XDM(1)                                                                  XDM(1)

       xdm - X Display Manager with support for XDMCP, host chooser

       xdm [ -config configuration_file ] [ -nodaemon ] [ -debug debug_level ]
       [ -error error_log_file  ]  [  -resources  resource_file  ]  [  -server
       server_entry ] [ -session session_program ]

       Xdm  manages a collection of X displays, which may be on the local host
       or remote servers.  The design of xdm was guided by the needs of X ter-
       minals  as well as The Open Group standard XDMCP, the X Display Manager
       Control Protocol.  Xdm provides services similar to those  provided  by
       init,  getty and login on character terminals: prompting for login name
       and password, authenticating the user, and running a ``session.''

       A ``session'' is defined by the lifetime of a  particular  process;  in
       the  traditional character-based terminal world, it is the user's login
       shell.  In the xdm context, it is an arbitrary session  manager.   This
       is  because  in  a  windowing environment, a user's login shell process
       does not necessarily have any terminal-like  interface  with  which  to
       connect.   When  a real session manager is not available, a window man-
       ager or terminal emulator is typically used as the ``session manager,''
       meaning that termination of this process terminates the user's session.

       When the session is terminated, xdm resets the X  server  and  (option-
       ally) restarts the whole process.

       When  xdm  receives  an  Indirect query via XDMCP, it can run a chooser
       process to perform an XDMCP BroadcastQuery (or an XDMCP Query to speci-
       fied hosts) on behalf of the display and offer a menu of possible hosts
       that offer XDMCP display management.  This feature  is  useful  with  X
       terminals that do not offer a host menu themselves.

       Xdm  can  be configured to ignore BroadcastQuery messages from selected
       hosts.  This is useful when you don't want the host to appear in  menus
       produced by chooser or X terminals themselves.

       Because  xdm  provides  the  first interface that users will see, it is
       designed to be simple to use and easy to customize to the  needs  of  a
       particular  site.   Xdm has many options, most of which have reasonable
       defaults.  Browse through the various sections of this manual,  picking
       and  choosing  the things you want to change.  Pay particular attention
       to the Session Program section, which will describe how to set  up  the
       style of session desired.

       xdm  is highly configurable, and most of its behavior can be controlled
       by resource files and shell scripts.  The names of  these  files  them-
       selves are resources read from the file xdm-config or the file named by
       the -config option.

       xdm offers display management two different  ways.   It  can  manage  X
       servers  running on the local machine and specified in Xservers, and it
       can manage remote X servers (typically X terminals)  using  XDMCP  (the
       XDM Control Protocol) as specified in the Xaccess file.

       The  resources  of the X clients run by xdm outside the user's session,
       including xdm's own login window, can be affected by setting  resources
       in the Xresources file.

       For  X  terminals that do not offer a menu of hosts to get display man-
       agement from, xdm can collect willing hosts and run the chooser program
       to offer the user a menu.  For X displays attached to a host, this step
       is typically not used, as the local host does the display management.

       After resetting the X server, xdm runs the Xsetup script to  assist  in
       setting up the screen the user sees along with the xlogin widget.

       The  xlogin  widget,  which xdm presents, offers the familiar login and
       password prompts.

       After the user logs in, xdm runs the Xstartup script as root.

       Then xdm runs the Xsession script as the  user.   This  system  session
       file  may  do  some additional startup and typically runs the .xsession
       script in the user's home directory.  When the Xsession  script  exits,
       the session is over.

       At  the end of the session, the Xreset script is run to clean up, the X
       server is reset, and the cycle starts over.

       The file  /var/log/xdm.log will contain error  messages  from  xdm  and
       anything  output  to  stderr  by  Xsetup, Xstartup, Xsession or Xreset.
       When you have trouble getting xdm working, check this file  to  see  if
       xdm has any clues to the trouble.

       All  of  these  options, except -config itself, specify values that can
       also be specified in the configuration file as resources.

       -config configuration_file
              Names the configuration file, which specifies resources to  con-
              trol  the  behavior  of  xdm.   /etc/X11/xdm/xdm-config  is  the
              default.  See the section Configuration File.

              Specifies ``false'' as the value for the  DisplayManager.daemon-
              Mode  resource.   This  suppresses  the  normal daemon behavior,
              which is for xdm to close  all  file  descriptors,  disassociate
              itself  from  the  controlling  terminal,  and put itself in the
              background when it first starts up.

