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
- -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)
- -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.
- -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 -displayfd.
- -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 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).
- -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
- 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.
- -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 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 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
- -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:
- -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 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.
- -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 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
- -schedInterval interval
- 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 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 session.
- -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
- -indirect hostname
- enables XDMCP and send IndirectQuery packets to the specified
- -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
- -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 line!).
- -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 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
- [+-]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
- -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 keystrokes).
- -xkbmap filename
- 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
manual page to learn how to specify which transport type clients should try to
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
- 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
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 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
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