XENODM(1)

NAME
xenodm - X Display Manager

SYNOPSIS
xenodm [-config configuration_file] [-nodaemon] [-debug debug_level] [-error error_log_file] [-resources resource_file] [-server server_entry] [-session session_program]

DESCRIPTION
xenodm manages a collection of X displays on the local host. xenodm provides services similar to those provided by getty(8) and login(1) 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 xenodm 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, xenodm resets the X server and (optionally) restarts the whole process.

Because xenodm 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. xenodm 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
xenodm 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 xenodm-config or the file named by the -config option.

xenodm can manage X servers running on the local machine and specified in Xservers.

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

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

The xlogin widget, which xenodm presents, offers the familiar login and password prompts, unless autoLogin is set.

After the user logs in, xenodm runs the Xstartup script as root.

Then xenodm runs the Xsession script as the user. This system session file may do some additional startup and typically runs the .xsession 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 /var/log/xenodm.log will contain error messages from xenodm and anything output to stderr by Xsetup, Xstartup, Xsession or Xreset. When you have trouble getting xenodm working, check this file to see if xenodm has any clues to the trouble.

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 xenodm. /etc/X11/xenodm/xenodm-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 xenodm 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 xenodm to print lots of debugging statements to the terminal; it also disables the DisplayManager.daemonMode resource, forcing xenodm to run synchronously. To interpret these debugging messages, a copy of the source code for xenodm 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 xenodm 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(1) 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.

-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 xenodm can be controlled through the use of its configuration file, which is in the X resource format. Some resources modify the behavior of xenodm 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.

Because the resource manager uses colons to separate the name of the resource from its value and dots to separate resource name parts, xenodm 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.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(3) 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, Xsession 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 xenodm, which would normally not be useful.

DisplayManager.daemonMode
    Normally, xenodm 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.authDir
    This names a directory under which xenodm stores authorization files while initializing the session. The default value is /etc/X11/xenodm. Can be overridden for specific displays by DisplayManager.DISPLAY.authFile.

DisplayManager.autoRescan
    This boolean controls whether xenodm 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 xenodm to reread these files by sending a SIGHUP to the main process.

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

DisplayManager.DISPLAY.autoLogin
    This resource specifies the name of an user that will be logged in automatically, without displaying the xlogin widget.

DisplayManager.DISPLAY.resources
    This resource specifies the name of the file to be loaded by xrdb(1) as the resource database onto the root window of screen 0 of the display. The Xsetup program and the Login widget will use the resources set in this file. This resource database 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 /etc/X11/xenodm/Xresources is the conventional name.

DisplayManager.DISPLAY.xrdb
    Specifies the program used to load the resources. By default, xenodm uses /usr/X11R6/bin/xrdb.

DisplayManager.DISPLAY.cpp
    This specifies the name of the C preprocessor which is used by xrdb(1).

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(1) 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/X11R6/bin/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. 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

DisplayManager.DISPLAY.reservAttempts
    These numeric resources control the behavior of xenodm 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, xenodm 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 bound reservAttempts is the number of times a successful connect is allowed to be followed by a fatal error. When reached, the display is disabled. The default values are openDelay: 15, openRepeat: 5, openTimeout: 120, startAttempts: 4 and reservAttempts: 2.

DisplayManager.DISPLAY.terminateServer
    This boolean resource specifies 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
    xenodm 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. The default value is “/bin:/usr/bin:/sbin:/usr/sbin:/usr/X11R6/bin:/usr/local/bin:/usr/local/sbin”.

DisplayManager.DISPLAY.systemPath
    xenodm sets the PATH environment variable for the startup and reset scripts to the value of this resource. The default for this resource is “/sbin:/usr/sbin:/bin:/usr/bin:/usr/X11R6/bin”. 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
    xenodm sets the SHELL environment variable for the startup and reset scripts to the value of this resource. It is /bin/sh by default.

DisplayManager.DISPLAY.failsafeClient
    If the default session fails to execute, xenodm 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/X11R6/bin/xterm is used.

DisplayManager.DISPLAY.grabServer

DisplayManager.DISPLAY.grabTimeout
    To improve security, xenodm grabs the server and keyboard while reading the login name and password. The grabServer 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 xenodm 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, xenodm kills and restarts the server (if possible) and the session.

