XDM(1) X11 R4.11MU05 XDM(1)
NAME
xdm - X Display Manager with support for XDMCP
SYNOPSIS
xdm [ -config configurationfile ] [ -nodaemon ] [ -debug debuglevel
] [ -error errorlogfile ] [ -resources resourcefile ] [ -server
serverentry ] [ -session sessionprogram ]
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 a login name and usually a 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 BroadcastQuery (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.
TYPICAL USAGE
Actually, xdm is designed to operate in such a wide variety of
environments that typical is probably a misnomer.
First, the xdm configuration file should be set up. Make a directory
(usually /usr/lib/X11/xdm) to contain all of the relevant files.
Here is a reasonable configuration file, which could be named xdm-
config:
DisplayManager.servers: /usr/lib/X11/xdm/Xservers
DisplayManager.errorLogFile: /usr/lib/X11/xdm/xdm-errors
DisplayManager*resources: /usr/lib/X11/xdm/Xresources
DisplayManager*startup: /usr/lib/X11/xdm/Xstartup
DisplayManager*session: /usr/lib/X11/xdm/Xsession
DisplayManager.pidFile: /usr/lib/X11/xdm/xdm-pid
DisplayManager._0.authorize: true
DisplayManager*authorize: false
Note that this file simply 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.
The first file, /usr/lib/X11/xdm/Xservers, contains the list of
displays to manage that are not using XDMCP. Most workstations have
only one display, numbered 0, so the file will look something like
this:
:0 Local local /usr/bin/X11/X :0
This will keep /usr/bin/X11/X running on this display and manage a
continuous cycle of sessions.
The file /usr/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.
The next configuration entry, /usr/lib/X11/xdm/Xresources, is loaded
onto the display as a resource database using xrdb. As the
authentication dialog reads this database before starting up, it
usually contains parameters for that dialog:
xlogin*translations: #override\
Ctrl<Key>R: reset-session() \n\
Ctrl<Key>X: restart-session() \n\
Ctrl<Key>Z: terminate-session() \n\
Ctrl<Key>plus: allow-all-access()
xlogin.borderWidth: 3
xlogin.loginForm.borderWidth: 3
xlogin.loginForm.scrolledWindow.height: 200
xlogin.loginForm.scrolledWindow.width: 350
xlogin.loginForm*getText.fontList: fixed
#ifndef COLOR
xlogin*foreground: black
xlogin*background: white
#else
xlogin*foreground: MidnightBlue
xlogin*background: LightSteelBlue
#endif
Please note the translations entry; it specifies a few new
translations for the authentication dialog that 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.
The Xstartup file shown here simply prevents login while the file
/etc/nologin exists. As there is no provision for displaying any
messages here (there isn't any core X client which displays files),
the user will probably be baffled by this behavior. 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 with enhanced capabilities after the user
# is verified
#
if [ -f /etc/nologin ]; then
exit 1
fi
exit 0
The most interesting script is Xsession. This version recognizes the
special ``failsafe'' mode, to provide an escape from the ordinary
session. The actual Xsession file delivered is more complicated. It
runs the file /usr/lib/X11/xdm/system.Xsession if the user's
$HOME/.Xsession file is not found. It also runs the user's login
scripts (ie. ~/.login) in an xterm prior to running the .Xsession
script.
#!/bin/sh
#
# Xsession
#
# This is the program that is run as the client
# for the display manager. This example is
# quite friendly as it attempts to run a per-user
# .Xsession file instead of forcing a particular
# session layout
#
case $# in
1)
case $1 in
failsafe)
exec xterm -geometry 80x24-0-0 -ls
;;
esac
esac
startup=$HOME/.Xsession
resources=$HOME/.Xdefaults
if [ -f $startup ]; then
exec $startup
exec /bin/sh $startup
else
if [ ! -f $resources ]; then
resources=$HOME/.Xdefaults
fi
if [ -f $resources ]; then
xrdb -load $resources
fi
twm &
exec xterm -geometry 80x24+10+10 -ls
fi
OPTIONS
All of these options, except -config, specify values that can also be
specified in the configuration file as resources.
-config configurationfile
Names the configuration file, which specifies resources to
control the behavior of xdm. /usr/lib/X11/xdm/xdm-config is
the default.
