Xvnc(1) Virtual Network Computing Xvnc(1)NAMEXvnc - the X VNC server
SYNOPSISXvnc [options] :display#
DESCRIPTIONXvnc 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.
OPTIONSXvnc 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 - any‐
thing 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 signif‐
icant three represent red), the default for depth 16 is RGB565
and for depth 24 is RGB888.
-interface IP address
Listen on interface. By default Xvnc listens on all available
interfaces.
-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 Xorg server via Options
entries in the xorg.conf file.
Parameters can be turned on with -param or off with -param=0. Parame‐
ters 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 direc‐
tory. 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 perfor‐
mance 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 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.
-AlwaysSetDeferUpdateTimer
Keep delaying sending the screen update to the client(s) each
time the screen is updated. Otherwise the delay is from the
first update. Default is off.
-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.
-MaxCutText bytes
The maximum size of a clipboard update that will be accepted
from a client. Default is 262144.
-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).
-ZlibLevel
Zlib compression level for ZRLE encoding (it does not affect
Tight encoding). Acceptable values are between 0 and 9.
Default is to use the standard compression level provided by the
zlib(3) compression library.
-ImprovedHextile
Use improved compression algorithm for Hextile encoding which
achieves better compression ratios by the cost of using slightly
more CPU time. Default is on.
-SecurityTypes sec-types
Specify which security scheme to use for incoming connections.
Valid values are a comma separated list of None, VncAuth, Plain,
TLSNone, TLSVnc, TLSPlain, X509None, X509Vnc and X509Plain.
Default is VncAuth,TLSVnc.
-Password password
Obfuscated binary encoding of the password which clients must
supply to access the server. Using this parameter is insecure,
use PasswordFile parameter instead.
-PlainUsers user-list
A comma separated list of user names that are allowed to authen‐
ticate via any of the "Plain" security types (Plain, TLSPlain,
etc.). Specify * to allow any user to authenticate using this
security type. Default is to deny all users.
-pam_service name, -PAMService name
PAM service name to use when authentication users using any of
the "Plain" security types. Default is vnc.
-X509Cert path
Path to a X509 certificate in PEM format to be used for all X509
based security types (X509None, X509Vnc, etc.).
-X509Key path
Private key counter part to the certificate given in X509Cert.
Must also be in PEM format.
-BlacklistThreshold count
The number of unauthenticated connection attempts allowed from
any individual host before that host is black-listed. Default
is 5.
-BlacklistTimeout seconds
The initial timeout applied when a host is first black-listed.
The host cannot re-attempt a connection until the timeout
expires. Default is 10.
-IdleTimeout seconds
The number of seconds after which an idle VNC connection will be
dropped (default is 0, which means that idle connections will
never be dropped).
-MaxDisconnectionTime seconds
Terminate when no client has been connected for N seconds.
Default is 0.
-MaxConnectionTime seconds
Terminate when a client has been connected for N seconds.
Default is 0.
-MaxIdleTime seconds
Terminate after N seconds of user inactivity. Default is 0.
-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.
-QueryConnectTimeout seconds
Number of seconds to show the Accept Connection dialog before
rejecting the connection. Default is 10.
-localhost
Only allow connections from the same machine. Useful if you use
SSH and want to stop non-SSH connections from any other hosts.
-Log logname:dest:level
Configures the debug log settings. dest can currently be
stderr, stdout or syslog, 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
-AvoidShiftNumLock
Key affected by NumLock often require a fake Shift to be
inserted in order for the correct symbol to be generated.
Turning on this option avoids these extra fake Shift events
but may result in a slightly different symbol (e.g. a Return
instead of a keypad Enter).
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 usu‐
ally 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.
SEE ALSOvncconfig(1), vncpasswd(1), vncserver(1), vncviewer(1), Xserver(1),
inetd(1)
http://www.tigervnc.org
AUTHOR
Tristan Richardson, RealVNC Ltd. and others.
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 have since par‐
ticipated in development, testing and support. This manual is part of
the TigerVNC software suite.
TigerVNCXvnc(1)
