Xvnc
NAMESYNOPSIS
DESCRIPTION
OPTIONS
PARAMETERS
USAGE WITH INETD
SEE ALSO
AUTHOR
NAME
Xvnc − the X VNC server
SYNOPSIS
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 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.
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 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 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.
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-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 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 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 authenticate 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 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-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 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. 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 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 Olivetti Research Ltd / AT&T Laboratories Cambridge. TightVNC additions were implemented by Constantin Kaplinsky. Many other people have since participated in development, testing and support. This manual is part of the TigerVNC software suite.
More Linux Commands
manpages/waddnwstr.3ncurses.html
waddnwstr(3ncurses) - add a string of wide characters to a c
These functions write the characters of the (null-terminated) wchar_t character string wstr on the given window. It is similar to constructing a cchar_t for eac
manpages/zshcalsys.1.html
zshcalsys(1) - zsh calendar system - Linux manual page......
The shell is supplied with a series of functions to replace and enhance the traditional Unix calendar programme, which warns the user of imminent or future even
manpages/sudoedit.8.html
sudoedit(8) - execute a command as another user (Man Page)
sudo allows a permitted user to execute a command as the superuser or another user, as specified by the security policy. sudo supports a plugin architecture for
manpages/lzmadec.1.html
lzmadec(1) - Small .xz and .lzma decompressors (Man Page)...
xzdec is a liblzma-based decompression-only tool for .xz (and only .xz) files. xzdec is intended to work as a drop-in replacement for xz(1) in the most common s
manpages/getaliasent.3.html
getaliasent(3) - read an alias entry - Linux manual page....
One of the databases available with the Name Service Switch (NSS) is the aliases database, that contains mail aliases. (To find out which databases are supporte
manpages/winicon.1.html
winicon(1) (Commands - Linux manual page)..................
A Microsoft Windows icon file contains one or more images, at resolutions up to 256 by 256 pixels and various bpp values. The images are encoded either as Porta
manpages/yuvycsnoise.1.html
yuvycsnoise(1) - Noise filter specialized for NTSC Y/C separ
If video capture hardware has only a poor Y/C separator, at vertical stripe (especially red/blue), noises appear which seem checker flag and bright/dark invert
manpages/XTestCompareCurrentCursorWithWindow.3.html
XTestCompareCurrentCursorWithWindow(3) - XTest extension fun
This extension is a minimal set of client and server extensions required to completely test the X11 server with no user intervention. This extension is not inte
manpages/XtInsertEventHandler.3.html
XtInsertEventHandler(3) - add and remove event handlers.....
The XtAddEventHandler function registers a procedure with the dispatch mechanism that is to be called when an event that matches the mask occurs on the specifie
manpages/asciitopgm.1.html
asciitopgm(1) - convert ASCII graphics into a PGM (ManPage)
This program is part of Netpbm(1) asciitopgm reads ASCII data as input and produces a PGM image with pixel values which are an approximation of the brightness o
manpages/icontopbm.1.html
icontopbm(1) - convert a Sun icon image to PBM (Man Page)...
This program is part of Netpbm(1) icontopbm was obsoleted by sunicontopnm(1) , introduced with Netpbm 10.53 (December 2010). sunicontopnm is backward compatible
manpages/strsignal.3.html
strsignal(3) - return string describing signal (Man Page)...
The strsignal() function returns a string describing the signal number passed in the argument sig. The string can be used only until the next call to strsignal(
