XDM(1) USER COMMANDS 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 ``ses-
sion.''
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 neces-
sarily have any terminal-like interface with which to con-
nect. When a real session manager is not available, a win-
dow manager or terminal emulator is typically used as the
``session manager,'' meaning that termination of this pro-
cess 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 custom-
ize 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.
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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 discus-
sion.
The first file, /usr/lib/X11/xdm/Xservers, contains the list
of displays to manage that are not using XDMCP. Most works-
tations 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 mes-
sages 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
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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).
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)
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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 $resources ]; then
resources=$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 con-
trolling 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 neces-
sity. No attempt has been made to rationalize or
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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.
-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 sin-
gle 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
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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 con-
sole. 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 descrip-
tions of problems in those scripts as well.
DisplayManager.debugLevel
If the integer value of this resource is greater than
zero, reams of debugging information will be printed.
It also disables daemon mode, which would redirect the
information into the bit-bucket, and allows non-root
users to run xdm, which would normally not be useful.
DisplayManager.daemonMode
Normally, xdm attempts to make itself into a daemon
process unassociated with any terminal. This is accom-
plished 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
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authorization files while initializing the session.
The default value is /usr/lib/X11/xdm.
DisplayManager.autoRescan
This boolean controls whether xdm rescans the confi-
guration, 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 con-
taining 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 for-
warding of XDMCP IndirectQuery requests, this file con-
tains 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 Con-
trol.
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 authoriza-
tion keys. This should be a file that changes fre-
quently. 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
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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.
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 sec-
tion Reset Program.
DisplayManager.DISPLAY.openDelay
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DisplayManager.DISPLAY.openRepeat
DisplayManager.DISPLAY.openTimeout
DisplayManager.DISPLAY.startAttempts
These numeric resources control the behavior of xdm
when attempting to open intransigent servers. openDe-
lay 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 max-
imum time spent in the connect(2) system call) and
startAttempts is the number of times this entire pro-
cess is done before giving up on the server. After
openRepeat attempts have been made, or if openTimeout
seconds elapse in any particular attempt, xdm ter-
minates and restarts the server, attempting to connect
again. This process is repeated startAttempts times,
at which point the display is declared dead and dis-
abled. 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 startAt-
tempts.
DisplayManager.DISPLAY.pingInterval
DisplayManager.DISPLAY.pingTimeout
To discover when remote displays disappear, xdm occa-
sionally 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 ter-
minated. By default, both are set to 5 minutes. If
you frequently use X terminals which can become iso-
lated from the managing host, you may wish to increase
this value. The only worry is that sessions will con-
tinue 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
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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 Defaul-
tUserPath;
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 sec-
tion Session Program). By default, /usr/bin/X11/xterm
is used.
DisplayManager.DISPLAY.grabServer
DisplayManager.DISPLAY.grabTimeout
To improve security, xdm grabs the server and keyboard
while reading the login name and password. The grab-
Server resource specifies if the server should be held
for the duration of the name/password reading. When
``false,'' the server is ungrabbed after the keyboard
grab succeeds, otherwise the server is grabbed until
just before the session begins. The default is
``false.'' The grabTimeout resource specifies the max-
imum 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
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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 mechan-
isms to use. XDMCP connections dynamically specify
which authorization mechanisms are supported, so auth-
Name 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, disa-
bling the authorization mechanism in the server.
DisplayManager.DISPLAY.authComplain
If set to ``false,'' disables the use of the unsecure-
Greeting in the login window. See the section Authen-
tication 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 con-
nection. As xdm generates the authorization informa-
tion just before connecting to the display, an old
server would not get up-to-date authorization informa-
tion. 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 authori-
zation 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 com-
parison, so ensure that you do not attempt to match aliases.
Preceding either a host name or a pattern with a `!' charac-
ter 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 dis-
tinguish 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 deter-
mines 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 delim-
iter causing the rest of that line to be ignored, and `\new-
line' causes the newline to be ignored, allowing indirect
host lists to span multiple lines.
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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 specifi-
cation or, if the values starts with a slash (/), the name
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of a file containing server specifications, one per line.
Each specification indicates a display which should con-
stantly be managed and which is not using XDMCP. Each con-
sists 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 collec-
tion 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 secu-
rity. 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
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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 poten-
tial 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 con-
trolled with a resource. Resources for this widget should
be put into the file named by
DisplayManager.DISPLAY.resources. All of these have reason-
able default values, so it is not necessary to specify any
of them.
xlogin.Login.y
xlogin.Login.width, xlogin.Login.height, xlogin.Login.x,
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 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: ''
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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.
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.
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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, 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 configura-
tion. 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 overwrit-
ten 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.
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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 mes-
sage 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 ses-
sion and starts another authentication cycle.
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.
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An argument may be passed to this program from the authenti-
cation 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 adminis-
trative intervention. The section Typical Usage demon-
strates 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 sig-
nals.
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
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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 ter-
minals. The configuration for this is identical to the sam-
ple 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 descrip-
tion 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 author-
ized 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
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/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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