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(7) 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(7) manual pages.
-bs disables backing store support on all screens.
-br sets the default root window to solid black instead of the
standard root weave pattern.
-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.
sets name of RGB color database. The default is
-core causes the server to generate a core dump on fatal errors.
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 feep (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.
sets the maximum big request to size MB.
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.
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.
sets screen-saver timeout time in minutes.
-su disables save under support on all screens.
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.
-logo turns on the X Window System logo display in the screen-saver.
There is currently no way to change this from a client.
nologo turns off the X Window System logo display in the screen-saver.
There is currently no way to change this from a client.
-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 /usr/X11R6/lib/X11/xkb.
[+-]kb enables(+) or disables(-) the XKEYBOARD extension.
[+-]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.
SECURITY EXTENSION OPTIONS
X servers that support the SECURITY extension accept the following
causes the server to attempt to read and interpret filename as
a security policy file with the format described below. The
file is read at server startup and reread at each server reset.
The syntax of the security policy file is as follows. Notation: "*"
means zero or more occurrences of the preceding element, and "+" means
one or more occurrences. To interpret <foo/bar>, ignore the text after
the /; it is used to distinguish between instances of <foo> in the next
<policy file> ::= <version line> <other line>*
<version line> ::= <string/v> '\n'
<other line > ::= <comment> | <access rule> | <site policy> | <blank line>
<comment> ::= # <not newline>* '\n'
<blank line> ::= <space> '\n'
<site policy> ::= sitepolicy <string/sp> '\n'
<access rule> ::= property <property/ar> <window> <perms> '\n'
<property> ::= <string>
<window> ::= any | root | <required property>
<required property> ::= <property/rp> | <property with value>
<property with value> ::= <property/rpv> = <string/rv>
<perms> ::= [ <operation> | <action> | <space> ]*
<operation> ::= r | w | d
<action> ::= a | i | e
<string> ::= <dbl quoted string> | <single quoted string> | <unquoted string>
<dbl quoted string> ::= <space> " <not dqoute>* " <space>
<single quoted string> ::= <space> ' <not squote>* ' <space>
<unquoted string> ::= <space> <not space>+ <space>
<space> ::= [ ' ' | '\t' ]*
<not newline> ::= any character except '\n'
<not dqoute> ::= any character except "
<not squote> ::= any character except '
<not space> ::= any character except those in <space>
The semantics associated with the above syntax are as follows.
<version line>, the first line in the file, specifies the file format
version. If the server does not recognize the version <string/v>, it
ignores the rest of the file. The version string for the file format
described here is "version-1" .
Once past the <version line>, lines that do not match the above syntax
<comment> lines are ignored.
<sitepolicy> lines are currently ignored. They are intended to specify
the site policies used by the XC-QUERY-SECURITY-1 authorization method.
<access rule> lines specify how the server should react to untrusted
client requests that affect the X Window property named <property/ar>.
The rest of this section describes the interpretation of an <access
For an <access rule> to apply to a given instance of <property/ar>,
<property/ar> must be on a window that is in the set of windows speci-
fied by <window>. If <window> is any, the rule applies to <prop-
erty/ar> on any window. If <window> is root, the rule applies to
<property/ar> only on root windows.
If <window> is <required property>, the following apply. If <required
property> is a <property/rp>, the rule applies when the window also has
that <property/rp>, regardless of its value. If <required property> is
a <property with value>, <property/rpv> must also have the value speci-
fied by <string/rv>. In this case, the property must have type STRING
and format 8, and should contain one or more null-terminated strings.
If any of the strings match <string/rv>, the rule applies.
The definition of string matching is simple case-sensitive string com-
parison with one elaboration: the occurrence of the character '*' in
<string/rv> is a wildcard meaning "any string." A <string/rv> can con-
tain multiple wildcards anywhere in the string. For example, "x*"
matches strings that begin with x, "*x" matches strings that end with
x, "*x*" matches strings containing x, and "x*y*" matches strings that
start with x and subsequently contain y.
There may be multiple <access rule> lines for a given <property/ar>.
The rules are tested in the order that they appear in the file. The
first rule that applies is used.
<perms> specify operations that untrusted clients may attempt, and the
actions that the server should take in response to those operations.
<operation> can be r (read), w (write), or d (delete). The following
table shows how X Protocol property requests map to these operations in
The Open Group server implementation.
GetProperty r, or r and d if delete = True
RotateProperties r and w
ListProperties none, untrusted clients can always list all properties
<action> can be a (allow), i (ignore), or e (error). Allow means exe-
cute the request as if it had been issued by a trusted client. Ignore
means treat the request as a no-op. In the case of GetProperty, ignore
means return an empty property value if the property exists, regardless
of its actual value. Error means do not execute the request and return
a BadAtom error with the atom set to the property name. Error is the
default action for all properties, including those not listed in the
security policy file.