DisplayManager.DISPLAY.authorize

DisplayManager.DISPLAY.authName
    authorize is a boolean resource which controls whether xenodm 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. 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 “MIT-MAGIC-COOKIE-1”, or, if XDM-AUTHORIZATION-1 is available, “XDM-AUTHORIZATION-1 MIT-MAGIC-COOKIE-1”.

DisplayManager.DISPLAY.authFile
    This file is used to communicate the authorization data from xenodm 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. If not specified, a name is generated from DisplayManager.authDir and the name of the display.

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 xenodm sends to reset the server. See the section CONTROLLING THE SERVER. The default is 1 (SIGHUP).

DisplayManager.DISPLAY.termSignal
    The number of the signal xenodm 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 xenodm generates the authorization information just before connecting to the display, an old server would not get up-to-date authorization information. This resource causes xenodm 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.listenTcp
    If set to true, enable the listen tcp option for the given X server. When this setting is set to false, xenodm will only generate authorizations for the local (ie Unix socket) transport mechanism. Otherwise full authorization for all possible transport mechanisms will be generated. The default is false.

CONFIGURATION FILE
First, the xenodm configuration file should be set up. Make a directory (usually /etc/X11/xenodm) to contain all of the relevant files.

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

    DisplayManager.servers:      /etc/X11/xenodm/Xservers
    DisplayManager.errorLogFile: /var/log/xenodm.log
    DisplayManager*resources:    /etc/X11/xenodm/Xresources
    DisplayManager*startup:      /etc/X11/xenodm/Xstartup
    DisplayManager*session:      /etc/X11/xenodm/Xsession
    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.

LOCAL SERVER SPECIFICATION
The resource DisplayManager.servers gives a server specification or, if the value 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. If the resource or the file named by the resource is empty, xenodm will exit.

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

    :0 local /usr/X11R6/bin/X :0

The only recognized display type is:
local | local display: xenodm will run the 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 local /usr/X11R6/bin/X :0” instead of “localhost:0 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 xenodm starts a session, it sets up authorization data for the server. For local servers, xenodm passes “-auth filename” on the server's command line to point it at its authorization data.

RESOURCES FILE
The Xresources file is loaded onto the display as a resource database using xrdb(1). As the authentication widget reads this database before starting up, it usually contains parameters for that widget:

    xlogin*login.translations: #override\
    	<Key>F1: set-session-argument(failsafe) finish-field()\n\
    	<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.

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.DISPLAY.systemPath
SHELL
    the value of DisplayManager.DISPLAY.systemShell
XAUTHORITY
    may be set to an authority file

Note that since xenodm 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.DISPLAY.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.DISPLAY.resources.

Here is a sample Xsetup script:

    #!/bin/sh
    # Xsetup_0 - setup script for one workstation
    xcmsdb < /etc/X11/xenodm/monitors/alex.0
    xconsole -geometry 480x130-0-0 -notify -verbose -exitOnFail &

AUTHENTICATION WIDGET
The authentication widget prompts the user for the username, password, and/or other required authentication data 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.DISPLAY.resources. All of these have reasonable default values, so it is not necessary to specify any of them.

The resource file is loaded with xrdb(1) so it may use the substitutions defined by that program such as CLIENTHOST for the client hostname in the login message, or C pre-processor #ifdef statements to produce different displays depending on color depth or other variables.

xenodm is compiled with support for the Xft(3) library for font rendering. Font faces are specified using the resources with names ending in “face” in the fontconfig face format described in the “Font Names” section of fonts.conf(5).

xlogin.Login.width, xlogin.Login.height, xlogin.Login.x, xlogin.Login.y
    The geometry of the Login widget is normally computed automatically. If you wish to position it elsewhere, specify each of these resources.

xlogin.Login.foreground
    The color used to display the input typed by the user.

xlogin.Login.face
    The face used to display the input typed by the user. The default is “Serif-18”.

xlogin.Login.greeting
    A string which identifies this window. The default is “X Window System”.

xlogin.Login.unsecureGreeting
    When X authorization is requested in the configuration file for this display and none is in use, this greeting replaces the standard greeting. The default is “This is an unsecure session”.

xlogin.Login.greetFace
    The face used to display the greeting. The default is “Serif-24:italic”.

xlogin.Login.greetColor
    The color used to display the greeting.

xlogin.Login.namePrompt
    The string displayed to prompt for a user name. xrdb(1) strips trailing white space from resource values, so to add spaces at the end of the prompt (usually a nice thing), add spaces escaped with backslashes. The default is “Login: ”.

