NAME [Toc] [Back]
X - X Window System server
SYNOPSIS [Toc] [Back]
X :displaynumber [-option] ttyname
DESCRIPTION [Toc] [Back]
X is the generic name for the window system server. It is started by
the dtlogin program which is typically run by init(1M). Alternatively
it may be started from the xinit(1) program, which is called by
x11start. The displaynumber argument is used by clients in their
DISPLAY environment variables to indicate which server to contact
(machines may have several displays attached). This number can be any
number. If no number is specified 0 is used. This number is also
used in determining the names of various startup files. The ttyname
argument is passed in by init and isn't used.
The Hewlett-Packard server has support for the following protocols:
The server listens on port 6000+N, where N is the display
Local Socket IPC Mechanism [Toc] [Back]
The file name for the socket is "/var/spool/sockets/X11/*"
where "*" is the display number.
Shared Memory IPC [Toc] [Back]
If the Shared Memory Transport (SMT) option is enabled in the
Xserver, this will be the default connection that the X
Library will use to connect to an X server on the same machine
if the DISPLAY environment variable is set to "local:*" or
":*" where "*" is the number of the display. Currently, SMT
is not enabled by default. Please see /etc/X11/X0screens
and/or /usr/lib/X11/Xserver/info/screens/hp for more
information about SMT.
When the server starts up, it takes over the display. If you are
running on a workstation whose console is the display, you cannot log
into the console while the server is running.
OPTIONS [Toc] [Back]
The following options can be given on the command line to the X
sets pointer acceleration (i.e. the ratio of how much is
reported to how much the user actually moved the pointer).
Sets the audit trail level. The default level is 1, meaning
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only connection rejections are reported. Level 2 additionally
reports all successful connections and disconnects. Level 4
enables messages from the SECURITY extension, 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.
bc disables certain kinds of error checking, for bug
compatibility with previous releases (e.g., to work around
bugs in R2 and R3 xterms and toolkits). Deprecated.
-bs disables backing store support on all screens.
-c turns off key-click.
sets key-click volume (allowable range: 0-100).
sets name of RGB color database.
-core causes the server to generate a core dump on fatal errors.
sets the resolution of the screen, in dots per inch. To be
used when the server cannot determine the screen size from the
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 server searches for
-help prints a usage message.
-I causes all remaining command line arguments to be ignored.
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-logo turns on the X Window System logo display in the screen-saver.
There is currently no way to change this from a client. You
also need to specify -v to enable the logo to appear.
nologo turns off the X Window System logo display in the screensaver.
There is currently no way to change this from a
sets screen-saver pattern cycle time in minutes.
-pn allows X server to run even if one or more communications
mechanisms fails to initialize.
-pn permits the server to continue running if it fails to
establish all of its well-known sockets, but establishes at
-r turns off keyboard auto-repeat.
r turns on keyboard auto-repeat.
sets screen-saver timeout time in minutes.
causes the server to attempt to read and interpret filename as
a security policy file with the format described in the
SECURITY FILE FORMAT section below. The file is read at server
startup and reread at each server reset. The default file is
-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
continuing to run.
sets default connection timeout in seconds.
-tst disables all testing extensions (e.g., XTEST,
ttyxx ignored, for servers started the ancient way (from init).
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causes server to terminate when all clients disconnect.
v sets video-on screen-saver preference. A window that changes
regularly will be used to save the screen.
-v sets video-off screen-saver preference. The screen will be
blanked to save the screen.
-wm forces the default backing-store of all windows to be
WhenMapped; a less expensive way of getting backing-store to
apply to all windows.
You can also have the X server connect to xdm(1) or dtlogin(1X) using
XDMCP. Although this is not typically useful as it doesn't allow
xdm to manage the server process, it can be used to debug XDMCP
implementations, and serves as a sample implementation of the
server side of XDMCP. The following options control the behavior
Enable XDMCP and send Query packets to the specified host.
Enable XDMCP and broadcast BroadcastQuery packets to the
network. The first responding display manager will be chosen
for the session.
Enable XDMCP and send IndirectQuery packets to the specified
Use an alternate port number for XDMCP packets. Must be
specified before any -query, -broadcast or -indirect options.
Default port number is 177.
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's very private, being
on the command line and all...).
Yet another XDMCP specific value, this one allows the display
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manager to identify each display so that it can locate the
XVFB OPTIONS [Toc] [Back]
The X server can be configured to run in virtual frame buffer (Xvfb)
mode (see the X server information file
/usr/lib/X11/Xserver/info/screens/hp). Xvfb mode emulates a dumb
framebuffer using virtual memory so it can be run on machines with no
display hardware and no physical input devices.
