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XDM(1)									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
       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.

       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	__projectroot__/lib/X11/xdm/xdm-errors will contain error mes-
       sages from xdm and anything output to stderr by Xsetup, Xstartup, Xses-
       sion 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
	      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	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
	      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 any-
	      thing 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
	      requests.	 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
       resources modify	the behavior of	xdm on all displays, while others mod-
       ify  its	 behavior on a single display.	Where actions relate to	a spe-
       cific 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

       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
	      entries,	one  per line (if the value starts with	a slash), or a
	      single server entry.  See	the section Local Server Specification
	      for the details.

	      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
	      descriptors  and	releasing  the	controlling terminal.  In some
	      environments this	is not desired	(in  particular,  when	debug-
	      ging).   Setting	this  resource	to ``false'' will disable this

	      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
	      __projectroot__/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
	      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.''

	      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.

	      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 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

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

	      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  __project-
	      root__/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.  __project-
	      root__/lib/X11/xdm/chooser is the	 default.   See	 the  sections
	      XDMCP Access Control and Chooser.

	      Specifies	 the  program used to load the resources.  By default,
	      xdm uses __projectroot__/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
	      authentication 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, __projectroot__/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
	      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	 star-
	      tAttempts	 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	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
	      resource 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
	      reset scripts to the value of this resource.  It is  /bin/sh  by

	      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,
	      __projectroot__/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,
	      instead of when checking the initial connection.	As xdm	gener-
	      ates 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 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
	      directory	 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	 __projectroot__/lib/X11/xdm)  to  contain all of the relevant

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

	    DisplayManager.servers:	       /usr/X11R6/lib/X11/xdm/Xservers
	    DisplayManager.errorLogFile:       /usr/X11R6/lib/X11/xdm/xdm-errors
	    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

       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 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.

	      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()	\

	      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.

       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
       logins 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
       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.

       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
       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 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
       ordinary	session.  It also requires that	the  .xsession	file  be  exe-
       cutable 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 __projectroot__/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

X Version 11			  Release 6.6				XDM(1)


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