From Linux Man Pages
Xdmx - Distributed Multi-head X server
Xdmx [:display] [option ...]
DESCRIPTION
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 con-
figuration. 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 avail-
able X server extensions.
OPTIONS
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 speci-
fied 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:
dummy
A set of dummy core input drivers are used. These never generate any input events.
local
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 key-
board driver), and usb-oth (a USB non-keyboard, non-mouse driver). Additional drivers may be imple-
mented in the future. Appropriate defaults will be used if no comma-separated list is provided.
display-name
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 input.)
If the display-name is followed by ",xkb", then the next 1 to 3 comma-separated parameters will spec-
ify 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 cur-
sor will have 4 lines instead of only 2.
Ctrl-Alt-F1 through Ctrl-Alt-F12 will switch to another VC in local (raw) mode.
-shadowfb
This option turns on (legacy) support for the shadow frame buffer.
-noshadowfb
This option turns off (legacy) support for the shadow frame buffer. Note that this option has been dep-
recated and will be removed in the next release.
-nomulticursor
This option turns off support for displaying multiple cursors on overlapped back-end displays. This
option is available for testing and benchmarking purposes.
-fontpath
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 regard-
ing 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 configu-
ration 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.
-nooffscreenopt
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 opti-
mization.
-nowindowopt
This option disables the lazy window creation optimization.
-nosubdivprims
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 dis-
able all use of XKB.)
-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.
-norender
This option disables the RENDER extension.
-noglxproxy
This option disables GLX proxy -- the build-in GLX extension implementation that is DMX aware.
-noglxswapgroup
This option disables the swap group and swap barrier extensions in GLX proxy.
-glxsyncswap
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 pro-
cessed.
-glxfinishswap
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.
-ignorebadfontpaths
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.
-addremovescreens
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 informa-
tion.
XkbRules
Defaults to "xfree86". Other values may include "sgi" and "sun".
XkbModel
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".
XkbLayout
Defaults to "us". Other country codes and "dvorak" are usually available.
XkbVariant
Defaults to "".
XkbOptions
Defaults to "".
CONFIGURATION FILE GRAMMAR
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 follow-
ing 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.
CONFIGURATION FILE EXAMPLES
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 approxi-
mate 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;
}
FONT PATHS
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 line:
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 example.
Font servers can also be specified with the -fontpath option. For example, let's assume that a properly config-
ured font server is running on host d0. Then, the following command line
Xdmx :1 -display d0:0 -display d1:0 -fontpath tcp/d0:7100 +xinerama
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 -font-
path command line option.
The -fontpath option can also be added to the configuration file as described above.
COMMAND-LINE EXAMPLES
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 display:
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 +xinerama
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 ses-
sion 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 example2
With this configuration file line:
option -input :0 +xinerama;
the command line can be shortened to:
Xdmx :1 -configfile filename -config example2
USING THE USB DEVICE DRIVERS
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 device.
KEYBOARD INITIALIZATION
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.
MULTIPLE CORE 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 keyboard.
RELATED
DMX(3X), X(7), Xserver(1), xdmxconfig(1), vdltodmx(1), xfs(1), xkbcomp(1)
CATEGORY