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man pages section 1: User Commands

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Updated: Wednesday, February 10, 2021

Xvnc (1)


Xvnc - the X VNC server


Xvnc [options] :display#


Xvnc(1)                    Virtual Network Computing                   Xvnc(1)

       Xvnc - the X VNC server

       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
              Listen  on  interface.  By default Xvnc listens on all available

       -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, 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.  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).

       -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.

              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.

              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

       -MaxCutText bytes
              The  maximum  size  of  a clipboard update that will be accepted
              from a client.  Default is 262144.

              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).

              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.

              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 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.

       -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.

              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.

              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:


                 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).

                 Comma separated list of parameters that can be modified using
                 VNC extension.  Parameters can be modified for example  using
                 vncconfig(1) program from inside a running session.

                 Allowing  override  of parameters such as PAMService or Pass-
                 wordFile can negatively impact security if  Xvnc  runs  under
                 different  user  than  the  programs  allowed to override the

                 When NoClipboard parameter is set, allowing override of Send-
                 CutText and AcceptCutText has no effect.

                 Default is desktop,AcceptPointerEvents,SendCutText,AcceptCut-

       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 attributes(7) for descriptions of the following attributes:

       |Availability   | x11/server/xvnc  |
       |Stability      | Volatile         |
       vncconfig(1),  vncpasswd(1),  vncserver(1),  vncviewer(1),  Xserver(1),

       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 par-
       ticipated in development, testing and support. This manual is  part  of
       the TigerVNC software suite.

       This     software     was    built    from    source    available    at
       https://github.com/oracle/solaris-userland.   The  original   community
       source  was  downloaded  from  https://github.com/TigerVNC/tigervnc/ar-

       Further information about this software can be found on the open source
       community website at http://tigervnc.org/.

TigerVNC                                                               Xvnc(1)