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.

-geometry widthxheight
Specify the size of the desktop to be created. Default is 640x480.

-depth depth
Specify the pixel depth in bits of the desktop to be created. Default is 8, other possible values are 15, 16 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. Note that viewing such a desktop can be painful because it usually results in a full-screen redraw every time an entry in the colour map changes. 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.

-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
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).

Don't draw a cursor. This can be useful when debugging a viewer to make the updates drawn more predictable.

-rfbauth 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).

-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.

-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.

The server normally uses a lookup table for translating pixel values when the viewer requests a different format from the native one used by the server. This can use up to 256Kbytes per connected viewer, so if you have many viewers you may wish to specify this option which will save memory at the expense of a little bit of speed. Only relevant for 16-bit-deep desktops.

-maxrects num
Sets the maximum number of rectangles Xvnc will send in one update. If an update would consist of more than this many rectangles, then an update of a single bounding rectangle is sent instead. This makes sense because sending a large number of small rectangles is less efficient than sending one large rectangle, even when this means updating pixels which haven't actually changed. The default is 50.

-desktop desktop-name
Each desktop has a name which may be displayed by the viewer. It defaults to "x11".

Always treat new clients as shared (i.e. ignore client's shared flag).

Never treat new clients as shared (i.e. ignore client's shared flag).

Don't disconnect existing clients when a new "non-shared" connection comes in. Instead the new connection is refused. New "shared" connections are still allowed in the normal way.

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.

This significantly changes Xvnc's behaviour so that it can be launched from inetd. Instead of listening for TCP connections it uses its standard input and standard output as a connection to the VNC viewer. See the information on the extras page on the web site for details.



vncconnect(1), vncpasswd(1), vncserver(1), vncviewer(1), Xserver(1)



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 for details.