Xserver - X Window System display server
X is the generic name for the X Window System display
server. It is frequently a link or a copy of the appropriate server binary
for driving the most frequently used server on a given machine.
The X server is usually started from the X Display Manager program
xdm(1) or a similar display manager program. This utility is run from
the system boot files and takes care of keeping the server running,
prompting for usernames and passwords, and starting up the user
Installations that run more than one window system may need to use
the xinit(1) utility instead of a display manager. However,
xinit is to be considered a tool for building startup scripts and is
not intended for use by end users. Site administrators are strongly
urged to use a display manager, or build other interfaces for novice
The X server may also be started directly by the user, though this
method is usually reserved for testing and is not recommended for normal
operation. On some platforms, the user must have special permission to start
the X server, often because access to certain devices (e.g.
/dev/mouse) is restricted.
When the X server starts up, it typically takes over the display.
If you are running on a workstation whose console is the display, you may
not be able to log into the console while the server is running.
Many X servers have device-specific command line options. See the
manual pages for the individual servers for more details; a list of
server-specific manual pages is provided in the SEE ALSO section below.
All of the X servers accept the command line options described
below. Some X servers may have alternative ways of providing the parameters
described here, but the values provided via the command line options should
override values specified via other mechanisms.
- The X server runs as the given displaynumber, which by default is
0. If multiple X servers are to run simultaneously on a host, each must
have a unique display number. See the DISPLAY NAMES section of the
X(7) manual page to learn how to specify which display number
clients should try to use.
- -a number
- sets pointer acceleration (i.e. the ratio of how much is reported to how
much the user actually moved the pointer).
- disables host-based access control mechanisms. Enables access by any host,
and permits any host to modify the access control list. Use with extreme
caution. This option exists primarily for running test suites
- sets the audit trail level. The default level is 1, meaning only
connection rejections are reported. Level 2 additionally reports all
successful connections and disconnects. Level 4 enables messages from the
SECURITY extension, if present, including generation and revocation of
authorizations and violations of the security policy. Level 0 turns off
the audit trail. Audit lines are sent as standard error output.
- specifies a file which contains a collection of authorization records used
to authenticate access. See also the xdm(1) and Xsecurity(7)
- -background none
- Asks the driver not to clear the background on startup, if the driver
supports that. May be useful for smooth transition with eg. fbdev driver.
For security reasons this is not the default as the screen contents might
show a previous user session.
- sets the default root window to solid black instead of the standard root
weave pattern. This is the default unless -retro or -wr is specified.
- disables backing store support on all screens.
- turns off key-click.
- c volume
- sets key-click volume (allowable range: 0-100).
- -cc class
- sets the visual class for the root window of color screens. The class
numbers are as specified in the X protocol. Not obeyed by all
- causes the server to generate a core dump on fatal errors.
- specifies a file descriptor in the launching process. Rather than specify
a display number, the X server will attempt to listen on successively
higher display numbers, and upon finding a free one, will write the
display number back on this file descriptor as a newline-terminated
string. The -pn option is ignored when using -displayfd.
- specifies the types of fonts for which the server should attempt to use
deferred glyph loading. whichfonts can be all (all fonts), none (no
fonts), or 16 (16 bit fonts only).
- sets the resolution for all screens, in dots per inch. To be used when the
server cannot determine the screen size(s) from the hardware.
- enables DPMS (display power management services), where supported. The
default state is platform and configuration specific.
- disables DPMS (display power management services). The default state is
platform and configuration specific.
- disables named extension. If an unknown extension name is specified, a
list of accepted extension names is printed.
- enables named extension. If an unknown extension name is specified, a list
of accepted extension names is printed.
- -f volume
- sets beep (bell) volume (allowable range: 0-100).
- sets default cursor font.
- -fn font
- sets the default font.
- sets the search path for fonts. This path is a comma separated list of
directories which the X server searches for font databases. See the FONTS
section of this manual page for more information and the default
- prints a usage message.
- causes all remaining command line arguments to be ignored.
