Provided by: xdm_1.1.11-1ubuntu1_amd64 bug


       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  terminals  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 manager 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 (optionally) 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 specified 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

       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


       xdm is highly configurable, and most of its behavior can be controlled by  resource  files
       and  shell  scripts.  The names of these files themselves 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 management 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 control 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.daemonMode 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 debugging statements to  the  terminal;  it  also
              disables  the DisplayManager.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 anything  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

       -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 Toolkit 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 modify its behavior on a single display.  Where actions relate to a
       specific   display,   the  display  name  is  inserted  into  the  resource  name  between
       ``DisplayManager'' and the final resource name segment.

       For local displays, the resource name and class are as read from the Xservers file.

       For remote displays, the resource name is what the network address of the display resolves
       to.   See the removeDomain resource.  The name must match exactly; xdm is not aware of all
       the network aliases that might reach a given display.  If  the  name  resolve  fails,  the
       address  is  used.   The  resource  class  is  as  sent by the display in the XDMCP Manage

       Because the resource manager uses colons to separate the name of  the  resource  from  its
       value  and dots to separate resource name parts, xdm substitutes underscores for both dots
       and    colons     when     generating     the     resource     name.      For     example,
       DisplayManager.expo_x_org_0.startup  is the name of the resource which defines the startup
       shell file for the ``'' display.

              This resource either specifies a file name full of server entries, one per line (if
              the  value  starts  with a slash), or a single server entry.  See the section Local
              Server Specification for the details.

              This indicates the UDP port number which xdm uses  to  listen  for  incoming  XDMCP
              requests.   Unless  you need to debug the system, leave this with its default value
              of 177.

              Error output is normally directed at the system console.  To redirect 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 disables 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 debugging).  Setting this
              resource to ``false'' will disable this feature.

              The filename specified will be created to contain an ASCII  representation  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 locking to keep multiple
              display managers from running amok.  On System V, this uses the lockf library call,
              while on BSD it uses flock.

              This   names   a  directory  under  which  xdm  stores  authorization  files  while
              initializing the session.  The default value is  /var/lib/xdm.  Can  be  overridden
              for specific displays by DisplayManager.DISPLAY.authFile.

              This  boolean  controls  whether  xdm  rescans  the  configuration, servers, access
              control and authentication keys files after a session terminates and the files have
              changed.   By  default  it is ``true.''  You can force xdm to reread these files by
              sending a SIGHUP to the main process.

              When computing the display name for XDMCP clients, the name resolver will typically
              create  a  fully  qualified  host  name  for  the  terminal.   As this is sometimes
              confusing, xdm will remove the domain name portion of the host name if  it  is  the
              same  as  the  domain name of the local host when this variable is set.  By default
              the value is ``true.''

              XDM-AUTHENTICATION-1 style XDMCP authentication requires  that  a  private  key  be
              shared  between  xdm and the terminal.  This resource specifies the file containing
              those values.  Each entry in the file consists of a display  name  and  the  shared
              key.   By  default,  xdm  does  not include support for XDM-AUTHENTICATION-1, as it
              requires DES which is not generally distributable because of United  States  export

              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 forwarded 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 programs.

              A file to checksum to generate the seed of authorization keys.  This  should  be  a
              file that changes frequently.  The default is /dev/mem.

              A  file  to  read  8  bytes  from  to generate the seed of authorization 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 generate 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 ( 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

       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 multihomed 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 displayed 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 various 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

              This specifies the name of the C preprocessor which is used by 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
              program 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

              This  specifies  a program which is run (as root) after the session terminates.  By
              default, no program is run.  The conventional 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 startAttempts 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   developed   and   works  quite  well  on  most  systems.   The  bound
              reservAttempts is the number of  times  a  successful  connect  is  allowed  to  be
              followed  by  a  fatal  error.  When reached, the display is disabled.  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, pingTimeout specifies the maximum amount of time (in minutes) to
              wait for the terminal to respond to the request.  If the terminal does not respond,
              the  session  is  declared  dead  and  terminated.   By  default, both are set to 5
              minutes.  If you frequently use X terminals which  can  become  isolated  from  the
              managing  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 workstation 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 ``/usr/local/bin:/usr/bin:/bin:/usr/games''.

              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/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin''.  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 default.

              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 generates 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  supported,  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,   ``XDM-

              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
              DisplayManager.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 (SIGTERM).

              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 generates 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 information 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-config:

            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 display, by replacing  the  ``*''  with  the  display-name,  but
       normally this is not very useful.  See the Resources section for a complete discussion.


       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 patterns, 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

       To only respond to Direct queries for a host  or  pattern,  it  can  be  followed  by  the
       optional  ``NOBROADCAST''  keyword.   This  can  be  used  to  prevent  an xdm server from
       appearing on menus based on Broadcast queries.

       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 sent.

       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 nested.

       Indirect  entries  may  also  specify  to have xdm run chooser to offer a menu of hosts to
       connect to.  See the section Chooser.

