NAME

X − a portable, network transparent window system

SYNOPSIS

X is a network transparent window system developed at MIT which runs on a wide range of computing and graphics machines.  The core distribution from MIT has both client and server support for the following operating systems:

4.3+tahoe
ULTRIX 3.0 FT2 (also compiles under ULTRIX 2.0)
SunOS 3.4
HP-UX 6.01
Apollo Domain/IX 9.7 (and 9.6 according to its developers)
IBM AOS 4.3 (according to its developers)
A/UX 1.0

Commercial implementations are also available for a much wider 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 Reference Manual, Volume Two, the X Window System Protocol specification, and various toolkit documents. 

The number of programs that use X is growing rapidly.  Of particular interest are: a terminal emulator (xterm), a window manager (uwm), a display manager (xdm), mail managing utilities (xmh and xbiff), a manual page browser (xman), a bitmap editor (bitmap), an access control program (xhost), user preference setting programs (xrdb, xset, xsetroot, and xmodmap), a load monitor (xload), clock (xclock), a font displayer (xfd), utilities for listing information about fonts, windows, and displays (xlsfonts, xlswins, xwininfo, xdpyinfo, and xprop), a protocol translator for running X10 programs (x10tox11), a diagnostic for seeing what events are generated and when (xev), screen image manipulation utilities (xwd, xwud, and xmag), and various demos (xeyes, ico, muncher, puzzle, etc.). 

Many other utilities, window managers, games, toolkits, etc. are available from the user-contributed distribution.  See your site administrator for details. 

STARTING UP

There are currently three ways of getting the X server and an initial set of client applications started.  The particular method used depends on which operating system you are running and on whether you use other window systems in addition to X. 

xdm (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 ENTERafter 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 such as the background, the speed of the pointer, etc.).  Your site administrator can provide details. 

xterm −L (started from /etc/init)
Some versions of the UNIX System that are derived from 4.3BSD support starting the window system and an initial xterm window from the system terminal line configuration file /etc/ttys.  As with xdm, there will be a window requesting your username and password.  However, this window will become your primary window and is not configurable on a per-user basis.  Sites using this method should switch to xdm, as xterm −L may not be supported in future releases. 

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 user-specified 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 do 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 the UNIX System, 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

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.  The sample servers from MIT support the following types of connections:

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. 

UNIX System domain sockets or STREAMS pipe
The hostname part of the display name should be the string unix (in lowercase letters).  For example:  unix:0, unix:1, and unix: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. 

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. 

−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 upper left-hand corner

−0+0 upper right-hand corner

−0−0 lower right-hand corner

+0−0 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 &

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 core distribution comes with a window manager named uwm which supports overlapping windows, popup menus, point-and-click or click-to-type input models, and minimal use of screen real estate (i.e., it doesn’t provide title bars around windows).  It tries to stay out of the way as much as possible, but can be somewhat difficult to master. 

Several other window managers are available in the user-contributed distribution:

awm This window manager is descended from uwm but provides optional title bars with a layout that can be tailored by the user. 

twm This window manager provides title bars, resize and reposition boxes, and specially designed icons.  It is known for its small size and simplicity. 

rtl This is a tiling window manager that rearranges and resizes windows on the screen to prevent them from ever overlapping. 

People who find that none of these window managers are acceptable are encouraged to write their own. 

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. 

Sets of font families of the same resolution (usually measured in dots per inch) are further grouped into directories (so named because they are initially stored in file system directories).  Each directory contains a database which lists the name of the font and information on how to find the font.  The server uses these databases to translate font names (which have nothing to do with file names) into font data. 

The list of font directories in which the server looks when trying to find a font is controlled by the font path.  Although most installations will choose to have the server start up with all of the commonly used font directories, 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 default font path for the sample server contains three directories:

/usr/lib/X11/fonts/misc
This directory contains several miscellaneous fonts that are useful on all systems.  It contains a very small family of fixed-width fonts (6x10, 6x12, 6x13, 8x13, 8x13bold, and 9x15) and the cursor font.  It also has font name aliases for the commonly used fonts fixed and variable. 