- Prohibit creating indirect GLX contexts. Indirect GLX is of limited use,
since it lacks support for many modern OpenGL features and extensions;
it's slower than direct contexts; and it opens a large attack surface for
protocol parsing errors. This is the default unless +iglx is
- Allow creating indirect GLX contexts.
- sets the maximum big request to size MB.
- disable the display of the pointer cursor.
- disables a transport type. For example, TCP/IP connections can be disabled
with -nolisten tcp. This option may be issued multiple times to
disable listening to different transport types. Supported transport types
are platform dependent, but commonly include:
|tcp TCP over IPv4 or IPv6
|inet TCP over IPv4 only
|inet6 TCP over IPv6 only
|unix UNIX Domain Sockets
|local Platform preferred local connection method
- enables a transport type. For example, TCP/IP connections can be enabled
with -listen tcp. This option may be issued multiple times to
enable listening to different transport types.
- prevents a server reset when the last client connection is closed. This
overrides a previous -terminate command line option.
- -p minutes
- sets screen-saver pattern cycle time in minutes.
- permits the server to continue running if it fails to establish all of its
well-known sockets (connection points for clients), but establishes at
least one. This option is set by default.
- causes the server to exit if it fails to establish all of its well-known
sockets (connection points for clients).
- turns off auto-repeat.
- turns on auto-repeat.
- starts the server with the classic stipple and cursor visible. The default
is to start with a black root window, and to suppress display of the
cursor until the first time an application calls XDefineCursor(). For
kdrive servers, this implies -zap.
- -s minutes
- sets screen-saver timeout time in minutes.
- disables save under support on all screens.
- seat to run on. Takes a string identifying a seat in a platform specific
syntax. On platforms which support this feature this may be used to limit
the server to expose only a specific subset of devices connected to the
- -t number
- sets pointer acceleration threshold in pixels (i.e. after how many pixels
pointer acceleration should take effect).
- causes the server to terminate at server reset, instead of continuing to
run. This overrides a previous -noreset command line option.
- -to seconds
- sets default connection timeout in seconds.
- disables all testing extensions (e.g., XTEST, XTrap, XTestExtension1,
- ignored, for servers started the ancient way (from init).
- sets video-off screen-saver preference.
- sets video-on screen-saver preference.
- forces the default backing-store of all windows to be WhenMapped. This is
a backdoor way of getting backing-store to apply to all windows. Although
all mapped windows will have backing store, the backing store attribute
value reported by the server for a window will be the last value
established by a client. If it has never been set by a client, the server
will report the default value, NotUseful. This behavior is required by the
X protocol, which allows the server to exceed the client's backing store
expectations but does not provide a way to tell the client that it is
- sets the default root window to solid white instead of the standard root
- -x extension
- loads the specified extension at init. This is a no-op for most
- enables(+) or disables(-) the XINERAMA extension. The default state is
platform and configuration specific.
Some X servers accept the following options:
- sets the data space limit of the server to the specified number of
kilobytes. A value of zero makes the data size as large as possible. The
default value of -1 leaves the data space limit unchanged.
- -lf files
- sets the number-of-open-files limit of the server to the specified number.
A value of zero makes the limit as large as possible. The default value of
-1 leaves the limit unchanged.
- sets the stack space limit of the server to the specified number of
kilobytes. A value of zero makes the stack size as large as possible. The
default value of -1 leaves the stack space limit unchanged.
- 64|128|256|512 Set the maximum number of
clients allowed to connect to the X server. Acceptable values are 64, 128,
256 or 512.
- default|mono|gray|color sets the color
allocation policy that will be used by the render extension.
- selects the default policy defined for the display depth of the X
- don't use any color cell.
- use a gray map of 13 color cells for the X render extension.
- use a color cube of at most 4*4*4 colors (that is 64 color cells).
- disables smart scheduling on platforms that support the smart
- sets the smart scheduler's scheduling interval to interval
X servers that support XDMCP have the following options. See the
X Display Manager Control Protocol specification for more
- enables XDMCP and sends Query packets to the specified
- enable XDMCP and broadcasts BroadcastQuery packets to the network. The
first responding display manager will be chosen for the session.
