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       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

       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 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
       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

       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 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
              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

              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

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

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

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

              To prevent unauthorized XDMCP service and to allow forwarding of
              XDMCP  IndirectQuery  requests, this file contains a database of
              hostnames  which  are  either  allowed  direct  access  to  this
              machine,  or  have  a  list  of hosts to which queries should be
              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

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

              A   file   to  read  8  bytes  from  to  generate  the  seed  of
              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 /tmp/entropy.

       On systems that don't have such a daemon, a fall-back entropy gathering
       system,  based on various log file contents hashed by the MD5 algorithm
       is used instead.

              On systems that support a dynamically-loadable greeter  library,
              the name of the library.  The default is

              Number  of seconds to wait for display to respond after user has
              selected a host from the chooser.  If the display sends an XDMCP
              IndirectQuery  within this time, the request is forwarded to the
              chosen host.  Otherwise, it is assumed to be from a new  session
              and the chooser is offered again.  Default is 15.

              Use  the  numeric  IP  address  of  the  incoming  connection on
              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  /usr/bin/xrdb.

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

              This specifies a program which is run (as root) before  offering
              the  Login window.  This may be used to change the appearance of
              the screen around the Login window or to put  up  other  windows
              (e.g.,  you  may  want  to  run  xconsole here).  By default, no
              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 Program.

              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

              Xdm sets the PATH environment variable for the startup and reset
              scripts  to  the  value  of this resource.  The default for this
              resource                                                      is
              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
              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-AUTHORIZATION-1 MIT-MAGIC-

              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

              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-

            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


       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 excluded.

       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

       An Indirect entry also contains a host name or pattern, but follows  it
       with a list of host names or macros to which indirect queries should be

       A macro definition contains a macro name and a list of host  names  and
       other  macros  that  the  macro expands to.  To distinguish macros from
       hostnames, macro names start with  a  `%'  character.   Macros  may  be

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

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

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

       Here is an example Xaccess file:

       # Xaccess - XDMCP access control file

       # Direct/Broadcast query entries

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

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

       # Indirect query entries

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

       If  compiled  with  IPv6  support, multicast address groups may also be
       included in  the  list  of  addresses  indirect  queries  are  set  to.
       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 display.

       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

         :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 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()
                 <Key>F1: set-session-argument(failsafe) finish-field()
                 <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 support.

              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

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

              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 ``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
              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 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>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
              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

              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 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
       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 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
       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

       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 xinit.


       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

              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

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