The primary use of this mode was intended to be server testing. The
mfb or cfb code for any depth can be exercised with this server
without the need for real hardware that supports the desired depths.
The X community has found many other novel uses for Xvfb mode,
including testing clients against unusual depths and screen
configurations, doing batch processing with Xvfb as a background
rendering engine, load testing, as an aid to porting the X server to a
new platform, and providing an unobtrusive way to run applications
that don't really need an X server but insist on having one anyway.
When run in Xvfb mode, the X server supports the following additional
-screen screennum WxHxD
This option creates screen screennum and sets its width, height,
and depth to W, H, and D respectively. By default, only screen 0
exists and has the dimensions 1280x1024x8.
This option specifies a list of pixmap depths that the server
should support in addition to the depths implied by the supported
screens. list-of-depths is a space-separated list of integers
that can have values from 1 to 32.
This option specifies the directory in which the memory mapped
files containing the framebuffer memory should be created. See
FILES. This option only exists on machines that have the mmap and
msync system calls.
This option specifies that the framebuffer should be put in shared
memory. The shared memory ID for each screen will be printed by
the server. The shared memory is in xwd format. This option only
exists on machines that support the System V shared memory
If neither -shmem nor -fbdir is specified, the framebuffer memory will
be allocated with malloc().
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This option specifies how to adjust the pixelization of thin
lines. The value n is a bitmask of octants in which to prefer an
axial step when the Bresenham error term is exactly zero. See the
file Xserver/mi/miline.h for more information. This option is
probably only useful to server developers to experiment with the
range of line pixelization possible with the cfb and mfb code.
-blackpixel pixel-value, -whitepixel pixel-value
These options specify the black and white pixel values the server
SECURITY FILE FORMAT [Toc] [Back]
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 section.
<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> | <unqouted string>
<dbl quoted string> ::= <space> " <not dqoute>* " <space>
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<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
<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
specified by <window>. If <window> is any, the rule applies to
<property/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 specified by <string/rv>. In this case, the property must
have type STRING and format 8, and should contain one or more nullterminated
strings. If any of the strings match <string/rv>, the rule
The definition of string matching is simple case-sensitive string
comparison with one elaboration: the occurence of the character '*' in
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<string/rv> is a wildcard meaning "any string." A <string/rv> can
contain 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
execute 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.
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# 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 may want these.
property _MOTIF_DEFAULT_BINDINGS root ar 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 root ar
property XDCCC_LINEAR_RGB_MATRICES root ar
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property XDCCC_GRAY_SCREENWHITEPOINT root ar
property XDCCC_GRAY_CORRECTION root ar
# To let untrusted clients use the overlay visuals that many vendors
# support, include this line.
property SERVER_OVERLAY_VISUALS root ar
# 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
RUNNING FROM INIT [Toc] [Back]
Though X will usually be run by dtlogin from init, it is possible to
run X directly from init. For information about running X from
dtlogin, see the dtlogin man page.
To run X directly from init, it is necessary to modify /etc/inittab
and /etc/gettydefs. Detailed information on these files may be
obtained from the inittab(4) and gettydefs(4) man pages.
To run X from init on display 0, with a login xterm running on
/dev/ttypf, in init state 3, the following line must be added to
X0:3:respawn:env PATH=/bin:/usr/bin/X11:/usr/bin xinit -L ttyqf
To run X with a login hpterm, the following should be used instead:
X0:3:respawn:env PATH=/bin:/usr/bin/X11:/usr/bin xinit hpterm
=+1+1 -n login -L ttyqf -- :0
In addition, the following line must be added to /etc/gettydefs (this
should be a single line):
Xwindow# B9600 HUPCL PARENB CS7 # B9600 SANE PARENB CS7 ISTRIP
IXANY TAB3 #X login: #Xwindow
There should not be a getty running against the display whenever X is
run from xinit.
GRANTING ACCESS [Toc] [Back]
The sample server implements a simplistic authorization protocol,
MIT-MAGIC-COOKIE-1 which uses data private to authorized clients and
the server. This is a rather trivial scheme; if the client passes
authorization data which is the same as the server has, it is allowed
access. This scheme is inferior to host-based access control
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mechanisms in environments with unsecure networks as it allows any
host to connect, given that it has discovered the private key. But in
many environments, this level of security is better than the hostbased
scheme as it allows access control per-user instead of per-host.
