X Window System User's Guide

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NAME: xdm - X Display Manager with support for XDMCP, host chooser
SYNOPSIS: xdm[- config configuration_file ][ - nodaemon] [- debug debug_level] [- error error_log_file] [- resources resource_file][- server server_entry ][- session session_program]
DESCRIPTION: Xdm manages a collection of X displays, which may be on the local host or remote servers. The design of xdm was guided by the needs of X terminals as well as the X Consortium standard XDMCP, the X Display Manager Control Protocol. Xdm provides services similar to those provided by init, getty and login on character terminals: prompting for login name and password, authenticating the user, and running a "session."

A "session" is defined by the lifetime of a particular process; in the traditional character-based terminal world, it is the user's login shell. In the xdm context, it is an arbitrary session manager. This is because in a windowing environment, a user's login shell process does not necessarily have any terminal-like interface with which to connect. When a real session manager is not available, a window manager or terminal emulator is typically used as the "session manager," meaning that termination of this process terminates the user's session.

When the session is terminated, xdm resets the X server and (optionally) restarts the whole process.

When xdm receives an Indirect query via XDMCP, it can run a chooser process to perform an XDMCP Broadcast Query (or an XDMCP Query to specified hosts) on behalf of the display and offer a menu of possible hosts that offer XDMCP display management. This feature is useful with X terminals that do not offer a host menu themselves.

Because xdm provides the first interface that users will see, it is designed to be simple to use and easy to customize to the needs of a particular site. Xdm has many options, most of which have reasonable defaults. Browse through the various sections of this manual, picking and choosing the things you want to change. Pay particular attention to the Session Program section, which will describe how to set up the style of session desired.
OVERVIEW: xdm is highly configurable, and most of its behavior can be controlled by resource files and shell scripts. The names of these files themselves are resources read from the file xdm-config or the file named by the - config option.

xdm offers display management two different ways. It can manage X servers running on the local machine and specified in Xservers, and it can manage remote X servers (typically X terminals) using XDMCP (the XDM Control Protocol) as specified in the Xaccess file.

The resources of the X clients run by xdm outside the user's session, including xdm's own login window, can be affected by setting resources in the Xresources file.

For X terminals that do not offer a menu of hosts to get display management from, xdm can collect willing hosts and run the chooser program to offer the user a menu. For X displays attached to a host, this step is typically not used, as the local host does the display management.

After resetting the X server, xdm runs the Xsetup script to assist in setting up the screen the user sees along with the xiogin widget.

When the user logs in, xdm runs the Xstartup script as root.

Then xdm runs the Xsession script as the user. This system session file may do some additional startup and typically runs a script in the user's home directory. When the Xsession script exits, the session is over.

At the end of the session, the Xreset script is run to clean up, the X server is reset, and the cycle starts over.

The file /usr/X11R6/lib/X11/xdm/xdm-errors will contain error messages from xdm and anything output to stderr by Xsetup, Xstartup, Xsession or Xreset. When you have trouble getting xdm working, check this file to see if xdm has any clues to the trouble.

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OPTIONS: All of these options, except - config itself, specify values that can also be specified in the configuration file as resources.
- config configuration_file: Names the configuration file, which specifies resources to control the behavior of xdm. < XRoot>/lib/X11/xdm/xdm-config is the default. See the section Configuration File.
- nodaemon: Specifies "false" as the value for the DisplayManager.daemonMode resource. This suppresses the normal daemon behavior, which is for xdm to close all file descriptors, disassociate itself from the controlling terminal, and put itself in the background when it first starts up.
- debug debug_level: Specifies the numeric value for the DisplayManager.debugLevel resource. A non-zero value causes xdm to print lots of debugging statements to the terminal; it also disables the DisplayManager.daemonMode resource, forcing xdm to run synchronously. To interpret these debugging messages, a copy of the source code for xdm is almost a necessity. No attempt has been made to rationalize or standardize the output.
- error error_log_file: Specifies the value for the DisplayManager.errorLogFile resource. This file contains errors from xdm as well as anything written to stderr by the various scripts and programs run during the progress of the session.
- resources resource_file: Specifies the value for the DisplayManager*resources resource. This file is loaded using xrdb to specify configuration parameters for the authentication widget.
- server server_entry: Specifies the value for the DisplayManager.servers resource. See the section Local Server Specification for a description of this resource.
- udpPort port_number: Specifies the value for the Display Manager.requestPort resource. This sets the port-number which xdm will monitor for XDMCP requests. As XDMCP uses the registered well-known UDP port 177, this resource should not be changed except for debugging.
- session session_program: Specifies the value for the DisplayManager*session resource. This indicates the program to run as the session after the user has logged in.
- xrm resource_specification: Allows an arbitrary resource to be specified, as in most X Toolkit applications.
RESOURCES: At many stages the actions of xdm can be controlled through the use of its configuration file, which is in the X resource format. Some resources modify the behavior of xdm on all displays, while others modify its behavior on a single display. Where actions relate to a specific display, the display name is inserted into the resource name between "DisplayManager" and the final resource name segment.

For local displays, the resource name and class are as read from the Xservers file.

For remote displays, the resource name is what the network address of the display resolves to. See the removeDomain resource. The name must match exactly; xdm is not aware of all the network aliases that might reach a given display. If the name resolve fails, the address is used. The resource class is as sent by the display in the XDMCP Manage request.

