Ubuntu Manpage: Xvnc - the X VNC server

name
synopsis
description
options
parameters
usage with inetd
see also
author

Provided by: vnc4server_4.1.1+xorg4.3.0-37.3ubuntu2_amd64

NAME

       Xvnc - the X VNC server

SYNOPSIS

       Xvnc [options] :display#

DESCRIPTION

       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.

OPTIONS

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

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

USAGE WITH INETD

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.

AUTHOR

       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.