       -debug debug_level
              Specifies the numeric value  for  the  DisplayManager.debugLevel
              resource.   A  non-zero value causes xdm to print lots of debug-
              ging statements to the terminal; it also disables  the  Display-
              Manager.daemonMode  resource,  forcing xdm to run synchronously.
              To interpret these debugging messages, a copy of the source code
              for  xdm  is  almost  a  necessity.  No attempt has been made to
              rationalize or standardize the output.

       -error error_log_file
              Specifies  the   value   for   the   DisplayManager.errorLogFile
              resource.   This  file  contains errors from xdm as well as any-
              thing written to stderr by the various scripts and programs  run
              during the progress of the session.

       -resources resource_file
              Specifies  the  value for the DisplayManager*resources resource.
              This file is  loaded  using  xrdb(1)  to  specify  configuration
              parameters for the authentication widget.

       -server server_entry
              Specifies  the  value  for  the DisplayManager.servers resource.
              See the section Local Server Specification for a description  of
              this resource.

       -udpPort port_number
              Specifies the value for the DisplayManager.requestPort resource.
              This sets the port-number  which  xdm  will  monitor  for  XDMCP
              requests.  If set to 0, xdm will not listen for XDMCP or Chooser
              requests.  As XDMCP uses the registered well-known UDP port 177,
              this  resource  should  not  be changed to a value other than 0,
              except for debugging.

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

       -xrm resource_specification
              Allows an arbitrary resource to be specified, as in most X Tool-
              kit applications.

       At  many stages the actions of xdm can be controlled through the use of
       its configuration file, which  is  in  the  X  resource  format.   Some
       resources modify the behavior of xdm on all displays, while others mod-
       ify its behavior on a single display.  Where actions relate to  a  spe-
       cific  display,  the  display  name  is inserted into the resource name
       between ``DisplayManager'' and the final resource name segment.

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

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

       Because the resource manager uses colons to separate the  name  of  the
       resource  from  its value and dots to separate resource name parts, xdm
       substitutes underscores for both dots and colons  when  generating  the
       resource name.  For example, DisplayManager.expo_x_org_0.startup is the
       name of the resource which defines  the  startup  shell  file  for  the
       ``expo.x.org:0'' display.

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

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

              Error output is normally directed at the system console.  To re-
              direct  it,  set this resource to a file name.  A method to send
              these messages to syslog should be developed for  systems  which
              support  it;  however,  the wide variety of interfaces precludes
              any system-independent implementation.  This file also  contains
              any  output directed to stderr by the Xsetup, Xstartup, Xsession
              and Xreset files, so it will contain descriptions of problems in
              those scripts as well.

              If  the  integer  value  of  this resource is greater than zero,
              reams of debugging information will be printed.   It  also  dis-
              ables daemon mode, which would redirect the information into the
              bit-bucket, and allows non-root users to run  xdm,  which  would
              normally not be useful.

              Normally,  xdm  attempts  to  make  itself into a daemon process
              unassociated with any terminal.  This is accomplished by forking
              and  leaving  the  parent  process  to  exit,  then closing file
              descriptors and releasing the  controlling  terminal.   In  some
              environments  this  is  not  desired (in particular, when debug-
              ging).  Setting this resource to  ``false''  will  disable  this

              The  filename specified will be created to contain an ASCII rep-
              resentation of the process-id of the main xdm process.  Xdm also
              uses  file locking on this file to attempt to eliminate multiple
              daemons running on the same machine, which would cause  quite  a
              bit of havoc.

              This  is the resource which controls whether xdm uses file lock-
              ing to keep multiple display managers  from  running  amok.   On
              System V, this uses the lockf library call, while on BSD it uses

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

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

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

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

              To prevent unauthorized XDMCP service and to allow forwarding of
              XDMCP  IndirectQuery  requests, this file contains a database of
              hostnames  which  are  either  allowed  direct  access  to  this
              machine, or have a list of hosts to which queries should be for-
              warded to.  The format of this file is described in the  section
              XDMCP Access Control.

              A  list  of additional environment variables, separated by white
              space, to pass on to the Xsetup, Xstartup, Xsession, and  Xreset

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

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

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

              Use the numeric IP address of the incoming connection on  multi-
              homed hosts instead of the host name. This is to avoid trying to
              connect on the wrong interface which might be down at this time.