Because the resource manager uses colons to separate the name of the resource from its value and dots to separate resource name parts, xdm substitutes underscores for both dots and colons when generating the resource name. For example, DisplayManager.expo_x_org_0.startup is the name of the resource which defines the startup shell file for the "expo.x.org:0" display.
DisplayManager.servers: This resource either specifies a file name full of server entries, one per line (if the value starts with a slash), or a single server entry. See the section Local Server Specification for the details.
DisplayManager.requestPort: This indicates the UDP port number which xdm uses to listen for incoming XDMCP requests. Unless you need to debug the system, leave this with its default value of 177.
DisplayManager.errorLogFile: Error output is normally directed at the system console. To redirect it, set this resource to a file name. A method to send these messages to syslog should be developed for systems which support it; however, the wide variety of interfaces precludes any system-independent implementation. This file also contains any output directed to stderr by the Xsetup, Xstartup, Xsessio and Xreset files, so it will contain descriptions of problems in those scripts as well.
DisplayManager.debugLevel: If the integer value of this resource is greater than zero, reams of debugging information will be printed. It also disables daemon mode, which would redirect the information into the bit-bucket, and allows non-root users to run xdm, which would normally not be useful.
DisplayManager.daemonMode: Normally, xdm attempts to make itself into a daemon process unassociated with any terminal. This is accomplished by forking and leaving the parent process to exit, then closing file descriptors and releasing the controlling terminal. In some environments this is not desired (in particular, when debugging). Setting this resource to "false" will disable this feature.
DisplayManager.PidFile: The filename specified will be created to contain an ASCII representation of the process-id of the main xdm process. xdm also uses file locking on this file to attempt to eliminate multiple daemons running on the same machine, which would cause quite a bit of havoc.
DisplayManager.lockPidFile: This is the resource which controls whether xdm uses file locking to keep multiple display managers from running amok. On System V, this uses the lockf library call, while on BSD it uses flock.
DisplayManager.authDir: This names a directory in which xdm stores authorization files while initializing the session. The default value is /usr/lib/X11/xdm.
DisplayManager.autoRescan: This boolean controls whether xdm rescans the configuration, servers, access control and authentication keys files after a session terminates and the files have changed. By default it is "true." You can force xdm to reread these files by sending a SIGHUP to the main process.
DisplayManager.removeDomainname: When computing the display name for XDMCP clients, the name resolver will typically create a fully qualified host name for the terminal. As this is sometimes confusing, xdm will remove the domain name portion of the host name if it is the same as the domain name of the local host when this variable is set. By default the value is "true."
DisplayManager.keyFile: XDM-AUTHENTICATION-1 style XDMCP authentication requires that a private key be shared between xdm and the terminal. This resource specifies the file containing those values. Each entry in the file consists of a display name and the shared key. By default, xdm does not include support for XDM-AUTHENTICATION-1, as it requires DES which is not generally distributable because of United States export restrictions.
DlsplayManager.accessFile: To prevent unauthorized XDMCP service and to allow forwarding of XDMCP IndirectQuery requests, this file contains a database of hostnames which are either allowed direct access to this machine, or have a list of hosts to which queries should be forwarded to. The format of this file is described in the section XDMCP Access Control.

DisplayManager.exportList; A list of additional environment variables, separated by white space, to pass on to the Xsetup, Xstartup, Xsession, and Xreset programs.

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DisplayManager.randomFile: A file to checksum to generate the seed of authorization keys. This should be a file that changes frequently. The default is /dev/mem.
DisplayManager.greeterLib: On systems that support a dynamically-loadable greeter library, the name of the library. Default is /usr/lib/X11/xdm/libXdmGreet.so.
DisplayManager.choice Timeout: Number of seconds to wait for display to respond after user has selected a host from the chooser. If the display sends an XDMCP IndirectQuery within this time, the request is forwarded to the chosen host. Otherwise, it is assumed to be from a new session and the chooser is offered again. Default is 15.
DisplayManager.DlSPLAY. resources: This resource specifies the name of the file to be loaded by xrdb as the resource database onto the root window of screen 0 of the display. The Xsetup program, the Login widget, and chooser will use the resources set in this file. This resource data base is loaded just before the authentication procedure is started, so it can control the appearance of the login window. See the section Authentication Widget, which describes the various resources that are appropriate to place in this file. There is no default value for this resource, but /usr/lib/X11/xdm/Xresources is the conventional name.
DisplayManager.DISPLAY.chooser: Specifies the program run to offer a host menu for Indirect queries redirected to the special host name CHOOSER. /usr/lib/X11/xdm/chooser is the default. See the sections XDMCP Access Control and Chooser
DisplayManager.DISPLAY.xrdb: Specifies the program used to load the resources. By default, xdm uses /usr/bin/X11/xrdb.
DisplayManager.DISPLAY.cpp: This specifies the name of the C preprocessor which is used by xrdb.
DisplayManager.DISPLAY.setup: This specifies a program which is run (as root) before offering the Login window. This may be used to change the appearance of the screen around the Login window or to put up other windows (e.g., you may want to run xconsole here). By default, no program is run. The conventional name for a file used here is Xsetup. See the section Setup Program.
DisplayManager.DISPLAY.startup: This specifies a program which is run (as root) after the authentication process succeeds. By default, no program is run. The conventional name for a file used here is Xstartup. See the section Startup Program.
DisplayManager.DISPLAY.session: This specifies the session to be executed (not running as root). By default, /usr/bin/X11/xterm is run. The conventional name is Xsession. See the section Session Program.
DisplayManager.DISPLAY.reset: This specifies a program which is run (as root) after the session terminates. Again, by default no program is run. The conventional name is Xreset. See the section Reset Program.
DisplayManager.DISPLAY.openDelay
DisplayManager.DISPLAY.openRepeat
DisplayManager.DISPLAY.openTimeout
DisplayManager.DISPLAY.startAttempts: These numeric resources control the behavior of xdm when attempting to open intransigent servers. openDelay is the length of the pause (in seconds) between successive attempts, openRepeat is the number of attempts to make, openTimeout is the amount of time to wait while actually attempting the open (i.e., the maximum time spent in the connect(2) system call) and startAttempts is the number of times this entire process is done before giving up on the server. After openRepeat attempts have been made, or if openTimeout seconds elapse in any particular attempt, xdm terminates and restarts the server, attempting to connect again. This process is repeated startAttempts times, at which point the display is declared dead and disabled. Although this behavior may seem arbitrary, it has been empirically developed and works quite well on most systems. The default values are 5 for openDelay, 5 for open Repeat, 30 for openTimeout and 4 for startAttempts.
DisplayManager.DISPLAY. pinglnterval
DisplayManager.DISPLAY. pingTimeout: To discover when remote displays disappear, xdm occasionally pings them, using an X connection and XSync calls. Ping Interval specifies the time (in minutes) between each ping attempt, pingTimeout specifies the maximum amount of time (in minutes) to wait for the terminal to respond to the request. If the terminal does not respond, the session is declared dead and terminated. By default, both are set to 5 minutes. If you frequently use X terminals which can become isolated from the managing host, you may wish to increase this value. The only worry is that sessions will continue to exist after the terminal has been accidentally disabled. xdm will not ping local displays. Although it would seem harmless, it is unpleasant when the workstation session is terminated as a result of the server hanging for NFS service and not responding to the ping.
DlsplayManager.DISPLAY.terminateServer: This boolean resource specifics whether the X server should be terminated when a session terminates (instead of resetting it). This option can be used when the server tends to grow without bound over time, in order to limit the amount of time the server is run. The default value is "false. "
DisplayManager.DISPLAY.userPath: Xdm sets the PATH environment variable for the session to this value. It should be a colon separated list of directories; see sh(1) for a full description. ":/bin:/usr/bin:/usr/X11R6/bin:/usr/ucb" is a common setting. The default value can be specified at build time in the X system configuration file with DefaultUserPath.
DisplayManager.DISPLAY.systemPath: Xdm sets the PATH environment variable for the startup and reset scripts to the value of this resource. The default for this resource is specified at build time by the DefaultSystemPath entry in the system configuration file; "/etc:/bin:/usr/bin:/usr/X11R6/bin:/usr/ucb" is a common choice. Note the absence of "." from this entry. This is a good practice to follow for root; it avoids many common Trojan Horse system penetration schemes.
DisplayManager.DISPLAY. systemShell: Xdm sets the SHELL environment variable for the startup and reset scripts to the value of this resource. It is /bii/sh by default.
DisplayManager.DISPLAY.failsafeClient: If the default session fails to execute, xdm will fall back to this program. This program is executed with no arguments, but executes using the same environment variables as the session would have had (see the section Session Program). By default, /usr/bin/X11/xterm is used.
DisplayManager.DISPLAY.grabServer
DisplayManager.DISPLAY.grabTimeout: To improve security, xdm grabs the server and keyboard while reading the login name and password. The grab Server resource specifies if the server should be held for the duration of the name/password reading. When "false, " the server is ungrabbed after the keyboard grab succeeds, otherwise the server is grabbed until just before the session begins. The default is "false." The grabTimeout resource specifies the maximum time xdm will wait for the grab to succeed. The grab may fail if some other client has the server grabbed, or possibly if the network latencies are very high. This resource has a default value of 3 seconds; you should be cautious when raising it, as a user can be spoofed by a look-alike window on the display. If the grab fails, xdm kills and restarts the server (if possible) and the session.