An <action> applies to all <operation>s that follow it, until the next
<action> is encountered. Thus, irwad means ignore read and write,
GetProperty and RotateProperties may do multiple operations (r and d,
or r and w). If different actions apply to the operations, the most
severe action is applied to the whole request; there is no partial
request execution. The severity ordering is: allow < ignore < error.
Thus, if the <perms> for a property are ired (ignore read, error
delete), and an untrusted client attempts GetProperty on that property
with delete = True, an error is returned, but the property value is
not. Similarly, if any of the properties in a RotateProperties do not
allow both read and write, an error is returned without changing any
Here is an example security policy file.
# Allow reading of application resources, but not writing.
property RESOURCE_MANAGER root ar iw
property SCREEN_RESOURCES root ar iw
# Ignore attempts to use cut buffers. Giving errors causes apps to crash,
# and allowing access may give away too much information.
property CUT_BUFFER0 root irw
property CUT_BUFFER1 root irw
property CUT_BUFFER2 root irw
property CUT_BUFFER3 root irw
property CUT_BUFFER4 root irw
property CUT_BUFFER5 root irw
property CUT_BUFFER6 root irw
property CUT_BUFFER7 root irw
# If you are using Motif, you probably want these.
property _MOTIF_DEFAULT_BINDINGS rootar iw
property _MOTIF_DRAG_WINDOW root ar iw
property _MOTIF_DRAG_TARGETS any ar iw
property _MOTIF_DRAG_ATOMS any ar iw
property _MOTIF_DRAG_ATOM_PAIRS any ar iw
# The next two rules let xwininfo -tree work when untrusted.
property WM_NAME any ar
# Allow read of WM_CLASS, but only for windows with WM_NAME.
# This might be more restrictive than necessary, but demonstrates
# the <required property> facility, and is also an attempt to
# say "top level windows only."
property WM_CLASS WM_NAME ar
# These next three let xlsclients work untrusted. Think carefully
# before including these; giving away the client machine name and command
# may be exposing too much.
property WM_STATE WM_NAME ar
property WM_CLIENT_MACHINE WM_NAME ar
property WM_COMMAND WM_NAME ar
# To let untrusted clients use the standard colormaps created by
# xstdcmap, include these lines.
property RGB_DEFAULT_MAP root ar
property RGB_BEST_MAP root ar
property RGB_RED_MAP root ar
property RGB_GREEN_MAP root ar
property RGB_BLUE_MAP root ar
property RGB_GRAY_MAP root ar
# To let untrusted clients use the color management database created
# by xcmsdb, include these lines.
property XDCCC_LINEAR_RGB_CORRECTION rootar
property XDCCC_LINEAR_RGB_MATRICES rootar
property XDCCC_GRAY_SCREENWHITEPOINT rootar
property XDCCC_GRAY_CORRECTION rootar
# To let untrusted clients use the overlay visuals that many vendors
# support, include this line.
property SERVER_OVERLAY_VISUALS rootar
# Dumb examples to show other capabilities.
# oddball property names and explicit specification of error conditions
property "property with spaces" 'property with "'aw er ed
# Allow deletion of Woo-Hoo if window also has property OhBoy with value
# ending in "son". Reads and writes will cause an error.
property Woo-Hoo OhBoy = "*son"ad
The X server supports client connections via a platform-dependent sub-
set of the following transport types: TCPIP, Unix Domain sockets, DEC-
net, 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 protocols.
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 DECnet hostname in
double colon format (e.g. hydra::) 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 /usr/X11R6/lib/X11/fonts/misc/,
The font path can be set with the -fp option or by xset(1) after the
server has started.
/etc/Xn.hosts Initial access control list for display
Bitmap font directories
Outline font directories
/usr/X11R6/share/X11/rgb.txt Color database
/tmp/.X11-unix/Xn Unix domain socket for display number n
/tmp/rcXn Kerberos 5 replay cache for display num-
/usr/adm/Xnmsgs 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 Conventions
Security: Xsecurity(7), xauth(1), Xau(1), xdm(1), xhost(1), xfwp(1),
Security Extension Specification
Starting the server: xdm(1), xinit(1)
Controlling the server once started: xset(1), xsetroot(1), xhost(1)
Server-specific man pages: Xorg(1), Xdmx(1), Xnest(1), Xvfb(1), XDar-
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.
X Version 11 xorg-server 1.2.0 XSERVER(1)
Man(1) output converted with