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man pages section 8: System Administration Commands

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Updated: Wednesday, July 27, 2022

xdm (8)


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(8)                      System Manager's Manual                     XDM(8)

       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.  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
       ``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
              /var/run/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.

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

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

              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 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 ``/usr/bin:/usr/sbin''.  Note the absence  of  ``.''
              from this entry.  This is a good practice to follow for root; it
              avoids many common Trojan Horse system penetration schemes.

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

              If the default session fails to execute, xdm will fall  back  to
              this  program.   This program is executed with no arguments, but
              executes using the same environment  variables  as  the  session
              would  have  had (see the section Session Program).  By default,
              /usr/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/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 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/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: #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 < /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 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()
              Ctrl<Key>D:       delete-character()
              Ctrl<Key>B:       move-backward-character()
              Ctrl<Key>F:       move-forward-character()
              Ctrl<Key>A:       move-to-begining()
              Ctrl<Key>E:       move-to-end()
              Ctrl<Key>K:       erase-to-end-of-line()
              Ctrl<Key>U:       erase-line()
              Ctrl<Key>X:       erase-line()
              Ctrl<Key>C:       restart-session()
              Ctrl<Key>\\:      abort-session()
              <Key>BackSpace:   delete-previous-character()
              <Key>Delete:      delete-previous-character()
              <Key>Return:      finish-field()
              <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 /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, 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 /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

       See attributes(7) for descriptions of the following attributes:

       |Availability   | system/display-manager/xdm |
       |Stability      | Volatile                   |

       X(7),    xinit(1),   xauth(1),   xrdb(1),   Xsecurity(7),   sessreg(1),
       Xserver(1), xdmshell(8), fonts.conf(5).
       X Display Manager Control Protocol
       IETF RFC 4291: IP Version 6 Addressing Architecture.

       Keith Packard, MIT X Consortium

       Source code for open source software components in Oracle  Solaris  can
       be found at https://www.oracle.com/downloads/opensource/solaris-source-

       This    software    was    built    from    source     available     at
       https://github.com/oracle/solaris-userland.    The  original  community
       source   was   downloaded   from    https://www.x.org/releases/individ-

       Further information about this software can be found on the open source
       community website at https://www.x.org.

X Version 11                      xdm 1.1.12                            XDM(8)