XSERVER(1)

XSERVER(1) 💖 the display server glow-up

okay bestie, pull up a chair because we're talking about the X Window System display server — the actual main character of your graphical session. this is the General Commands Manual entry, and we're doing it in three parts, so buckle up 🎀

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✨ NAME ✨

Xserver — the X Window System display server. yes that's the whole name. iconic, brief, no notes 💅

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✨ SYNOPSIS ✨

X [option ...]

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✨ DESCRIPTION ✨

X is the generic name for the X Window System display server, bestie. it's frequently a link or a copy of the appropriate server binary for driving the most frequently used server on a given machine. so like, X is the vibe, and under the hood it's whatever binary actually matches your machine 🌸

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🌈 STARTING THE SERVER 🌈

so how does this whole thing wake up? usually the X server gets started from the X Display Manager program xdm(1) or some similar display manager program. that utility runs from the system boot files and handles the whole everything: keeping the server running, prompting for usernames and passwords, and starting up the user sessions. it's the responsible older sibling fr fr 🫶

installations that run more than one window system may need to use the xinit(1) utility instead of a display manager. but — and this is important — 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. like, don't hand a newbie xinit, that's not the move 😭

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. where applicable, the X server notifies systemd when it is ready to process requests 🦋

heads up!! 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. the server said "this screen is MINE now" and meant it 💀

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✨ 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. command line stays winning 👑

• :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. do not make this your everyday look, bestie 🙈

• -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. yeah, that's a yikes 🫣
• -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.
• +byteswappedclients — allow connections from clients with an endianess different to that of the server. this is the default unless -byteswappedclients is specified.
• -byteswappedclients — prohibit connections from clients with an endianess different to that of the server.
• -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.
• -extension extensionName — disables named extension. if an unknown extension name is specified, a list of accepted extension names is printed.
• +extension extensionName — 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).
• -fakescreenfps ps — sets fake presenter screen default fps (allowable range: 1-600).
• -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. like, the rest of the line just stops existing 💀
• -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 [delay] — causes the server to terminate at server reset, instead of continuing to run. this overrides a previous -noreset command line option. if a delay in seconds is specified, the server waits for at least the delay. at the end of this grace period if no client is connected, the server terminates immediately.
• -tst — disables all testing extensions (e.g., XTEST, XTrap, XTestExtension1, RECORD).
• ttyxx — ignored, for servers started the ancient way (from init). truly a relic, we respect the history tho 🏺
• v — sets video-off screen-saver preference.
• -v — sets video-on screen-saver preference.
• -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.

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okay that's the first chunk bestie — more parts coming, don't go anywhere 💜

✨ SERVER DEPENDENT OPTIONS ✨

Okay so some X servers vibe with these extra options, not all of them, it's giving "depends on your build" energy:

• -ld kilobytes — sets the data space limit of the server to that exact number of kilobytes. A value of 0 makes the data size as large as possible. And the default value of -1 leaves the data space limit totally unchanged (iconic, no notes).
• -lf files — sets the number-of-open-files limit of the server to that number of files. A value of 0 makes the limit as large as possible. Default -1 leaves the limit unchanged. periodt.
• -ls kilobytes — sets the stack space limit of the server to that number of kilobytes. A value of 0 makes the stack size as large as possible. Default -1 leaves the stack space limit unchanged. bestie it's the same trio, they're a set 💅
• -maxclients 64|128|256|512 — sets the maximum number of clients allowed to connect to the X server. The acceptable values are 64, 128, 256 or 512. That's it, those are the options, no custom numbers, the server said pick one 🎀
• -render default|mono|gray|color — sets the color allocation policy used by the render extension. The choices lowkey each have their own whole personality:
  • 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. Yeah it's literally called dumb, the naming committee ate with that one 💀
• -schedInterval interval — sets the smart scheduler's scheduling interval to interval milliseconds.

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🌈 XDMCP OPTIONS 🌈

X servers that support XDMCP get these options. Need the full lore? Go read the X Display Manager Control Protocol specification. It's giving ✨required reading✨.

• -query hostname — enables XDMCP and sends Query packets to the specified hostname.
• -broadcast — enable XDMCP and broadcast BroadcastQuery packets to the network. The first responding display manager gets chosen for the session. first come first served, no cap 🫶
• -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's 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. local only, keeping it cozy 🧚
• -indirect hostname — enables XDMCP and sends 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. Order matters bestie, don't skip this one.
• -from local-address — specifies the local address to connect from (super 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. one and done, no reruns 🌸
• -class display-class — XDMCP has an additional display qualifier used in resource lookup for display-specific options. This option sets that value, and by default it's "MIT-unspecified" (which, and I quote, is 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. Note: it is not that private, being right there on the command line! 🙈
• -displayID display-id — Yet another XDMCP specific value, this one lets the display manager identify each display so it can locate the shared key.

