"Fossies" - the Fresh Open Source Software archive 
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Xvnc - the X VNC server
Xvnc [options] :display#
Xvnc
is the X VNC (Virtual Network Computing) server. It is based on a standard
X server, but it has a "virtual" screen rather than a physical one. X applications
display themselves on it as if it were a normal X display, but they can
only be accessed via a VNC viewer - see vncviewer(1).
So Xvnc is really
two servers in one. To the applications it is an X server, and to the remote
VNC users it is a VNC server. By convention we have arranged that the VNC
server display number will be the same as the X server display number,
which means you can use eg. snoopy:2 to refer to display 2 on machine "snoopy"
in both the X world and the VNC world.
The best way of starting Xvnc is
via the vncserver script. This sets up the environment appropriately and
runs some X applications to get you going. See the manual page for vncserver(1)
for more information.
Xvnc takes lots of options - running Xvnc -help
gives a list. Many of these are standard X server options, which are described
in the Xserver(1) manual page. In addition to options which can only be
set via the command-line, there are also "parameters" which can be set both
via the command-line and through the vncconfig(1) program.
- -geometry widthxheight
- Specify the size of the desktop to be created. Default is 1024x768.
- -depth
depth
- Specify the pixel depth in bits of the desktop to be created. Default
is 16, other possible values are 8, 15, and 24 - anything else is likely
to cause strange behaviour by applications.
- -pixelformat format
- Specify
pixel format for server to use (BGRnnn or RGBnnn). The default for depth
8 is BGR233 (meaning the most significant two bits represent blue, the
next three green, and the least significant three represent red), the default
for depth 16 is RGB565 and for depth 24 is RGB888.
- -cc 3
- As an alternative
to the default TrueColor visual, this allows you to run an Xvnc server
with a PseudoColor visual (i.e. one which uses a colour map or palette),
which can be useful for running some old X applications which only work
on such a display. Values other than 3 (PseudoColor) and 4 (TrueColor)
for the -cc option may result in strange behaviour, and PseudoColor desktops
must be 8 bits deep (i.e. -depth 8).
- -inetd
- This significantly changes Xvnc’s
behaviour so that it can be launched from inetd. See the section below
on usage with inetd.
- -help
- List all the options and parameters
VNC
parameters can be set both via the command-line and through the vncconfig(1)
program, and with a VNC-enabled XFree86 server via Options entries in the
XF86Config file.
Parameters can be turned on with -param or off with -param=0.
Parameters which take a value can be specified as -param value. Other valid
forms are param=value -param=value --param=value. Parameter names are case-insensitive.
- -desktop desktop-name
- Each desktop has a name which may be displayed by
the viewer. It defaults to "x11".
- -rfbport port
- Specifies the TCP port on
which Xvnc listens for connections from viewers (the protocol used in VNC
is called RFB - "remote framebuffer"). The default is 5900 plus the display
number.
- -rfbwait time, -ClientWaitTimeMillis time
-
Time in milliseconds to
wait for a viewer which is blocking Xvnc. This is necessary because Xvnc
is single-threaded and sometimes blocks until the viewer has finished sending
or receiving a message - note that this does not mean an update will be
aborted after this time. Default is 20000 (20 seconds).
- -httpd directory
- Run a mini-HTTP server which serves files from the given directory. Normally
the directory will contain the classes for the Java viewer. In addition,
files with a .vnc extension will have certain substitutions made so that
a single installation of the Java VNC viewer can be served by separate
instances of Xvnc.
- -httpPort port
- Specifies the port on which the mini-HTTP
server runs. Default is 5800 plus the display number.
- -rfbauth passwd-file,
-PasswordFile passwd-file
- Specifies the file containing the password used
to authenticate viewers. The file is accessed each time a connection comes
in, so it can be changed on the fly via vncpasswd(1).
- -deferUpdate time
- Xvnc uses a "deferred update" mechanism which enhances performance in many
cases. After any change to the framebuffer, Xvnc waits for this number of
milliseconds (default 40) before sending an update to any waiting clients.
This means that more changes tend to get coalesced together in a single
update. Setting it to 0 results in the same behaviour as earlier versions
of Xvnc, where the first change to the framebuffer causes an immediate
update to any waiting clients.
- -SendCutText
- Send clipboard changes to clients
(default is on). Note that you must also run vncconfig(1) to get the clipboard
to work.
- -AcceptCutText
- Accept clipboard updates from clients (default is
on). Note that you must also run vncconfig(1) to get the clipboard to work.
- -AcceptPointerEvents
- Accept pointer press and release events from clients
(default is on).
- -AcceptKeyEvents
- Accept key press and release events from
clients (default is on).
