XDM(1) X Version 11(Release 5) XDM(1)
NAME
xdm - X Display Manager with support for XDMCP
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 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
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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
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
#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).
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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 as root 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, specified in the translations in the
Xresources file above, to provide an escape from the ordinary session:
#!/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/.Xresources
if [ -f $startup ]; then
exec $startup
exec /bin/sh $startup
else
if [ ! -f $resources ]; then
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resources=$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 configuration_file
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 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 Server Specification for a description of this
resource.
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-udpPort port_number
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 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 example,
DisplayManager.expo_0.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
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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.
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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 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 appearence 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.
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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 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
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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.
``:/bin:/usr/bin:/usr/bin/X11:/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/bin/X11:/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 /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
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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 ``true''; 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.
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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
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#
!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:
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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 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 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 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.DISPLAY.resources. All of these have reasonable default
values, so it is not necessary to specify any of them.
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.
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xlogin.Login.foreground
The color used to display the typed-in user name.
xlogin.Login.font
The font used to display the typed-in user name.
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.greetFont
The font used to display the greeting.
xlogin.Login.greetColor
The color used to display the greeting.
xlogin.Login.namePrompt
The string displayed to prompt for a user name. Xrdb 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. The default is
``Password: ''
xlogin.Login.promptFont
The font used to display both prompts.
xlogin.Login.promptColor
The color used to display both prompts.
xlogin.Login.fail
A message which is displayed when the authentication fails. The
default is ``Login incorrect''
xlogin.Login.failFont
The font used to display the failure message.
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 30.
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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>: 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
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name/password pair. If the name/password pair is valid, xdm 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 is a rash action and is
not accessible in the default configuration. It can be used to
stop xdm when shutting the system down or when using xdmshell.
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 sections Session Program and Typical Usage.
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.
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, 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.
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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.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, 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 section Typical Usage demonstrates this
feature.
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.
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.
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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, 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/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
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/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), 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
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