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Xserver - X Window System display server
X [option ...]
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 driv-
ing the most frequently used server on a given machine.
STARTING THE SERVER
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 ses-
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 dis-
play 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 nor-
mal operation. On some platforms, the user must have special permis-
sion 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 man-
ual 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(@miscmansuffix@) manual page to learn
how to specify which display number clients should try to use.
sets pointer acceleration (i.e. the ratio of how much is
reported to how much the user actually moved the pointer).
-ac 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.
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 vio-
lations 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(@miscmansuffix@) manual pages.
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.
-br 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.
-bs disables backing store support on all screens.
-c turns off key-click.
sets key-click volume (allowable range: 0-100).
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 servers.
-core 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
dpms enables DPMS (display power management services), where sup-
ported. The default state is platform and configuration spe-
-dpms 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.
sets beep (bell) volume (allowable range: 0-100).
sets default cursor 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 data-
bases. See the FONTS section of this manual page for more
information and the default list.
-help prints a usage message.
-I causes all remaining command line arguments to be ignored.
-iglx Prohibit creating indirect GLX contexts. Indirect GLX is of
limited use, since it lacks support for many modern OpenGL fea-
tures 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 specified.
+iglx 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 mul-
tiple times to disable listening to different transport types.
Supported transport types are platform dependent, but commonly
l l. 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 multi-
ple 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
sets screen-saver pattern cycle time in minutes.
-pn 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.
-nopn causes the server to exit if it fails to establish all of its
well-known sockets (connection points for clients).
-r turns off auto-repeat.
r turns on auto-repeat.
-retro starts the server with the classic stipple and cursor visible.
The default is to start with a black root window, and to sup-
press display of the cursor until the first time an application
calls XDefineCursor(). For kdrive servers, this implies -zap.
sets screen-saver timeout time in minutes.
-su 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 sub-
set of devices connected to the system.
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 con-
tinuing to run. This overrides a previous -noreset command
sets default connection timeout in seconds.
-tst disables all testing extensions (e.g., XTEST, XTrap, XTestEx-
ttyxx ignored, for servers started the ancient way (from init).
v sets video-off screen-saver preference.
-v sets video-on screen-saver preference.
-wm forces the default backing-store of all windows to be When-
Mapped. 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.
-wr sets the default root window to solid white instead of the
standard root weave pattern.
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.
SERVER DEPENDENT OPTIONS
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
sets the number-of-open-files limit of the server to the speci-
fied number. A value of zero makes the limit as large as pos-
sible. The default value of -1 leaves the limit unchanged.
sets the stack space limit of the server to the specified num-
ber 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
-render default|mono|gray|color sets the color allocation policy that
will be used by the render extension.
default selects the default policy defined for the display
depth of the X server.
mono don't use any color cell.
gray use a gray map of 13 color cells for the X render
color use a color cube of at most 4*4*4 colors (that is 64
disables smart scheduling on platforms that support the smart
sets the smart scheduler's scheduling interval to interval mil-
X servers that support XDMCP have the following options. See the X
Display Manager Control Protocol specification for more information.
enables XDMCP and sends Query packets to the specified host-
enable XDMCP and broadcasts BroadcastQuery packets to the net-
work. The first responding display manager will be chosen for
-multicast [address [hop count]]
Enable XDMCP and multicast BroadcastQuery packets to the net-
work. 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 mul-
ticast. 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.
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 con-
necting host has multiple network interfaces). The local-
address may be expressed in any form acceptable to the host
platform's gethostbyname(3) implementation.
-once causes the server to terminate (rather than reset) when the
XDMCP session ends.
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
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
Yet another XDMCP specific value, this one allows the display
manager to identify each display so that it can locate the
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 speci-
fied as the relative path from the XKB base directory. The default XKB
base directory is @projectroot@/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 different).
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 sub-
set 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(@miscmansuffix@) 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 Xsecu-
rity(@miscmansuffix@) manual page for information on the operation of
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 automat-
ically 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 main-
tenance 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 /etc/Xn.hosts, where n is the dis-
play 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 config-
uration 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 opera-
tion 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 SECU-
RITY 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 pro-
vide additional security models.
The X server attaches special meaning to the following signals:
SIGHUP This signal causes the server to close all existing connec-
tions, 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.
SIGTERM This signal causes the server to exit cleanly.
SIGUSR1 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 @default_font_path@ .
A special kind of directory can be specified using the catalogue: pre-
fix. 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(1) after the
server has started.
You can specify a special kind of font path in the form cata-
logue:<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 excep-
tion 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:
/etc/Xn.hosts Initial access control list for display
Bitmap font directories
Outline font directories
/tmp/.X11-unix/Xn Unix domain socket for display number n
/usr/adm/Xnmsgs Error log file for display number n if
run from init(@adminmansuffix@)
Default error log file if the server is
run from xdm(1)
General information: X(@miscmansuffix@)
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 Conventions
Security: Xsecurity(@miscmansuffix@), xauth(1), Xau(1), xdm(1),
xhost(1), xfwp(1), Security Extension Specification
Starting the server: startx(1), xdm(1), xinit(1)
Controlling the server once started: xset(1), xsetroot(1), xhost(1),
Server-specific man pages: Xorg(1), Xdmx(1), Xephyr(1), Xnest(1),
Xvfb(1), Xquartz(1), XWin(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 Corpo-
ration, 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.