/usr/lib/X11/fonts/75dpi
This directory contains fonts contributed by Adobe Systems, Inc. and Digital Equipment Corporation and by Bitstream, 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. 

Font databases are created by running the mkfontdir program in the directory containing the source or compiled versions of the fonts (in both compressed and uncompressed formats).  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.snf ~/myfonts
        %  mkfontdir ~/myfonts
        %  xset fp rehash

The xlsfonts program can be used to list all of the fonts that are found in font databases in the current font path.  Font names tend to be fairly long as they contain all of the information needed to uniquely identify individual fonts.  However, the sample server supports wildcarding of font names, so the full specification:

-adobe-courier-medium-r-normal--10-100-75-75-m-60-iso8859-1

could be abbreviated as:

*-courier-medium-r-normal--*-100-*

Because the shell also has special meanings for * and ?, wildcarded font names should be quoted:

        %  xlsfonts -fn ’*-courier-medium-r-normal--*-100-*’

If more than one font in a given directory in the font path matches a wildcarded font name, the choice of which particular font to return is left to the server.  However, if fonts from more than one directory match a name, the returned font will always be from the first such directory in the font path.  The example given above will match fonts in both the 75dpi and 100dpi directories; if the 75dpi directory is ahead of the 100dpi directory in the font path, the smaller version of the font will be used. 

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.  Although black and white displays don’t provide much of a choice, color displays frequently allow anywhere between 16 and 16 million different colors. 

Colors are usually specified by their commonly used names (for example, red, white, or medium slate blue).  The server translates these names into appropriate screen colors using a color database that can usually be found in /usr/lib/X11/rgb.txt.  Color names are case-insensitive, meaning that red, Red, and RED all refer to the same color. 

Many applications also accept color specifications of the following form:

#rgb
#rrggbb
#rrrgggbbb
#rrrrggggbbbb

where r, g, and b are hexidecimal numbers indicating how much red, green, and blue should be displayed (zero being none and ffff being on full).  Each field in the specification must have the same number of digits (e.g., #rrgb or #gbb are not allowed).  Fields that have fewer than four digits (e.g. #rgb) are padded out with zero’s following each digit (e.g. #r000g000b000).  The eight primary colors can be represented as:

black#000000000000(no color at all)
red#ffff00000000
green#0000ffff0000
blue#00000000ffff
yellow#ffffffff0000(full red and green, no blue)
magenta#ffff0000ffff
cyan#0000ffffffff
white#ffffffffffff(full red, green, and blue)

Unfortunately, RGB color specifications are highly unportable since different monitors produce different shades when given the same inputs.  Similarly, color names aren’t portable because there is no standard naming scheme and because the color database needs to be tuned for each monitor. 

Application developers should take care to make their colors tailorable. 

KEYS

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 SHIFTa generates a capital A, and CTRLl generates a formfeed 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 modifer 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 that contains one row for each keycode and one column for each of the modifiers.  This table is initialized by the server to correspond to normal typewriter conventions, but is only used by client programs. 

Although most programs deal with keysyms directly (such as those written with the X Toolkit), most programming libraries provide routines for converting keysyms into the appropriate type of string (such as ISO Latin-1).  However, programs that use such routines are usually less portable and not as flexible. 

OPTIONS

Most X programs attempt to use the same names for command line options and arguments.  All applications written with the X Toolkit 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 been 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. 

−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.

−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.

RESOURCES

To make the tailoring of applications to personal preferences easier, X supports several mechanisms for storing default values for program resources (e.g., background color, window title, etc.)  Resources are specified as strings of the form:

name*subname*subsubname...: value

that are read in from various places when an application is run.  The Xlib routine XGetDefault(3X) and the resource utilities within the X Toolkit obtain resources from the following 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 using the xrdb program.  This is frequently taken care of when the user starts up X through the display manager or xinit. 

application-specific files
Any application- or machine-specific resources can be stored in the class resource files located in the XAPPLOADDIR directory (this is a configuration parameter that is /usr/lib/X11/app-defaults in the standard distribution).  Programs that use the X Toolkit will also look in the directory named by the environment variable XAPPLRESDIR (default value is user’s home directory) for files named Class, where Class is the class name of the particular application.  ­XAPPLOADDIR and XAPPLRESDIR configuration files are actually loaded before the RESOURCE_MANAGER property, so that the property can override the values. 