[address [hop count]]
- Enable XDMCP and multicast BroadcastQuery packets to the network. The
first responding display manager is chosen for the session. If an address
is specified, the multicast is sent to that address. If no address is
specified, the multicast is sent to the default XDMCP IPv6 multicast
group. If a hop count is specified, it is used as the maximum hop count
for the multicast. If no hop count is specified, the multicast is set to a
maximum of 1 hop, to prevent the multicast from being routed beyond the
- enables XDMCP and send IndirectQuery packets to the specified
- uses the specified port-number for XDMCP packets, instead of the
default. This option must be specified before any -query, -broadcast,
-multicast, or -indirect options.
- specifies the local address to connect from (useful if the connecting host
has multiple network interfaces). The local-address may be
expressed in any form acceptable to the host platform's
- causes the server to terminate (rather than reset) when the XDMCP session
- XDMCP has an additional display qualifier used in resource lookup for
display-specific options. This option sets that value, by default it is
"MIT-unspecified" (not a very useful value).
- When testing XDM-AUTHENTICATION-1, a private key is shared between the
server and the manager. This option sets the value of that private data
(not that it is very private, being on the command line!).
- Yet another XDMCP specific value, this one allows the display manager to
identify each display so that it can locate the shared key.
X servers that support the XKEYBOARD (a.k.a. "XKB")
extension accept the following options. All layout files specified on the
command line must be located in the XKB base directory or a subdirectory,
and specified as the relative path from the XKB base directory. The default
XKB base directory is /usr/X11R6/lib/X11/xkb.
- [+-]accessx [ timeout [ timeout_mask [
feedback [ options_mask ] ] ] ]
- enables(+) or disables(-) AccessX key sequences.
- base directory for keyboard layout files. This option is not available for
setuid X servers (i.e., when the X server's real and effective uids are
- sets the autorepeat delay (length of time in milliseconds that a key must
be depressed before autorepeat starts).
- sets the autorepeat interval (length of time in milliseconds that should
elapse between autorepeat-generated keystrokes).
- loads keyboard description in filename on server startup.
The X server supports client connections via a platform-dependent
subset of the following transport types: TCP/IP, Unix Domain sockets, and
several varieties of SVR4 local connections. See the DISPLAY NAMES section
of the X(7) manual page to learn how to specify which transport type
clients should try to use.
The X server implements a platform-dependent subset of the
following authorization protocols: MIT-MAGIC-COOKIE-1, XDM-AUTHORIZATION-1,
XDM-AUTHORIZATION-2, SUN-DES-1, and MIT-KERBEROS-5. See the
Xsecurity(7) manual page for information on the operation of these
Authorization data required by the above protocols is passed to
the server in a private file named with the -auth command line
option. Each time the server is about to accept the first connection after a
reset (or when the server is starting), it reads this file. If this file
contains any authorization records, the local host is not automatically
allowed access to the server, and only clients which send one of the
authorization records contained in the file in the connection setup
information will be allowed access. See the Xau manual page for a
description of the binary format of this file. See xauth(1) for
maintenance of this file, and distribution of its contents to remote
The X server also uses a host-based access control list for
deciding whether or not to accept connections from clients on a particular
machine. If no other authorization mechanism is being used, this list
initially consists of the host on which the server is running as well as any
machines listed in the file /etc/Xn.hosts, where
n is the display number of the server. Each line of the file should
contain either an Internet hostname (e.g. expo.lcs.mit.edu) or a complete
name in the format family:name as described in the
xhost(1) manual page. There should be no leading or trailing spaces
on any lines. For example:
Users can add or remove hosts from this list and enable or disable
access control using the xhost command from the same machine as the
If the X FireWall Proxy (xfwp) is being used without a
sitepolicy, host-based authorization must be turned on for clients to be
able to connect to the X server via the xfwp. If xfwp is run
without a configuration file and thus no sitepolicy is defined, if
xfwp is using an X server where xhost + has been run to turn off
host-based authorization checks, when a client tries to connect to this X
server via xfwp, the X server will deny the connection. See
xfwp(1) for more information about this proxy.
