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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
       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   /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
	      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
	      /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
	      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


	      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
	      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,  /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
	      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,
	      /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,
	      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	 /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
       included	in the list of addresses indirect queries are set to.	Multi-
       cast  addresses	may  be	 followed  by  an optional / character and hop
       count. If no hop	count is specified, the	multicast hop  count  defaults
       to  1,  keeping 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
       addresses  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.
	      Refer to the X Toolkit documentation for a  complete  discussion
	      on translations.	The default translation	table is:

		   Ctrl<Key>H:	  delete-previous-character() \n\
		   Ctrl<Key>D:	  delete-character() \n\
		   Ctrl<Key>B:	  move-backward-character() \n\
		   Ctrl<Key>F:	  move-forward-character() \n\
		   Ctrl<Key>A:	  move-to-begining() \n\
		   Ctrl<Key>E:	  move-to-end()	\n\
		   Ctrl<Key>K:	  erase-to-end-of-line() \n\
		   Ctrl<Key>U:	  erase-line() \n\
		   Ctrl<Key>X:	  erase-line() \n\
		   Ctrl<Key>C:	  restart-session() \n\
		   Ctrl<Key>\\:	  abort-session() \n\
		   <Key>BackSpace:delete-previous-character() \n\
		   <Key>Delete:	  delete-previous-character() \n\
		   <Key>Return:	  finish-field() \n\
		   <Key>:	  insert-char()	\

       The actions which are supported by the widget are:

	      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 /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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