- -DisconnectClients
- Disconnect existing clients
if an incoming connection is non-shared (default is on). If DisconnectClients
is false, then a new non-shared connection will be refused while there is
a client active. When combined with NeverShared this means only one client
is allowed at a time.
- -NeverShared
- Never treat incoming connections as shared,
regardless of the client-specified setting (default is off).
- -AlwaysShared
- Always treat incoming connections as shared, regardless of the client-specified
setting (default is off).
- -Protocol3.3
- Always use protocol version 3.3 for
backwards compatibility with badly-behaved clients (default is off).
- -CompareFB
- Perform pixel comparison on framebuffer to reduce unnecessary updates (default
is on).
- -SecurityTypes sec-types
- Specify which security schemes to use separated
by commas. At present only "None" and "VncAuth" are supported. The default
is "VncAuth" - note that if you want a server which does not require a password,
you must set this parameter to "None".
- -IdleTimeout seconds
- The number of
seconds after which an idle VNC connection will be dropped (default is
3600 i.e. an hour).
- -QueryConnect
- Prompts the user of the desktop to explicitly
accept or reject incoming connections. This is most useful when using the
vnc.so module or x0vncserver(1) program to access an existing X desktop
via VNC.
The vncconfig(1) program must be running on the desktop in order
for QueryConnect to be supported by the vnc.so(1) module or Xvnc(1) program.
The x0vncserver(1) program does not require vncconfig(1) to be running.
- -localhost
- Only allow connections from the same machine. Useful if you use
SSH and want to stop non-SSH connections from any other hosts. See the guide
to using VNC with SSH on the web site.
- -log logname:dest:level
- Configures
the debug log settings. dest can currently be stderr or stdout, and level
is between 0 and 100, 100 meaning most verbose output. logname is usually
* meaning all, but you can target a specific source file if you know the
name of its "LogWriter". Default is *:stderr:30.
- -RemapKeys mapping
- Sets
up a keyboard mapping. mapping is a comma-separated string of character mappings,
each of the form char->char, or char<>char, where char is a hexadecimal keysym.
For example, to exchange the " and @ symbols you would specify the following:
- RemapKeys=0x22<>0x40
-
By configuring the inetd(1) service
appropriately, Xvnc can be launched on demand when a connection comes in,
rather than having to be started manually. When given the -inetd option,
instead of listening for TCP connections on a given port it uses its standard
input and standard output. There are two modes controlled by the wait/nowait
entry in the inetd.conf file.
In the nowait mode, Xvnc uses its standard
input and output directly as the connection to a viewer. It never has a
listening socket, so cannot accept further connections from viewers (it
can however connect out to listening viewers by use of the vncconfig program).
Further viewer connections to the same TCP port result in inetd spawning
off a new Xvnc to deal with each connection. When the connection to the
viewer dies, the Xvnc and any associated X clients die. This behaviour
is most useful when combined with the XDMCP options -query and -once. An
typical example in inetd.conf might be (all on one line):
5950 stream
tcp nowait nobody /usr/local/bin/Xvnc Xvnc -inetd -query localhost -once
securitytypes=none
In this example a viewer connection to :50 will result
in a new Xvnc for that connection which should display the standard XDM
login screen on that machine. Because the user needs to login via XDM, it
is usually OK to accept connections without a VNC password in this case.
In the wait mode, when the first connection comes in, inetd gives the
listening socket to Xvnc. This means that for a given TCP port, there is
only ever one Xvnc at a time. Further viewer connections to the same port
are accepted by the same Xvnc in the normal way. Even when the original
connection is broken, the Xvnc will continue to run. If this is used with
the XDMCP options -query and -once, the Xvnc and associated X clients will
die when the user logs out of the X session in the normal way. It is important
to use a VNC password in this case. A typical entry in inetd.conf might
be:
5951 stream tcp wait james /usr/local/bin/Xvnc Xvnc -inetd
-
query localhost -once passwordFile=/home/james/.vnc/passwd
In fact typically,
you would have one entry for each user who uses VNC regularly, each of
whom has their own dedicated TCP port which they use. In this example,
when user "james" connects to :51, he enters his VNC password, then gets
the XDM login screen where he logs in in the normal way. However, unlike
the previous example, if he disconnects, the session remains persistent,
and when he reconnects he will get the same session back again. When he
logs out of the X session, the Xvnc will die, but of course a new one will
be created automatically the next time he connects.
vncconfig(1),
vncpasswd(1), vncserver(1), vncviewer(1), Xserver(1), inetd(1)
http://www.realvnc.com
Tristan Richardson, RealVNC Ltd.
VNC was originally
developed by the RealVNC team while at Olivetti Research Ltd / AT&T Laboratories
Cambridge. It is now being maintained by RealVNC Ltd. See http://www.realvnc.com
for details.
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