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       Xdmx - Distributed Multi-head X server


       Xdmx [:display] [option ...]


       Xdmx  is  a proxy X server that uses one or more other X servers as its
       display devices.  It provides multi-head X functionality  for  displays
       that  might  be  located  on  different  machines.  Xdmx functions as a
       front-end X server that acts as a proxy to a set of back-end X servers.
       All  of  the  visible  rendering  is  passed to the back-end X servers.
       Clients connect to the Xdmx front-end, and  everything  appears  as  it
       would  in  a  regular multi-head configuration.  If Xinerama is enabled
       (e.g., with +xinerama on the command line), the clients  see  a  single
       large screen.

       Xdmx  communicates  to  the  back-end  X servers using the standard X11
       protocol, and standard and/or commonly available X server extensions.


       In addition to the normal X server options described in the  Xserver(1)
       manual page, Xdmx accepts the following command line switches:

       -display display-name
               This  specifies the name(s) of the back-end X server display(s)
               to connect to.  This option may be specified multiple times  to
               connect  to  more than one back-end display.  The first is used
               as screen 0, the second as screen 1, etc.  If  this  option  is
               omitted,  the  $DISPLAY  environment  variable  is  used as the
               single back-end X server display.

       -xinput input-source
               This specifies the source to use for XInput extension  devices.
               The  choices  are  the  same  as  for -input , described below,
               except that core devices on backend servers cannot  be  treated
               as  XInput  extension  devices.  (Although extension devices on
               backend and console servers are supported as extension  devices
               under Xdmx).

       -input input-source
               This  specifies  the  source to use for the core input devices.
               The choices are:

                   A set of dummy core input drivers are  used.   These  never
                   generate any input events.

                   The  raw  keyboard  and pointer from the local computer are
                   used.  A  comma-separated  list  of  driver  names  can  be
                   appended.    For  example,  to  select  the  example  Linux
                   keyboard and PS/2 mouse driver use:  -input  local,kbd,ps2.
                   The following drivers have been implemented for Linux: kbd,
                   ms (a two-button Microsoft mouse driver), ps2 (a PS/2 mouse
                   driver),  usb-mou  (a  USB  mouse  driver),  usb-kbd (a USB
                   keyboard driver), and usb-oth  (a  USB  non-keyboard,  non-
                   mouse  driver).   Additional  drivers may be implemented in
                   the future.  Appropriate defaults will be used if no comma-
                   separated list is provided.

                   If  the  display-name is a back-end server, then core input
                   events are taken from the server specified.   Otherwise,  a
                   console window will be opened on the specified display.

                   If  the  display-name  is  followed  by  ",xi"  then XInput
                   extension devices on the  display  will  be  used  as  Xdmx
                   XInput  extension devices.  If the display-name is followed
                   by ",noxi" then XInput extension  devices  on  the  display
                   will   not  be  used  as  Xdmx  XInput  extension  devices.
                   Currently, the default is ",xi".

                   If the display-name  is  followed  by  ",console"  and  the
                   display-name  refers to a display that is used as a backend
                   display, then a console  window  will  be  opened  on  that
                   display  and  that  display  will  be  treated as a backend
                   display.  Otherwise  (or  if  ",noconsole"  is  used),  the
                   display  will  be  treated purely as a backend or a console
                   display, as described above.

                   If  the  display-name  is  followed  by  ",windows",   then
                   outlines  of  the  windows on the backend will be displayed
                   inside the console window.  Otherwise (or  if  ",nowindows"
                   is  used), the console window will not display the outlines
                   of backend windows.  (This option only applies  to  console

                   If  the display-name is followed by ",xkb", then the next 1
                   to 3 comma-separated parameters will specify the  keycodes,
                   symbols,  and  geometry  of  the  keyboard  for  this input
                   device.  For  example,  ",xkb,xfree86,pc104"  will  specify
                   that  the "xfree86" keycodes and the "pc104" symbols should
                   be used to initialize the keyboard.  For an  SGI  keyboard,
                   ",xkb,sgi/indy(pc102)"   might   be   useful.   A  list  of
                   keycodes,  symbols,  and  geometries  can   be   found   in
                   /usr/X11R6/lib/X11/xkb.   If  this option is not specified,
                   the  input  device  will  be  queried,  perhaps  using  the
                   XKEYBOARD extension.