-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 debuglevel
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 errorlogfile
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 resourcefile
Specifies the value for the DisplayManager*resources resource.
This file is loaded using xrdb to specify configuration
parameters for the authentication dialog.
-server serverentry
Specifies the value for the DisplayManager.servers resource.
See the section Server Specification for a description of this
resource.
-udpPort portnumber
Specifies the value for the DisplayManager.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 sessionprogram
Specifies the value for the DisplayManager*session resource.
This indicates the program to run as the session after the
user has logged in.
-xrm resourcespecification
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
example, DisplayManager.expo0.startup is the name of the resource
which defines the startup shell file on the ``expo:0'' display.
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.
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 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, 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-privileged 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.
DisplayManager.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 whitespace-separated list of additional environment
variables to pass on to the Xsetup, Xstartup, Xsession, and
Xreset programs.
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.DISPLAY.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 Xlogin 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 (with enhanced
capabilities) before offering the Xlogin window. This may be
used to change the appearance of the screen around the Xlogin
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 (with enhanced
capabilities) 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 (running with the
user's capabilities). 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 (with enhanced
capabilities) 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
openRepeat, 30 for openTimeout and 4 for startAttempts.
DisplayManager.DISPLAY.pingInterval
DisplayManager.DISPLAY.pingTimeout
To discover when remote displays disappear, xdm occasionally
pings them, using an X connection and XSync calls.
pingInterval 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.
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
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. The default value is
``usr/bin:/usr/bin/X11''.
DisplayManager.DISPLAY.systemPath
Xdm sets the PATH environment variable for the startup and
reset scripts to the value of this resource. The default is
``/etc:/usr/bin:/usr/bin/X11''. Note the conspicuous absence
of "." from this entry. This is a good practice to follow for
privileged users; 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 /bin/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 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 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.
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
whitespace-separated list of authorization mechanisms to use.
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
``false''; authName is ``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.
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
*.lcs.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
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. Resources for this program
can be put into the file named by DisplayManager.DISPLAY.resources.
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. Each 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/bin/X11/X :0
The display types are:
local local display: xdm must run the server
foreign remote 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 local /usr/bin/X11/X :0'' instead of ``localhost:0 local
/usr/bin/X11/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
(like 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.
SETUP PROGRAM
The Xsetup file is run after the server is reset, but before the
Xlogin window is offered. The file is typically a shell script. It
is run with enhanced capabilities, 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
Xlogin 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 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.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.
AUTHENTICATION DIALOG
On a generic DG/UX system, the authentication dialog asks for a user
name and if appropriate, the user's password to authenticate the
user.
On a system with DG/UX information security, the authentication
dialog asks for a user name, followed by prompts for other types of
authentication information as specified in the A&A database. In
addition, the user can specify a MAC label when logging in by using
the -l option. For example,
Login: nathan -l acrlo
In this case, xdm creates the session with a process clearance (MAC
label) of acrlo, if the A&A database authorizations for the xdm
service permits this.
Nearly every imaginable parameter of the authentication dialog can be
controlled with a resource. Resources for this dialog 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 authentication dialog box is made up of Motif widgets, thus any
Motif widget resource may be set for this dialog. The class name for
the authentication dialog is Xlogin. The instance name is xlogin.
Some of the widgets that make up a typical authentication dialog
include:
xlogin (applicationShellWidgetClass)
loginForm (xmFormWidgetClass)
title (xmLabelWidgetClass)
scrolledWindow (xmScrolledWindowWidgetClass)
actionList (xmRowColumnWidgetClass)
An actionList may have one of more of
the following children:
showText (xmLabelWidgetClass)
getTextBB (xmBulletinBoardWidgetClass)
showText (xmLabelWidgetClass)
getText (xmTextWidgetClass)
selectListForm (xmFormWidgetClass)
scrolledSelectList (xmScrolledWindowWidgetClass)
selectList (xmListWidgetClass)
selectListConfirm (xmPushButtonWidgetClass)
showAckForm (xmFormWidgetClass)
OK (xmPushButtonWidgetClass)
failsafeToggle (xmToggleButtonWidgetClass)
buttonMenu (xmRowColumnWidgetClass)
resetButton (xmPushButtonWidgetClass)
restartButton (xmPushButtonWidgetClass)
terminateButton (xmPushButtonWidgetClass)
In addition to standard Motif resources, the authentication dialog
has the following special resources:
xlogin.greeting
A string that identifies this window. The default is ``X
Window System.''
xlogin.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.namePrompt
The string displayed to prompt for a user name. The default
is ``Login:''.
xlogin.failMessage
A message that is displayed when the authentication fails.
