NAME
X - a portable, network-transparent window system
SYNOPSIS
The X Window System is a network transparent window system developed at MIT which runs on a wide range of computing and graphics machines. It should be relatively straightforward to build the MIT 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
X Window System
X Version 11
X Window System, Version 11 X11
X Window System is a trademark of the Massachusetts Institute of Technology.
DESCRIPTION
X Window System servers run on computers with bitmap displays. The server distributes user input to and accepts output requests from various client programs through a variety of different interprocess communication channels. Although the most common case is for the client programs to be running on the same machine as the server, clients can be run transparently from other machines (including machines with different architectures and operating systems) as well.
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 MIT distribution include: a terminal emulator (xterm), a window manager (twm), a display manager (xdm), a console redirect program (xconsole), mail managing utilities (xmh and xbiff), a manual page browser (xman), a bitmap editor (bitmap), a resource editor (editres), a ditroff previewer (xditview), access control programs (xauth and xhost), user preference setting programs (xrdb, xcmsdb, xset, xsetroot, xstdcmap, and xmodmap), a load monitor (xload), clocks (xclock and oclock), a font displayer (xfd), utilities for listing information about fonts, windows, and displays (xlsfonts, xfontsel, xwininfo, xlsclients, xdpyinfo, and xprop), a diagnostic for seeing what events are generated and when (xev), screen image manipulation utilities (xwd, xwud, xpr, and xmag), and various demos (xeyes, ico, xgc, x11perf, etc.).
Many other utilities, window managers, games, toolkits, etc. are included as user-contributed software in the MIT distribution, or are available using anonymous ftp on the Internet. See your site administrator for details.
STARTING UP
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 on whether or not you use other window systems in addition to X.
xdm (the X Display Manager)
If you want to always have X running on your display, your site administrator can set your machine up to use the X Display Manager xdm. This program is typically started by the system at boot time and takes care of keeping the server running and getting users logged in. If you are running xdm, you will see a window on the screen welcoming you to the system and asking for your username and password. Simply type them in as you would at a normal terminal, pressing the Return key after each. If you make a mistake, xdm will display an error message and ask you to try again. After you have successfully logged in, xdm will start up your X environment. By default, if you have an executable file named .xsession in your home directory, xdm will treat it as a program (or shell script) to run to start up your initial clients (such as terminal emulators, clocks, a window manager, user settings for things like the background, the speed of the pointer, etc.). Your site administrator can provide details.
xinit (run manually from the shell)
Sites that support more than one window system might choose to use the xinit program for starting X manually. If this is true for your machine, your site administrator will probably have provided a program named "x11", "startx", or "xstart" that will do site-specific initialization (such as loading convenient default resources, running a window manager, displaying a clock, and starting several terminal emulators) in a nice way. If not, you can build such a script using the xinit program. This utility simply runs one userspecified program to start the server, runs another to start up any desired clients, and then waits for either to finish. Since either or both of the user-specified programs may be a shell script, this gives substantial flexibility at the expense of a nice interface. For this reason, xinit is not intended for end users.
DISPLAY NAMES
From the user's prospective, every X server has a display name of the form:
hostname:displaynumber.screennumber
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):
hostname
The hostname specifies the name of the machine to which the display is physically connected. If the hostname is not given, the most efficient way of communicating to a server on the same machine will be used.
displaynumber
The phrase "display" is usually used to refer to collection of monitors that share a common keyboard and pointer (mouse, tablet, etc.). Most workstations tend to only have one keyboard, and therefore, only one display. Larger, multi-user systems, however, will frequently have several displays so that more than one person can be doing graphics work at once. To avoid confusion, each display on a machine is assigned a display number (beginning at 0) when the X server for that display is started. The display number must always be given in a display name.
screennumber
Some displays share a single keyboard and pointer among two or more monitors. Since each monitor has its own set of windows, each screen is assigned a screen number (beginning at 0) when the X server for that display is started. If the screen number is not given, then screen 0 will be used.
