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MAN page from openSUSE Leap 42 xorg-x11-Xvnc-1.9.0-196.1.x86_64.rpm

Xvnc

Section: Virtual Network Computing (1)
Updated:
Index 

NAME

Xvnc - the X VNC server  

SYNOPSIS

Xvnc[options]:display# 

DESCRIPTION

Xvncis the X VNC (Virtual Network Computing) server. It is based on a standard Xserver, but it has a "virtual" screen rather than a physical one. Xapplications display themselves on it as if it were a normal X display, butthey 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 arrangedthat the VNC server display number will be the same as the X server displaynumber, 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. Thissets up the environment appropriately and runs some X applications to get yougoing. See the manual page for vncserver(1) for more information.

 

OPTIONS

Xvnctakes lots of options - running Xvnc -help gives a list. Many of theseare standard X server options, which are described in the Xserver(1)manual page. In addition to options which can only be set via thecommand-line, there are also "parameters" which can be set both via thecommand-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 causestrange behaviour by applications.
-pixelformat format
Specify pixel format for server to use (BGRnnn or RGBnnn). The default fordepth 8 is BGR233 (meaning the most significant two bits represent blue, thenext three green, and the least significant three represent red), the defaultfor 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 frominetd. 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 thevncconfig(1) program, and with a VNC-enabled Xorg server via Optionsentries in the xorg.conf file.

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 arecase-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 (theprotocol used in VNC is called RFB - "remote framebuffer"). The default is5900 plus the display number.
-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 Xvnc listens forconnections from viewers, instead of listening on a TCP port.
-rfbunixmode mode
Specifies the mode of the Unix domain socket. The default is 0600.
-rfbwait time, -ClientWaitTimeMillis time
Time in milliseconds to wait for a viewer which is blocking the server. This isnecessary because the server is single-threaded and sometimes blocks until theviewer has finished sending or receiving a message - note that this does notmean 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. Normallythe directory will contain the classes for the Java viewer. In addition, fileswith a .vnc extension will have certain substitutions made so that a singleinstallation of the Java VNC viewer can be served by separate instances ofXvnc.
-httpPort port
Specifies the port on which the mini-HTTP server runs. Default is 5800 plusthe display number.
-rfbauth passwd-file, -PasswordFile passwd-file
Password file for VNC authentication. There is no default, you shouldspecify the password file explicitly. Password file should be created withthe vncpasswd(1) utility. The file is accessed each time a connectioncomes 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 theclipboard 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 ison. If DisconnectClients is false, then a new non-shared connection willbe refused while there is a client active. When combined withNeverShared this means only one client is allowed at a time.
-NeverShared
Never treat incoming connections as shared, regardless of the client-specifiedsetting. Default is off.
-AlwaysShared
Always treat incoming connections as shared, regardless of the client-specifiedsetting. Default is off.
-Protocol3.3
Always use protocol version 3.3 for backwards compatibility with badly-behavedclients. Default is off.
-FrameRate fps
The maximum number of updates per second sent to each client. If the screenupdates any faster then those changes will be aggregated and sent in a singleupdate to the client. Note that this only controls the maximum rate and aclient may get a lower rate when resources are limited. Default is 60.
-CompareFB mode
Perform pixel comparison on framebuffer to reduce unnecessary updates. Canbe either 0 (off), 1 (always) or 2 (auto). Default is2.
-ZlibLevel level
Zlib compression level for ZRLE encoding (it does not affect Tight encoding).Acceptable values are between 0 and 9. Default is to use the standardcompression level provided by the zlib(3) compression library.
-ImprovedHextile
Use improved compression algorithm for Hextile encoding which achieves bettercompression ratios by the cost of using slightly more CPU time. Default ison.
-SecurityTypes sec-types
Specify which security scheme to use for incoming connections. Valid valuesare a comma separated list of None, VncAuth, Plain,TLSNone, TLSVnc, TLSPlain, X509None, X509Vncand X509Plain. Default is VncAuth,TLSVnc.
-Password password
Obfuscated binary encoding of the password which clients must supply toaccess the server. Using this parameter is insecure, use PasswordFileparameter instead.
-PlainUsers user-list
A comma separated list of user names that are allowed to authenticate viaany of the "Plain" security types (Plain, TLSPlain, etc.). Specify *to allow any user to authenticate using this security type. Default is todeny 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 basedsecurity types (X509None, X509Vnc, etc.).
-X509Key path
Private key counter part to the certificate given in X509Cert. Mustalso be in PEM format.
-GnuTLSPriority priority
GnuTLS priority string that controls the TLS session’s handshake algorithms.See the GnuTLS manual for possible values. Default is NORMAL.
-BlacklistThreshold count
The number of unauthenticated connection attempts allowed from any individualhost before that host is black-listed. Default is 5.
-BlacklistTimeout seconds
The initial timeout applied when a host is first black-listed. The hostcannot 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 is0.
-MaxConnectionTime seconds
Terminate when a client has been connected for N seconds. Default is0.
-MaxIdleTime seconds
Terminate after N seconds of user inactivity. Default is 0.
-QueryConnect
Prompts the user of the desktop to explicitly accept or reject incomingconnections. Default is off.

