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man pages section 1: User Commands

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Updated: July 2017

Xvnc (1)


Xvnc - the X VNC server


/usr/bin/Xvnc [options] :display#


Xvnc(1)                    Virtual Network Computing                   Xvnc(1)

       Xvnc - the X VNC server

       /usr/bin/Xvnc [options] :display#

       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

       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

       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.

       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

       -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 or -i IP address
              Listen  on  interface.  By default Xvnc listens on all available

       -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 color map or palette), which can be useful for run-
              ning  some old X applications which only work on such a display.
              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

       VNC  parameters  can  be  set both via the command-line and through the
       vncconfig(1) program.

       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

       -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.

              Send clipboard changes to clients (default is  on).   Note  that
              you must also run vncconfig(1) to get the clipboard to work.

              Accept  clipboard  updates  from  clients (default is on).  Note
              that you must also run vncconfig(1)  to  get  the  clipboard  to

              Accept pointer press and release events from clients (default is

              Accept key press and release events  from  clients  (default  is

              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.

              Never  treat  incoming  connections as shared, regardless of the
              client-specified setting (default is off).

              Always treat incoming connections as shared, regardless  of  the
              client-specified setting (default is off).

              Always use protocol version 3.3 for backwards compatibility with
              badly-behaved clients (default is off).

              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  0, which means that idle connections will
              never be dropped).

              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.

              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:


       By  configuring  the  inetd(1M)  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.

       The provided application/x11/xvnc-inetd service defaults to running

       /usr/bin/Xvnc -inetd -query localhost -once securitytypes=none

       in  nowait mode.   This service can be enabled via svcadm(1m), and con-
       figured to use other modes or arguments via svccfg(1m).

       In this configuration, connecting to :0 will result in a new  Xvnc  for
       that  connection  which  should  display  the  standard graphical login
       screen on that machine.   (To enable this, you will also have to enable
       XDMCP  network  connections  on  the  login  screen.    See  gdm(1) for
       details.)  Because the user needs to login via this screen, 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  command  line to include in the service exec property might

       /usr/bin/Xvnc   Xvnc   -inetd   -query   localhost   -once    password-

       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, he enters his VNC
       password, then gets the login screen where he logs  in  in  the  normal
       way.  However, unlike the previous example, if he disconnects, the ses-
       sion 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.

       vncconfig(1),  vncpasswd(1),  vncserver(1),  vncviewer(1),  Xserver(1),

       Tristan Richardson, RealVNC Ltd.

       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 participated  in
       development, testing and support.

       See attributes(5) for descriptions of the following attributes:

       |      ATTRIBUTE TYPE         |      ATTRIBUTE VALUE        |
       |Availability                 |x11/server/xvnc              |
       |Interface Stability          |Volatile                     |

TigerVNC                          17 Apr 2006                          Xvnc(1)