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DisplayManager.DISPLAY.authorize

DisplayManager.DISPLAY.authName

authorize is a boolean resource which controls whether xdm generates and uses authorization for the local server connections. If authorization is used, authName is a list of authorization mechanisms to use, separated by white space. XDMCP connections dynamically specify which authorization mechanisms are supported, so authName is ignored in this case. When authorize is set for a display and authorization is not available, the user is informed by having a different message displayed in the login widget. By default, authorize is "true." authName is "MITMAGIC-COOKIE-1," or, if XDM-AUTHORIZATION-1 is available, "XDMAUTHORIZATION-1 MIT-MAGIC-COOKIE-1."

DisplayManager.DISPLAY.authFile

This file is used to communicate the authorization data from xdm to the server, using the - auth server command line option. It should be kept in a directory which is not world-writable as it could easily be removed, disabling the authorization mechanism in the server.

DisplayManager.DISPLAY.authComplain

If set to "false," disables the use of the unsecureGreeting in the login window. See the section Authentication Widget. The default is "true."

DisplayManager.DISPLAY.resetSignal

The number of the signal xdm sends to reset the server. See the section Controlling the Server. The default is 1 (SIGHUP).

DisplayManager.DISPLAY.termSignal

The number of the signal xdm sends to terminate the server. See the section Controlling the Server. The default is 15 (SIGTERM).

DisplayManager.DISPLAY.resetForAuth

The original implementation of authorization in the sample server reread the authorization file at server reset time, instead of when checking the initial connection. As xdm generates the authorization information just before connecting to the display, an old server would not get up-to-date authorization information. This resource causes xdm to send SIGHUP to the server after setting up the file, causing an additional server reset to occur, during which time the new authorization information will be read. The default is "false," which will work for all MIT servers.

DisplayManager.DISPLAY.userAuthDir

When xdm is unable to write to the usual user authorization file ($HOME/.Xauthority), it creates a unique file name in this directory and points the environment variable XAUTHORITY at the created file. It uses /tmp by default.

CONFIGURATION FILE

First, the xdm configuration file should be set up. Make a directory (usually < XRoot>/lib/X11/xdm, where < XRoot> refers to the root of the X11 install tree) to contain all of the relevant files. In the examples that follow, we use /usr/X11R6 as the value of < XRoot> .

Here is a reasonable configuration file, which could be named xdm-config:

DisplayManager.servers:	/usr/X11R6/iib/X11/xdm/Xservers
DisplayManager.errorLogFile:	/usr/X11R6/lib/X11/xdm/xdm-errors
DisplayManager*resources:	/usr/S11R6/iib/X11/xdm/Xresources
DisplayManager*startup:	/usr/X11R6/lib/X11/xdm/Xstartup
DisplayManager*session:	/usr/X11R6/lib/X11/xdm/Xsession
DisplayManager.pidFile:	/usr/X11R6/lib/X11/xdm/xdm-pid
DisplayManager._0.authorize:	true
DisplayManager*authorize:	false

Note that this file mostly contains references to other files. Note also that some of the resources are specified with "*" separating the components. These resources can be made unique for each different display, by replacing the "*" with the display-name, but normally this is not very useful. See the Resources section for a complete discussion.

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XDMCP ACCESS CONTROL

The database file specified by the DisplayManager.accessFile provides information which xdm uses to control access from displays requesting XDMCP service. This file contains three types of entries: entries which control the response to Direct and Broadcast queries, entries which control the response to Indirect queries, and macro definitions.

