X Windows
A portable, network-transparent window system.
Table of Contents
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-compliant 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.
X Window System servers run on computers with bit-mapped 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, refer to:
- Xlib - C Language X Interface,
- The X Window System Protocol specification,
- X Toolkit Intrinsics - C Language Interface, and
- The 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.).
Hewlett-Packard provides a graphical user environment called The Common
Desktop Environment (CDE). HP CDE is the user interface, enabling the
user to control a workstation by directly manipulating graphic objects instead
of typing commands on a command-line prompt. See the CDE User's Guide
for complete information on HP CDE.
Hewlett-Packard does not provide or support the entire core MIT distribution.
Many of these programs or clients are sample implementations, or perform tasks
that are accomplished by other clients in Hewlett-Packard's Common Desktop
Environment. The primary differences between the core MIT distribution and
the Hewlett-Packard X11 release are listed below:
- Terminal Emulation
- Although hpterm is the primary terminal emulator, xterm
is also provided and supported.
- Window Management
- twm is replaced by mwm and dtwm.
- Display Manager
- xdm is replaced by an enhanced version called dtlogin.
- Bitmap Editing
- bitmap is replaced by dticon.
- Font Display
- This is handled by the terminal emulation option "-fn override".
xfd is supplied but not supported.
- Demos
- Obtained from the InterWorks users group.
A number of unsupported core MIT clients and miscellaneous utilities are
provided in /usr/contrib/bin. In addition, the entire core MIT
distribution, compiled for Hewlett-Packard platforms, can be obtained from
HP's users group InterWorks for a nominal fee.
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.
Normally, the X Window System is started on Hewlett-Packard systems by
dtlogin, which is an enhanced version of the MIT client
xdm. dtlogin can be used to bring up a full CDE session, a
light CDE session, or a fail-safe session that uses no other part of CDE. If
dtlogin is not used, xinit may be used with
x11start. See the reference pages for these functions for more
information.
From the user's perspective, 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 the
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 (C Shell)
$ DISPLAY=myws:0; export DISPLAY (Korn Shell)
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,
$ xload -display joesws:0 -geometry 100x100+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:
- local
- The hostname part of the display name should be the empty string. For
example: ":0", ":1", or ":0.1". The most
efficient local transport is chosen.
- TCP/IP
- 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.
An X server can use several types of access control. Mechanisms provided in
Release 5 are:
- Host Access (simple host-based access control);
- MIT-MAGIC-COOKIE-1 (shared plain-text "cookies");
- XDM-AUTHORIZATION-1 (secure DES based private-keys); and
- SUN-DES-1 (based on Sun's secure rpc system).
dtlogin/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. dtlogin/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 log in, 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 should know the exact semantics of the particular authorization
data to know if this is actually a problem.
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 (or
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.
- -xoff
- The right edge of the window is to be placed xoff pixels in from
the right edge of the screen. xoff may be negative, in which case
the window's right edge will be off the screen.
The Y offset has similar meanings:
- +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.
- -yoff
- The bottom edge of the window is to be yoff pixels above the bottom
edge of the screen. yoff may be negative, in which case the
window's bottom edge will be off the screen.
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:
- +0+0 (the upper left-hand corner)
- -0+0 (the upper right-hand corner)
- -0-0 (the lower right-hand corner)
- +0-0 (the lower left-hand corner)
In the following examples, a terminal emulator will be placed in roughly the
center of the screen and a load average monitor, mailbox, and clock will be
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 &
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 Hewlett-Packard distribution
comes with window managers named mwm and dtwm, which
support 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.
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, slantedness, and
character set). Similarly, collections of fonts that are based on a common
type face
the variations are usually
called roman, bold, italic (or oblique), and bold italic (or 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 on
large point sizes 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. Usually, fonts used by X servers and font servers can be found
in subdirectories under /usr/lib/X11/fonts:
- /usr/lib/X11/fonts/iso_8859.1/75dpi
- This directory contains bitmap fonts contributed by Adobe Systems, Inc.,
Digital Equipment Corporation, Bitstream, Inc., Bigelow and Holmes, and
Sun Microsystems, Inc. for 75 dot-per-inch displays. An integrated
selection of sizes, styles, and weights are provided for each family.
- /usr/lib/X11/fonts/iso_8859.1/100dpi
- This directory contains 100 dot-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 xlsfonts program can be used to list 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, as in:
$ 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.
One of the following forms can be used to name a font server that accepts TCP
connections:
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. For example:
tcp/expo.lcs.mit.edu:7000
tcp/18.30.0.212:7001/all.
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 device-dependent (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
where red, green, and blue are encoded as h,
hh, hhh, or hhhh, and h represents a single
hexadecimal digit.
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 "pound-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 indicating 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
"-"sign, 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:
- Modifier List
- Some keys (such as Shift, Control, and Caps Lock) are known as
modifiers and are used to select different symbols that are
attached to a single key (such as Shift-a, which generates a capital "A",
and Control-l, which 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.
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:
- -display display
- This option specifies the name of the X server to use.
- -geometry geometry
- This option specifies the initial size and location of the window.
- -bg color, -background color
- Either option specifies the color to use for the window background.
- -bd color, -bordercolor color
- Either option specifies the color to use for the window border.
- -bw number, -borderwidth number
- Either option specifies the width in pixels of the window border.
