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XDM(1)			    General Commands Manual			XDM(1)

       xdm - X Display Manager with support for	XDMCP, host chooser

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

       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 ter-
       minals  as well as The Open Group 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 man-
       ager 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 (option-
       ally) 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	speci-
       fied 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.

       Xdm can be configured to	ignore BroadcastQuery messages	from  selected
       hosts.	This is	useful when you	don't want the host to appear in menus
       produced	by chooser or X	terminals themselves.

       Because xdm provides the	first interface	that users will	see, it	is de-
       signed to be simple to use and easy to customize	to the needs of	a par-
       ticular site.  Xdm has many options, most of which have reasonable  de-
       faults.	 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.

       xdm is highly configurable, and most of its behavior can	be  controlled
       by  resource  files  and	shell scripts.	The names of these files them-
       selves are resources read from the file xdm-config or the file named by
       the -config option.

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

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

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

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

       The xlogin widget, which	xdm presents, offers the  familiar  login  and
       password	prompts.

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

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

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

       The  file   /var/log/xdm.log  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.

       All of these options, except -config itself, specify  values  that  can
       also be specified in the	configuration file as resources.

       -config configuration_file
	      Names  the configuration file, which specifies resources to con-
	      trol the behavior	of xdm.	 /usr/X11R6/lib/X11/xdm/xdm-config  is
	      the default.  See	the section Configuration File.

	      Specifies	 ``false'' as the value	for the	DisplayManager.daemon-
	      Mode resource.  This  suppresses	the  normal  daemon  behavior,
	      which is for xdm to close	all file descriptors, disassociate it-
	      self from	the controlling	terminal, and put itself in the	 back-
	      ground 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	debug-
	      ging  statements	to the terminal; it also disables the Display-
	      Manager.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  ra-
	      tionalize	or standardize the output.

       -error error_log_file
	      Specifies	 the  value  for  the  DisplayManager.errorLogFile re-
	      source.  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 parame-
	      ters for the authentication widget.

       -server server_entry
	      Specifies	the value  for	the  DisplayManager.servers  resource.
	      See  the section Local Server Specification for a	description of
	      this resource.

       -udpPort	port_number
	      Specifies	the value for the DisplayManager.requestPort resource.
	      This  sets  the port-number which	xdm will monitor for XDMCP re-
	      quests.  As XDMCP	uses the registered well-known UDP  port  177,
	      this resource should not be changed except for debugging.	If set
	      to 0 xdm will not	listen for XDMCP or Chooser requests.

       -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 Tool-
	      kit applications.

       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  re-
       sources modify the behavior of xdm on all displays, while others	modify
       its behavior on a single	display.  Where	actions	relate to  a  specific
       display,	 the  display  name is inserted	into the resource name between
       ``DisplayManager'' and the final	resource name segment.

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

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

       Because the resource manager uses colons	to separate the	 name  of  the
       resource	 from  its value and dots to separate resource name parts, xdm
       substitutes underscores for both	dots and colons	 when  generating  the
       resource	name.  For example, DisplayManager.expo_x_org_0.startup	is the
       name of the resource which defines  the	startup	 shell	file  for  the
       ``''	display.

	      This  resource  either  specifies	a file name full of server en-
	      tries, one per line (if the value	starts with  a	slash),	 or  a
	      single server entry.  See	the section Local Server Specification
	      for the details.

	      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.

	      Error output is normally directed	at the system console.	To re-
	      direct  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.

	      If  the  integer	value  of  this	resource is greater than zero,
	      reams of debugging information will be printed.	It  also  dis-
	      ables 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.

	      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 de-
	      scriptors	and releasing the controlling terminal.	 In some envi-
	      ronments	this  is  not desired (in particular, when debugging).
	      Setting this resource to ``false'' will disable this feature.

	      The filename specified will be created to	contain	an ASCII  rep-
	      resentation 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.

	      This is the resource which controls whether xdm uses file	 lock-
	      ing  to  keep  multiple  display managers	from running amok.  On
	      System V,	this uses the lockf library call, while	on BSD it uses

	      This  names  a  directory	 under	which xdm stores authorization
	      files while initializing the  session.   The  default  value  is
	      /usr/X11R6/lib/X11/xdm.  Can be overridden for specific displays
	      by DisplayManager.DISPLAY.authFile.