xlogin.Login.passwdPrompt
    The string displayed to prompt for a password, when not using an authentication system such as PAM that provides its own prompts. The default is “Password: ”.

xlogin.Login.promptFace
    The face used to display prompts. The default is “Serif-18:bold”.

xlogin.Login.promptColor
    The color used to display prompts.

xlogin.Login.changePasswdMessage
    A message which is displayed when the user's password has expired. The default is “Password Change Required”.

xlogin.Login.fail
    A message which is displayed when the authentication fails, when not using an authentication system such as PAM that provides its own prompts. The default is “Login incorrect”.

xlogin.Login.failFace
    The face used to display the failure message. The default is “Serif-18:bold”.

xlogin.Login.failColor
    The color used to display the failure message.

xlogin.Login.failTimeout
    The number of seconds that the failure message is displayed. The default is 10.

xlogin.Login.logoFileName
    Name of an XPM format pixmap to display in the greeter window, if built with XPM support. The default is no pixmap.

xlogin.Login.logoPadding
    Number of pixels of space between the logo pixmap and other elements of the greeter window, if the pixmap is displayed. The default is 5.

xlogin.Login.useShape
    If set to true, when built with XPM support, attempt to use the X Non-Rectangular Window Shape Extension to set the window shape. The default is true.

xlogin.Login.hiColor, xlogin.Login.shdColor
    Raised appearance bezels may be drawn around the greeter frame and text input boxes by setting these resources. hiColor is the highlight color, used on the top and left sides of the frame, and the bottom and right sides of text input areas. shdColor is the shadow color, used on the bottom and right sides of the frame, and the top and left sides of text input areas. The default for both is the foreground color, providing a flat appearance.

xlogin.Login.frameWidth
    frameWidth is the width in pixels of the area around the greeter frame drawn in hiColor and shdColor.

xlogin.Login.innerFramesWidth
    innerFramesWidth is the width in pixels of the area around text input areas drawn in hiColor and shdColor.

xlogin.Login.sepWidth
    sepWidth is the width in pixels of the bezeled line between the greeting and input areas drawn in hiColor and shdColor.

xlogin.Login.allowRootLogin
    If set to false, don't allow root (and any other user with uid = 0) to log in directly. The default is true. This setting is only checked by some of the authentication backends at this time.

xlogin.Login.allowNullPasswd
    If set to true, allow an otherwise failing password match to succeed if the account does not require a password at all. The default is false, so only users that have passwords assigned can log in.

xlogin.Login.echoPasswd
    If set to true, a placeholder character (echoPasswdChar) will be shown for fields normally set to not echo, such as password input. The default is false.

xlogin.Login.echoPasswdChar
    Character to display if echoPasswd is true. The default is ‘*’. If set to an empty value, the cursor will advance for each character input, but no text will be drawn.

xlogin.Login.translations
    This specifies the translations used for the login widget. Refer to the X Toolkit documentation for a complete discussion on translations. The default translation table is:

        Ctrl<Key>H:     delete-previous-character() \n\
        Ctrl<Key>D:     delete-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:     restart-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>Escape:	erase-line() \n\
        <Key>:          insert-char() \

    The actions which are supported by the widget are:

    delete-previous-character
        Erases the character before the cursor.

    delete-character
        Erases the character after the cursor.

    move-backward-character
        Moves the cursor backward.

    move-forward-character
        Moves the cursor forward.

    move-to-begining
        (Apologies about the spelling error.) Moves the cursor to the beginning of the editable text.

    move-to-end
        Moves the cursor to the end of the editable text.

    erase-to-end-of-line
        Erases all text after the cursor.

    erase-line
        Erases the entire text.

    finish-field
        If the cursor is in the name field, proceeds to the password field; if the cursor is in the password field, checks the current name/password pair. If the name/password pair is valid, xenodm starts the session. Otherwise the failure message is displayed and the user is prompted again.

    abort-session
        Terminates and restarts the server.

    abort-display
        Terminates the server, disabling it. This action is not accessible in the default configuration. There are various reasons to stop xenodm on a system console, such as when shutting the system down, or to generally access the console. Sending xenodm a SIGHUP will restart the display. See the section CONTROLLING XENODM.

    restart-session
        Resets the X server and starts a new session. This can be used when the resources have been changed and you want to test them or when the screen has been overwritten with system messages.

    insert-char
        Inserts the character typed.

    set-session-argument
        Specifies a single word argument which is passed to the session at startup. See the section SESSION PROGRAM.

    allow-all-access
        Disables access control in the server. This can be used when the .Xauthority file cannot be created by xenodm. Be very careful using this; it might be better to disconnect the machine from the network before doing this.