In addition, the server provides support for a DES-based authorization
scheme, XDM-AUTHORIZATION-1, which is more secure (given a secure key
distribution mechanism), but as DES is not generally distributable,
the implementation is missing routines to encrypt and decrypt the
authorization data. This authorization scheme can be used in
conjunction with XDMCP's authentication scheme, XDM-AUTHENTICATION-1
or in isolation.
The authorization data 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. Maintenance of this
file, and distribution of its contents to remote sites for use there
is left as an exercise for the reader.
The sample server also uses a host-based access control list for
deciding whether or not to accept connections from clients on a
particular machine. 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 an Internet hostname (e.g.
expo.lcs.mit.edu.) 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. For example:
% xhost +janesworkstation
janesworkstation being added to access control list
% xhost +
all hosts being allowed (access control disabled)
% xhost -
all hosts being restricted (access control enabled)
access control enabled (only the following hosts are allowed)
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SIGNALS [Toc] [Back]
The X server attaches special meaning to the following signals:
SIGHUP This signal causes the server to close all existing
connections, free all resources, and restore all defaults. It
is sent by the display manager (xdm or dtlogin) whenever the
main user's main application 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
FONTS [Toc] [Back]
Fonts are usually stored as individual files in directories. The list
of directories in which the server looks when trying to open a font is
controlled by the font path. Although most sites will choose to have
the server start up with the appropriate font path (using the -fp
option mentioned above), it can be overridden using the xset program.
Font databases are created by running the mkfontdir or stmkdirs
program in the directory containing the compiled versions of the fonts
(mkfontdir) or font outlines (stmkdirs.) Whenever fonts are added to a
directory, mkfontdir or stmkdirs should be rerun so that the server
can find the new fonts. If mkfontdir or stmkdirs is not run, the
server will not be able to find any of the new fonts in the directory.
In addition, the X server supports font servers. A font server is a
networked program that supplies fonts to X servers and other capable
programs. In order to communicate with a font server, the font
servers address must be supplied as part of the X server's font path.
A font server's address is specified as
where transport is always tcp, hostname is the hostname of the machine
being connected to (no hostname means a local connection) and port-
number is the tcp address that the font server is listening at
DIAGNOSTICS [Toc] [Back]
Too numerous to list them all. If run from DE, errors are logged in
the file /var/dt/Xerrors,
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FILES [Toc] [Back]
/etc/inittab Script for the init process
/etc/gettydefs Speed and terminal settings used by
/etc/X*.hosts Initial access control list
/usr/lib/X11/fonts Top level font directory
/usr/lib/X11/rgb.txt Color database
/usr/lib/X11/rgb.pag Color database
/usr/lib/X11/rgb.dir Color database
/usr/spool/sockets/X11/* IPC mechanism socket
/var/dt/Xerrors Error log file
/etc/X11/X*devices Input devices used by the server. This
file contains many example
/etc/X11/X*screens Screens used by the server. This file
contains many example configurations.
/etc/X11/X*pointerkeys Keyboard pointer device file. This file
contains many example configurations.
/etc/X11/XHPkeymaps Key device database used by the X
/etc/X11/SecurityPolicy Default Security Policy file used by the
These files are created if the -fbdir
option is given. They are the memory
mapped file containing screen n's
framebuffer memory, one file per screen.
Each file is in xwd format. Thus,
taking a full-screen snapshot can be
done with a file copy command, and the
resulting snapshot will even contain the
NOTES [Toc] [Back]
The option syntax is inconsistent between itself and xset(1).
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The acceleration option should take a numerator and a denominator like
The color database is missing a large number of colors. However,
there doesn't seem to be a better one available that can generate RGB
COPYRIGHT [Toc] [Back]
Copyright 1996, 1998 The Open Group Copyright 1984, 1985, 1986, 1987,
1988, 1989, 1990, 1991, 1992 Massachusetts Institute of Technology.
Copyright 1992 Hewlett Packard Company.
See X(1) for a full statement of rights and permissions.
ORIGIN [Toc] [Back]
SEE ALSO [Toc] [Back]
Xserver(1), Xf86(1), dtlogin(1), bdftopcf(1), fs(1), getty(1M),
gettydefs(4), gwindstop(1), hpterm(1), init(1M), inittab(4),
mkfontdir(1), rgb(1), stmkdirs(1), x11start(1), xauth(1) xclock(1),
xfd(1), xhost(1), xinit(1), xinitcolormap(1), xload(1), xmodmap(1),
xrefresh(1), xseethru(1), xset(1), xsetroot(1), xterm(1), xwcreate(1),
xwd(1), xwdestroy(1), xwininfo(1), xwud(1)
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