               If this option isn't specified, the default input source is the
               first back-end server (the one used for screen 0).  The console
               window  shows the layout of the back-end display(s) and pointer
               movements and key presses within the  console  window  will  be
               used as core input devices.

               Several  special  function  keys  are  active, depending on the
               input source:

                      Ctrl-Alt-q will terminate the Xdmx server in all  modes.

                      Ctrl-Alt-g  will toggle a server grab in console mode (a
                      special cursor, currently a spider, is used to  indicate
                      an active server grab).

                      Ctrl-Alt-f will toggle fine-grain motion in console mode
                      (a special cursor, currently a cross hair,  is  used  to
                      indicate  this  mode).   If this mode is combined with a
                      server grab, then the cursor will have 4  lines  instead
                      of only 2.

                      Ctrl-Alt-F1  through Ctrl-Alt-F12 will switch to another
                      VC in local (raw) mode.

               This option turns on (legacy)  support  for  the  shadow  frame

               This  option  turns  off  (legacy) support for the shadow frame
               buffer.  Note that this option has been deprecated and will  be
               removed in the next release.

               This  option  turns off support for displaying multiple cursors
               on overlapped back-end displays.  This option is available  for
               testing and benchmarking purposes.

               This  option  sets  the  Xdmx server's default font path.  This
               option can be specified multiple times to accommodate  multiple
               font  paths.   See  the  FONT  PATHS  section  below  for  very
               important information regarding setting the default font  path.

       -configfile filename
               Specify  the configuration file that should be read.  Note that
               if  the  -display  command-line  option  is  used,   then   the
               configuration file will be ignored.

       -config name
               Specify  a  configuration  to  use.   The name will be the name
               following the virtual keyword in the configuration file.

       -stat interval screens
               This option enables the display of performance statistics.  The
               interval  is  in seconds.  The screens is a count of the number
               of back-end screens for which data is  printed  each  interval.
               Specifying 0 for screens will display data for all screens.

               For  each  screen,  the  following  information is printed: the
               screen number, an absolute count of the number of XSync() calls
               made  (SyncCount),  the rate of these calls during the previous
               interval   (Sync/s),   the   average   round-trip   time    (in
               microseconds)  of  the  last  10  XSync()  calls  (avSync), the
               maximum round-trip time (in microseconds) of the last 10  XSync
               calls  (mxSync),  the  average  number of XSync() requests that
               were pending but not yet processed for  each  of  the  last  10
               processed XSync() calls, the maximum number of XSync() requests
               that were pending but not yet processed for each of the last 10
               processed   XSync()   calls,   and   a  histogram  showing  the
               distribution of the times of all of the XSync() calls that were
               made during the previous interval.

               (The  length  of the moving average and the number and value of
               histogram  bins  are  configurable  at  compile  time  in   the
               dmxstat.h header file.)

       -syncbatch interval
               This  option  sets  the  interval  in  milliseconds for XSync()
               batching.  An interval less than or equal  to  0  will  disable
               XSync() batching.  The default interval is 100 ms.

               This  option  disables  the  offscreen optimization.  Since the
               lazy  window  creation  optimization  requires  the   offscreen
               optimization  to  be enabled, this option will also disable the
               lazy window creation optimization.

               This option disables the lazy window creation optimization.

               This option disables the primitive subdivision optimization.

       -noxkb  Disable use of the XKB extension  for  communication  with  the
               back  end  displays.   (Combine  with -kb to disable all use of

       -depth int
               This  option  sets  the  root  window's  default  depth.   When
               choosing  a default visual from those available on the back-end
               X  server,  the  first  visual  with  that  matches  the  depth
               specified is used.

               This  option  can  be  combined  with  the  -cc  option,  which
               specifies the default color visual class, to force the use of a
               specific depth and color class for the root window.