              This specifies a program which is run (as) root when an an XDMCP
              BroadcastQuery is received and this host is configured to  offer
              XDMCP display management. The output of this program may be dis-
              played on a chooser window.  If no  program  is  specified,  the
              string Willing to manage is sent.

              This  resource  specifies  the  name of the file to be loaded by
              xrdb as the resource database onto the root window of  screen  0
              of  the  display.   The  Xsetup  program,  the Login widget, and
              chooser will use the resources set in this file.  This  resource
              data  base is loaded just before the authentication procedure is
              started, so it can control the appearance of the  login  window.
              See the section Authentication Widget, which describes the vari-
              ous resources that are appropriate to place in this file.  There
              is no default value for this resource, but
               /etc/X11/xdm/Xresources is the conventional name.

              Specifies  the  program  run  to  offer a host menu for Indirect
              queries redirected to the special host name CHOOSER.
               /usr/X11R7/libexec/chooser  is the default.  See  the  sections
              XDMCP Access Control and Chooser.

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

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

              This  specifies a program which is run (as root) before offering
              the Login window.  This may be used to change the appearance  of
              the  screen  around  the Login window or to put up other windows
              (e.g., you may want to run xconsole here).  By default, no  pro-
              gram  is  run.   The  conventional  name for a file used here is
              Xsetup.  See the section Setup Program.

              This specifies a program  which  is  run  (as  root)  after  the
              authentication process succeeds.  By default, no program is run.
              The conventional name for a file used here is Xstartup.  See the
              section Startup Program.

              This specifies the session to be executed (not running as root).
              By default,  BINDIR/xterm is  run.   The  conventional  name  is
              Xsession.  See the section Session Program.

              This  specifies  a program which is run (as root) after the ses-
              sion terminates.  By default, no program is  run.   The  conven-
              tional name is Xreset.  See the section Reset Program.





              These  numeric  resources  control  the  behavior  of  xdm  when
              attempting to  open  intransigent  servers.   openDelay  is  the
              length  of  the  pause  in  seconds between successive attempts,
              openRepeat is the number of attempts to make, openTimeout is the
              amount of time to wait while actually attempting the open (i.e.,
              the maximum time spent in the connect(2) system call) and  star-
              tAttempts  is  the  number  of times this entire process is done
              before giving up on the server.  After openRepeat attempts  have
              been  made,  or  if openTimeout seconds elapse in any particular
              attempt, xdm terminates and restarts the server,  attempting  to
              connect again.  This process is repeated startAttempts times, at
              which point the display is declared dead and disabled.  Although
              this behavior may seem arbitrary, it has been empirically devel-
              oped and works quite well on most systems.  The bound  reservAt-
              tempts is the number of times a successful connect is allowed to
              be followed by a fatal error.  When reached, the display is dis-
              abled.   The  default  values  are openDelay: 15, openRepeat: 5,
              openTimeout: 120, startAttempts: 4 and reservAttempts: 2.


              To discover when remote  displays  disappear,  xdm  occasionally
              pings them, using an X connection and XSync calls.  pingInterval
              specifies the time (in minutes) between each ping attempt, ping-
              Timeout  specifies  the  maximum  amount of time (in minutes) to
              wait for the terminal to respond to the request.  If the  termi-
              nal  does  not  respond, the session is declared dead and termi-
              nated.  By default, both are set to  5  minutes.   If  you  fre-
              quently  use X terminals which can become isolated from the man-
              aging host, you may wish to increase this value.  The only worry
              is  that  sessions will continue to exist after the terminal has
              been accidentally disabled.  xdm will not ping  local  displays.
              Although it would seem harmless, it is unpleasant when the work-
              station session is terminated as a result of the server  hanging
              for NFS service and not responding to the ping.

              This  boolean  resource specifies whether the X server should be
              terminated when a session terminates (instead of resetting  it).
              This  option  can  be used when the server tends to grow without
              bound over time, in order to limit the amount of time the server
              is run.  The default value is ``false.''

              Xdm  sets  the PATH environment variable for the session to this
              value.  It should be a colon separated list of directories;  see
              sh(1)   for   a   full   description.    The  default  value  is

              Xdm sets the PATH environment variable for the startup and reset
              scripts  to  the  value  of this resource.  The default for this
              resource is ``DEF_SYSTEM_PATH''.  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,
              BINDIR/xterm is used.