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, the X Toolkit looks for a file named .Xdefaults-hostname, where hostname is the name of the host where the application is executing. 

−xrm resourcestring
Applications that use the X Toolkit can have resources 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 concatentated with the first letter of the succeeding words capitalized.  Applications written with the X Toolkit 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 X Toolkit applications 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:  #5b7686
emacs*Foreground:  white
emacs*Cursor:  white
emacs*BorderColor:  white
emacs*Font:  6x10
xmag*geometry:  -0-0
xmag*borderColor:  white
uwm*bordercolor:  black
uwm*Foreground:  #f00
uwm*Background:  #ede7e2
uwm*borderwidth:  0
uwm*iborderwidth:  0
uwm*mborderwidth:  1

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 Reference Manual, Volume Two section on “Using the Resource Manager” 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 −load $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 ’#888’
%  xset b 100 400 c 50 s 1800 r on
%  xset q
%  uwm
%  xmag
%  xclock −geometry 48x48-0+0 −bg blue −fg white
%  xeyes −geometry 48x48-48+0
%  xbiff −update 20
%  xlsfonts ’*helvetica*’
%  xlswins −l
%  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 $*

DIAGNOSTICS

A wide variety of error messages are generated from various programs.  Various toolkits are encouraged to provide a common mechanism for locating error text so that applications can be tailored easily.  Programs written to interface directly to the Xlib C language library are expected to do their own error checking. 

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 encounters 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 versus monochrome, many fonts versus 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 Toolkit to always print string conversion error messages, the following resource should be placed at the top of 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

BUGS

If you encounter a repeatable bug, please contact your site administrator for instructions on how to submit an X Bug Report. 

SEE ALSO

Xcpqag(1), Xcvc(1), Xdcaga(1), Xgp(1), Xhrc(1), Xigsp(1), Xlvp(1), Xmfg(1), Xmsfdp(1), Xnnp(1), Xnnpi(1), Xpgs1(1), Xpw(1), Xrren2(1) Xserver(1), Xsp200(1), Xtisdb(1), Xv256(1), Xvga(1), Xviking(1), Xwge(1), bdftosnf(1), bitmap(1), mkfontdir(1), resize(1), uwm(1), x10tox11(1), xbiff(1), xcalc(1), xclock(1), xdpyinfo(1), xedit(1), xev(1), xfd(1), xhost(1), xinit(1), xkill(1), xload(1), xlogo(1), xlsfonts(1), xlswins(1), xmag(1), xmodmap(1), xprop(1), xrdb(1), xrefresh(1), xset(1), xsetroot(1), xterm(1), xwd(1), xwininfo(1), xwud(1). 
init(1M) in the INTERACTIVE UNIX System User’s/System Administrator’s Reference Manual. 
inittab(4) in the INTERACTIVE SDS Guide and Programmer’s Reference Manual. 
Xlib Reference Manual, Volume Two.
X Toolkit Intrinsics − C Language X Interface.
Using and Specifying X Resources.

COPYRIGHT

The following copyright and permission notice outlines the rights and restrictions covering most parts of the standard 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, Massachusetts Institute of Technology. Permission to use, copy, modify, and distribute this software and its documentation for any purpose and without fee is hereby granted, 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 M.I.T. not be used in advertising or publicity pertaining to distribution of the software without specific, written prior permission.  M.I.T. makes no representations about the suitability of this software for any purpose.  It is provided “as is” without express or implied warranty.  This software is not subject to any license of the American Telephone and Telegraph Company or of the Regents of the University of ­California.

AUTHORS

There are too many to credit here.  See the file /doc/contributors in the standard sources for some of the names. 

\*U  —  Version 1.0