- -fg color, -foreground color
- Either option specifies the color to use for text or graphics.
- -fn font, -font font
- Either option specifies the font to use for displaying text.
- -iconic
- This option indicates that the user would prefer that the application's
windows initially not be visible as if the windows had be immediately
iconified by the user. Window managers may choose not to honor the
application's request.
- -name
- This option specifies the name under which resources for the application
should be found. This option is useful in shell aliases to distinguish
between invocations of an application, without resorting to creating links
to alter the executable file name.
- -rv, -reverse
- Either option indicates that the program should simulate reverse video if
possible, often by swapping the foreground and background colors. Not all
programs honor this or implement it correctly. It is usually only used on
monochrome displays.
- +rv
- This option indicates that the program should not simulate reverse video.
This is used to override any defaults since reverse video doesn't always
work properly.
- -selectionTimeout
- This option specifies the timeout in milliseconds within which two
communicating applications must respond to one another for a selection
request.
- -synchronous
- This option indicates that requests to the X server should be sent
synchronously, instead of asynchronously. Since Xlib normally buffers
requests to the server, errors do not necessarily get reported immediately
after they occur. This option turns off the buffering so that the
application can be debugged. It should never be used with a working
program.
- -title string
- This option specifies the title to be used for this window. This
information is sometimes used by a window manager to provide some sort of
header identifying the window.
- -xnllanguagelanguage[_territory][.codeset]
- This option specifies the language, territory, and codeset for use in
resolving resource and other filenames.
- -xrm resourcestring
- This option specifies a resource name and value to override any defaults.
It is also very useful for setting resources that don't have explicit
command line arguments.
To make the tailoring of applications to personal preferences easier, X
provides a mechanism for storing default values for program resources (e.g.,
background color, window title, etc.). Resources are specified as strings
that are read in from various places when an application is run. Program
components are named in a hierarchical fashion, with each node in the
hierarchy identified by a class and an instance name. At the top level is the
class and instance name of the application itself. By convention, the class
name of the application is the same as the program name, but with the first
letter capitalized, although some programs that begin with the letter "x" also
capitalize the second letter for historical reasons.
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. Braces
("{"..."}") indicate zero or more repetitions of the
enclosed elements. 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:
- An entry that contains a matching component (whether name, class, or
"?") takes precedence over entries that elide the level (that is,
entries that match the level in a loose binding).
- 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
"?".
- An entry preceded by a tight binding takes precedence over entries
preceded by a loose binding.
Programs based on the X Tookit Intrinsics obtain resources from the following
sources (other programs usually support some subset of these sources):
- 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 X through the display manager.
- 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 application-specific 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/.Xdefaults-hostname is looked for instead,
where hostname is the name of the host where the application is
executing.
- -xrm resourcestring
- Resources can also be specified from the command line. The
resourcestring is a single resource name and value as shown above.
Note that if the string contains characters interpreted by the shell
(e.g., asterisk), they must be quoted. Any number of -xrm
arguments may be given on the command line.
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 uppercase
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:
- background (class Background)
- This resource specifies the color to use for the window background.
- 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,
dticon*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
hpterm*Geometry: 80x65-0-0
hpterm*Background: rgb:5b/76/86
hpterm*Foreground: white
hpterm*Cursor: white
hpterm*BorderColor: white
hpterm*Font: 6x10
If these resources were stored in a file called .Xdefaults in your
home directory, they could be added to any existing resources in the server
with the following command:
$ xrdb -merge $HOME/.Xdefaults
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.
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/.Xdefaults
$ 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
$ mwm
$ xclock -geometry 48x48-0+0 -bg blue -fg white
$ xlsfonts '*helvetica*'
$ xwininfo -root
$ xhost -joesworkstation
$ xwd | xwud
$ xterm -geometry 80x66-0-0 -name myxterm $*
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 .Xdefaults
file in the user's home directory. This file is then loaded into the
RESOURCE_MANAGER property using the xrdb program:
*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
bdftopcf(1), bitmap(1), fs(1), hpterm(1)
mkfontdir(1), mwm(1), xauth(1), xclock(1),
xcmsdb(1), xfd(1), xhost(1),
xinitcolor(1), xload(1), xlsfonts(1),
xmodmap(1), xpr(1), xprop(1), xrdb(1),
xrefresh(1), xset(1), xsetroot(1),
xterm(1), xwd(1), xwininfo(1), xwud(1),
Xserver(1), Xlib - C Language X
Interface, and X Toolkit Intrinsics - C Language Interface.
The following copyright and permission notice outlines the rights and
restrictions covering most parts of the core distribution of the X Window
System from MIT. Other parts have additional or different copyrights and
permissions; see the individual source files.
Copyright 1984, 1985, 1986, 1987, 1988, 1989, 1990, 1991 by the Massachusetts
Institute of Technology.
Permission to use, copy, modify, distribute, and sell this software and its
documentation for any purpose is hereby granted without fee, provided that the
above copyright notice appear in all copies and that both that copyright
notice and this permission notice appear in supporting documentation, and that
the name of MIT not be used in advertising or publicity pertaining to
distribution of the software without specific, written prior permission. MIT
makes no representations about the suitability of this software for any
purpose. It is provided "as is" without express or implied warranty.
X Window System is a trademark of MIT.
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).