The X Window System is a network transparent window system which runs on a wide range of computing and graphics machines. It should be relatively straightforward to build the X Consortium software distribution on most ANSI C and POSIX compliant systems. Commercial implementations are also available for a wide range of platforms.
The X Consortium requests that the following names be used when referring to this software:
X Window System is a trademark of X Consortium, Inc.
X supports overlapping hierarchical subwindows and text and graphics operations, on both monochrome and color displays. For a full explanation of the functions that are available, see the Xlib - C Language X Interface manual, the X Window System Protocol specification, the X Toolkit Intrinsics - C Language Interface manual, and various toolkit documents.
The number of programs that use X is quite large. Programs provided in the core X Consortium distribution include: a terminal emulator, xterm; a window manager, twm; a display manager, xdm; a console redirect program, xconsole; a mail interface, xmh; a bitmap editor, bitmap; resource listing/manipulation tools, appres, editres; access control programs, xauth, xhost, and iceauth; user preference setting programs, xrdb, xcmsdb, xset, xsetroot, xstdcmap, and xmodmap; clocks, xclock and oclock; a font displayer, (xfd; utilities for listing information about fonts, windows, and displays, xlsfonts, xwininfo, xlsclients, xdpyinfo, xlsatoms, and xprop; screen image manipulation utilities, xwd, xwud, and xmag; a performance measurement utility, x11perf; a font compiler, bdftopcf; a font server and related utilities, xfs, fsinfo, fslsfonts, fstobdf; an X Image Extension exerciser, xieperf; a display server and related utilities, Xserver, rgb, mkfontdir; remote execution utilities, rstart and xon; a clipboard manager, xclipboard; keyboard description compiler and related utilities, xkbcomp, xkbprint, xkbbell, xkbevd, xkbvleds, and xkbwatch; a utility to terminate clients, xkill; an optimized X protocol proxy, lbxproxy; a firewall security proxy, xfwp; a proxy manager to control them, proxymngr; a utility to find proxies, xfindproxy; Netscape Navigator Plug-ins, libxrx.so and libxrxnest.so; an RX MIME-type helper program, xrx; and a utility to cause part or all of the screen to be redrawn, xrefresh.
Many other utilities, window managers, games, toolkits, etc. are included as user-contributed software in the X Consortium distribution, or are available using anonymous ftp on the Internet. See your site administrator for details.
There are two main ways of getting the X server and an initial set of client applications started. The particular method used depends on what operating system you are running and whether or not you use other window systems in addition to X.
From the user's perspective, every X server has a display name of the form:
This information is used by the application to determine how it should connect to the server and which screen it should use by default (on displays with multiple monitors):
On POSIX systems, the default display name is stored in your DISPLAY environment variable. This variable is set automatically by the xterm terminal emulator. However, when you log into another machine on a network, you will need to set DISPLAY by hand to point to your display. For example,
% setenv DISPLAY myws:0
$ DISPLAY=myws:0; export DISPLAY
The xon script can be used to start an X program on a remote machine; it
automatically sets the DISPLAY variable correctly. Finally, most X programs accept a command line option of -display displayname to temporarily override the contents of DISPLAY. This is most commonly used to pop windows on another person's screen or as part of a "remote shell" command to start an xterm pointing back to your display. For example,
% xeyes -display joesws:0 -geometry 1000x1000+0+0
% rsh big xterm -display myws:0 -ls </dev/null &
X servers listen for connections on a variety of different communications channels (network byte streams, shared memory, etc.). Since there can be more than one way of contacting a given server, The hostname part of the display name is used to determine the type of channel (also called a transport layer) to be used. X servers generally support the following types of connections:
Host Access Simple host-based access control.
MIT-MAGIC-COOKIE-1 Shared plain-text "cookies".
XDM-AUTHORIZATION-1 Secure DES based private-keys.
SUN-DES-1 Based on Sun's secure rpc system.
MIT-KERBEROS-5 Kerberos Version 5 user-to-user.
Xdm initializes access control for the server and also places authorization information in a file accessible to the user. Normally, the list of hosts from which connections are always accepted should be empty, so that only clients with are explicitly authorized can connect to the display. When you add entries to the host list (with xhost), the server no longer performs any authorization on connections from those machines. Be careful with this.
The file from which Xlib extracts authorization data can be specified with the environment variable XAUTHORITY, and defaults to the file .Xauthority in the home directory. Xdm uses $HOME/.Xauthority and will create it or merge in authorization records if it already exists when a user logs in.