              To improve security, xdm grabs the  server  and  keyboard  while
              reading  the  login  name and password.  The grabServer resource
              specifies if the server should be held for the duration  of  the
              name/password  reading.  When ``false,'' the server is ungrabbed
              after the  keyboard  grab  succeeds,  otherwise  the  server  is
              grabbed  until  just  before the session begins.  The default is
              ``false.''  The grabTimeout resource specifies the maximum  time
              xdm  will  wait  for  the grab to succeed.  The grab may fail if
              some other client has the server grabbed,  or  possibly  if  the
              network  latencies  are  very high.  This resource has a default
              value of 3 seconds; you should be cautious when raising it, as a
              user  can  be spoofed by a look-alike window on the display.  If
              the grab fails, xdm kills and restarts the server (if  possible)
              and the session.


              authorize  is a boolean resource which controls whether xdm gen-
              erates and uses authorization for the local server  connections.
              If  authorization  is  used, authName is a list of authorization
              mechanisms to use, separated by white space.  XDMCP  connections
              dynamically  specify  which  authorization  mechanisms  are sup-
              ported, so authName is ignored in this case.  When authorize  is
              set  for  a display and authorization is not available, the user
              is informed by having a different message displayed in the login
              widget.   By default, authorize is ``true,''  authName is ``MIT-
              MAGIC-COOKIE-1,''  or,  if  XDM-AUTHORIZATION-1  is   available,

              This file is used to communicate the authorization data from xdm
              to the server, using the -auth server command line  option.   It
              should  be kept in a directory which is not world-writable as it
              could easily be removed, disabling the  authorization  mechanism
              in  the server.  If not specified, a name is generated from Dis-
              playManager.authDir and the name of the display.

              If set to ``false,'' disables the use of the unsecureGreeting in
              the  login  window.  See the section Authentication Widget.  The
              default is ``true.''

              The number of the signal xdm sends to reset the server.  See the
              section Controlling the Server.  The default is 1 (SIGHUP).

              The number of the signal xdm sends to terminate the server.  See
              the  section  Controlling  the  Server.   The  default   is   15

              The  original  implementation  of  authorization  in  the sample
              server reread the  authorization  file  at  server  reset  time,
              instead  of when checking the initial connection.  As xdm gener-
              ates the authorization information just before connecting to the
              display,  an  old  server would not get up-to-date authorization
              information.  This resource causes xdm to  send  SIGHUP  to  the
              server  after  setting up the file, causing an additional server
              reset to occur, during which time the new authorization informa-
              tion  will  be  read.  The default is ``false,'' which will work
              for all MIT servers.

              When xdm is unable to write to the usual user authorization file
              ($HOME/.Xauthority),  it  creates  a  unique  file  name in this
              directory and points the environment variable XAUTHORITY at  the
              created file.  It uses /tmp by default.

       First,  the  xdm configuration file should be set up.  Make a directory
       (usually  /etc/X11/xdm) to contain all of the relevant files.

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

            DisplayManager.servers:            /etc/X11/xdm/Xservers
            DisplayManager.errorLogFile:       /var/log/xdm.log
            DisplayManager*resources:          /etc/X11/xdm/Xresources
            DisplayManager*startup:            /etc/X11/xdm/Xstartup
            DisplayManager*session:            /etc/X11/xdm/Xsession
            DisplayManager.pidFile:            /var/run/xdm-pid
            DisplayManager._0.authorize:       true
            DisplayManager*authorize:          false

       Note  that  this  file mostly contains references to other files.  Note
       also that some of the resources are specified with ``*'' separating the
       components.  These resources can be made unique for each different dis-
       play, by replacing the ``*'' with the display-name, but  normally  this
       is  not  very useful.  See the Resources section for a complete discus-

       The database file specified by the  DisplayManager.accessFile  provides
       information  which  xdm uses to control access from displays requesting
       XDMCP service.  This file contains three  types  of  entries:   entries
       which  control  the  response  to Direct and Broadcast queries, entries
       which control the response to Indirect queries, and macro  definitions.

       The  format  of  the  Direct entries is simple, either a host name or a
       pattern, which is distinguished from a host name by  the  inclusion  of
       one  or  more  meta  characters  (`*' matches any sequence of 0 or more
       characters, and `?' matches any single character)  which  are  compared
       against  the  host  name of the display device.  If the entry is a host
       name, all comparisons are done using network  addresses,  so  any  name
       which  converts  to  the correct network address may be used.  For pat-
       terns, only canonical host names are used in the comparison, so  ensure
       that you do not attempt to match aliases.  Preceding either a host name
       or a pattern with a `!' character causes hosts which match  that  entry
       to be excluded.