               This option disables the RENDER extension.

               This  option  disables  GLX proxy -- the build-in GLX extension
               implementation that is DMX aware.

               This option disables the swap group and swap barrier extensions
               in GLX proxy.

               This  option  enables synchronization after a swap buffers call
               by waiting until all X protocol has  been  processed.   When  a
               client  issues  a  glXSwapBuffers  request,  Xdmx  relays  that
               request to each back-end  X  server,  and  those  requests  are
               buffered  along  with all other protocol requests.  However, in
               systems that have large network  buffers,  this  buffering  can
               lead to the set of back-end X servers handling the swap buffers
               request asynchronously.  With this option, an  XSync()  request
               is  issued  to  each  back-end  X server after sending the swap
               buffers request.  The XSync() requests will flush all  buffered
               protocol  (including  the swap buffers requests) and wait until
               the back-end X servers have  processed  those  requests  before
               continuing.   This  option  does not wait until all GL commands
               have  been  processed  so  there  might  be  previously  issued
               commands that are still being processed in the GL pipe when the
               XSync() request returns.  See the -glxfinishswap  option  below
               if  Xdmx should wait until the GL commands have been processed.

               This option enables synchronization after a swap  buffers  call
               by  waiting  until  all GL commands have been completed.  It is
               similar to the -glxsyncswap option above; however,  instead  of
               issuing  an  XSync(),  it  issues  a glFinish() request to each
               back-end X server after sending the swap buffers requests.  The
               glFinish()  request  will flush all buffered protocol requests,
               process both X and GL requests, and wait until  all  previously
               called GL commands are complete before returning.

               This  option  ignores  font paths that are not available on all
               back-end servers by removing the  bad  font  path(s)  from  the
               default  font path list.  If no valid font paths are left after
               removing the bad paths, an error to that effect is  printed  in
               the log.

               This  option  enables  the  dynamic  addition  and  removal  of
               screens, which is disabled by default.  Note that GLXProxy  and
               Render  do  not  yet  support  dynamic  addition and removal of
               screens, and must be disabled via the -noglxproxy and -norender
               command line options described above.

       -param  This   option   specifies   parameters  on  the  command  line.
               Currently, only parameters dealing with XKEYBOARD configuration
               are  supported.   These  parameters  apply  only  to  the  core
               keyboard.  Parameter values are installation-dependent.  Please
               see  /usr/X11R6/lib/X11/xkb or a similar directory for complete

                       Defaults to "xfree86".  Other values may include  "sgi"
                       and "sun".

                       Defaults  to  "pc101".  When used with "xfree86" rules,
                       other values may  include  "pc102",  "pc104",  "pc105",
                       "microsoft",  and  many  others.   When used with "sun"
                       rules, other values may include "type4" and "type5".

                       Defaults to "us".  Other country codes and "dvorak" are
                       usually available.

                       Defaults to "".

                       Defaults to "".


       The following words and tokens are reserved:
              virtual display wall option param { } ; #

       Comments  start  with a # mark and extend to the end of the line.  They
       may appear anywhere.  If a configuration file is read into  xdmxconfig,
       the  comments in that file will be preserved, but will not be editable.

       The grammar is as follows:
              virtual-list ::= [ virtual-list ] | virtual

              virtual ::= virtual [ name ] [ dim ] { dw-list }

              dw-list ::= [ dw-list ] | dw

              dw ::= display | wall | option

              display ::= display name [ geometry ] [ / geometry ] [ origin  ]

              wall ::= wall [ dim ] [ dim ] name-list ;

              option ::= option name-list ;

              param ::= param name-list ;

              param ::= param { param-list }

              param-list ::= [ param-list ] | name-list ;

              name-list ::= [ name-list ] | name

              name ::= string | double-quoted-string

              dim ::= integer x integer

              geometry  ::=  [  integer  x  integer ] [ signed-integer signed-
              integer ]

              origin ::= @ integer x integer

       The  name  following  virtual  is  used  as  an  identifier   for   the
       configuration, and may be passed to Xdmx using the -config command line
       option.  The name of a display  should  be  standard  X  display  name,
       although no checking is performed (e.g., "machine:0").

