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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	 /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/local/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(1)  to	specify	 configuration
	      parameters 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.	 If set	to 0, xdm will not listen for XDMCP or Chooser
	      requests.	 As XDMCP uses the registered well-known UDP port 177,
	      this  resource  should  not  be changed to a value other than 0,
	      except for debugging.

       -session	session_program
	      Specifies	the value  for	the  DisplayManager*session  resource.
	      This  indicates the program to run as the	session	after the user
	      has logged in.

       -xrm resource_specification
	      Allows an	arbitrary resource to be specified, as in most X 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
	      /var/db/xdm.  Can	be overridden for specific  displays  by  Dis-

	      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 read 8 bytes from to generate	the seed of authoriza-
	      tion keys.  The default is  /dev/urandom . If this  file	cannot
	      be  read,	or if a	read blocks for	more than 5 seconds, xdm falls
	      back to using a checksum of DisplayManager.randomFile to	gener-
	      ate the seed.

	      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/local/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/local/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/local/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/local/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 bound  reservAt-
	      tempts is	the number of times a successful connect is allowed to
	      be followed by a fatal error.  When reached, the display is dis-
	      abled.   The  default  values  are openDelay: 15,	openRepeat: 5,
	      openTimeout: 120,	startAttempts: 4 and reservAttempts: 2.


	      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.    The  default  value  is

	      Xdm sets the PATH	environment variable for the startup and reset
	      scripts to the value of this resource.   The  default  for  this
	      resource	 is  ``/bin:/usr/bin:/sbin:/usr/sbin:/usr/local/bin''.
	      Note the absence of ``.''	from this entry.  This is a good prac-
	      tice to follow for root; it avoids many common Trojan Horse sys-
	      tem 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/local/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/local/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/local/lib/X11/xdm/Xservers
	    DisplayManager.errorLogFile:       /var/log/xdm.log
	    DisplayManager*resources:	       /usr/local/lib/X11/xdm/Xresources
	    DisplayManager*startup:	       /usr/local/lib/X11/xdm/Xstartup
	    DisplayManager*session:	       /usr/local/lib/X11/xdm/Xsession
	    DisplayManager.pidFile:	       /var/run/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	address	representing a network
	      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 Interface-Local,	2  for	Link-Local,  5
       for  Site-Local,	 and so	on.  (See IETF RFC 4291	or its replacement for
       further 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/local/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/local/bin/X :0'' instead of ``localhost:0 Sun-
       CG3 local /usr/local/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/local/lib/X11/xdm/monitors/alex.0
	    xconsole -geometry 480x130-0-0 -notify -verbose -exitOnFail	&

       The authentication widget prompts the user for the username,  password,
       and/or  other  required	authentication data 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.

       The  resource  file  is loaded with xrdb(1) so it may use the substitu-
       tions defined by	that program such as CLIENTHOST	for the	 client	 host-
       name in the login message, or C pre-processor #ifdef statements to pro-
       duce different displays depending on color depth	or other variables.

       Xdm can be compiled with	support	for the	Xft(3) library for  font  ren-
       dering.	  If  this  support is present,	font faces are specified using
       the resources with names	ending in ``face'' in the fontconfig face for-
       mat described in	the Font Names section of fonts.conf(5).  If not, then
       fonts are specified using the resources with names ending  in  ``font''
       in  the	traditional X Logical Font Description format described	in the
       Font Names section of X(7).

       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 input typed	by the user.

	      The face used to display the input typed by the user when	 built
	      with Xft support.	 The default is	``Serif-18''.

	      The  font	 used  to display the input typed by the user when not
	      built with Xft support.

	      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 face used to display the greeting when built with  Xft  sup-
	      port.  The default is ``Serif-24:italic''.

	      The  font	 used  to display the greeting when not	built with Xft

	      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, when not using an
	      authentication system such as PAM	that provides its own prompts.
	      The default is ``Password:  ''

	      The  face	 used  to display prompts when built with Xft support.
	      The default is ``Serif-18:bold''.

	      The font used to display prompts when not	built  with  Xft  sup-

	      The color	used to	display	prompts.

	      A	 message  which	 is  displayed	when  the  users  password has
	      expired.	The default is ``Password Change Required''
	      A	message	which is displayed when	the authentication fails, when
	      not using	an authentication system such as PAM that provides its
	      own prompts.  The	default	is ``Login incorrect''

	      The face used to display the failure message when	built with Xft
	      support.	The default is ``Serif-18:bold''.

	      The font used to display the failure message when	not built with
	      Xft support.

	      The color	used to	display	the failure message.

	      The number of seconds that the  failure  message	is  displayed.
	      The default is 10.

	      Name  of	an XPM format pixmap to	display	in the greeter window,
	      if built with XPM	support.   The default is no pixmap.

	      Number of	pixels of space	between	the logo pixmap	and other ele-
	      ments  of	 the  greeter window, if the pixmap is displayed.  The
	      default is 5.

	      If set to	``true'', when built with XPM support, attempt to  use
	      the  X  Non-Rectangular Window Shape Extension to	set the	window
	      shape.  The default is ``true''.

       xlogin.Login.hiColor, xlogin.Login.shdColor
	      Raised appearance	bezels may be drawn around the	greeter	 frame
	      and text input boxes by setting these resources.	hiColor	is the
	      highlight	color, used on the top and left	sides  of  the	frame,
	      and  the	bottom and right sides of text input areas.   shdColor
	      is the shadow color, used	on the bottom and right	sides  of  the
	      frame,  and  the	top  and  left sides of	text input areas.  The
	      default for both is  the	foreground  color,  providing  a  flat

	      frameWidth is the	width in pixels	of the area around the greeter
	      frame drawn in hiColor and shdColor.

	      innerFramesWidth is the width in pixels of the area around  text
	      input areas drawn	in hiColor and shdColor.

	      sepWidth	is the width in	pixels of the bezeled line between the
	      greeting and input areas drawn in	hiColor	and shdColor.

	      If set to	``false'', don't allow root (and any other  user  with
	      uid  =  0)  to  log in directly.	The default is ``true''.  This
	      setting is only checked by some of the  authentication  backends
	      at this time.

	      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.

	      If set to	``true'',  a  placeholder  character  (echoPasswdChar)
	      will be shown for	fields normally	set to not echo, such as pass-
	      word input.  The default is ``false''.

	      Character	to display if echoPasswd  is  true.   The  default  is
	      ``*''.   If  set	to an empty value, the cursor will advance for
	      each character input, but	no text	will be	drawn.

	      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  utmp  or  wtmp  files,  (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
	    WINDOWPATH	   may be set to the "window path" leading to the X server

       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/local/lib/X11/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
	    WINDOWPATH	   may be set to the "window path" leading to the X server

       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.

       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, updating entries in	utmp  or  wtmp
       files,  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/local/lib/X11/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/local/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/local/bin/xrdb the default resource	database loader

       /usr/local/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),   xrdb(1),	  Xsecurity(7),	   sessreg(1),
       Xserver(1), xdmshell(1),	fonts.conf(5).
       X Display Manager Control Protocol
       IETF RFC	4291: IP Version 6 Addressing Architecture.

       Keith Packard, MIT X Consortium

X Version 11			  xdm 1.1.11				XDM(1)


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