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⌨️ XKEYBOARD OPTIONS ⌨️

X servers that support the XKEYBOARD (a.k.a. "XKB") extension accept the following options. Real talk: all layout files specified on the command line must be located in the XKB base directory or a subdirectory of it, 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. Heads up: this option is not available for setuid X servers (i.e., when the X server's real and effective uids are different). security said no 💅
• -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 the keyboard description in filename on server startup.

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🦋 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. Wanna know how to specify which transport type clients should try to use? Pop over to the DISPLAY NAMES section of the X(7) manual page. it's all there 🫶

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🔐 GRANTING ACCESS 🔐

The X server implements a platform-dependent subset of the following authorization protocols: MIT-MAGIC-COOKIE-1, XDM-AUTHORIZATION-1, SUN-DES-1, Host Access, and Server Interpreted. Want the full breakdown on how these protocols operate? See the Xsecurity(7) manual page.

Authorization data required by the above protocols is passed to the server in a private file named with the -auth command line option. Every single time the server is about to accept the first connection after a reset (or when the server is starting), it reads this file. Here's the tea: 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. 📜 For the binary format of this file, see the Xau manual page. For maintenance of this file and distribution of its contents to remote hosts, see xauth(1).

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. Important: 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.

Now for the part that's giving unhinged in the worst way: 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. For a complete list of these restrictions, see the SECURITY extension specification.

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. build your own ✨

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🚨 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's 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. it's giving "reset the whole vibe" 💅
• SIGTERM — This signal causes the server to exit cleanly. graceful exit, we love her 🎀
• 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. sneaky little handshake 🤝

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🎀 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 `catalogue:/etc/X11/fontpath.d,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. 👑 curated, indirect, just like our playlist

The font path can be set with the -fp option or by xset(1) after the server has started.

🎀 FONTPATH.D 🎀

okay bestie this one's a whole vibe, stay with me 💖

So there's a special flavor of font path you can write, and it looks like catalogue:<dir>.

The directory you drop after the catalogue: prefix? It gets scanned for symlinks, and every single symlink destination gets added as a local fontfile FPE. That's it, that's the whole trick. ✨

You can also suffix the symlink with attributes like 'unscaled', and those get passed straight through to the underlying fontfile FPE. The one exception is the newly introduced 'pri' attribute — that one isn't passed through, it's used for ordering the font paths that the symlinks specify. Periodt.

Here's an example config, because reading about it is giving nothing and seeing it is giving everything:

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

So what does that actually do, bestie? It adds /usr/share/X11/fonts/misc as the first FPE with the attribute 'unscaled', then the second FPE is /usr/share/X11/fonts/75dpi, also with the attribute 'unscaled', etc. Look at the pri numbers — 10, 20, 40, 50, 60. That's the ordering, no cap.

And this is functionally equivalent to just setting this font path by hand:

/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

Same thing, different outfit. 💅

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📁 FILES 📁

Everything the server touches on disk, in one glorious little list 🫶

• /etc/Xn.hosts — the initial access control list for display number n. Your first guest list, basically.
• /usr/share/fonts/X11/misc, /usr/share/fonts/X11/75dpi, /usr/share/fonts/X11/100dpi — bitmap font directories ✨
• /usr/share/fonts/X11/TTF, /usr/share/fonts/X11/Type1 — outline font directories 🦋
• /tmp/.X11-unix/Xn — the Unix domain socket for display number n
• /usr/adm/Xnmsgs — error log file for display number n, but only if you run it from init(8)
• /usr/lib/X11/xdm/xdm-errors — the default error log file if the server is run from xdm(1)

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👀 SEE ALSO 👀

The whole friend group, grouped by their whole deal 💜

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

Keyboards: xkeyboard-config(7)

Security: Xsecurity(7), xauth(1), Xau(1), xdm(1), xhost(1) Security Extension Specification

Starting the server: startx(1), xdm(1), xinit(1)

Controlling the server once started: xset(1), xsetroot(1), xhost(1), xinput(1), xrandr(1)

Server-specific man pages: Xorg(1), Xwayland(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

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💖 AUTHORS 💖

the literal icons who built this 👑

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. (a large cast!! ensemble energy fr fr)

It has since been extensively rewritten by Keith Packard and Bob Scheifler, from MIT. 🎀

And Dave Wiggins took over post-R5 and made substantial improvements. 💅

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and that's the whole page bestie!! 💀

Okay so this was XSERVER(1) — part of X Version 11, specifically xorg-server 21.1.25. You made it to the end, which honestly? Main character energy. 🌈✨

Go forth and run your X server. I'm obsessed. 🫶🎀🦋