If you use several machines and share a common home directory across all of the machines by means of a network file system, you never really have to worry about authorization files, the system should work correctly by default. Otherwise, as the authorization files are machine-independent, you can simply copy the files to share them. To manage authorization files, use xauth. This program allows you to extract records and insert them into other files. Using this, you can send authorization to remote machines when you login, if the remote machine does not share a common home directory with your local machine. Note that authorization information transmitted ``in the clear'' through a network file system or using ftp or rcp can be ``stolen'' by a network eavesdropper, and as such may enable unauthorized access. In many environments, this level of security is not a concern, but if it is, you need to know the exact semantics of the particular authorization data to know if this is actually a problem.
For more information on access control, see the Xsecurity manual page.
The WIDTH and HEIGHT parts of the geometry specification are usually measured in either pixels or characters, depending on the application. The XOFF and YOFF parts are measured in pixels and are used to specify the distance of the window from the left or right and top and bottom edges of the screen, respectively. Both types of offsets are measured from the indicated edge of the screen to the corresponding edge of the window. The X offset may be specified in the following ways:
The Y offset has similar meanings:
Offsets must be given as pairs; in other words, in order to specify either XOFF or YOFF both must be present. Windows can be placed in the four corners of the screen using the following specifications:
In the following examples, a terminal emulator is placed in roughly the center of the screen and a load average monitor, mailbox, and clock are placed in the upper right hand corner:
xterm -fn 6x10 -geometry 80x24+30+200 &
xclock -geometry 48x48-0+0 &
xload -geometry 48x48-96+0 &
xbiff -geometry 48x48-48+0 &
Since window managers are regular (albeit complex) client programs, a variety of different user interfaces can be built. The X Consortium distribution comes with a window manager named twm which supports overlapping windows, popup menus, point-and-click or click-to-type input models, title bars, nice icons (and an icon manager for those who don't like separate icon windows).
See the user-contributed software in the X Consortium distribution for other popular window managers.
Fonts come in various sizes. The X server supports scalable fonts, meaning it is possible to create a font of arbitrary size from a single source for the font. The server supports scaling from outline fonts and bitmap fonts. Scaling from outline fonts usually produces significantly better results than scaling from bitmap fonts.
An X server can obtain fonts from individual files stored in directories in the file system, or from one or more font servers, or from a mixtures of directories and font servers. The list of places the server looks when trying to find a font is controlled by its font path. Although most installations will choose to have the server start up with all of the commonly used font directories in the font path, the font path can be changed at any time with the xset program. However, it is important to remember that the directory names are on the server's machine, not on the application's.
Bitmap font files are usually created by compiling a textual font description into binary form, using bdftopcf. Font databases are created by running the mkfontdir program in the directory containing the source or compiled versions of the fonts. Whenever fonts are added to a directory, mkfontdir should be rerun so that the server can find the new fonts. To make the server reread the font database, reset the font path with the xset program. For example, to add a font to a private directory, the following commands could be used:
% cp newfont.pcf ~/myfonts
% mkfontdir ~/myfonts
% xset fp rehash
The xfontsel and xlsfonts programs can be used to browse through the fonts available on a server. Font names tend to be fairly long as they contain all of the information needed to uniquely identify individual fonts. However, the X server supports wildcarding of font names, so the full specification
-adobe-courier-medium-r-normal--10-100-75-75-m-60-iso8859-1
might be abbreviated as:
-*-courier-medium-r-normal--*-100-*-*-*-*-iso8859-1
Because the shell also has special meanings for * and ?, wildcarded font names should be quoted:
% xlsfonts -fn '-*-courier-medium-r-normal--*-100-*-*-*-*-*-*'
The xlsfonts program can be used to list all of the fonts that match a given pattern. With no arguments, it lists all available fonts. This will usually list the same font at many different sizes. To see just the base scalable font names, try using one of the following patterns:
-*-*-*-*-*-*-0-0-0-0-*-0-*-*
-*-*-*-*-*-*-0-0-75-75-*-0-*-*
-*-*-*-*-*-*-0-0-100-100-*-0-*-*
To convert one of the resulting names into a font at a specific size, replace one of the first two zeros with a nonzero value. The field containing the first zero is for the pixel size; replace it with a specific height in pixels to name a font at that size. Alternatively, the field containing the second zero is for the point size; replace it with a specific size in decipoints (there are 722.7 decipoints to the inch) to name a font at that size. The last zero is an average width field, measured in tenths of pixels; some servers will anamorphically scale if this value is specified.
tcp/hostname:port
tcp/hostname:port/cataloguelist
The hostname specifies the name (or decimal numeric address) of the machine on which the font server is running. The port is the decimal TCP port on which the font server is listening for connections. The cataloguelist specifies a list of catalogue names, with '+' as a separator.