The X protocol intrinsically does not have any notion of window
operation permissions or place any restrictions on what a client can do; if
a program can connect to a display, it has full run of the screen. X servers
that support the SECURITY extension fare better because clients can be
designated untrusted via the authorization they use to connect; see the
xauth(1) manual page for details. Restrictions are imposed on
untrusted clients that curtail the mischief they can do. See the SECURITY
extension specification for a complete list of these restrictions.
Sites that have better authentication and authorization systems
might wish to make use of the hooks in the libraries and the server to
provide additional security models.
The X server attaches special meaning to the following
- This signal causes the server to close all existing connections, free all
resources, and restore all defaults. It is sent by the display manager
whenever the main user's main application (usually an xterm or
window manager) exits to force the server to clean up and prepare for the
- This signal causes the server to exit cleanly.
- This signal is used quite differently from either of the above. When the
server starts, it checks to see if it has inherited SIGUSR1 as SIG_IGN
instead of the usual SIG_DFL. In this case, the server sends a SIGUSR1 to
its parent process after it has set up the various connection schemes.
Xdm uses this feature to recognize when connecting to the server is
The X server can obtain fonts from directories and/or from font
servers. The list of directories and font servers the X server uses when
trying to open a font is controlled by the font path.
The default font path is /usr/X11R6/lib/X11/fonts/misc/,
A special kind of directory can be specified using the
catalogue: prefix. Directories specified this way can contain
symlinks pointing to the real font directories. See the FONTPATH.D section
The font path can be set with the -fp option or by
xset(1) after the server has started.
You can specify a special kind of font path in the form
catalogue:<dir>. The directory specified after the catalogue:
prefix will be scanned for symlinks and each symlink destination will be
added as a local fontfile FPE.
The symlink can be suffixed by attributes such as
'unscaled', which will be passed through to the underlying fontfile
FPE. The only exception is the newly introduced 'pri' attribute,
which will be used for ordering the font paths specified by the
An example configuration:
75dpi:unscaled:pri=20 -> /usr/share/X11/fonts/75dpi
ghostscript:pri=60 -> /usr/share/fonts/default/ghostscript
misc:unscaled:pri=10 -> /usr/share/X11/fonts/misc
type1:pri=40 -> /usr/share/X11/fonts/Type1
type1:pri=50 -> /usr/share/fonts/default/Type1
This will add /usr/share/X11/fonts/misc as the first FPE with the
attribute 'unscaled', second FPE will be /usr/share/X11/fonts/75dpi, also
with the attribute 'unscaled' etc. This is functionally equivalent to
setting the following font path:
- Initial access control list for display number n
- Bitmap font directories
- Outline font directories
- Unix domain socket for display number n
- Error log file for display number n if run from init(8)
- Default error log file if the server is run from xdm(1)
General information: X(7)
Protocols: X Window System Protocol, The X Font Service
Protocol, X Display Manager Control Protocol
Fonts: bdftopcf(1), mkfontdir(1),
mkfontscale(1), xfs(1), xlsfonts(1),
xfontsel(1), xfd(1), X Logical Font Description
Security: Xsecurity(7), xauth(1), Xau(1),
xdm(1), xhost(1), xfwp(1), Security Extension
Starting the server: startx(1), xdm(1),
Controlling the server once started: xset(1),
xsetroot(1), xhost(1), xinput(1), xrandr(1)
Server-specific man pages: Xorg(1), Xdmx(1),
Xephyr(1), Xnest(1), Xvfb(1), Xquartz(1),
Server internal documentation: Definition of the Porting Layer
for the X v11 Sample Server
The sample server was originally written by Susan Angebranndt,
Raymond Drewry, Philip Karlton, and Todd Newman, from Digital Equipment
Corporation, with support from a large cast. It has since been extensively
rewritten by Keith Packard and Bob Scheifler, from MIT. Dave Wiggins took
over post-R5 and made substantial improvements.