Xvnc
(1)
Name
Xvnc - the X VNC server
Synopsis
/usr/bin/Xvnc [options] :display#
Description
Virtual Network Computing Xvnc(1)
NAME
Xvnc - the X VNC server
SYNOPSIS
/usr/bin/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 them-
selves 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 num-
ber, which means you can use eg. snoopy:2 to refer to dis-
play 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 vnc-
server(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 24, other possible values are 8,
15, and 16 - 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
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three green, and the least significant three represent
red), the default for depth 16 is RGB565 and for depth
24 is RGB888.
-interface IP address or -i IP
Listen on interface. By default Xvnc listens on all
available interfaces.
-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 color 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.
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-insen-
sitive.
-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 con-
nections from viewers (the protocol used in VNC is
called RFB - "remote framebuffer"). The default is
5900 plus the display number.
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-rfbwait time, -ClientWaitTimeMillis time
Time in milliseconds to wait for a viewer which is
blocking Xvnc. This is necessary because Xvnc is sin-
gle-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 1) before sending an update to any waiting
clients. This means that more changes tend to get coa-
lesced 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
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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 compati-
bility 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 com-
mas. At present only "None" and "VncAuth" are sup-
ported. 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
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connection will be dropped (default is 0, which means
that idle connections will never be dropped).
-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 x0vnc-
server(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-sepa-
rated 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(1M) 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.
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In the nowait mode, Xvnc uses its standard input and output
directly as the connection to a viewer. It never has a lis-
tening 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.
The provided application/x11/xvnc-inetd service defaults to
running
/usr/bin/Xvnc -inetd -query localhost -once security-
types=none
in nowait mode. This service can be enabled via
svcadm(1m), and configured to use other modes or arguments
via svccfg(1m).
In this configuration, connecting to :0 will result in a new
Xvnc for that connection which should display the standard
graphical login screen on that machine. (To enable this,
you will also have to enable XDMCP network connections on
the login screen. See gdm(1) for details.) Because the
user needs to login via this screen, 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. Fur-
ther viewer connections to the same port are accepted by the
same Xvnc in the normal way. Even when the original connec-
tion 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 command line to include in
the service exec property might be:
/usr/bin/Xvnc Xvnc -inetd -query localhost -once password-
File=/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, he enters his VNC password, then gets the 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 ses-
sion back again. When he logs out of the X session, the
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Xvnc will die, but of course a new one will be created auto-
matically the next time he connects.
SEE ALSO
vncconfig(1), vncpasswd(1), vncserver(1), vncviewer(1),
Xserver(1), inetd(1)
http://www.tigervnc.org
AUTHOR
Tristan Richardson, RealVNC Ltd.
VNC was originally developed by the RealVNC team while at
Olivetti Research Ltd / AT&T Laboratories Cambridge.
TightVNC additions were implemented by Constantin Kaplinsky.
Many other people participated in development, testing and
support.
ATTRIBUTES
See attributes(5) for descriptions of the following
attributes:
+-----------------------------+-----------------------------+
| ATTRIBUTE TYPE | ATTRIBUTE VALUE |
+-----------------------------+-----------------------------+
|Availability |x11/server/xvnc |
+-----------------------------+-----------------------------+
|Interface Stability |Volatile |
+-----------------------------+-----------------------------+
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