The format of the Direct entries is simple, either a host name or a pattern, which is distinguished from a host name by the inclusion of one or more meta characters ('*' matches any sequence of 0 or more characters, and '?' matches any single character) which are compared against the host name of the display device. If the entry is a host name, all comparisons are done using network addresses, so any name which converts to the correct network address may be used. For patterns, only canonical host names are used in the comparison, so ensure that you do not attempt to match aliases. Preceding either a host name or a pattern with a '!' character causes hosts which match that entry to be excluded.

An Indirect entry also contains a host name or pattern, but follows it with a list of host names or macros to which indirect queries should be sent.

A macro definition contains a macro name and a list of host names and other macros that the macro expands to. To distinguish macros from hostnames, macro names start with a '%' character. Macros may be nested.

Indirect entries may also specify to have xdm run chooser to offer a menu of hosts to connect to. See the section Chooser.

When checking access for a particular display host, each entry is scanned in turn and the first matching entry determines the response. Direct and Broadcast entries are ignored when scanning for an Indirect entry and vice-versa.

Blank lines are ignored, '#' is treated as a comment delimiter causing the rest of that line to be ignored, and 'newline' causes the newline to be ignored, allowing indirect host lists to span multiple lines.

Here is an example Xaccess file:

# Xaccess - XDMCP access control file

# Direct/Broadcast query entries

!xtra.lcs.mit.edu	# disallow direct/broadcast service for xtra
bambi.ogi.edu	# allow access from this particular display
*.lss.mit.edu	# allow access from any display in LCS

# Indirect query entries

%HOSTS	expo.lcs.mit.edu xenon.lcs.mit.edu

excess.lcs.mit.edu kanga.lcs.mit.edu

extract.lcs.mit.edu	xenon.lcs.mit.edu	# force extract to contact xenon
!xtra.lcs.mit.edu	dummy	#disallow indirect access
*.lcs.mit.edu	%HOSTS	# all others get to choose

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CHOOSER

For X terminals that do not offer a host menu for use with Broadcast or Indirect queries, the chooser program can do this for them. In the Xaccess file, specify "CHOOSER" as the first entry in the Indirect host list. Chooser will send a Query request to each of the remaining host names in the list and offer a menu of all the hosts that respond.

The list may consist of the word "BROADCAST," in which case chooser will send a Broadcast instead, again offering a menu of all hosts that respond. Note that on some operating systems, UDP packets cannot be broadcast, so this feature will not work.

Example Xaccess file using chooser:

extract.lcs.mit.edu	CHOOSER %HOSTS	# offer a menu of these hosts
xtra.lcs.mit.edu	CHOOSER BROADCAST	# offer a menu of all hosts

The program to use for chooser is specified by the DisplayManager.DISPLAY.chooser resource. For more flexibility at this step, the chooser could be a shell script. Chooser is the session manager here; it is run instead of a child xdm to manage the display.

Resources for this program can be put into the file named by DlsplayManager.DISPLAY.resources.

When the user selects a host, chooser prints the host chosen, which is read by the parent xdm, and exits. xdm closes its connection to the X server, and the server resets and sends another Indirect XDMCP request. xdm remembers the user's choice (for DisplayManager.choiceTimeout seconds) and forwards the request to the chosen host, which starts a session on that display.

LOCAL SERVER SPECIFICATION

The resource DisplayManager.servers gives a server specification or, if the values starts with a slash (/), the name of a file containing server specifications, one per line.

Each specification indicates a display which should constantly be managed and which is not using XDMCP. This method is used typically for local servers only. If the resource or the file named by the resource is empty, xdm will offer XDMCP service only.

Each specification consists of at least three parts: a display name, a display class, a display type, and (for local servers) a command line to start the server. A typical entry for local display number 0 would be:

:0 Digital-QV local /usr/X11R6/bin/X :0

The display types are:

local	local display: xdm must run the server
foreign	emote display: xdm opens an X connection to a running server

The display name must be something that can be passed in the - display option to an X program. This string is used to generate the display-specific resource names, so be careful to match the names (e.g., use ":0 Sun-CG3 local /usr/X11R6/bin/X :0" instead of "localhost:0 Sun-CG3 local /usr/X11R6/bin/X :0" if your other resources are specified as "DisplayManager._0.session"). The display class portion is also used in the display-specific resources, as the class of the resource. This is useful if you have a large collection of similar displays (such as a corral of X terminals) and would like to set resources for groups of them. When using XDMCP, the display is required to specify the display class, so the manual for your particular X terminal should document the display class string for your device. If it doesn't, you can run xdm in debug mode and look at the resource strings which it generates for that device, which will include the class string.

When xdm starts a session, it sets up authorization data for the server. For local servers, xdm passes "- auth filename" on the server's command line to point it at its authorization data. For XDMCP servers, xdm passes the authorization data to the server via the Accept XDMCP request.

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RESOURCES FILE

The Xresources file is loaded onto the display as a resource database using xrdb. As the authentication widget reads this database before starting up, it usually contains parameters for that widget:

xlogin*login.translations: # override

Ctrl< Key> R: abort-display( )

< Key> F1: set-session-argument(failsafe) finish-field( )

< Key> Return: set-session-argument( ) finish-field( )

xlogin*borderWidth: 3
xlogin*greeting: CLIENTHOST
# ifdef COLOR
xlogin*greetColor: CadetBlue
xlogin*failColor: red
# endif

Please note the translations entry; it specifies a few new translations for the widget which allow users to escape from the default session (and avoid troubles that may occur in it). Note that if # override is not specified, the default translations are removed and replaced by the new value, not a very useful result as some of the default translations are quite useful (such as "< Key>: insert-char ( )" which responds to normal typing).

This file may also contain resources for the setup program and chooser.

SETUP PROGRAM

The Xsetup file is run after the server is reset, but before the Login window is offered. The file is typically a shell script. It is run as root, so should be careful about security. This is the place to change the root background or bring up other windows that should appear on the screen along with the Login widget.