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

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

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

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

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

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

       Here is an example Xaccess file:

       # Xaccess - XDMCP access control file

       # Direct/Broadcast query entries

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

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

       # Indirect query entries

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

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

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


       rincewind.sample.net ff02::1                 #IPv6 Multicast to ff02::1
                                                    #with a hop count of 1
       ponder.sample.net    CHOOSER  #Offer a menu of hosts
                                                    #who respond to IPv4 Multicast
                                                    # to with a TTL of 16

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

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

       Example Xaccess file using chooser:

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

       The program to use for chooser is specified by the  DisplayManager.DIS-
       PLAY.chooser  resource.  For more flexibility at this step, the chooser
       could be a shell script.  Chooser is the session manager  here;  it  is
       run instead of a child xdm to manage the display.

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

       When the user selects a host, chooser prints the host chosen, which  is
       read  by the parent xdm, and exits.  xdm closes its connection to the X
       server, and the server resets and sends another Indirect XDMCP request.
       xdm  remembers the user's choice (for DisplayManager.choiceTimeout sec-
       onds) and forwards the request to the chosen host, which starts a  ses-
       sion on that display.

       The  following  configuration directive is also defined for the Xaccess
       configuration file:

       LISTEN interface [list of multicast group addresses]
              interface may be a hostname or IP address representing a network
              interface  on  this  machine, or the wildcard * to represent all
              available network interfaces.

       If one or more LISTEN lines are specified, xdm only listens  for  XDMCP
       connections  on  the specified interfaces. If multicast group addresses
       are listed on a listen line, xdm joins  the  multicast  groups  on  the
       given interface.

       If no LISTEN lines are given, the original behavior of listening on all
       interfaces is preserved for backwards compatibility.  Additionally,  if
       no  LISTEN  is  specified,  xdm  joins the default XDMCP IPv6 multicast
       group, when compiled with IPv6 support.

       To disable listening for XDMCP connections altogther, a line of  LISTEN
       with  no addresses may be specified, or the previously supported method
       of setting DisplayManager.requestPort to 0 may be used.

       LISTEN * ff02::1    # Listen on all interfaces and to the
                           # ff02::1 IPv6 multicast group.
       LISTEN  # Listen only on this interface, as long
                           # as no other listen directives appear in
                           # file.

       The   Internet   Assigned   Numbers   Authority   has   has    assigned
       ff0X:0:0:0:0:0:0:12b  as  the  permanently  assigned range of multicast
       addresses for XDMCP. The X in the prefix may be replaced by  any  valid
       scope  identifier,  such  as 1 for Interface-Local, 2 for Link-Local, 5
       for Site-Local, and so on.  (See IETF RFC 4291 or its  replacement  for
       further  details  and scope definitions.)  xdm defaults to listening on
       the Link-Local scope address ff02:0:0:0:0:0:0:12b to most closely match
       the old IPv4 subnet broadcast behavior.

       The resource DisplayManager.servers gives a server specification or, if
       the values starts with a slash (/),  the  name  of  a  file  containing
       server specifications, one per line.

       Each  specification indicates a display which should constantly be man-
       aged and which is not using XDMCP.  This method is used  typically  for
       local  servers only.  If the resource or the file named by the resource
       is empty, xdm will offer XDMCP service only.

       Each specification consists of at least three parts:  a display name, a
       display  class,  a display type, and (for local servers) a command line
       to start the server.  A typical entry for local display number 0  would

         :0 Digital-QV local BINDIR/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 BINDIR/X :0'' instead of ``localhost:0 Sun-CG3 local
       BINDIR/X  :0''  if  your other resources are specified as ``DisplayMan-
       ager._0.session'').  The display class portion is also used in the dis-
       play-specific  resources, as the class of the resource.  This is useful
       if you have a large collection of similar displays (such as a corral of
       X  terminals) and would like to set resources for groups of them.  When
       using XDMCP, the display is required to specify the display  class,  so
       the  manual  for your particular X terminal should document the display
       class string for your device.  If it doesn't, you can run xdm in  debug
       mode  and  look  at  the  resource  strings which it generates for that
       device, which will include the class string.