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'll 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
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:
local
The hostname part of the display name should be the empty string. For example: :0, :1, and :0.1. The most efficient local transport will be chosen.
TCPIP
The hostname part of the display name should be the server machine's IP address name. Full Internet names, abbreviated names, and IP addresses are all allowed. For example: expo.lcs.mit.edu:0, expo:0, 18.30.0.212:0, bigmachine:1, and hydra:0.1.
DECnet
The hostname part of the display name should be the server machine's nodename followed by two colons instead of one. For example: myws::0, big::1, and hydra::0.1.
ACCESS CONTROL
An X server can use several types of access control. Mechanisms provided in Release 5 are:
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, then 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
GEOMETRY SPECIFICATIONS
One of the advantages of using window systems instead of hardwired terminals is that applications don't have to be restricted to a particular size or location on the screen. Although the layout of windows on a display is controlled by the window manager that the user is running (described below), most X programs accept a command line argument of the form -geometry WIDTHxHEIGHT+XOFF+YOFF (where WIDTH, HEIGHT, XOFF, and YOFF are numbers) for specifying a preferred size and location for this application's main window.
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:
+XOFF The left edge of the window is to be placed XOFF pixels in from the left edge of the screen (i.e. the X coordinate of the window's origin will be XOFF). XOFF may be negative, in which case the window's left edge will be off the screen.
+YOFF The top edge of the window is to be YOFF pixels below the top edge of the screen (i.e. the Y coordinate of the window's origin will be YOFF). YOFF may be negative, in which case the window's top edge will be off the screen.
xterm -fn 6x10 -geometry 80x24+30+200 & xclock -geometry 48x48-0+0 &
xload -geometry 48x48-96+0 &
xbiff -geometry 48x48-48+0 &
WINDOW MANAGERS
The layout of windows on the screen is controlled by special programs called window managers. Although many window managers will honor geometry specifications as given, others may choose to ignore them (requiring the user to explicitly draw the window's region on the screen with the pointer, for example).
Since window managers are regular (albeit complex) client programs, a variety of different user interfaces can be built. The MIT 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 MIT distribution for other popular window managers.
FONT NAMES
Collections of characters for displaying text and symbols in X are known as fonts. A font typically contains images that share a common appearance and look nice together (for example, a single size, boldness, slant, and character set). Similarly, collections of fonts that are based on a common type face (the variations are usually called roman, bold, italic, bold italic, oblique, and bold oblique) are called families.
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. The most common fonts use by X servers and font servers can be found in four directories:
/usr/lib/X11/fonts/misc
This directory contains many miscellaneous bitmap fonts that are useful on all systems. It contains a family of fixed-width fonts, a family of fixedwidth fonts from Dale Schumacher, several Kana fonts from Sony Corporation, two JIS Kanji fonts, two Hangul fonts from Daewoo Electronics, two Hebrew fonts from Joseph Friedman, the standard cursor font, two cursor fonts from Digital Equipment Corporation, and cursor and glyph fonts from Sun Microsystems. It also has various font name aliases for the fonts, including fixed and variable.
/usr/lib/X11/fonts/Speedo
This directory contains outline fonts for Bitstream's Speedo rasterizer. A single font face, in normal, bold, italic, and bold italic, is provided, contributed by Bitstream, Inc.
/usr/lib/X11/fonts/75dpi
This directory contains bitmap fonts contributed by Adobe Systems, Inc., Digital Equipment Corporation, Bitstream, Inc., Bigelow and Holmes, and Sun Microsystems, Inc. for 75 dots per inch displays. An integrated selection of sizes, styles, and weights are provided for each family.
/usr/lib/X11/fonts/100dpi
This directory contains 100 dots per inch versions of some of the fonts in the 75dpi directory.
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
% 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:
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.
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.
COLOR NAMES
Most applications provide ways of tailoring (usually through resources or command line arguments) the colors of various elements in the text and graphics they display. A color can be specified either by an abstract color name, or by a numerical color specification. The numerical specification can identify a color in either devicedependent (RGB) or device-independent terms. Color strings are case-insensitive.