In addition to any specified by DisplayManager.exportList, the following environment variables are passed:

DISPLAY	the associated display name
PATH	the value of DisplayManager.DlSPLAY.systemPath
SHELL	the value of DisplayManager.DlSPLAY.systemShell
XAUTHORITY	may be set to an authority file

Note that since xdm grabs the keyboard, any other windows will not be able to receive keyboard input. They will be able to interact with the mouse, however; beware of potential security holes here. If DisplayManager.DlSPLAY.grabServer is set, Xsetup will not be able to connect to the display at all. Resources for this program can be put into the file named by DisplayManager.DlSPLAY.resources.

Here is a sample Xsetup script:

# !/bin/sh

# Xsetup_0 - setup script for one workstation

xcmsdb < /usr/X11R6/lib/monitors/alex.0

xconsole - geometry 480

l30- 0- 0 - notify - verbose - exitOnFail &

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AUTHENTICATION WIDGET: The authentication widget reads a name/password pair from the keyboard. Nearly every imaginable parameter can be controlled with a resource. Resources for this widget should be put into the file named by DisplayManager.DlSPLAY.resources. All of these have reasonable default values, so it is not necessary to specify any of them.

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STARTUP PROGRAM

The Xstartup file is typically a shell script. It is run as root and should be very careful about security. This is the place to put commands which add entries to /etc/utmp (the sessreg program may be useful here), mount users' home directories from file servers, display the message of the day, or abort the session if logins are not allowed.

In addition to any specified by DisplagManager.exportList, the following environment variables are passed:

DISPLAY	the associated display name
HOME	the initial working directory of the user
USER	the user name
PATH	the value of DisplayManager.DlSPLAY.systemPath
SHELL	the value of DisplayManager.DlSPLAY.systemShell
XAUTHORITY	may be set to an authority file

No arguments are passed to the script. Xdm waits until this script exits before starting the user session. If the exit value of this script is non-zero, xdm discontinues the session and starts another authentication cycle.

The sample Xstartup file shown here prevents login while the file /etc/nologin exists. Thus this is not a complete example, but simply a demonstration of the available functionality.

Here is a sample Xstartup script;

            #!/bin/sh
            #
            # Xstartup
            #
            # This program is run as root after the user is verified
            #
            if[- f /etc/nologin]; then
                     xmessage - file /etc/nologin
                     exit 1
            fi
            sessreg - a - 1 $DISPLAY - x /usr/X11R6/lib/xdm/Xservers $USER
            /usr/X11R6/lib/xdm/GiveConsole
            exit 0

SESSION PROGRAM

The Xsession program is the command which is run as the user's session. It is run with the permissions of the authorized user.

In addition to any specified by DisplayManager.exportList, the following environment variables are passed:

DISPLAY	the associated display name
HOME	the initial working directory of the user
USER	the user name
PATH	the value of DisplayManager.DlSPLAY.userPath
SHELL	the user's default shell (from getpwnam)
XAUTHORITY	may be set to a non-standard authority file
KRB5CCNAME	may be set to a Kerberos credentials cache file

At most installations, Xsession should look in $HOME for a file .xsession, which contains commands that each user would like to use as a session. Xsession should also implement a system default session if no user-specified session exists. See the section Typical Usage.

An argument may be passed to this program from the authentication widget using the 'set-session-argument' action. This can be used to select different styles of session. One good use of this feature is to allow the user to escape from the ordinary session when it fails. This allows users to repair their own .xsession if it fails, without requiring administrative intervention. The example following demonstrates this feature.

This example recognizes the special "failsafe" mode, specified in the translations in the Xresources file, to provide an escape from the ordinary session. It also requires that the .xsession file be executable so we don't have to guess what shell it wants to use.

             # !/bin/sh
             #
             # Xsession
             #
             # This is the program that is run as the client
             # for the display manager.
case $# in
             1)
                     case $1 in
                     failsafe)
                              exec xterm - geometry 8024- 0- 0
                              ;;
                     esac
             esac
             startup= $HOME/.xsession
             resources= $HOME/.Xresources
if [ - f "$startup" ]; then
                      exec "$startup"
             else
                      if [ - f "$resources" ]; then
                                 xrdb - load "$resources"
fi
                      twm &
                      xman - geometry + 10-10 &
                      exec xterm - geometry 8024+ 10+10 - ls
             fi

The user's .xsession file might look something like this example. Don't forget that the file must have execute permission.

             # ! /bin/csh
             # no - f in the previous line so .cshrc gets run to set $PATH
             twm &
             xrdb - merge "$HOME/.Xresources"
             emacs - geometry + 0+ 50 &
             xbiff- geometry - 430+ 5 &
             xterm - geometry - 0+ 50 -ls

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RESET PROGRAM: Symmetrical with Xstartup, the Xreset script is run after the user session has terminated. Run as root, it should contain commands that undo the effects of commands in Xstartup, removing entries from /etc/utmp or unmounting directories from file servers. The environment variables that were passed to Xstartup are also passed to Xreset.

A sample Xreset script:; # !/bin/sh
#
# Xreset
#
# This program is run as root after the session ends
#
sessreg - d - 1 $DISPLAY - x /usr/X11R6/lib/xdm/Xservers $USER
/usr/X11R6/lib/xdm/TakeConsole
exit 0
CONTROLLING THE SERVER: Xdm controls local servers using POSIX signals. SICHUP is expected to reset the server, closing all client connections and performing other cleanup duties. SIGTERM is expected to terminate the server. If these signals do not perform the expected actions, the resources DisplayManager.DISPLAY.resetSignal and DisplayManager.DISPLAY.termSignal can specify alternate signals.

To control remote terminals not using XDMCP, xdm searches the window hierarchy on the display and uses the protocol request KillClient in an attempt to clean up the terminal for the next session. This may not actually kill all of the clients, as only those which have created windows will be noticed. XDMCP provides a more sure mechanism; when xdm closes its initial connection, the session is over and the terminal is required to close all other connections.
CONTROLLING XDM: Xdm responds to two signals: SIGHUP and SIGTERM. When sent a SIGHUP, xdm rereads the configuration file, the access control file, and the servers file. For the servers file, it notices if entries have been added or removed. If a new entry has been added, xdm starts a session on the associated display. Entries which have been removed are disabled immediately, meaning that any session in progress will be terminated without notice and no new session will be started.