The default is ``Login incorrect.''
xlogin.createFailsafeToggle
This boolean resource directs the xlogin widget to create the
``failsafe'' toggle button.
xlogin.createTerminateCommand
This boolean resource directs the xlogin widget to create the
``terminate'' push button.
xlogin.createRestartCommand
This boolean resource directs the xlogin widget to create the
``restart'' push button.
xlogin.createResetCommand
This boolean resource directs the xlogin widget to create the
``reset'' push button.
The following new actions are supported by the translation table for
the xlogin widget:
restart-session
Terminates and restarts the server.
terminate-session
Terminates the server, disabling it. This is a rash action.
It can be used to stop xdm when shutting the system down or
when using xdmshell.
reset-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.
allow-all-access
Disables access control in the server. This can be used when
the .Xauthority file cannot be created by xdm. Be very
careful using this; it might be better to disconnect the
machine from the network before doing this.
Three buttons are provided for controlling the display: "Reset",
"Restart" and "Terminate". On local displays, all three buttons can
be created, and they directly control the Xserver process. "Reset"
resets the X server and starts a new session; "restart" terminates
and restarts the X server; "terminate" terminates the server,
stopping the xdm daemon.
On foreign displays, the "Restart" button is not created because xdm
has no way to restart the Xserver on a foreign display. In addition,
on foreign displays, the "Terminate" button simply terminates
management of the display; it does not affect the xdm daemon.
On a display using XDMCP, only the "Reset" button is created. The
action of the "Reset" button is determined by the Xserver that
generated the XDMCP management request.
The Xstartup file
This file is typically a shell script. It is run with enhanced
capabilities and should be very careful about security. This is the
place to put commands that make fake entries in /etc/utmp, mount
users' home directories from file servers,
STARTUP PROGRAM
The Xstartup file is typically a shell script. It is run with
enhanced capabilities and should be very careful about security.
This is the place to put commands that add entries to /etc/utmp,
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 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.DISPLAY.systemPath
SHELL the value of DisplayManager.DISPLAY.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.
SESSION PROGRAM
The Xsession program is the command that 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.DISPLAY.userPath
SHELL the user's default shell (from getpwnam)
XAUTHORITY may be set to a non-standard authority file
At most installations, Xsession should look in $HOME for a file
.Xsession, that 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.
The ``failsafe'' argument may be passed to this program from the
authentication dialog. 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 section Typical Usage demonstrates
this feature.
RESET PROGRAM
Symmetrical with Xstartup, the Xreset script is run after the user
session has terminated. Run with enhanced capabilities, 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.
CONTROLLING THE SERVER
Xdm 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.
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.
OTHER POSSIBILITIES
You can use xdm to run a single session at a time by specifying the
server on the command line:
xdm -server ":0 local /usr/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-TOWERVIEW3000 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).
LIMITATIONS
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
/usr/lib/X11/xdm/Xaccess
the default access file, listing authorized
displays
/usr/lib/X11/xdm/Xservers
the default server file, listing non-XDMCP
servers to manage
$(HOME)/.Xauthority user authorization file where xdm stores keys for
clients to read
/usr/lib/X11/xdm/chooser
the default chooser
/usr/bin/X11/xrdb the default resource database loader
/usr/bin/X11/X the default server
/usr/bin/X11/xterm the default session program and failsafe client
/usr/lib/X11/xdm/A<host>-<suffix>
the default place for authorization files
SEE ALSO
X(1), xinit(1), xauth(1), Xsecurity(1), Xsession(5) and XDMCP
COPYRIGHT
Copyright 1988, Massachusetts Institute of Technology.
See X(1) for a full statement of rights and permissions.
AUTHOR
Keith Packard, MIT X Consortium
Licensed material--property of copyright holder(s)