On some systems (OpenBSD) the user's shell must be listed in /etc/shells to allow login through xenodm. The normal password and account expiration dates are enforced too.

STARTUP PROGRAM
The Xstartup program is run as root when the user logs in. It is typically a shell script. Since it is run as root, Xstartup should be very careful about security. This is the place to put commands which add entries to utmp(5) or wtmp(5) files (the sessreg(1) program may be useful here), mount users' home directories from file servers, or abort the session if logins are not allowed.

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
LOGNAME
    the user name
USER
    the user name
PATH
    the value of DisplayManager.DISPLAY.systemPath
SHELL
    the value of DisplayManager.DISPLAY.systemShell
XAUTHORITY
    may be set to an authority file
WINDOWPATH
    may be set to the window path leading to the X server

No arguments are passed to the script. xenodm waits until this script exits before starting the user session. If the exit value of this script is non-zero, xenodm 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 -timeout 30 -center
    	exit 1
    fi
    sessreg -a -l $DISPLAY -x /etc/X11/xenodm/Xservers $LOGNAME
    /etc/X11/xenodm/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
LOGNAME
    the user name
USER
    the user name
PATH
    the value of DisplayManager.DISPLAY.userPath
SHELL
    the user's default shell (from getpwnam(3))
XAUTHORITY
    may be set to a non-standard authority file
WINDOWPATH
    may be set to the window path leading to the X server

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.

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 $1 in
    	failsafe)
    		exec xterm -geometry 80x24-0-0
    		;;
    	esac
    esac
    startup=$HOME/.xsession
    resources=$HOME/.Xresources
    if [ -f "$startup" ]; then
    	exec "$startup"
    else
    	if [ -f "$resources" ]; then
    		xrdb -load "$resources"
    	fi
    	xclock -geometry 100x100-0+0 &
    	xterm -geometry 80x24+10+10 -ls &
    	exec twm
    fi

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

    #! /bin/sh
    xrdb -merge "$HOME/.Xresources"
    emacs -geometry +0+50 &
    xbiff -geometry -430+5 &
    xterm -geometry -0+50 -ls &
    exec twm

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, updating entries in utmp(5) or wtmp(5) files, 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 -l $DISPLAY -x /etc/X11/xenodm/Xservers $LOGNAME
    /etc/X11/xenodm/TakeConsole
    exit 0

CONTROLLING THE SERVER
xenodm controls local servers using POSIX signals. SIGHUP 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.

CONTROLLING XENODM
xenodm responds to two signals: SIGHUP and SIGTERM. When sent a SIGHUP, xenodm 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, xenodm 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, xenodm terminates all sessions in progress and exits. This can be used when shutting down the system.

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

ADDITIONAL LOCAL DISPLAYS
To add an additional local display, add a line for it to the Xservers file. (See the section LOCAL SERVER SPECIFICATION.)

Examine the display-specific resources in xenodm-config (e.g., DisplayManager._0.authorize) and consider which of them should be copied for the new display. The default xenodm-config has all the appropriate lines for displays :0 and :1.

OTHER POSSIBILITIES
You can use xenodm to run a single session at a time, using the 4.3 init(8) options or other suitable daemon by specifying the server on the command line:

    xenodm -server ":0 local /usr/X11R6/bin/X :0"

LIMITATIONS
One thing that xenodm 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(1).

FILES
/etc/X11/xenodm/xenodm-config
    the default configuration file
$HOME/.Xauthority
    user authorization file where xenodm stores keys for clients to read
/usr/X11R6/bin/xrdb
    the default resource database loader
/usr/X11R6/bin/X
    the default server
/usr/X11R6/bin/xterm
    the default session program and failsafe client
/etc/X11/xenodm/Adisplay-suffix
    the default place for authorization files

SEE ALSO
sessreg(1), xauth(1), xinit(1), xrdb(1), Xserver(1), fonts.conf(5), X(7), Xsecurity(7) X Display Manager Control Protocol. R. Hinden, S. Deering, February 2006, RFC 4291, IP Version 6 Addressing Architecture.

AUTHOR
Keith Packard, MIT X Consortium