When sent a SIGTERM, xdm terminates all sessions in progress and exits. This can be used when shutting down the system.

Xdm attempts to mark its various sub-processes for ps(1) by editing the command line argument list in place. Because xdm can't allocate additional space for this task; it is useful to start xdm with a reasonably long command line (using the full path name should be enough). Each process which is servicing a display is marked - display.

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OTHER POSSIBILITIES

You can use xdm to run a single session at a time, using the 4.3 init options or other suitable daemon by specifying the server on the command line:

xdm - server ":0 SUN-3/60CG4 local /usr/X11R6/bin/X :0"

Or, you might have a file server and a collection of X terminals. The configuration for this is identical to the sample above, except the Xservers file would look like

extol:0 VISUAL-19 foreign

exalt:0 NCD-19 foreign

explode:0 NCR -TOWER VIEW3000 foreign

This directs xdm to manage sessions on all three of these terminals. See the section Controlling Xdm for a description of using signals to enable and disable these terminals in a manner reminiscent of init(8) .

LlMITATIONS

One thing that xdm isn't very good at doing is coexisting with other window systems. To use multiple window systems on the same hardware, you'll probably be more interested in xinit.

FILES

usr/lib/X11/xdm/xdm-config

the default configuration file

$HOME/.Xauthority user authorization file where xdm stores keys for clients to read

< XRoot> /1ib/X11/xdm/chooser

the default chooser

< XRoot> /bin/X11/xrdb
the default resource database loader

< XRoot> /bin/X11/X the default server

< XRoot> /bin/X11/xterm
the default session program and failsafe client

< XRoot> /lib/X11/xdm/A < display > - < suffix>
the default place for authorization files

/tmp/K5C< display> Kerberos credentials cache

Note: < XRoot> refers to the root of the X11 install tree.

SEE ALSO

X (1),xinit (1),xauth (1),Xsecurity (1),sessreg (1),Xserver (1),
X Display Manager Control Protocol

AUTHOR

Keith Packard, MIT X Consortium

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NAME: xdpyinfo - display information utility for X
SYNOPSIS: xdpyinfo [- display displayname] [- queryExtensions]
DESCRIPTION: Xdpyinfo is a utility for displaying information about an X server. It is used to examine the capabilities of a server, the predefined values for various parameters used in communicating between clients and the server, and the different types of screens and visuals that are available.

By default, numeric information (opcode, base event, base error) about protocol extensions is not displayed. This information can be obtained with the - queryExtensions option. Use of this option on servers that dynamically load extensions will likely cause all possible extensions to be loaded, which can be slow and can consume significant server resources.
ENVIRONMENT: DISPLAY; To get the default host, display number, and screen.
SEE ALSO: X(1), xwininfo(1), xprop(1), xrdb(1)
AUTHOR: Jim Fulton, MIT X Consortium

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NAME

xedit - simple text editor for X

SYNOPSIS

xedit [ -toolkitoption . . . ] [filename ]

DESCRIPTION

Xedit provides a window consisting of the following four areas:

Commands Section	A set of commands that allow you to exit xedit, save the file, or load a new file into the edit window.
Message Window	Displays xedit messages. In addition, this window can be used as a scratch pad.
Filename Display	Displays the name of the file currently being edited, and whether this file is Read-Write or Read Only.
Edit Window	Displays the text of the file that you are editing or creating.

OPTIONS

Xedit: accepts all of the standard X Toolkit command line options (see X(1)). The order of the command line options is not important.
filename: Specifies the file that is to be loaded during start-up. This is the file which will be edited. If a file is not specified, xedit lets you load a file or create a new file after it has started up.

EDITING

The Athena Text widget is used for the three sections of this application that allow text input. The characters typed will go to the Text widget that the pointer cursor is currently over. If the pointer cursor is not over a text widget then the keypresses will have no effect on the application. This is also true for the special key sequences that popup dialog widgets, so typing Control-S in the filename widget will enable searching in that widget, not the edit widget.

Both the message window and the edit window will create a scrollbar if the text to display is too large to fit in that window. Horizontal scrolling is not allowed by default, but can be turned on through the Text widget's resources, see the Athena Widget Set - C Language Interface in SUPER-UX X Toolkit Programming Manual for the exact resource definition.

The following keystroke combinations are defined:

Ctrl-a	Beginning Of Line	Meta-b	Backward Word
Ctrl-b	Backward Character	Meta-f	Forward Word
Ctrl-d	Delete Next Character	Meta-i	Insert File
Ctrl-e	End Of Line	Meta-k	Kill To End Of Paragraph
Ctrl-f	Forward Character	Meta-q	Form Paragraph
Ctrl-g	Multiply Reset	Meta-v	Previous Page
Ctrl-h	Delete Previous Character	Meta-y	Insert Current Selection
Ctrl-j	Newline And Indent	Meta-z	Scroll One Line Down
Ctrl-k	Kill To End Of Line	Meta-d	Delete Next Word
Ctrl-l	Redraw Display	Meta-D	Kill Word
Ctrl-m	Newline	Meta-h	Delete Previous Word
Ctrl-n	Next Line	Meta-H	Backward Kill Word
Ctrl-o	Newline And Backup	Meta-<	Beginning Of File
Ctrl-p	Previous Line	Meta->	End Of File
Ctrl-r	Search/Replace Backward	Meta-]	Forward Paragraph
Ctrl-s	Search/Replace Forward	Meta-[	Backward Paragraph
Ctrl-t	Transpose Characters
Ctrl-u	Multiply by 4	Meta-Delete	Delete Previous Word
Ctrl-v	Next Page	Meta-Shift Delete	Kill Previous Word
Ctrl-w	Kill Selection	Meta-Backspace	Delete Previous Word
Ctrl-y	Unkill	Meta-Shift Backspace	Kill Previous Word
Ctrl-z	Scroll One Line Up

In addition, the pointer may be used to cut and paste text:

Button 1 Down	Start Selection
Button 1 Motion	Adjust Selection
Button 1 Up	End Selection (cut)
Button 2 Down	Insert Current Selection (paste)
Button 3 Down	Extend Current Selection
Button 3 Motion	Adjust Selection
Button 3 Up	End Selection (cut)

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COMMANDS

Quit: Quits the current editing session. If any changes have not been saved, xedit displays a warning message, allowing the user to save the file.
Save: If file backups arc enabled (see RESOURCES, below) xedit stores a copy of the original, unedited file in < prefix>file< suffix>, then overwrites the file with the contents of the edit window. The filename is retrieved from the Text widget directly to the right of the Load button.
Load: Loads the file named in the text widget immediately to the right of the this button and displays it in the Edit window. If the currently displayed file has been
modified a warning message will ask the user to save the changes, or press Load again.