Examples: tcp/x.org:7100, tcp/198.112.45.11:7100/all.
One of the following forms can be used to name a font server that accepts DECnet connections:
decnet/nodename::font$objname
decnet/nodename::font$objname/cataloguelist
The nodename specifies the name (or decimal numeric address) of the machine on which the font server is running. The objname is a normal, case-insensitive DECnet object name. The cataloguelist specifies a list of catalogue names, with '+' as a separator.
Examples: DECnet/SRVNOD::FONT$DEFAULT, decnet/44.70::font$special/symbols.
X supports the use of abstract color names, for example, "red", "blue". A value for this abstract name is obtained by searching one or more color name databases. Xlib first searches zero or more client-side databases; the number, location, and content of these databases is implementation dependent. If the name is not found, the color is looked up in the X server's database. The text form of this database is commonly stored in the file <XRoot>/lib/X11/rgb.txt, where <XRoot> is replaced by the root of the X11 install tree.
A numerical color specification consists of a color space name and a set of values in the following syntax:
<color_space_name>:<value>/.../<value>
An RGB Device specification is identified by the prefix "rgb:" and has the following syntax:
rgb:<red>/<green>/<blue>
<red>, <green>, <blue> := h | hh | hhh | hhhh
h := single hexadecimal digits
Note that h indicates the value scaled in 4 bits, hh the value scaled
in 8 bits, hhh the value scaled in 12 bits, and hhhh the value scaled in
16 bits, respectively. These values are passed directly to the X server,
and are assumed to be gamma corrected. The eight primary colors can be represented as:
black rgb:0/0/0
red rgb:ffff/0/0
green rgb:0/ffff/0
blue rgb:0/0/ffff
yellow rgb:ffff/ffff/0
magenta rgb:ffff/0/ffff
cyan rgb:0/ffff/ffff
white rgb:ffff/ffff/ffff
For backward compatibility, an older syntax for RGB Device is supported, but its continued use is not encouraged. The syntax is an initial sharp sign character followed by a numeric specification, in one of the following formats:
#RGB (4 bits each)
#RRGGBB (8 bits each)
#RRRGGGBBB (12 bits each)
#RRRRGGGGBBBB (16 bits each)
The R, G, and B represent single hexadecimal digits. When fewer than 16 bits each are specified, they represent the most-significant bits of the value (unlike the "rgb:" syntax, in which values are scaled). For example, #3a7 is the same as #3000a0007000.
An RGB intensity specification is identified by the prefix "rgbi:" and has the following syntax:
rgbi:<red>/<green>/<blue>
The red, green, and blue are floating point values between 0.0 and 1.0, inclusive. They represent linear intensity values, with 1.0 indicating full intensity, 0.5 half intensity, and so on. These values will be gamma corrected by Xlib before being sent to the X server. The input format for these values is an optional sign, a string of numbers possibly containing a decimal point, and an optional exponent field containing an E or e followed by a possibly signed integer string.
The standard device-independent string specifications have the following syntax:
CIEXYZ:<X>/<Y>/<Z> (none, 1, none)
CIEuvY:<u>/<v>/<Y> (~.6, ~.6, 1)
CIExyY:<x>/<y>/<Y> (~.75, ~.85, 1)
CIELab:<L>/<a>/<b> (100, none, none)
CIELuv:<L>/<u>/<v> (100, none, none)
TekHVC:<H>/<V>/<C> (360, 100, 100)
All of the values (C, H, V, X, Y, Z, a, b, u, v, y, x) are floating point values. Some of the values are constrained to be between zero and some upper bound; the upper bounds are given in parentheses above. The syntax for these values is an optional '+' or '-' sign, a string of digits possibly containing a decimal point, and an optional exponent field consisting of an 'E' or 'e' followed by an optional '+' or '-' followed by a string of digits.
For more information on device independent color, see the Xlib reference manual.
The X keyboard model is broken into two layers: server-specific codes (called keycodes) which represent the physical keys, and server-independent symbols (called keysyms) which represent the letters or words that appear on the keys. Two tables are kept in the server for converting keycodes to keysyms:
The first four elements of the list are split into two groups of keysyms. Group 1 contains the first and second keysyms; Group 2 contains the third and fourth keysyms. Within each group, if the first element is alphabetic and the the second element is the special keysym NoSymbol, then the group is treated as equivalent to a group in which the first element is the lowercase letter and the second element is the uppercase letter.
