Xserver - X Window System display server
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
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 sessions.
Installations that run more than one window system may need to use the
(1) utility instead of a display manager. However, xinit
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 users.
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
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 remotely.
- -audit level
- 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.
- -auth authorization-file
- specifies a file which contains a collection of
authorization records used to authenticate access. See also the
xdm(1) and Xsecurity(7) manual pages.
- -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
- 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
- -displayfd fd
- 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
- -deferglyphs whichfonts
- 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).
- -dpi resolution
- sets the resolution for all screens, in dots per inch. To
be used when the server cannot determine the screen size(s) from the
- 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).
- -fc cursorFont
- sets default cursor font.
- -fn font
- sets the default font.
- -fp fontPath
- 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 list.
- prints a usage message.
- causes all remaining command line arguments to be
- 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.
- -maxbigreqsize size
- sets the maximum big request to size MB.
- disable the display of the pointer cursor.
- -nolisten trans-type
- 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
- -listen trans-type
- 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
- -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 seat
- 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 system.
- -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
- -to seconds
- sets default connection timeout in seconds.
- disables all testing extensions (e.g., XTEST, XTrap,
- ignored, for servers started the ancient way (from
- 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 doing so.
- sets the default root window to solid white instead of the
standard root weave pattern.
- -x extension
- loads the specified extension at init. This is a no-op for
- enables(+) or disables(-) the XINERAMA extension. The
default state is platform and configuration specific.
Some X servers accept the following options:
- -ld kilobytes
- 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
- -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.
- -ls kilobytes
- 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
- 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
- selects the default policy defined for the display depth of
the X server.
- don't use any color cell.
- use a gray map of 13 color cells for the X render
- use a color cube of at most 4*4*4 colors (that is 64 color
- disables smart scheduling on platforms that support the
- -schedInterval interval
- sets the smart scheduler's scheduling interval to
X servers that support XDMCP have the following options. See the X Display
Manager Control Protocol
specification for more information.
- -query hostname
- 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
- -multicast [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 local network.
- -indirect hostname
- enables XDMCP and send IndirectQuery packets to the
- -port port-number
- 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.
- -from local-address
- 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 ends.
- -class display-class
- 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).
- -cookie xdm-auth-bits
- 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
- -displayID display-id
- Yet another XDMCP specific value, this one allows the
display manager to identify each display so that it can locate the shared
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
- [+-]accessx [ timeout [ timeout_mask [
feedback [ options_mask ] ] ] ]
- enables(+) or disables(-) AccessX key sequences.
- -xkbdir directory
- 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 different).
- -ardelay milliseconds
- sets the autorepeat delay (length of time in milliseconds
that a key must be depressed before autorepeat starts).
- -arinterval milliseconds
- sets the autorepeat interval (length of time in
milliseconds that should elapse between autorepeat-generated
- -xkbmap filename
- loads keyboard description in filename on server
The X server supports client connections via a platform-dependent subset of the
following transport types: TCP/IP, Unix Domain sockets, DECnet, and several
varieties of SVR4 local connections. See the DISPLAY NAMES section of the
(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
(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 hosts.
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
, 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
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 server.
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
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
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
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
The X server attaches special meaning to the following signals:
- 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 next user.
- 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 possible.
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
Directories specified this way can contain symlinks pointing to the real font
directories. See the FONTPATH.D section for details.
The font path can be set with the -fp
option or by xset
the server has started.
You can specify a special kind of font path in the form
. 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 symlinks.
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
- Bitmap font directories
- Outline font directories
- Unix domain socket for display number n
- Error log file for display number n if run from
- Default error log file if the server is run from
General information: X
Protocols: X Window System Protocol, The X Font Service Protocol,
X Display Manager Control Protocol
Logical Font Description Conventions
(1), Security Extension Specification
Starting the server: startx
Controlling the server once started: xset
Server-specific man pages: Xorg
Server internal documentation: Definition of the Porting Layer for the X v11
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