Xtigervnc(1) Virtual Network Computing Xtigervnc(1)
NAME
Xtigervnc - the X VNC server
SYNOPSIS
Xtigervnc [options] :display#
DESCRIPTION
Xtigervnc 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
xtigervncviewer(1).
So Xtigervnc 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 Xtigervnc is via tigervncsession. This sets
up the environment appropriately and starts a desktop environment. See
the manual page for tigervncsession(8) for more information.
OPTIONS
Xtigervnc takes lots of options - running Xtigervnc -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 tigervncconfig(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 16 and 32. Anything
else is likely to cause strange behaviour by applications and
may prevent the server from starting at all.
-pixelformat format
Specify pixel format for server to use (BGRnnn or RGBnnn). The
default for depth 16 is RGB565 and for depth 24 and 32 is
RGB888.
-interface IP address
Listen on interface. By default Xtigervnc listens on all avail-
able interfaces.
-inetd This significantly changes Xtigervnc's behaviour so that it can
be launched from inetd. See the section below on usage with in-
etd.
-help List all the options and parameters
PARAMETERS
VNC parameters can be set both via the command-line and through the
tigervncconfig(1) program, and with a VNC-enabled Xorg server via Op-
tions 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 "<user>@<hostname>".
-rfbport port
Specifies the TCP port on which Xtigervnc listens for connec-
tions from viewers (the protocol used in VNC is called RFB -
"remote framebuffer"). The default is 5900 plus the display
number. Specify -1 to disable listening on a TCP port.
-UseIPv4
Use IPv4 for incoming and outgoing connections. Default is on.
-UseIPv6
Use IPv6 for incoming and outgoing connections. Default is on.
-rfbunixpath path
Specifies the path of a Unix domain socket on which Xtigervnc
listens for connections from viewers.
-rfbunixmode mode
Specifies the mode of the Unix domain socket. The default is
0600.
-rfbauth passwd-file, -PasswordFile passwd-file
Password file for VNC authentication. There is no default, you
should specify the password file explicitly. Password file
should be created with the tigervncpasswd(1) utility. The file
is accessed each time a connection comes in, so it can be
changed on the fly.
-AcceptCutText
Accept clipboard updates from clients. Default is on.
-MaxCutText bytes
The maximum size of a clipboard update that will be accepted
from a client. Default is 262144.
-SendCutText
Send clipboard changes to clients. Default is on.
-SendPrimary
Send the primary selection and cut buffer to the server as well
as the clipboard selection. Default is on.
-AcceptPointerEvents
Accept pointer press and release events from clients. Default is
on.
-AcceptKeyEvents
Accept key press and release events from clients. Default is on.
-AcceptSetDesktopSize
Accept requests to resize the size of the desktop. 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.
-FrameRate fps
The maximum number of updates per second sent to each client. If
the screen updates any faster then those changes will be aggre-
gated and sent in a single update to the client. Note that this
only controls the maximum rate and a client may get a lower rate
when resources are limited. Default is 60.
-CompareFB mode
Perform pixel comparison on framebuffer to reduce unnecessary
updates. Can be either 0 (off), 1 (always) or 2 (auto). Default
is 2.
-ZlibLevel level
Zlib compression level for ZRLE encoding (it does not affect
Tight encoding). Acceptable values are between 0 and 9. De-
fault 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. De-
fault 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.
-GnuTLSPriority priority
GnuTLS priority string that controls the TLS session’s handshake
algorithms. See the GnuTLS manual for possible values. For
GnuTLS < 3.6.3 the default value will be NORMAL to use upstream
default. For newer versions of GnuTLS system-wide crypto policy
will be used.
-UseBlacklist
Temporarily reject connections from a host if it repeatedly
fails to authenticate. Default is on.
-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 ex-
pires. 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. De-
fault is 0.
-MaxConnectionTime seconds
Terminate when a client has been connected for N seconds. De-
fault 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. Default is off.
The tigervncconfig(1) program must be running on the desktop in
order for QueryConnect to be supported.
-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 in-
serted in order for the correct symbol to be generated. Turning
on this option avoids these extra fake Shift events but may re-
sult in a slightly different symbol (e.g. a Return instead of a
keypad Enter).
-RawKeyboard
Send keyboard events straight through and avoid mapping them to
the current keyboard layout. This effectively makes the keyboard
behave according to the layout configured on the server instead
of the layout configured on the client. Default is off.
-AllowOverride
Comma separated list of parameters that can be modified using
VNC extension. Parameters can be modified for example using
tigervncconfig(1) program from inside a running session.
Allowing override of parameters such as PAMService or Password-
File can negatively impact security if Xtigervnc runs under dif-
ferent user than the programs allowed to override the parame-
ters.
When NoClipboard parameter is set, allowing override of SendCut-
Text and AcceptCutText has no effect.
Default is desktop,AcceptPointerEvents,SendCutText,AcceptCut-
Text,SendPrimary,SetPrimary.
USAGE WITH INETD
By configuring the inetd(1) service appropriately, Xtigervnc 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 en-
try in the inetd.conf file.
In the nowait mode, Xtigervnc uses its standard input and output di-
rectly as the connection to a viewer. It never has a listening socket,
so cannot accept further connections from viewers (it can however con-
nect out to listening viewers by use of the tigervncconfig program).
Further viewer connections to the same TCP port result in inetd spawn-
ing off a new Xtigervnc to deal with each connection. When the connec-
tion to the viewer dies, the Xtigervnc and any associated X clients
die. This behaviour is most useful when combined with the XDMCP op-
tions -query and -once. An typical example in inetd.conf might be (all
on one line):
5950 stream tcp nowait nobody /usr/local/bin/Xtigervnc Xtigervnc
-inetd -query localhost -once securitytypes=none
In this example a viewer connection to :50 will result in a new
Xtigervnc for that connection which should display the standard XDM lo-
gin 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 Xtigervnc. This means that for a given TCP port,
there is only ever one Xtigervnc at a time. Further viewer connections
to the same port are accepted by the same Xtigervnc in the normal way.
Even when the original connection is broken, the Xtigervnc will con-
tinue to run. If this is used with the XDMCP options -query and -once,
the Xtigervnc 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 pass-
word in this case. A typical entry in inetd.conf might be:
5951 stream tcp wait james /usr/local/bin/Xtigervnc Xtigervnc
-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
Xtigervnc will die, but of course a new one will be created automati-
cally the next time he connects.
SEE ALSO
tigervncconfig(1), tigervncpasswd(1), xtigervncviewer(1), tigervncses-
sion(8), Xserver(1), inetd(1)
https://www.tigervnc.org
AUTHOR
Tristan Richardson, RealVNC Ltd. and others.
VNC was originally developed by the RealVNC team while at Olivetti Re-
search Ltd / AT&T Laboratories Cambridge. TightVNC additions were im-
plemented by Constantin Kaplinsky. Many other people have since partic-
ipated in development, testing and support. This manual is part of the
TigerVNC software suite.
TigerVNC Xtigervnc(1)
Generated by dwww version 1.15 on Wed Jun 26 01:57:49 CEST 2024.