       For  names,  double  quotes are optional unless the name is reserved or
       contains spaces.

       The first dimension following wall is the dimension for  tiling  (e.g.,
       2x4  or  4x4).  The second dimension following wall is the dimension of
       each display in the wall (e.g., 1280x1024).

       The first geometry following display is  the  geometry  of  the  screen
       window  on  the  backend  server.  The second geometry, which is always
       preceeded by a slash, is the geometry of the root window.  By  default,
       the root window has the same geometry as the screen window.

       The  option line can be used to specify any command-line options (e.g.,
       -input).  (It cannot be used to  specify  the  name  of  the  front-end
       display.)   The  option  line is processed once at server startup, just
       line command line options.  This behavior may be unexpected.


       Two displays being used for a desktop may be specified in  any  of  the
       following formats:
              virtual example0 {
                  display d0:0 1280x1024 @0x0;
                  display d1:0 1280x1024 @1280x0;

              virtual example1 {
                  display d0:0 1280x1024;
                  display d1:0 @1280x0;

              virtual example2 {
                  display "d0:0";
                  display "d1:0" @1280x0;

              virtual example3 { wall 2x1 d0:0 d1:0; }
       A  4x4  wall  of 16 total displays could be specified as follows (if no
       tiling dimension is specified, an approximate square is used):
              virtual example4 {
                  wall d0:0 d1:0 d2:0 d3:0
                       d4:0 d5:0 d6:0 d7:0
                       d8:0 d9:0 da:0 db:0
                       dc:0 dd:0 de:0 df:0;


       The font path used by the Xdmx front-end server will be  propagated  to
       each  back-end  server,which  requires  that  each back-end server have
       access to the exact same font paths as the front-end server.  This  can
       be  most easily handled by either using a font server (e.g., xfs) or by
       remotely mounting the font paths on  each  back-end  server,  and  then
       setting  the  Xdmx  server's  default font path with the -I "-fontpath"
       command line option described above.

       For example, if you specify a font  path  with  the  following  command
              Xdmx  :1  -display  d0:0  -fontpath  /usr/fonts/75dpi/ -fontpath
              /usr/fonts/Type1/ +xinerama
       Then, /usr/fonts/75dpi/ and /usr/fonts/Type1/ must be valid font  paths
       on  the  Xdmx  server  and  all  back-end  server,  which is d0 in this

       Font servers can also be specified  with  the  -fontpath  option.   For
       example, let's assume that a properly configured font server is running
       on host d0.  Then, the following command line
              Xdmx  :1  -display  d0:0  -display  d1:0  -fontpath  tcp/d0:7100
       will  initialize  the  front-end  Xdmx  server and each of the back-end
       servers to use the font server on d0.

       Some fonts might not be supported by either the front-end or the  back-
       end  servers.   For  example,  let's  assume  the front-end Xdmx server
       includes support Type1 fonts, but one of the back-end servers does not.
       Let's  also  assume  that the default font path for Xdmx includes Type1
       fonts in its font path.  Then, when Xdmx initializes the  default  font
       path  to load the default font, the font path that includes Type1 fonts
       (along with the other default font paths that  are  used  by  the  Xdmx
       server)  is sent to the back-end server that cannot handle Type1 fonts.
       That back-end server then rejects the font path and sends an error back
       to  the  Xdmx  server.   Xdmx  then  prints  an error message and exits
       because it failed to set the default font path and was unable load  the
       default font.

       To  fix  this  error,  the offending font path must be removed from the
       default font path by using a different -fontpath command line option.

       The -fontpath option can also be added to  the  configuration  file  as
       described above.