Switching between groups is controlled by the keysym named MODE SWITCH, by attaching that keysym to some key and attaching that key to any one of the modifiers Mod1 through Mod5. This modifier is called the ``group modifier.'' Group 1 is used when the group modifier is off, and Group 2 is used when the group modifier is on.
Within a group, the modifier state determines which keysym to use. The first keysym is used when the Shift and Lock modifiers are off. The second keysym is used when the Shift modifier is on, when the Lock modifier is on and the second keysym is uppercase alphabetic, or when the Lock modifier is on and is interpreted as ShiftLock. Otherwise, when the Lock modifier is on and is interpreted as CapsLock, the state of the Shift modifier is applied first to select a keysym; but if that keysym is lowercase alphabetic, then the corresponding uppercase keysym is used instead.
The precise syntax for resources is:
ResourceLine = Comment | IncludeFile | ResourceSpec | <empty line>
Comment = "!" {<any character except null or newline>}
IncludeFile = "#" WhiteSpace "include" WhiteSpace FileName WhiteSpace
FileName = <valid filename for operating system>
ResourceSpec = WhiteSpace ResourceName WhiteSpace ":" WhiteSpace Value
ResourceName = [Binding] {Component Binding} ComponentName
Binding = "." | "*"
WhiteSpace = {<space> | <horizontal tab>}
Component = "?" | ComponentName
ComponentName = NameChar {NameChar}
NameChar = "a"-"z" | "A"-"Z" | "0"-"9" | "_" | "-"
Value = {<any character except null or unescaped newline>}
Elements separated by vertical bar (|) are alternatives. Curly braces ({...}) indicate zero or more repetitions of the enclosed elements. Square brackets ([...]) indicate that the enclosed element is optional. Quotes ("...") are used around literal characters.
IncludeFile lines are interpreted by replacing the line with the contents of the specified file. The word "include" must be in lowercase. The filename is interpreted relative to the directory of the file in which the line occurs (for example, if the filename contains no directory or contains a relative directory specification).
If a ResourceName contains a contiguous sequence of two or more Binding characters, the sequence will be replaced with single "." character if the sequence contains only "." characters, otherwise the sequence will be replaced with a single "*" character.
A resource database never contains more than one entry for a given ResourceName. If a resource file contains multiple lines with the same ResourceName, the last line in the file is used.
Any whitespace character before or after the name or colon in a ResourceSpec are ignored. To allow a Value to begin with whitespace, the two-character sequence ``\space'' (backslash followed by space) is recognized and replaced by a space character, and the two-character sequence ``\tab'' (backslash followed by horizontal tab) is recognized and replaced by a horizontal tab character. To allow a Value to contain embedded newline characters, the two-character sequence ``\n'' is recognized and replaced by a newline character. To allow a Value to be broken across multiple lines in a text file, the two-character sequence ``\newline'' (backslash followed by newline) is recognized and removed from the value. To allow a Value to contain arbitrary character codes, the four-character sequence ``\nnn'', where each n is a digit character in the range of ``0''-``7'', is recognized and replaced with a single byte that contains the octal value specified by the sequence. Finally, the two-character sequence ``\\'' is recognized and replaced with a single backslash.
When an application looks for the value of a resource, it specifies a complete path in the hierarchy, with both class and instance names. However, resource values are usually given with only partially specified names and classes, using pattern matching constructs. An asterisk (*) is a loose binding and is used to represent any number of intervening components, including none. A period (.) is a tight binding and is used to separate immediately adjacent components. A question mark (?) is used to match any single component name or class. A database entry cannot end in a loose binding; the final component (which cannot be "?") must be specified. The lookup algorithm searches the resource database for the entry that most closely matches (is most specific for) the full name and class being queried. When more than one database entry matches the full name and class, precedence rules are used to select just one.
The full name and class are scanned from left to right (from highest level in the hierarchy to lowest), one component at a time. At each level, the corresponding component and/or binding of each matching entry is determined, and these matching components and bindings are compared according to precedence rules. Each of the rules is applied at each level, before moving to the next level, until a rule selects a single entry over all others. The rules (in order of precedence) are:
Programs based on the X Tookit Intrinsics obtain resources from the following sources (other programs usually support some subset of these sources):
Program resources are organized into groups called classes, so that collections of individual resources (each of which are called instances) can be set all at once. By convention, the instance name of a resource begins with a lowercase letter and class name with an upper case letter. Multiple word resources are concatenated with the first letter of the succeeding words capitalized. Applications written with the X Toolkit Intrinsics will have at least the following resources:
Most applications using the X Toolkit Intrinsics also have the resource foreground (class Foreground), specifying the color to use for text and graphics within the window.