	      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.

	      When computing the display name for XDMCP	clients, the name  re-
	      solver 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 de-
	      fault the	value is ``true.''

	      XDM-AUTHENTICATION-1  style XDMCP	authentication requires	that a
	      private key be shared between xdm	and the	 terminal.   This  re-
	      source  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.

	      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 ma-
	      chine, or	have a list of hosts to	which queries should  be  for-
	      warded  to.  The format of this file is described	in the section
	      XDMCP Access Control.

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

	      A	file to	checksum to generate the seed of  authorization	 keys.
	      This  should  be a file that changes frequently.	The default is


	      A	UNIX domain socket name	or a TCP socket	port number  on	 local
	      host  on which a Pseudo-Random Number Generator Daemon, like EGD
	      ( is listening, in order to  generate
	      the  autorization	keys. Either a non null	port or	a valid	socket
	      name must	be specified. The default is to	 use  the  Unix-domain
	      socket /tmp/entropy.

       On systems that don't have such a daemon, a fall-back entropy gathering
       system, based on	various	log file contents hashed by the	MD5  algorithm
       is used instead.

	      On  systems that support a dynamically-loadable greeter library,
	      the name of the library.	The default is

	      Number of	seconds	to wait	for display to respond after user  has
	      selected a host from the chooser.	 If the	display	sends an XDMCP
	      IndirectQuery within this	time, the request is forwarded to  the
	      chosen  host.  Otherwise,	it is assumed to be from a new session
	      and the chooser is offered again.	 Default is 15.

	      Use the numeric IP address of the	incoming connection on	multi-
	      homed hosts instead of the host name. This is to avoid trying to
	      connect on the wrong interface which might be down at this time.

	      This specifies a program which is	run (as) root when an an XDMCP
	      BroadcastQuery  is received and this host	is configured to offer
	      XDMCP display management.	The output of this program may be dis-
	      played  on  a  chooser  window.  If no program is	specified, the
	      string Willing to	manage is sent.

	      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 vari-
	      ous resources that are appropriate to place in this file.	 There
	      is no default value for this resource, but
	       /usr/X11R6/lib/X11/xdm/Xresources is the	conventional name.

	      Specifies	the program run	to offer  a  host  menu	 for  Indirect
	      queries redirected to the	special	host name CHOOSER.
	       /usr/X11R6/lib/X11/xdm/chooser	is  the	default.  See the sec-
	      tions XDMCP Access Control and Chooser.

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

	      This  specifies  the name	of the C preprocessor which is used by

	      This specifies a program which is	run (as	root) before  offering
	      the  Login window.  This may be used to change the appearance of
	      the screen around	the Login window or to put  up	other  windows
	      (e.g.,  you may want to run xconsole here).  By default, no pro-
	      gram is run.  The	conventional name for  a  file	used  here  is
	      Xsetup.  See the section Setup Program.

	      This  specifies  a  program which	is run (as root) after the au-
	      thentication process succeeds.  By default, no program  is  run.
	      The conventional name for	a file used here is Xstartup.  See the
	      section Startup Program.

	      This specifies the session to be executed	(not running as	root).
	      By default,  /usr/X11R6/bin/xterm	is run.	 The conventional name
	      is Xsession.  See	the section Session Program.

	      This specifies a program which is	run (as	root) after  the  ses-
	      sion  terminates.	  By  default, no program is run.  The conven-
	      tional name is Xreset.  See the section Reset Program.




	      These numeric resources control the behavior  of	xdm  when  at-
	      tempting	to open	intransigent servers.  openDelay is the	length
	      of the pause (in seconds)	between	successive  attempts,  openRe-
	      peat  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 star-
	      tAttempts	is the number of times this entire process is done be-
	      fore  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	devel-
	      oped  and	 works quite well on most systems.  The	default	values
	      are 5 for	openDelay, 5 for openRepeat, 30	for openTimeout	and  4
	      for startAttempts.


	      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, ping-
	      Timeout specifies	the maximum amount of  time  (in  minutes)  to
	      wait  for	the terminal to	respond	to the request.	 If the	termi-
	      nal does not respond, the	session	is declared  dead  and	termi-
	      nated.   By  default,  both  are	set to 5 minutes.  If you fre-
	      quently use X terminals which can	become isolated	from the  man-
	      aging 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 work-
	      station  session is terminated as	a result of the	server hanging
	      for NFS service and not responding to the	ping.

