Provided by: xdmx_1.20.13-1ubuntu1~20.04.18_amd64 
NAME
Xdmx - Distributed Multi-head X server
SYNOPSIS
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
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.
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 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:
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. The following drivers have
been implemented for Linux: 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.
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 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/share/X11/xkb. Use of keycodes, symbols and geometries for XKB
configuration is deprecated in favor of the rules, layout, model, variant and
options settings available via the -param command line switch. 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.
-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 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.
-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 optimization.
-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 disable 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 processed.
-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/share/X11/xkb or a similar directory for complete information.
XkbRules
Defaults to "evdev". Other values may include "sgi" and "sun".
XkbModel
Defaults to "pc105". When used with "base" rules, other values may
include "pc102", "pc104", "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 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.
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 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;
}
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 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 +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 -fontpath 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,usb-kbd,usb-mou +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 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 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.
SEE ALSO
DMX(3), X(7), Xserver(1), xdmxconfig(1), vdltodmx(1), xfs(1), xkbcomp(1), xkeyboard-
config(7)
AUTHORS
Kevin E. Martin <kem@redhat.com>, David H. Dawes <dawes@xfree86.org>, and Rickard E. (Rik)
Faith <faith@redhat.com>.
Portions of Xdmx are based on code from The XFree86 Project (http://www.xfree86.org) and
X.Org (https://www.x.org).