Xvnc



Xvnc(1)                    Virtual Network Computing                   Xvnc(1)




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  16,  other possible values are 8, 15, and 24 - 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.


       -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  colour  map or palette), which can be useful for
              running some old X applications which only work on such  a  dis-
              play.   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, and with a VNC-enabled XFree86 server via Options
       entries in the XF86Config 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 40) before send-
              ing an update to any  waiting  clients.  This  means  that  more
              changes  tend to get coalesced together in a single update. Set-
              ting 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  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 compatibility 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 commas.  At
              present only "None" and "VncAuth" are supported.  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 connection will be
              dropped (default is 3600 i.e. an hour).


       -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.


       -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 ver-
              bose output.  logname is usually * meaning all, but you can tar-
              get a specific source file if you know the  name  of  its  "Log-
              Writer".  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



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 ALSO

       vncconfig(1),  vncpasswd(1),  vncserver(1),  vncviewer(1),  Xserver(1),
       inetd(1)
       http://www.realvnc.com



AUTHOR

       Tristan Richardson, RealVNC Ltd.

       VNC  was  originally  developed  by  the RealVNC team while at Olivetti
       Research Ltd / AT&T Laboratories Cambridge.  It is now being maintained
       by RealVNC Ltd.  See http://www.realvnc.com for details.



RealVNC Ltd                       03 Mar 2005                          Xvnc(1)

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