RESOURCES

For xedit the available resources are:

enableBackups (Class EnableBackups): Specifies that, when edits made to an existing file are saved,xedit is to copy the original version of that file to <prefix>file<suffix> before it saves The changes. The default value for this resource is "off," stating that no backups should be created.
backupNamePrefix (Class BackupNamePrefix): Specifies a string that is to be prepended to the backup filename. The default is that no string shall be prepended.
backupNameSuffix (Class BackupNameSuffix): Specifies a string that is to be appended to the backup filename. The default is to use ".BAK" as the suffix.

WIDGETS

In order to specify resources, it is useful to know the hierarchy of the widgets which compose xedit. In the notation below, indentation indicates hierarchical structure. The widget class name is given first, followed by the widget instance name.

Xedit xedit: Paned paned
Paned buttons: Command quit; Command save; Command load; Text filename
Label bc_label
Text messageWindow
Label labelWindow
Text editWindow

ENVIRONMENT

DISPLAY	to get the default host and display number.
XENVIRONMENT	to get the name of a resource file that overrides the global resources stored in the RESOURCE_MANAGER property.

FILES

< XRoot> /lib/X11/app-defaults/Xedit: specifies required resources

SEE ALSO

X(1), xrdb(1),Athena Widget Set - C Language Interface in SUPER-UX X Toolkit Programming Manual

RESTRICTIONS

There is no undo function.

COPYRIGHT

Copyright 1988, Digital Equipment Corporation.
Copyright 1989, X Consortium
See X(1) for a full statement of rights and permissions.

AUTHOR

Chris D. Peterson, MIT X Consortium

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NAME: xev - print contents of X events
SYNOPSIS: xev [- display displayname] [- geometry geom] [- bw pixels] [- bs {NotUseful,WhenMapped,Always}] [- id windowid] [- s] [- name string] [- rv]
DESCRIPTION: Xev creates a window and then asks the X server to send it events whenever anything happens to the window (such as being moved, resized, typed in, clicked in, etc.). You can also attach it to an existing window. It is useful for seeing what causes events to occur and to display the information that they contain.
OPTIONS
SEE ALSO: X(1), xwininfo(1), xdpyinfo(1), Xlib Programmers Manual, X Protocol Specification
See X(1) for a full statement of rights and permissions.
AUTHOR: Jim Fulton, MIT X Consortium

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NAME: xfd- display all the characters in an X font
SYNOPSIS: xfd [- options ...] - fontname
DESCRIPTION: The xfd utility creates a window containing the name of the font being displayed, a row of command buttons, several lines of text for displaying character metrics, and a grid containing one glyph per cell. The characters are shown in increasing order from left to right, top to bottom. The first character displayed at the top left will be character number 0 unless the - start option has been supplied in which case the character with the number given in the - start option will be used.

The characters are displayed in a grid of boxes, each large enough to hold any single character in the font. Each character glyph is drawn using the PolyTextl6 request (used by the Xlib routine XDrawString16). If the - box option is given, a rectangle will be drawn around each character, showing where an ImageTextl6 request (used by the Xlib routine XDrawImageStringl6) would cause background color to be displayed.

The origin of each glyph is normally set so that the character is drawn in the upper left hand corner of the grid cell. However, if a glyph has a negative left bearing or an unusually large ascent, descent, or right bearing (as is the case with cursor font), some character may not appear in their own grid cells. The - center option may be used to force all glyphs to be centered in their respective cells.

All the characters in the font may not fit in the window at once. To see the next page of glyphs, press the Next button at the top of the window. To see the previous page, press Prev. To exit xfd, press Quit.

Individual character metrics (index, width, bearings, ascent and descent) can be displayed at the top of the window by clicking on the desired character.

The font name displayed at the top of the window is the full name of the font, as determined by the server. See xlsfonts for ways to generate lists of fonts, as well as more detailed summaries of their metrics and properties.
OPTIONS: xfd accepts all of the standard toolkit command line options along with the additional options listed below:

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WIDGETS

In order to specify resources, it is useful to know the widgets which compose xfd. In the notation below, indentation indicates hierarchical structure. The widget class name is given first, followed by the widget instance name. The application class name is Xfd.

Xfd xfd: Paned pane
Label fontname
Box box: Command quit; Command prev; Command next
Label metrics
Label range
Label start
Form form: FontGrid grid

FONTGRID RESOURCES

The FontGrid widget is an application-specific widget, and a subclass of the Simple widget in the Athena widget set. The effects and instance names of this widget's resources are given in the OPTIONS section. Capitalize the first letter of the resource instance name to get the corresponding class name.

APPLICATION SPECIFIC RESOURCES

The instance names of the application specific resources are given below. Capitalize the first letter of the resource instance name to get the corresponding class name. These resources are unlikely to be interesting unless you are localizing xfd for a different language.

selectFormat: Specifies a printf-style format string used to display information about the selected character.
The default is "character 0x%02x%02x (%u,%u) (%# o,%# o)". The arguments that will come after the format string are char.byte1, char.byte2, char.byte1, char.byte2, char.byte1, char.byte2. char.byte1 is byte 1 of the selected character. char.byte2 is byte 2 of the selected character .
metricsFormat: Specifies a printf-style format string used to display character metrics. The default is "width %d; left %d, right %d; ascent %d, descent %d (font %d, %d)". The arguments that will come after the format string are the character metrics width, lbearing, rbearing, character ascent, character descent, font ascent, and font descent.
rangeFormat: Specifies a printf-style format string used to display the range of characters currently being displayed. The default is "range: 0x%02x%02x (%u,%u) thru 0x%02x%02x (%u,%u)". The arguments that will come after the format string are the following fields from the XFontStruct that is returned from opening the font: min_byte1, min_char_or_byte2, min_byte1, min_char_or_byte2, max_byte1, max_char_or_byte2, max_byte1, max_char_or_byte2.
startFormat: Specifies a printf-style format string used to display information about the character at the upper left corner of the font grid. The default is "upper left: 0x%04x (%d,%d)". The arguments that will come after the format string are the new character, the high byte of the new character, and the low byte of the new character.
nocharFormat: Specifies a printf-style format string to display when the selected character does not exist. The default is "no such character 0x%02x%02x (%u,%u) (%#o,%#o)". The arguments that will come after the format string are the same as for the selectFormat resource.

