipbyteorder onetile noonetile
solid_color solid nosolid blackout xinerama noxinerama xtrap
noxtrap xrandr noxrandr xrandr_mode rotate padgeom quiet q
noquiet modtweak nomodtweak xkb noxkb capslock nocapslock
skip_lockkeys noskip_lockkeys skip_keycodes sloppy_keys
nosloppy_keys skip_dups noskip_dups add_keysyms noadd_keysyms
clear_mods noclear_mods clear_keys noclear_keys clear_all
clear_locks keystate remap repeat norepeat fb nofb bell nobell
sendbell sel nosel primary noprimary setprimary nosetprimary
clipboard noclipboard setclipboard nosetclipboard seldir cursor‐
shape nocursorshape cursorpos nocursorpos cursor_drag nocur‐
sor_drag cursor show_cursor noshow_cursor nocursor arrow xfixes
noxfixes xdamage noxdamage xd_area xd_mem alphacut alphafrac
alpharemove noalpharemove alphablend noalphablend xwarppointer
xwarp noxwarppointer noxwarp always_inject noalways_inject but‐
tonmap dragging nodragging ncache_cr noncache_cr
ncache_no_moveraise noncache_no_moveraise ncache_no_dtchange
noncache_no_dtchange ncache_no_rootpixmap noncache_no_rootpixmap
ncache_reset_rootpixmap ncrp ncache_keep_anims non‐
cache_keep_anims ncache_old_wm noncache_old_wm ncache_pad ncache
noncache ncache_size debug_ncache nodebug_ncache wireframe_mode
wireframe wf nowireframe nowf wireframelocal wfl nowireframelo‐
cal nowfl wirecopyrect wcr nowirecopyrect nowcr scr_area
scr_skip scr_inc scr_keys scr_term scr_keyrepeat scr_parms
scrollcopyrect scr noscrollcopyrect noscr fixscreen noxrecord
xrecord reset_record pointer_mode pm input_skip allinput
noallinput input_eagerly noinput_eagerly input grabkbd nograbkbd
grabptr nograbptr grabalways nograbalways grablocal client_input
ssltimeout speeds wmdt debug_pointer dp nodebug_pointer nodp
debug_keyboard dk nodebug_keyboard nodk keycode keysym ptr fake‐
buttonevent sleep get_xprop set_xprop wininfo bcx_xattach defer‐
update defer setdefer extra_fbur wait_ui wait_bog nowait_bog
slow_fb xrefresh wait readtimeout nap nonap sb screen_blank fbpm
nofbpm dpms nodpms clientdpms noclientdpms forcedpms noforcedpms
noserverdpms serverdpms noultraext ultraext chatwindow
nochatwindow chaton chatoff fs gaps grow fuzz snapfb nosnapfb
rawfb uinput_accel uinput_thresh uinput_reset uinput_always pro‐
gressive rfbport http nohttp httpport httpdir enablehttpproxy
noenablehttpproxy alwaysshared noalwaysshared nevershared noal‐
waysshared dontdisconnect nodontdisconnect desktop debug_xevents
nodebug_xevents debug_xevents debug_xdamage nodebug_xdamage
debug_xdamage debug_wireframe nodebug_wireframe debug_wireframe
debug_scroll nodebug_scroll debug_scroll debug_tiles dbt node‐
bug_tiles nodbt debug_tiles debug_grabs nodebug_grabs debug_sel
nodebug_sel dbg nodbg macnosaver macsaver nomacnosaver macnowait
macwait nomacnowait macwheel macnoswap macswap nomacnoswap mac‐
noresize macresize nomacnoresize maciconanim macmenu macnomenu
nomacmenu macuskbd nomacuskbd noremote
aro= noop display vncdisplay icon_mode autoport loop loopbg
desktopname guess_desktop guess_dbus http_url auth xauth users
rootshift clipshift scale_str scaled_x scaled_y scale_numer
scale_denom scale_fac_x scale_fac_y scaling_blend scal‐
ing_nomult4 scaling_pad scaling_interpolate inetd privremote
unsafe safer nocmds passwdfile unixpw unixpw_nis unixpw_list ssl
ssl_pem sslverify stunnel stunnel_pem https httpsredir usepw
using_shm logfile o flag rmflag rc norc h help V version lastmod
bg sigpipe threads readrate netrate netlatency pipeinput clients
client_count pid ext_xtest ext_xtrap ext_xrecord ext_xkb
ext_xshm ext_xinerama ext_overlay ext_xfixes ext_xdamage
ext_xrandr rootwin num_buttons button_mask mouse_x mouse_y
grab_state pointer_pos pointer_x pointer_y pointer_same
pointer_root pointer_mask bpp depth indexed_color dpy_x dpy_y
wdpy_x wdpy_y off_x off_y cdpy_x cdpy_y coff_x coff_y rfbauth
Just like -query variable, but returns the default value for
that parameter (no running x11vnc server is consulted)
By default -remote commands are run asynchronously, that is, the
request is posted and the program immediately exits. Use -sync
to have the program wait for an acknowledgement from the x11vnc
server that command was processed (somehow). On the other hand
-query requests are always processed synchronously because they
have to wait for the answer.
Also note that if both -remote and -query requests are supplied
on the command line, the -remote is processed first (syn‐
chronously: 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
(see the next paragraph) so if the x11vnc takes longer than that
to process the requests the requester will think that a failure
has taken place.