       The back-end machines are d0 and d1, core input is from the pointer and
       keyboard attached to d0, clients will refer to :1 when opening windows:
              Xdmx :1 -display d0:0 -display d1:0 +xinerama

       As above, except with core input from d1:
              Xdmx :1 -display d0:0 -display d1:0 -input d1:0 +xinerama

       As  above,  except  with  core input from a console window on the local
              Xdmx :1 -display d0:0 -display d1:0 -input :0 +xinerama

       As above, except with core input from the local keyboard and mouse:
              Xdmx  :1  -display  d0:0  -display  d1:0  -input   local,kbd,ps2
       Note  that  local input can be used under Linux while another X session
       is running on :0 (assuming the user can access the  Linux  console  tty
       and mouse devices): a new (blank) VC will be used for keyboard input on
       the local machine and the Ctrl-Alt-F* sequence  will  be  available  to
       change to another VC (possibly back to another X session running on the
       local  machine).   Using  Ctrl-Alt-Backspace  on  the  blank  VC   will
       terminate the Xdmx session and return to the original VC.

       This example uses the configuration file shown in the previous section:
              Xdmx  :1  -input  :0  +xinerama  -configfile  filename   -config
       With this configuration file line:
              option -input :0 +xinerama;
       the command line can be shortened to:
              Xdmx :1 -configfile filename -config example2


       The  USB  device  drivers  use  the  devices  called /dev/input/event0,
       /dev/input/event1, etc.  under Linux.  These devices are  driven  using
       the  evdev Linux kernel module, which is part of the hid suite.  Please
       note that if you load the mousedev or kbddev Linux kernel modules, then
       USB devices will appear as core Linux input devices and you will not be
       able to select between using the device only as an Xdmx core device  or
       an  Xdmx XInput extension device.  Further, you may be unable to unload
       the mousedev Linux kernel  module  if  XFree86  is  configured  to  use
       /dev/input/mice  as  an  input device (this is quite helpful for laptop
       users and is set up by default  under  some  Linux  distributions,  but
       should be changed if USB devices are to be used with Xdmx).

       The  USB  device drivers search through the Linux devices for the first
       mouse, keyboard, or non-mouse-non-keyboard Linux device  and  use  that


       If  Xdmx was invoked with -xkb or was not compiled to use the XKEYBOARD
       extension, then a keyboard on a backend or console will be  initialized
       using the map that the host X server provides.

       If  the XKEYBOARD extension is used for both Xdmx and the host X server
       for the keyboard (i.e., the backend or console X server), then the type
       of  the  keyboard  will  be  obtained  from  the  host X server and the
       keyboard  under  Xdmx  will  be  initialized  with  that   information.
       Otherwise,  the  default type of keyboard will be initialized.  In both
       cases, the map from the host X server will not  be  used.   This  means
       that   different  initial  behavior  may  be  noted  with  and  without
       XKEYBOARD.  Consistent and expected results will be obtained by running
       XKEYBOARD  on  all  servers  and  by avoiding the use of xmodmap on the
       backend or console X servers prior to starting Xdmx.

       If -xkbmap is specified on the Xdmx command line, then  that  map  will
       currently be used for all keyboards.


       X  was  not designed to support multiple core keyboards.  However, Xdmx
       provides some support for multiple core keyboards.  Best  results  will
       be  obtained if all of the keyboards are of the same type and are using
       the same keyboard map.  Because  the  X  server  passes  raw  key  code
       information  to  the X client, key symbols for keyboards with different
       key maps would be different if the key code for each keyboard was  sent
       without  translation  to  the  client.  Therefore, Xdmx will attempt to
       translate the key code from a core keyboard to the key code for the key
       with  the  same  key symbol of the first core keyboard that was loaded.
       If the key symbol appears in both maps, the results will  be  expected.
       Otherwise,  the  second core keyboard will return a NoSymbol key symbol
       for some keys that would have been translated if it was the first  core


       DMX(3X),   X(7),   Xserver(1),   xdmxconfig(1),   vdltodmx(1),  xfs(1),


       Kevin E. Martin <>, David H.  Dawes  <>,
       and Rickard E. (Rik) Faith <>.

       Portions   of   Xdmx  are  based  on  code  from  The  XFree86  Project
       ( and X.Org (