       When xdm starts a session,  it  sets  up  authorization  data  for  the
       server.   For  local  servers,  xdm  passes  ``-auth  filename'' on the
       server's command line to point it at its authorization data.  For XDMCP
       servers, xdm passes the authorization data to the server via the Accept
       XDMCP request.

       The Xresources file is loaded onto the display as a  resource  database
       using  xrdb.   As  the authentication widget reads this database before
       starting up, it usually contains parameters for that widget:

            xlogin*login.translations: #override\
                 Ctrl<Key>R: abort-display()\n\
                 <Key>F1: set-session-argument(failsafe) finish-field()\n\
                 <Key>Return: set-session-argument() finish-field()
            xlogin*borderWidth: 3
            xlogin*greeting: CLIENTHOST
            #ifdef COLOR
            xlogin*greetColor: CadetBlue
            xlogin*failColor: red

       Please note the translations entry; it specifies a few new translations
       for  the  widget  which  allow users to escape from the default session
       (and avoid troubles that may occur in it).  Note that if  #override  is
       not specified, the default translations are removed and replaced by the
       new value, not a very useful result as some of the default translations
       are  quite  useful (such as ``<Key>: insert-char ()'' which responds to
       normal typing).

       This file may also contain resources for the setup program and chooser.

       The  Xsetup file is run after the server is reset, but before the Login
       window is offered.  The file is typically a shell script.  It is run as
       root, so should be careful about security.  This is the place to change
       the root background or bring up other windows that should appear on the
       screen along with the Login widget.

       In  addition to any specified by DisplayManager.exportList, the follow-
       ing environment variables are passed:

            DISPLAY        the associated display name
            PATH           the value of DisplayManager.DISPLAY.systemPath
            SHELL          the value of DisplayManager.DISPLAY.systemShell
            XAUTHORITY     may be set to an authority file

       Note that since xdm grabs the keyboard, any other windows will  not  be
       able to receive keyboard input.  They will be able to interact with the
       mouse, however; beware of potential security holes here.   If  Display-
       Manager.DISPLAY.grabServer  is  set, Xsetup will not be able to connect
       to the display at all.  Resources for this program can be put into  the
       file named by DisplayManager.DISPLAY.resources.

       Here is a sample Xsetup script:

            # Xsetup_0 - setup script for one workstation
            xcmsdb < /etc/X11/xdm/monitors/alex.0
            xconsole -geometry 480x130-0-0 -notify -verbose -exitOnFail &

       The  authentication widget prompts the user for the username, password,
       and/or other required authentication data from  the  keyboard.   Nearly
       every   imaginable   parameter  can  be  controlled  with  a  resource.
       Resources for this widget should be put into the file named by Display-
       Manager.DISPLAY.resources.   All  of these have reasonable default val-
       ues, so it is not necessary to specify any of them.

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

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

       xlogin.Login.width, xlogin.Login.height, xlogin.Login.x, xlogin.Login.y
              The  geometry of the Login widget is normally computed automati-
              cally.  If you wish to position it elsewhere,  specify  each  of
              these resources.

              The color used to display the input typed by the user.

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

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

              A  string which identifies this window.  The default is ``X Win-
              dow System.''

              When X authorization is requested in the configuration file  for
              this  display  and  none  is  in use, this greeting replaces the
              standard greeting.  The default is ``This is  an  unsecure  ses-

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

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

              The color used to display the greeting.

              The  string  displayed  to  prompt for a user name.  Xrdb strips
              trailing white space from resource values, so to add  spaces  at
              the end of the prompt (usually a nice thing), add spaces escaped
              with backslashes.  The default is ``Login:  ''

              The string displayed to prompt for a password, when not using an
              authentication system such as PAM that provides its own prompts.
              The default is ``Password:  ''

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

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

              The color used to display prompts.

              A message  which  is  displayed  when  the  users  password  has
              expired.  The default is ``Password Change Required''

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

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

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

              The color used to display the failure message.

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

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

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

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

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

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

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

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

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

              If set to ``true'', allow an otherwise failing password match to
              succeed  if the account does not require a password at all.  The
              default is ``false'', so only users that have passwords assigned
              can log in.

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

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

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

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

       The actions which are supported by the widget are:

              Erases the character before the cursor.

              Erases the character after the cursor.

              Moves the cursor backward.

              Moves the cursor forward.

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

              Moves the cursor to the end of the editable text.

              Erases all text after the cursor.

              Erases the entire text.