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 /usr/lib/X11/rgb.txt.
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:
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:
For more information on device independent color, see the Xlib reference manual.
KEYBOARDS
The X keyboard model is broken into two layers: serverspecific 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:
modifier list
Some keys (such as Shift, Control, and Caps Lock) are known as modifier and are used to select different symbols that are attached to a single key (such as Shift-a generates a capital A, and Control-l generates a control character ^L). The server keeps a list of keycodes corresponding to the various modifier keys. Whenever a key is pressed or released, the server generates an event that contains the keycode of the indicated key as well as a mask that specifies which of the modifier keys are currently pressed. Most servers set up this list to initially contain the various shift, control, and shift lock keys on the keyboard.
keymap table
Applications translate event keycodes and modifier masks into keysyms using a keysym table which contains one row for each keycode and one column for various modifier states. This table is initialized by the server to correspond to normal typewriter conventions. The exact semantics of how the table is interpreted to produce keysyms depends on the particular program, libraries, and language input method used, but the following conventions for the first four keysyms in each row are generally adhered to:
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.
OPTIONS
Most X programs attempt to use the same names for command line options and arguments. All applications written with the X Toolkit Intrinsics automatically accept the following options:
The precise syntax for resources is:
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,
2. An entry with a matching name takes precedence over both entries with a matching class and entries that match using "?". An entry with a matching class takes precedence over entries that match using "?".
RESOURCE_MANAGER root window property
Any global resources that should be available to clients on all machines should be stored in the RESOURCE_MANAGER property on the root window of the first screen using the xrdb program. This is frequently taken care of when the user starts up X through the display manager or xinit.
SCREEN_RESOURCES root window property
Any resources specific to a given screen (e.g. colors) that should be available to clients on all machines should be stored in the SCREEN_RESOURCES property on the root window of that screen. The xrdb program will sort resources automatically and place them in RESOURCE_MANAGER or SCREEN_RESOURCES, as appropriate.
application-specific files
Directories named by the environment variable XUSERFILESEARCHPATH or the environment variable XAPPLRESDIR, plus directories in a standard place (usually under /usr/lib/X11/, but this can be overridden with the XFILESEARCHPATH environment variable) are searched for for applicationspecific resources. For example, application default resources are usually kept in /usr/lib/X11/app-defaults/. See the X Toolkit Intrinsics - C Language Interface manual for details.
XENVIRONMENT
Any user- and machine-specific resources may be specified by setting the XENVIRONMENT environment variable to the name of a resource file to be loaded by all applications. If this variable is not defined, a file named $HOME/.Xdefaultshostname is looked for instead, where hostname is the name of the host where the application is executing.
borderWidth (class BorderWidth)
This resource specifies the width in pixels of the window border.
borderColor (class BorderColor)
This resource specifies the color to use for the window border.
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.
EXAMPLES
The following is a collection of sample command lines for some of the more frequently used commands. For more information on a particular command, please refer to that command's manual page.
% 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
DIAGNOSTICS
A wide variety of error messages are generated from various programs. The default error handler in Xlib (also used by many toolkits) uses standard resources to construct diagnostic messages when errors occur. The defaults for these messages are usually stored in /usr/lib/X11/XErrorDB. If this file is not present, error messages will be rather terse and cryptic.
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
SEE ALSO
TRADEMARKS
X Window System is a trademark of MIT.
AUTHORS
A cast of thousands, literally. The MIT Release 5 distribution is brought to you by the MIT X Consortium. The names of all people who made it a reality will be found in the individual documents and source files. The staff members at MIT responsible for this release are: Donna Converse (MIT X Consortium), Stephen Gildea (MIT X Consortium), Susan Hardy (MIT X Consortium), Jay Hersh (MIT X Consortium), Keith Packard (MIT X Consortium), David Sternlicht (MIT X Consortium), Bob Scheifler (MIT X Consortium), and Ralph Swick (Digital/MIT Project Athena).