	      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.''

	      Xdm sets the PATH	environment variable for the session  to  this
	      value.   It should be a colon separated list of directories; see
	      sh(1)	    for		 a	    full	  description.
	      ``:/bin:/usr/bin:/usr/X11R6/bin:/usr/ucb''  is a common setting.
	      The default value	can be specified at build time in the X	system
	      configuration file with DefaultUserPath.

	      Xdm sets the PATH	environment variable for the startup and reset
	      scripts to the value of this resource.  The default for this re-
	      source is	specified at build time	by the DefaultSystemPath entry
	      in	the	    system	   configuration	 file;
	      ``/etc:/bin:/usr/bin:/usr/X11R6/bin:/usr/ucb''   is   a	common
	      choice.  Note the	absence	of ``.'' from this entry.  This	 is  a
	      good  practice  to follow	for root; it avoids many common	Trojan
	      Horse system penetration schemes.

	      Xdm sets the SHELL environment variable for the startup and  re-
	      set scripts to the value of this resource.  It is	/bin/sh	by de-

	      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/X11R6/bin/xterm is used.


	      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.


	      authorize	 is a boolean resource which controls whether xdm gen-
	      erates and uses authorization for	the local server  connections.
	      If  authorization	 is  used, authName is a list of authorization
	      mechanisms to use, separated by white space.  XDMCP  connections
	      dynamically  specify  which  authorization  mechanisms  are sup-
	      ported, 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,''	 or,  if  XDM-AUTHORIZATION-1  is   available,

	      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.  If not specified, a name	is generated from Dis-
	      playManager.authDir and the name of the display.

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

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

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

	      The  original  implementation  of	 authorization	in  the	sample
	      server reread the	authorization file at server reset  time,  in-
	      stead of when checking the initial connection.  As xdm generates
	      the authorization	information just before	connecting to the dis-
	      play,  an	 old server would not get up-to-date authorization in-
	      formation.  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 informa-
	      tion  will  be  read.  The default is ``false,'' which will work
	      for all MIT servers.

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

       First,  the  xdm	configuration file should be set up.  Make a directory
       (usually	 /usr/X11R6/lib/X11/xdm) to contain all	of the relevant	files.

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

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

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

       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  pat-
       terns,  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.

       To only respond to Direct queries for a host or pattern,	it can be fol-
       lowed  by  the  optional	 ``NOBROADCAST'' keyword.  This	can be used to
       prevent an xdm server  from  appearing  on  menus  based	 on  Broadcast

       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

       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

       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

       !   # disallow direct/broadcast service for xtra	   # allow access from this particular display
       *	   # allow access from any display in LCS

       *	   NOBROADCAST	       # allow only direct access
       *				       # allow direct and broadcast

       # Indirect query	entries

       %HOSTS \   #force extract to contact xenon
       !   dummy	       #disallow indirect access
       *	   %HOSTS	       #all others get to choose

       If compiled with	IPv6 support, multicast	address	groups may also	be in-
       cluded in the list of addresses indirect	queries	are set	to.  Multicast
       addresses may be	followed by an optional	/ character and	hop count.  If
       no hop count is specified, the multicast	hop count defaults to 1, keep-
       ing the packet on the local network. For	 IPv4  multicasting,  the  hop
       count is	used as	the TTL.

       Examples: ff02::1		    #IPv6 Multicast to ff02::1
						    #with a hop	count of 1    CHOOSER  #Offer a menu of hosts
						    #who respond to IPv4 Multicast
						    # to with a TTL	of 16

       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:  CHOOSER %HOSTS	    #offer a menu of these hosts	    CHOOSER BROADCAST	    #offer a menu of all hosts

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

       Resources  for  this program can	be put into the	file named by Display-

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

       The  following  configuration directive is also defined for the Xaccess
       configuration file:

       LISTEN interface	[list of multicast group addresses]
	      interface	may be a hostname or IP	addresss representing  a  net-
	      work  interface  on this machine,	or the wildcard	* to represent
	      all available network interfaces.

       If one or more LISTEN lines are specified, xdm only listens  for	 XDMCP
       connections  on	the specified interfaces. If multicast group addresses
       are listed on a listen line, xdm	joins  the  multicast  groups  on  the
       given interface.