              If the cursor is in the name field,  proceeds  to  the  password
              field;  if  the cursor is in the password field, checks the cur-
              rent name/password pair.  If the name/password  pair  is  valid,
              xdm  starts  the session.  Otherwise the failure message is dis-
              played and the user is prompted again.

              Terminates and restarts the server.

              Terminates the server, disabling it.  This action is not  acces-
              sible  in  the default configuration.  There are various reasons
              to stop xdm on a system console, such as when shutting the  sys-
              tem  down, when using xdmshell, to start another type of server,
              or to generally access the console.  Sending xdm a  SIGHUP  will
              restart the display.  See the section Controlling XDM.

              Resets  the X server and starts a new session.  This can be used
              when the resources have been changed and you want to  test  them
              or when the screen has been overwritten with system messages.

              Inserts the character typed.

              Specifies  a single word argument which is passed to the session
              at startup.  See the section Session Program.

              Disables access control in the server.  This can  be  used  when
              the  .Xauthority file cannot be created by xdm.  Be very careful
              using this; it might be better to disconnect  the  machine  from
              the network before doing this.

       On   some  systems  (OpenBSD)  the  user's  shell  must  be  listed  in
       /etc/shells to allow login through xdm. The normal password and account
       expiration dates are enforced too.

       The Xstartup program is run as root when the user logs in.  It is typi-
       cally a shell script.  Since it is run as root, Xstartup should be very
       careful  about  security.   This is the place to put commands which add
       entries to utmp or wtmp files,  (the  sessreg  program  may  be  useful
       here),  mount  users'  home directories from file servers, or abort the
       session if logins are not allowed.

       In addition to any specified by DisplayManager.exportList, the  follow-
       ing environment variables are passed:

            DISPLAY        the associated display name
            HOME           the initial working directory of the user
            LOGNAME        the user name
            USER           the user name
            PATH           the value of DisplayManager.DISPLAY.systemPath
            SHELL          the value of DisplayManager.DISPLAY.systemShell
            XAUTHORITY     may be set to an authority file
            WINDOWPATH     may be set to the "window path" leading to the X server

       No  arguments  are  passed  to the script.  Xdm waits until this script
       exits before starting the user session.  If  the  exit  value  of  this
       script  is  non-zero,  xdm  discontinues the session and starts another
       authentication cycle.

       The sample Xstartup file shown  here  prevents  login  while  the  file
       /etc/nologin exists.  Thus this is not a complete example, but simply a
       demonstration of the available functionality.

       Here is a sample Xstartup script:

            # Xstartup
            # This program is run as root after the user is verified
            if [ -f /etc/nologin ]; then
                 xmessage -file /etc/nologin -timeout 30 -center
                 exit 1
            sessreg -a -l $DISPLAY -x /etc/X11/xdm/Xservers $LOGNAME
            exit 0

       The Xsession program is the command which is run as the user's session.
       It is run with the permissions of the authorized user.

       In  addition to any specified by DisplayManager.exportList, the follow-
       ing environment variables are passed:

            DISPLAY        the associated display name
            HOME           the initial working directory of the user
            LOGNAME        the user name
            USER           the user name
            PATH           the value of DisplayManager.DISPLAY.userPath
            SHELL          the user's default shell (from getpwnam)
            XAUTHORITY     may be set to a non-standard authority file
            KRB5CCNAME     may be set to a Kerberos credentials cache name
            WINDOWPATH     may be set to the "window path" leading to the X server

       At most installations, Xsession should look in $HOME for a file  .xses-
       sion,  which  contains  commands  that each user would like to use as a
       session.  Xsession should also implement a system default session if no
       user-specified session exists.

       An  argument may be passed to this program from the authentication wid-
       get using the `set-session-argument'  action.   This  can  be  used  to
       select different styles of session.  One good use of this feature is to
       allow the user to escape from the ordinary session when it fails.  This
       allows users to repair their own .xsession if it fails, without requir-
       ing administrative intervention.  The  example  following  demonstrates
       this feature.

       This example recognizes the special ``failsafe'' mode, specified in the
       translations in the Xresources file, to  provide  an  escape  from  the
       ordinary  session.   It  also  requires that the .xsession file be exe-
       cutable so we don't have to guess what shell it wants to use.

