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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.   /etc/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.	 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
       ``expo.x.org:0'' 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
	      /etc/X11/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 checksum to generate the seed of authorization keys.
	      This should be a file that changes frequently.  The  default  is

	      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.


	      A	 UNIX  domain socket name or a TCP socket port number on local
	      host on which a Pseudo-Random Number Generator Daemon, like  EGD
	      (http://egd.sourceforge.net)  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
	       /etc/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/lib64/X11/xdm/chooser  is the default.  See	 the  sections
	      XDMCP Access Control and Chooser.

	      Specifies	 the  program used to load the resources.  By default,
	      xdm uses	/usr/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/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/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/bin:/usr/ucb''	is  a  common  choice.
	      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/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	 /etc/X11/xdm) to contain all of the relevant files.

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

	    DisplayManager.servers:	       /etc/X11/xdm/Xservers
	    DisplayManager.errorLogFile:       /var/log/xdm.log
	    DisplayManager*resources:	       /etc/X11/xdm/Xresources
	    DisplayManager*startup:	       /etc/X11/xdm/Xstartup
	    DisplayManager*session:	       /etc/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

       !xtra.lcs.mit.edu   # disallow direct/broadcast service for xtra
       bambi.ogi.edu	   # allow access from this particular display
       *.lcs.mit.edu	   # allow access from any display in LCS

       *.deshaw.com	   NOBROADCAST	       # allow only direct access
       *.gw.com				       # allow direct and broadcast

       # Indirect query entries

       %HOSTS		   expo.lcs.mit.edu xenon.lcs.mit.edu excess.lcs.mit.edu kanga.lcs.mit.edu

       extract.lcs.mit.edu xenon.lcs.mit.edu   #force extract to contact xenon
       !xtra.lcs.mit.edu   dummy	       #disallow indirect access
       *.lcs.mit.edu	   %HOSTS	       #all others get to choose

       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.


       rincewind.sample.net ff02::1		    #IPv6 Multicast to ff02::1
						    #with a hop count of 1
       ponder.sample.net    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:

       extract.lcs.mit.edu  CHOOSER %HOSTS	    #offer a menu of these hosts
       xtra.lcs.mit.edu	    CHOOSER BROADCAST	    #offer a menu of all hosts

       The  program to use for chooser is specified by the DisplayManager.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/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/bin/X	 :0'' instead of ``localhost:0 Sun-CG3
       local /usr/bin/X :0'' if your other resources are specified  as	``Dis‐
       playManager._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 display
       class, so the manual for your particular X terminal should document the
       display	class  string for your device.	If it doesn't, you can run xdm
       in debug mode and look at the resource strings which it	generates  for
       that device, which will include the class string.

       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: #overrideCtrl<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 < /etc/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 format
       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''.

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

       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 current name/password pair.  If
	      the name/password pair is valid, xdm
	      starts the session.  Otherwise the failure message is displayed and
	      the user is prompted again.

	      Terminates and restarts the server.

	      Terminates the server, disabling it.  This action
	      is not accessible in the default configuration.
	      There are various reasons to stop xdm on a system console, such as
	      when shutting the system 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
	      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
       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
	    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 /etc/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, 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 /etc/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/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/bin/xrdb	   the default resource database loader

       /usr/bin/X	   the default server

       /usr/bin/xterm	   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), fonts.conf(5).
       X Display Manager Control Protocol

       Keith Packard, MIT X Consortium

X Version 11			   xdm 1.1.6				XDM(1)

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