By combining class and instance specifications, application preferences can be set quickly and easily. Users of color displays will frequently want to set Background and Foreground classes to particular defaults. Specific color instances such as text cursors can then be overridden without having to define all of the related resources. For example,
bitmap*Dashed: off
XTerm*cursorColor: gold
XTerm*multiScroll: on
XTerm*jumpScroll: on
XTerm*reverseWrap: on
XTerm*curses: on
XTerm*Font: 6x10
XTerm*scrollBar: on
XTerm*scrollbar*thickness: 5
XTerm*multiClickTime: 500
XTerm*charClass: 33:48,37:48,45-47:48,64:48
XTerm*cutNewline: off
XTerm*cutToBeginningOfLine: off
XTerm*titeInhibit: on
XTerm*ttyModes: intr ^c erase ^? kill ^u
XLoad*Background: gold
XLoad*Foreground: red
XLoad*highlight: black
XLoad*borderWidth: 0
emacs*Geometry: 80x65-0-0
emacs*Background: rgb:5b/76/86
emacs*Foreground: white
emacs*Cursor: white
emacs*BorderColor: white
emacs*Font: 6x10
xmag*geometry: -0-0
xmag*borderColor: white
If these resources were stored in a file called .Xresources in your home directory, they could be added to any existing resources in the server with the following command:
% xrdb -merge $HOME/.Xresources
This is frequently how user-friendly startup scripts merge user-specific defaults into any site-wide defaults. All sites are encouraged to set up convenient ways of automatically loading resources. See the Xlib manual section Resource Manager Functions for more information.
% xrdb $HOME/.Xresources
% xmodmap -e "keysym BackSpace = Delete"
% mkfontdir /usr/local/lib/X11/otherfonts
% xset fp+ /usr/local/lib/X11/otherfonts
% xmodmap $HOME/.keymap.km
% xsetroot -solid 'rgbi:.8/.8/.8'
% xset b 100 400 c 50 s 1800 r on
% xset q
% twm
% xmag
% xclock -geometry 48x48-0+0 -bg blue -fg white
% xeyes -geometry 48x48-48+0
% xbiff -update 20
% xlsfonts '*helvetica*'
% xwininfo -root
% xdpyinfo -display joesworkstation:0
% xhost -joesworkstation
% xrefresh
% xwd | xwud
% bitmap companylogo.bm 32x32
% xcalc -bg blue -fg magenta
% xterm -geometry 80x66-0-0 -name myxterm $*
% xon filesysmachine xload
When the X Toolkit Intrinsics encounter errors converting resource strings to the appropriate internal format, no error messages are usually printed. This is convenient when it is desirable to have one set of resources across a variety of displays (e.g. color vs. monochrome, lots of fonts vs. very few, etc.), although it can pose problems for trying to determine why an application might be failing. This behavior can be overridden by the setting the StringConversionsWarning resource.
To force the X Toolkit Intrinsics to always print string conversion error messages, the following resource should be placed in the file that gets loaded onto the RESOURCE_MANAGER property using the xrdb program (frequently called .Xresources or .Xres in the user's home directory):
*StringConversionWarnings: on
To have conversion messages printed for just a particular application, the appropriate instance name can be placed before the asterisk:
xterm*StringConversionWarnings: on
Xlib - C Language X Interface, and X Toolkit Intrinsics - C Language Interface
X Window System is a trademark of X Consortium, Inc.
A cast of thousands, literally. The Release 6.3 distribution is brought to you by X Consortium, Inc. The names of all people who made it a reality will be found in the individual documents and source files. The staff members at the X Consortium responsible for this release are: Donna Converse (emeritus), Stephen Gildea (emeritus), Kaleb Keithley, Matt Landau (emeritus), Ralph Mor (emeritus), Janet O'Halloran, Bob Scheifler, Ralph Swick, Dave Wiggins (emeritus), and Reed Augliere.
The X Window System standard was originally developed at the Laboratory for Computer Science at the Massachusetts Institute of Technology, and all rights thereto were assigned to the X Consortium on January 1, 1994. X Consortium, Inc. closed its doors on December 31, 1996. All rights to the X Window System have been assigned to the Open Software Foundation.