SEE ALSO

X(1), xlsfonts(1), xrdb(1), xfontsel(1), X Logical Font Descriplion Conventions

BUGS

The program should skip over pages full of non-existent characters.

AUTHOR

Jim Fulton, MIT X Consortium; previous program of the same name by Mark Lillibridge, MIT Project Athena .

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NAME: xfontset - point & click interface for selecting X11 font names
SYNOPSIS: xfontsel [-toolkitoption ...] [-pattern fontname] [-print] [-sample text] [-samplel1 text16] [ noscaled]
DESCRIPTION: The xfontsel application provides a simple way to display the fonts known to your X server, examine samples of each, and retrieve the X Logical Font Description ("XLFD") full name for a font.

If -pattern is not specified, all fonts with XLFD 14-part names will be selectable. To work with only a subset of the fonts, specify -pattern followed by a partially or fully qualified font name; e.g., "-pattern *medium*" will select that subset of fonts which contain the string "medium" somewhere in their font name. Be careful about escaping wildcard characters in your shell.

If -print is specified on the command line the selected font specifier will be written to standard output when the quit button is activated. Regardless of whether or not -print was specified, the font specifier may be made the PRIMARY (text) selection by activating the select button.

The -sample option specifies the sample text to be used to display the selected font if the font is linearly indexed, overriding the default.

The -sample16 option specifies the sample text to be used to display the selected font if the font is matrix encoded, overriding the default.

The -noscaled option disables the ability to select scaled fonts at arbitrary pixel or point sizes. This makes it clear which bitmap sizes are advertised by the server, and can avoid an accidental and sometimes prolonged wait for a font to be scaled.
INTERACTIONS: Clicking any pointer button in one of the XLFD field names will pop up a menu of the currently-known possibilities for that field. If previous choices of other fields were made, only values for fonts which matched the previously selected fields will be selectable; to make other values selectable, you must deselect some other field(s) by choosing the "*" entry in that field. Unselectable values may be omitted from the menu entirely as a configuration option; see the ShowUnselectable resource, below. Whenever any change is made to a field value, xfontsel will assert ownership of the PRIMARY_FONT selection. Other applications (see, e.g., xterm) may then retrieve the selected font specification.

Scalable fonts come back from the server with zero for the pixel size, point size, and average width fields. Selecting a font name with a zero in these positions results in an implementation-dependent size. Any pixel or point size can be selected to scale the font to a particular size. Any average width can be selected to anamorphically scale the font (although you may find this challenging given the size of the average width menu).

Clicking the left pointer button in the select widget will cause the currently selected font name to become the PRIMARY text selection as well as the PRIMARY_FONT selection. This then allows you to paste the string into other applications. The select button remains highlighted to remind you of this fact, and de-highlights when some other application takes the PRIMARY selection away. The select widget is a toggle; pressing it when it is highlighted will cause xfontsel to release the selection ownership and de-highlight the widget. Activating the select widget twice is the only way to cause xfontsel to release the PRIMARY_FONT selection.
RESOURCES: The application class is XFontSel. Most of the user-interface is configured in the app-defaults file; if this file is missing a warning message will be printed to standard output and the resulting window will be nearly incomprehensible.

Most of the significant parts of the widget hierarchy are documented in the app-defaults file (normally < Xrooto> /lib/X11/app-defaults/XFontSel, where < XRoot> refers to the root of the X11 install tree.)

Application specific resources:
FlLES: $XFILESEARCHPATH/XFontSel
SEE ALSO: xrdb(1), xfd(1)
BUGS: Sufficiently ambiguous patterns can be misinterpreted and lead to an initial selection string which may not correspond to what the user intended and which may cause the initial sample text output to fail to match the proffered string. Selecting any new field value will correct the sample output, though possibly resulting in no matching font.

Should be able to return a FONT for the PRIMARY selection, not just a STRING.

Any change in a field value will cause xfontsel to assert ownership of the PRIMARY_FONT selection.
Perhaps this should be parameterized.

When running on a slow machine, it is possible for the user to request a field menu before the font names have been completely parsed. An error message indicating a missing menu is printed to stderr but otherwise nothing bad (or good) happens.

The average-width menu is too large to be useful.
COPYRIGHT: Copyright 1989, 1991, X Consortium
See X(1) for a full statement of rights and permissions.
AUTHOR: Ralph R. Swick, Digital Equipment Corporation/MIT Project Athena

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Contents

Previous Chapter

Chapter 1 Cont.

Next Chapter

Ctrl<Key>H:	delete-previous-character( ) n
Ctrl<Kcy>D:	delele-character( ) n
Ctrl<Key>B:	move-backward-character( ) n
Ctrl<Key>F:	move-forward-character( ) n
Ctrl<Key>A:	move-to-begining( ) n
Ctrl<Key>E:	move-to-end( ) n
Ctrl< Key> K:	erase-to-end-of-line( ) n
Ctrl< Key> U:	erase-line( ) n
Ctrl< Key> X:	erase-line( ) n
Ctrl< Key> C:	estart-session( ) n
Ctrl< Key> :	abort-session( ) n
< Key> BackSpace:	delete-previous-character( ) n
< Key> Delete:	delete-previous-character( ) n
< Key> Return:	finish-field( ) n
< Key> :	insert-char( )