       When checking access for a particular display host, each entry is scanned in turn and  the
       first  matching  entry  determines the response.  Direct and Broadcast entries are ignored
       when scanning for an Indirect entry and vice-versa.

       Blank lines are ignored, `#' is treated as a comment delimiter causing the  rest  of  that
       line  to  be  ignored,  and `\newline' causes the newline to be ignored, allowing indirect
       host lists to span multiple lines.

       Here is an example Xaccess file:

       # Xaccess - XDMCP access control file

       # Direct/Broadcast query entries

       !   # disallow direct/broadcast service for xtra       # allow access from this particular display
       *       # allow access from any display in LCS

       *        NOBROADCAST         # allow only direct access
       *                                # allow direct and broadcast

       # Indirect query entries

       %HOSTS     \
                    #force extract to contact xenon
       !   dummy               #disallow indirect access
       *       %HOSTS              #all others get to choose

       If compiled with IPv6 support, multicast address groups may also be included in  the  list
       of  addresses  indirect  queries  are  set  to.  Multicast addresses may be followed by an
       optional / character and hop count. If no hop count is specified, the multicast hop  count
       defaults  to  1,  keeping  the packet on the local network. For IPv4 multicasting, the hop
       count is used as the TTL.

       Examples: ff02::1                 #IPv6 Multicast to ff02::1
                                                    #with a hop count of 1    CHOOSER  #Offer a menu of hosts
                                                    #who respond to IPv4 Multicast
                                                    # to with a TTL of 16


       For X terminals that do not offer a host menu for use with Broadcast or Indirect  queries,
       the chooser program can do this for them.  In the Xaccess file, specify ``CHOOSER'' as the
       first entry in the Indirect host list.  Chooser will send a Query request to each  of  the
       remaining host names in the list and offer a menu of all the hosts that respond.

       The  list  may  consist  of  the  word  ``BROADCAST,''  in  which case chooser will send a
       Broadcast instead, again offering a menu of all hosts that respond.   Note  that  on  some
       operating systems, UDP packets cannot be broadcast, so this feature will not work.

       Example Xaccess file using chooser:  CHOOSER %HOSTS          #offer a menu of these hosts     CHOOSER BROADCAST       #offer a menu of all hosts

       The  program  to  use  for  chooser  is  specified  by  the DisplayManager.DISPLAY.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

       Resources   for   this   program    can    be    put    into    the    file    named    by

       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 seconds) and forwards the request to the chosen  host,  which
       starts a session 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 managed 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 be:

         :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
       ``DisplayManager._0.session'').  The display class portion is also used  in  the  display-
       specific  resources,  as  the  class  of the resource.  This is useful if you have a large
       collection of similar displays (such as a corral of X terminals) and  would  like  to  set
       resources  for  groups  of them.  When using XDMCP, the display is required to specify the
       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

       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 following 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 DisplayManager.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  DisplayManager.DISPLAY.resources.   All of these have reasonable default values, so it
       is not necessary to specify any of them.

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

       Xdm  can  be  compiled  with  support for the Xft(3) library for font rendering.   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 automatically.  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

              A string which identifies this window.  The default is ``X Window 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 session''

              The  face used to display the greeting when built with Xft support.  The default is

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

              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

              The font used to display prompts when not built with Xft support.

              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 elements 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

       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 appearance.

              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 password 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

              This  specifies the translations used for the login widget.  Refer to the X Toolkit
              documentation for a complete discussion on translations.  The  default  translation
              table is:

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

       The actions which are supported by the widget are:

              Erases the character before the cursor.

              Erases the character after the cursor.

              Moves the cursor backward.

              Moves the cursor forward.

              (Apologies  about  the  spelling  error.)  Moves the cursor to the beginning of the
              editable text.

              Moves the cursor to the end of the editable text.

              Erases all text after the cursor.

              Erases the entire text.

              If the cursor is in the name field, proceeds to the password field; if  the  cursor
              is  in  the  password  field,  checks  the  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  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 typically 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 following 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

       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 following 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 .xsession, 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 widget 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 requiring
       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 executable so we don't have to guess what  shell  it  wants  to

            # 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 session 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  DisplayManager.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 windows 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 disabled
       immediately, meaning that any session in progress will be terminated 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 additional 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.,  DisplayManager._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 command 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


       xdm uses SIGALRM and SIGUSR1 for its own inter-process  communication  purposes,  managing
       the  relationship  between the parent xdm process and its children.  Sending these signals
       to any xdm process may result in unexpected behavior.

       SIGHUP causes xdm to rescan its configuration files and reopen its log file.

              causes xdm to terminate its children and shut down.

              causes xdm to reopen its log file.  This is useful if log rotation is desired,  but
              SIGHUP is too disruptive.


                           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), xdmshell(1),
       fonts.conf(5), xdm.options(5).
       X Display Manager Control Protocol
       IETF RFC 4291: IP Version 6 Addressing Architecture.


       Keith Packard, MIT X Consortium