            # Xsession
            # This is the program that is run as the client
            # for the display manager.

            case $# in
                 case $1 in
                      exec xterm -geometry 80x24-0-0


            if [ -f "$startup" ]; then
                 exec "$startup"
                 if [ -f "$resources" ]; then
                      xrdb -load "$resources"
                 twm &
                 xman -geometry +10-10 &
                 exec xterm -geometry 80x24+10+10 -ls

       The user's .xsession file  might  look  something  like  this  example.
       Don't forget that the file must have execute permission.
            #! /bin/csh
            # no -f in the previous line so .cshrc gets run to set $PATH
            twm &
            xrdb -merge "$HOME/.Xresources"
            emacs -geometry +0+50 &
            xbiff -geometry -430+5 &
            xterm -geometry -0+50 -ls

       Symmetrical with Xstartup, the Xreset script is run after the user ses-
       sion has terminated.  Run as root, it should contain commands that undo
       the  effects  of commands in Xstartup, updating entries in utmp or wtmp
       files, or unmounting directories from file  servers.   The  environment
       variables that were passed to Xstartup are also passed to Xreset.

       A sample Xreset script:
            # Xreset
            # This program is run as root after the session ends
            sessreg -d -l $DISPLAY -x /etc/X11/xdm/Xservers $LOGNAME
            exit 0

       Xdm  controls local servers using POSIX signals.  SIGHUP is expected to
       reset the server, closing all client connections and  performing  other
       cleanup duties.  SIGTERM is expected to terminate the server.  If these
       signals do not perform the expected actions, the resources  DisplayMan-
       ager.DISPLAY.resetSignal   and   DisplayManager.DISPLAY.termSignal  can
       specify alternate signals.

       To control remote terminals not using XDMCP, xdm  searches  the  window
       hierarchy on the display and uses the protocol request KillClient in an
       attempt to clean up the terminal for the next session.   This  may  not
       actually kill all of the clients, as only those which have created win-
       dows will be noticed.  XDMCP provides a more sure mechanism;  when  xdm
       closes  its initial connection, the session is over and the terminal is
       required to close all other connections.

       Xdm responds to two signals: SIGHUP and SIGTERM.  When sent  a  SIGHUP,
       xdm  rereads  the  configuration file, the access control file, and the
       servers file.  For the servers file, it notices if  entries  have  been
       added  or removed.  If a new entry has been added, xdm starts a session
       on the associated display.  Entries which have been  removed  are  dis-
       abled  immediately, meaning that any session in progress will be termi-
       nated without notice and no new session will be started.

       When sent a SIGTERM, xdm terminates all sessions in progress and exits.
       This can be used when shutting down the system.

       Xdm attempts to mark its various sub-processes for ps(1) by editing the
       command line argument list in place.  Because xdm can't allocate  addi-
       tional space for this task, it is useful to start xdm with a reasonably
       long command line (using the full path name should  be  enough).   Each
       process which is servicing a display is marked -display.

       To  add  an additional local display, add a line for it to the Xservers
       file.  (See the section Local Server Specification.)

       Examine the display-specific resources in xdm-config (e.g., DisplayMan-
       ager._0.authorize)  and consider which of them should be copied for the
       new display.  The default xdm-config has all the appropriate lines  for
       displays :0 and :1.

       You  can  use xdm to run a single session at a time, using the 4.3 init
       options or other suitable daemon by specifying the server on  the  com-
       mand line:

            xdm -server ":0 SUN-3/60CG4 local BINDIR/X :0"

       Or,  you might have a file server and a collection of X terminals.  The
       configuration for this is identical to the  sample  above,  except  the
       Xservers file would look like

            extol:0 VISUAL-19 foreign
            exalt:0 NCD-19 foreign
            explode:0 NCR-TOWERVIEW3000 foreign

       This  directs  xdm  to manage sessions on all three of these terminals.
       See the section Controlling Xdm for a description of using  signals  to
       enable  and disable these terminals in a manner reminiscent of init(8).

       One thing that xdm isn't very good at doing is  coexisting  with  other
       window  systems.   To use multiple window systems on the same hardware,
       you'll probably be more interested in xinit.

                           the default configuration file

       $HOME/.Xauthority   user authorization file where xdm stores  keys  for
                           clients to read

                           the default chooser

       BINDIR/xrdb         the default resource database loader

       BINDIR/X            the default server

       BINDIR/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).
       X Display Manager Control Protocol
       IETF RFC 4291: IP Version 6 Addressing Architecture.

       Keith Packard, MIT X Consortium

                                 X Version 11                           XDM(1)

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