       If no LISTEN lines are given, the original behavior of listening	on all
       interfaces is preserved for backwards compatibility.  Additionally,  if
       no  LISTEN  is  specified,  xdm	joins the default XDMCP	IPv6 multicast
       group, when compiled with IPv6 support.

       To disable listening for	XDMCP connections altogther, a line of	LISTEN
       with  no	addresses may be specified, or the previously supported	method
       of setting DisplayManager.requestPort to	0 may be used.

       LISTEN *	ff02::1	   # Listen on all interfaces and to the
			   # ff02::1 IPv6 multicast group.
       LISTEN  # Listen only on this interface, as long
			   # as	no other listen	directives appear in
			   # file.

       The   Internet	Assigned   Numbers   Authority	 has   has    assigned
       ff0X:0:0:0:0:0:0:12b as the permanently assigned	range of multicast ad-
       dresses for XDMCP. The X	in the prefix may be  replaced	by  any	 valid
       scope  identifier,  such	 as  1 for Node-Local, 2 for Link-Local, 5 for
       Site-Local, and so on.  (See IETF RFC 2373 or its replacement for  fur-
       ther  details and scope definitions.)  xdm defaults to listening	on the
       Link-Local scope	address	ff02:0:0:0:0:0:0:12b to	most closely match the
       old IPv4	subnet broadcast behavior.

       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 man-
       aged and	which is not using XDMCP.  This	method is used	typically  for
       local  servers only.  If	the resource or	the file named by the resource
       is empty, xdm will offer	XDMCP service only.

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

	 :0 Digital-QV local /usr/X11R6/bin/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 Sun-CG3 local /usr/X11R6/bin/X :0''	instead	of ``localhost:0  Sun-
       CG3  local  /usr/X11R6/bin/X :0'' if your other resources are specified
       as ``DisplayManager._0.session'').  The display class portion  is  also
       used  in	 the display-specific resources, as the	class of the resource.
       This is useful if you have a large collection of	similar	displays (such
       as  a corral of X terminals) and	would like to set resources for	groups
       of them.	 When using XDMCP, the display is required to specify the dis-
       play  class,  so	the manual for your particular X terminal should docu-
       ment 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	gener-
       ates for	that device, which will	include	the class string.

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

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

	    xlogin*login.translations: #override\
		 Ctrl<Key>R: abort-display()\n\/&
		 <Key>F1: set-session-argument(failsafe) finish-field()\n\
		 <Key>Return: set-session-argument() finish-field()
	    xlogin*borderWidth:	3
	    xlogin*greeting: CLIENTHOST
	    #ifdef COLOR
	    xlogin*greetColor: CadetBlue
	    xlogin*failColor: red

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

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

       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  follow-
       ing 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 Display-
       Manager.DISPLAY.grabServer is set, Xsetup will not be able  to  connect
       to  the display at all.	Resources for this program can be put into the
       file named by DisplayManager.DISPLAY.resources.

       Here is a sample	Xsetup script:

	    # Xsetup_0 - setup script for one workstation
	    xcmsdb < /usr/X11R6/lib/monitors/alex.0
	    xconsole -geometry 480x130-0-0 -notify -verbose -exitOnFail	&

       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 Display-
       Manager.DISPLAY.resources.   All	 of these have reasonable default val-
       ues, 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  automati-
	      cally.   If  you	wish to	position it elsewhere, specify each of
	      these resources.

	      The color	used to	display	the typed-in user name.

	      The font used to display the typed-in user name.

	      A	string which identifies	this window.  The default is ``X  Win-
	      dow System.''

	      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 ses-

	      The font used to display the greeting.

	      The color	used to	display	the greeting.

	      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:  ''

	      The  string  displayed to	prompt for a password.	The default is
	      ``Password:  ''

	      The font used to display both prompts.

	      The color	used to	display	both prompts.
	      A	message	which is displayed when	the authentication fails.  The
	      default is ``Login incorrect''

	      The font used to display the failure message.

	      The color	used to	display	the failure message.

	      The  number  of  seconds	that the failure message is displayed.
	      The default is 30.

	      If set to	``false'', don't allow root (and any other  user  with
	      uid = 0) to log in directly.  The	default	is ``true''.

