Xserver - Online in the Cloud

PROGRAM:

NAME

Xserver - X Window System display server

SYNOPSIS

X [option ...]

DESCRIPTION

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 driving 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 sessions.

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 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) 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.

OPTIONS

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.

:displaynumber
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).

-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.

-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.

-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.

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 servers.

-core 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.

dpms enables DPMS (display power management services), where supported. The default
state is platform and configuration specific.

-dpms disables DPMS (display power management services). The default state is platform
and configuration specific.

-extensionextensionName
disables named extension. If an unknown extension name is specified, a list of
accepted extension names is printed.

+extensionextensionName
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.

-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 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 specified.

+iglx Allow creating indirect GLX contexts.

-maxbigreqsize size
sets the maximum big request to size MB.

-nocursor
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.

-noreset
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.

-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 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.

-su 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).

-terminate
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.

-tst disables all testing extensions (e.g., XTEST, XTrap, XTestExtension1, RECORD).

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 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.

-wr 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 most implementations.

[+-]xinerama
enables(+) or disables(-) the XINERAMA extension. The default state is platform
and configuration specific.

SERVER DEPENDENT OPTIONS

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.

-maxclients
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.

-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 extension.

color use a color cube of at most 4*4*4 colors (that is 64 color cells).

-dumbSched
disables smart scheduling on platforms that support the smart scheduler.

-schedInterval interval
sets the smart scheduler's scheduling interval to interval milliseconds.

XDMCP OPTIONS

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 hostname.

-broadcast
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 local network.

-indirect hostname
enables XDMCP and send IndirectQuery packets to the specified hostname.

-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 gethostbyname(3) implementation.

-once 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 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.

XKEYBOARD OPTIONS

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 /usr/lib/X11/xkb.

[+-]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 keystrokes).

-xkbmap filename
loads keyboard description in filename on server startup.

NETWORK CONNECTIONS

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(7) manual page to learn how to
specify which transport type clients should try to use.

GRANTING ACCESS

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 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 /etc/Xn.hosts, 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 family:name as described in the
xhost(1) manual page. There should be no leading or trailing spaces on any lines. For
example:

joesworkstation
corporate.company.com
inet:bigcpu
local:

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 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 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(1) 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 security models.

SIGNALS

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 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.

FONTS

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/share/fonts/X11/misc,/usr/share/fonts/X11/cyrillic,/usr/share/fonts/X11/100dpi/:unscaled,/usr/share/fonts/X11/75dpi/:unscaled,/usr/share/fonts/X11/Type1,/usr/share/fonts/X11/100dpi,/usr/share/fonts/X11/75dpi,built-
ins .

A special kind of directory can be specified using the catalogue: prefix. 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.

FONTPATH.D

You can specify a special kind of font path in the form catalogue:<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 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:

/usr/share/X11/fonts/misc:unscaled,
/usr/share/X11/fonts/75dpi:unscaled,
/usr/share/X11/fonts/Type1,
/usr/share/fonts/default/Type1,
/usr/share/fonts/default/ghostscript

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