The default is to wait 3.5 seconds. Or if cmd=stop only 1.0
seconds. If cmd matches 'script:' then it will wait up to 10.0
seconds. Set X11VNC_SYNC_TIMEOUT to the number of seconds you
want it to wait.
If a query fails to get a response from an x11vnc server, retry
up to n times. str is specified as n[:t][/match] Optionally
the delay between tries may be specified by "t" a floating point
time (default 0.5 seconds.) Note: the response is not checked
for validity or whether it corresponds to the query sent. The
query "ping:mystring" may be used to help uniquely identify the
query. Optionally, a matching string after a "/" will be used
to check the result text. Up to n retries will take place until
the matching string is found in the output text. If the match
string is never found the program's exit code is 1; if the match
is found it exits with 0. Note that there may be stdout printed
for each retry (i.e. multiple lines printed out to stdout.)
Example: -query_retries 4:1.5/grab_state
Enable a remote-control communication channel for connected VNC
clients. str is a non-empty string. If a VNC client sends rfb‐
CutText having the prefix str then the part after it is pro‐
cessed as though it were sent via 'x11vnc -remote ...'. If it
begins with neither 'cmd=' nor 'qry=' then 'qry=' is assumed.
Any corresponding output text for that remote control command is
sent back to all client as rfbCutText. The returned output is
also prefixed with str. Example: -remote_prefix DO_THIS:
Note that enabling -remote_prefix allows the remote VNC viewers
to run x11vnc -remote commands. Do not use this option if they
are not to be trusted.
Do not process any remote control commands or queries. Do
process remote control commands or queries. Default: -yesremote
A note about security wrt remote control commands. If someone
can connect to the X display and change the property
X11VNC_REMOTE, then they can remotely control x11vnc. Normally
access to the X display is protected. Note that if they can
modify X11VNC_REMOTE on the X server, they have enough permis‐
sions to also run their own x11vnc and thus have complete con‐
trol 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 dis‐
play and that file's write permissions. See -privremote below.
If you are paranoid and do not think -noremote is enough, to
disable the X11VNC_REMOTE property channel completely use
-novncconnect, or use the -safer option that shuts many things
A few remote commands are disabled by default (currently:
id:pick, accept:<cmd>, gone:<cmd>, and rawfb:setup:<cmd>)
because they are associated with running external programs. If
you specify -unsafe, then these remote-control commands are
allowed. Note that you can still specify these parameters on
the command line, they just cannot be invoked via remote-con‐
Equivalent to: -novncconnect -noremote and prohibiting -gui and
the -connect file. Shuts off communcation channels.
Perform some sanity checks and disable remote-control commands
if it appears that the X DISPLAY and/or connectfile can be
accessed by other users. Once remote-control is disabled it
cannot be turned back on.
No external commands (e.g. system(3) , popen(3) , exec(3) )
will be run at all.
list contains a comma separated list of the only external com‐
mands that can be run. The full list of associated options is:
stunnel, ssl, unixpw, WAIT, zeroconf, id, accept, afteraccept,
gone, pipeinput, v4l-info, rawfb-setup, dt, gui, ssh,
storepasswd, passwdfile, custom_passwd, findauth, crash.
See each option's help to learn the associated external command.
Note that the -nocmds option takes precedence and disables 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:
TCP port for RFB protocol
max time in ms to wait for RFB client
use authentication on RFB protocol (use 'x11vnc -storepasswd
pass file' to create a password file)
Set the version of the RFB we choose to advertise
permit file transfer support
use authentication (use plain-password as password, USE AT YOUR
time in ms to defer updates (default 40)
time in ms to defer pointer updates (default none)
VNC desktop name (default "LibVNCServer")
always treat new clients as shared
never treat new clients as shared
don't disconnect existing clients when a new non-shared connec‐
tion comes in (refuse new connection instead)
enable http server using dir-path home
use portnum for http connection
enable http proxy support
enable progressive updating for slow links
listen for connections only on network interface with addr
ipaddr. '-listen localhost' and hostname work too.
disable file transfer
set ftp root
DISPLAY, XAUTHORITY, HOME
The following are set for the auxiliary commands run by -accept, -gone
and other cases:
RFB_CLIENT_IP, RFB_CLIENT_PORT, RFB_SERVER_IP, RFB_SERVER_PORT,
RFB_X11VNC_PID, RFB_CLIENT_ID, RFB_CLIENT_COUNT, RFB_MODE RFB_STATE
RFB_LOGIN_VIEWONLY RFB_LOGIN_TIME RFB_CURRENT_TIME RFB_USERNAME
vncviewer(1), vncpasswd(1), vncconnect(1), vncserver(1), Xvnc(1),
xev(1), xdpyinfo(1), xwininfo(1), xprop(1), xmodmap(1), xrandr(1),
Xserver(1), xauth(1), xhost(1), Xsecurity(7), xmessage(1), XGetIm‐
age(3X11), ipcrm(1), inetd(1), xdm(1), gdm(1), kdm(1), ssh(1), stun‐
nel(8), su(1), http://www.tightvnc.com, http://www.realvnc.com,
x11vnc was written by Karl J. Runge <email@example.com>, it is part
of the LibVNCServer project <https://github.com/LibVNC/libvncserver>.
This manual page is based one the one written by Ludovic Drolez
<firstname.lastname@example.org>, for the Debian project (both may be used by oth‐
x11vnc February 2018 X11VNC(1)