xc/programs/Xserver/Xvnc.man

.TH Xvnc 1 "30 December 2004" "TightVNC" "Virtual Network Computing"
.SH NAME
Xvnc \- the X VNC server 
.SH SYNOPSIS
.B Xvnc
.RI [ options ] 
.RI : display#
.SH DESCRIPTION
.B 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 \fBvncviewer\fP(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 \fBXvnc\fP is via the \fBvncserver\fP script.  This
sets up the environment appropriately and runs some X applications to get you
going.  See the manual page for \fBvncserver\fP(1) for more information.

.SH OPTIONS
.B Xvnc
takes lots of options - running \fBXvnc -help\fP gives a list.  Many of these
are standard X server options, which are described in the \fBXserver\fP(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 \fBvncconfig\fP(1) program.

.TP
.B \-geometry \fIwidth\fPx\fIheight\fP
Specify the size of the desktop to be created. Default is 1024x768.

.TP
.B \-depth \fIdepth\fP
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.

.TP
.B \-pixelformat \fIformat\fP
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.

.TP
.B \-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. \fB-depth 8\fP).

.TP
.B \-inetd 
This significantly changes Xvnc's behaviour so that it can be launched from
inetd.  See the section below on usage with inetd.

.TP
.B \-help
List all the options and parameters

.SH PARAMETERS
VNC parameters can be set both via the command-line and through the
\fBvncconfig\fP(1) program, and with a VNC-enabled XFree86 server via Options
entries in the XF86Config file.

Parameters can be turned on with -\fIparam\fP or off with
-\fIparam\fP=0.  Parameters which take a value can be specified as
-\fIparam\fP \fIvalue\fP.  Other valid forms are \fIparam\fP\fB=\fP\fIvalue\fP
-\fIparam\fP=\fIvalue\fP --\fIparam\fP=\fIvalue\fP.  Parameter names are
case-insensitive.

.TP
.B \-desktop \fIdesktop-name\fP
Each desktop has a name which may be displayed by the viewer. It defaults to
"x11".

.TP
.B \-rfbport \fIport\fP
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.

.TP
.B \-rfbwait \fItime\fP, \-ClientWaitTimeMillis \fItime\fP

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).

.TP
.B \-httpd \fIdirectory\fP
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.

.TP
.B \-httpPort \fIport\fP
Specifies the port on which the mini-HTTP server runs.  Default is 5800 plus
the display number.

.TP
.B \-rfbauth \fIpasswd-file\fP, \-PasswordFile \fIpasswd-file\fP
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 \fBvncpasswd\fP(1).

.TP
.B \-deferUpdate \fItime\fP
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.

.TP
.B \-SendCutText
Send clipboard changes to clients (default is on).  Note that you must also run
\fBvncconfig\fP(1) to get the clipboard to work.

.TP
.B \-AcceptCutText
Accept clipboard updates from clients (default is on).  Note that you must also
run \fBvncconfig\fP(1) to get the clipboard to work.

.TP
.B \-AcceptPointerEvents
Accept pointer press and release events from clients (default is on).

.TP
.B \-AcceptKeyEvents
Accept key press and release events from clients (default is on).

.TP
.B \-DisconnectClients
Disconnect existing clients if an incoming connection is non-shared (default is
on). If \fBDisconnectClients\fP is false, then a new non-shared connection will
be refused while there is a client active.  When combined with
\fBNeverShared\fP this means only one client is allowed at a time.

.TP
.B \-NeverShared
Never treat incoming connections as shared, regardless of the client-specified
setting (default is off).

.TP
.B \-AlwaysShared
Always treat incoming connections as shared, regardless of the client-specified
setting (default is off).

.TP
.B \-Protocol3.3
Always use protocol version 3.3 for backwards compatibility with badly-behaved
clients (default is off).

.TP
.B \-CompareFB
Perform pixel comparison on framebuffer to reduce unnecessary updates (default
is on).

.TP
.B \-SecurityTypes \fIsec-types\fP
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".

.TP
.B \-IdleTimeout \fIseconds\fP
The number of seconds after which an idle VNC connection will be dropped
(default is 3600 i.e. an hour).

.TP
.B \-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.

.TP
.B \-log \fIlogname\fP:\fIdest\fP:\fIlevel\fP
Configures the debug log settings.  \fIdest\fP can currently be \fBstderr\fP or
\fBstdout\fP, and \fIlevel\fP is between 0 and 100, 100 meaning most verbose
output.  \fIlogname\fP is usually \fB*\fP meaning all, but you can target a
specific source file if you know the name of its "LogWriter".  Default is
\fB*:stderr:30\fP.

.SH USAGE WITH INETD
By configuring the \fBinetd\fP(1) service appropriately, Xvnc can be launched
on demand when a connection comes in, rather than having to be started
manually.  When given the \fB-inetd\fP 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.

.SH SEE ALSO
.BR vncconfig (1),
.BR vncpasswd (1),
.BR vncserver (1),
.BR vncviewer (1),
.BR Xserver (1),
.BR inetd (1)
.br
http://www.tightvnc.com

.SH AUTHOR
Tristan Richardson, RealVNC Ltd.

VNC was originally developed by the RealVNC team while at Olivetti
Research Ltd / AT&T Laboratories Cambridge.  TightVNC additions was
implemented by Constantin Kaplinsky. Many other people participated in
development, testing and support.