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

	      This specifies the translations used for the login widget.   Re-
	      fer  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:

	      Erases the character before the cursor.

	      Erases the character after the cursor.

	      Moves the	cursor backward.

	      Moves the	cursor forward.

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

	      Moves the	cursor to the end of the editable text.

	      Erases all text after the	cursor.

	      Erases the entire	text.

	      If  the  cursor  is  in the name field, proceeds to the password
	      field; if	the cursor is in the password field, checks  the  cur-
	      rent  name/password  pair.   If the name/password	pair is	valid,
	      xdm starts the session.  Otherwise the failure message  is  dis-
	      played and the user is prompted again.

	      Terminates and restarts the server.

	      Terminates  the server, disabling	it.  This action is not	acces-
	      sible in the default configuration.  There are  various  reasons
	      to  stop xdm on a	system console,	such as	when shutting the sys-
	      tem down,	when using xdmshell, to	start another type of  server,
	      or  to  generally	access the console.  Sending xdm a SIGHUP will
	      restart the display.  See	the section Controlling	XDM.

	      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.

	      Inserts the character typed.

	      Specifies	a single word argument which is	passed to the  session
	      at startup.  See the section Session Program.

	      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.

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

       The Xstartup program is run as root when	the user logs in.  It is typi-
       cally a shell script.  Since it is run as root, Xstartup	should be very
       careful about security.	This is	the place to put  commands  which  add
       entries	to  /etc/utmp  (the sessreg program may	be useful here), mount
       users' home directories from file servers, or abort the session if  lo-
       gins are	not allowed.

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

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

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

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

       Here is a sample	Xstartup script:

	    # Xstartup
	    # This program is run as root after	the user is verified
	    if [ -f /etc/nologin ]; then
		 xmessage -file	/etc/nologin -timeout 30 -center
		 exit 1
	    sessreg -a -l $DISPLAY -x /usr/X11R6/lib/xdm/Xservers $LOGNAME
	    exit 0

       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  follow-
       ing environment variables are passed:

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

       At  most	installations, Xsession	should look in $HOME for a file	.xses-
       sion, 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  wid-
       get  using  the `set-session-argument' action.  This can	be used	to se-
       lect 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 requir-
       ing  administrative  intervention.   The	example	following demonstrates
       this feature.

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

	    # Xsession
	    # This is the program that is run as the client
	    # for the display manager.

	    case $# in
		 case $1 in
		      exec xterm -geometry 80x24-0-0


	    if [ -f "$startup" ]; then
		 exec "$startup"
		 if [ -f "$resources" ]; then
		      xrdb -load "$resources"
		 twm &
		 xman -geometry	+10-10 &
		 exec xterm -geometry 80x24+10+10 -ls

       The  user's  .xsession  file  might  look  something like this example.
       Don't forget that the file must have execute permission.
	    #! /bin/csh
	    # no -f in the previous line so .cshrc gets	run to set $PATH
	    twm	&
	    xrdb -merge	"$HOME/.Xresources"
	    emacs -geometry +0+50 &
	    xbiff -geometry -430+5 &
	    xterm -geometry -0+50 -ls

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

       A sample	Xreset script:
	    # Xreset
	    # This program is run as root after	the session ends
	    sessreg -d -l $DISPLAY -x /usr/X11R6/lib/xdm/Xservers $LOGNAME
	    exit 0

       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 DisplayMan-
       ager.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 win-
       dows  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.

       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 dis-
       abled immediately, meaning that any session in progress will be	termi-
       nated 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 addi-
       tional 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.

       To add an additional local display, add a line for it to	 the  Xservers
       file.  (See the section Local Server Specification.)

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

       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 com-
       mand line:

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

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

	    extol:0 VISUAL-19 foreign
	    exalt:0 NCD-19 foreign
	    explode:0 NCR-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).

       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.

			   the default configuration file

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

			   the default chooser

       /usr/X11R6/bin/xrdb the default resource	database loader

       /usr/X11R6/bin/X	   the default server

			   the default session program and failsafe client

			   the default place for authorization files

       /tmp/K5C_display_   Kerberos credentials	cache

       X(7), xinit(1), xauth(1), Xsecurity(7), sessreg(1), Xserver(1),
       X Display Manager Control Protocol

       Keith Packard, MIT X Consortium

XFree86				 Version 4.7.0				XDM(1)


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