The vncconfig(1) program must be running on the desktop in order forQueryConnect to be supported.

-QueryConnectTimeout seconds
Number of seconds to show the Accept Connection dialog before rejecting theconnection. Default is 10.
-localhost
Only allow connections from the same machine. Useful if you use SSH and want tostop 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 meaningmost verbose output. logname is usually * meaning all, but you cantarget a specific source file if you know the name of its "LogWriter". Defaultis *:stderr:30.
-RemapKeys mapping
Sets up a keyboard mapping.mappingis a comma-separated string of character mappings, each of the formchar->char,orchar<>char,wherecharis 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 orderfor the correct symbol to be generated. Turning on this option avoids theseextra fake Shift events but may result 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 currentkeyboard layout. This effectively makes the keyboard behave according to thelayout configured on the server instead of the layout configured on theclient. Default is off.
-AllowOverride
Comma separated list of parameters that can be modified using VNC extension.Parameters can be modified for example using vncconfig(1) program frominside a running session.

Allowing override of parameters such as PAMService or PasswordFilecan negatively impact security if Xvnc runs under different user than theprograms allowed to override the parameters.

When NoClipboard parameter is set, allowing override of SendCutTextand AcceptCutText has no effect.

Default is desktop,AcceptPointerEvents,SendCutText,AcceptCutText,SendPrimary,SetPrimary.

 

USAGE WITH INETD

By configuring the inetd(1) service appropriately, Xvnc can be launchedon demand when a connection comes in, rather than having to be startedmanually. When given the -inetd option, instead of listening for TCPconnections 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 theconnection to a viewer. It never has a listening socket, so cannot acceptfurther connections from viewers (it can however connect out to listeningviewers by use of the vncconfig program). Further viewer connections to thesame TCP port result in inetd spawning off a new Xvnc to deal with eachconnection. When the connection to the viewer dies, the Xvnc and anyassociated X clients die. This behaviour is most useful when combined with theXDMCP options -query and -once. An typical example in inetd.conf might be (allon one line):

5950 stream tcp nowait nobody /usr/local/bin/Xvnc Xvnc -inetd -querylocalhost -once securitytypes=none

In this example a viewer connection to :50 will result in a new Xvnc for thatconnection 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 connectionswithout a VNC password in this case.

In the wait mode, when the first connection comes in, inetd gives the listeningsocket to Xvnc. This means that for a given TCP port, there is only ever oneXvnc at a time. Further viewer connections to the same port are accepted bythe 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 -queryand -once, the Xvnc and associated X clients will die when the user logs out ofthe X session in the normal way. It is important to use a VNC password in thiscase. 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 VNCregularly, each of whom has their own dedicated TCP port which they use. Inthis 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 logsout of the X session, the Xvnc will die, but of course a new one will becreated automatically 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. and others.

VNC was originally developed by the RealVNC team while at OlivettiResearch Ltd / AT&T Laboratories Cambridge. TightVNC additions wereimplemented by Constantin Kaplinsky. Many other people have sinceparticipated in development, testing and support. This manual is partof the TigerVNC software suite.


 

Index

NAME
SYNOPSIS
DESCRIPTION
OPTIONS
PARAMETERS
USAGE WITH INETD
SEE ALSO
AUTHOR

This document was created byman2html,using the manual pages.