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    Command:

    xdm

    
    
    

    SYNOPSIS

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

    DESCRIPTION

           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.
    
    
    

    OVERVIEW

           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
    
           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.
    
    
    

    OPTIONS

           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.
    
           -nodaemon
                  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.
                  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.
    
    
    

    RESOURCES

           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
           request.
    
           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.
    
           DisplayManager.servers
                  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.
    
           DisplayManager.requestPort
                  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.
    
           DisplayManager.errorLogFile
                  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
                  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
                  feature.
    
           DisplayManager.pidFile
                  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.
    
           DisplayManager.lockPidFile
                  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
                  flock.
    
           DisplayManager.authDir
                  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 Dis-
                  playManager.DISPLAY.authFile.
    
           DisplayManager.autoRescan
                  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.
    
           DisplayManager.removeDomainname
                  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.''
    
           DisplayManager.keyFile
                  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.
    
           DisplayManager.accessFile
                  To prevent unauthorized XDMCP service and to allow forwarding of
                  /dev/mem.
    
           DisplayManager.randomDevice
                  A file to read 8 bytes from to generate the seed  of  authoriza-
                  tion  keys.   The default is  /dev/urandom . If this file cannot
                  be read, or if a read blocks for more than 5 seconds, xdm  falls
                  back  to using a checksum of DisplayManager.randomFile to gener-
                  ate the seed.
    
           DisplayManager.prngdSocket
    
           DisplayManager.prngPort
                  A UNIX domain socket name or a TCP socket port number  on  local
                  host  on which a Pseudo-Random Number Generator Daemon, like EGD
                  (http://egd.sourceforge.net) is listening, in order to  generate
                  the  autorization keys. Either a non null port or a valid socket
                  name must be specified. The default is to  use  the  Unix-domain
                  socket /tmp/entropy.
    
           On systems that don't have such a daemon, a fall-back entropy gathering
           system, based on various log file contents hashed by the MD5  algorithm
           is used instead.
    
           DisplayManager.greeterLib
                  On  systems that support a dynamically-loadable greeter library,
                  the name of the library.  The default is
                   /usr/lib/X11/xdm/libXdmGreet.so.
    
           DisplayManager.choiceTimeout
                  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.
    
           DisplayManager.sourceAddress
                  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.
    
           DisplayManager.willing
                  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.
    
           DisplayManager.DISPLAY.resources
                  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
    
           DisplayManager.DISPLAY.xrdb
                  Specifies  the  program used to load the resources.  By default,
                  xdm uses  /usr/bin/xrdb.
    
           DisplayManager.DISPLAY.cpp
                  This specifies the name of the C preprocessor which is  used  by
                  xrdb.
    
           DisplayManager.DISPLAY.setup
                  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.
    
           DisplayManager.DISPLAY.startup
                  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.
    
           DisplayManager.DISPLAY.session
                  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.
    
           DisplayManager.DISPLAY.reset
                  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.
    
           DisplayManager.DISPLAY.openDelay
    
           DisplayManager.DISPLAY.openRepeat
    
           DisplayManager.DISPLAY.openTimeout
    
           DisplayManager.DISPLAY.startAttempts
    
           DisplayManager.DISPLAY.reservAttempts
                  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
                  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.
    
           DisplayManager.DISPLAY.terminateServer
                  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.''
    
           DisplayManager.DISPLAY.userPath
                  Xdm  sets  the PATH environment variable for the session to this
                  value.  It should be a colon separated list of directories;  see
                  sh(1)   for   a   full   description.    The  default  value  is
                  ''/usr/local/bin:/usr/bin:/bin:/usr/games''.
    
           DisplayManager.DISPLAY.systemPath
                  Xdm sets the PATH environment variable for the startup and reset
                  scripts  to  the  value  of this resource.  The default for this
                  resource                                                      is
                  ''/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin''.
                  Note the absence of ''.'' from this entry.  This is a good prac-
                  tice to follow for root; it avoids many common Trojan Horse sys-
                  tem penetration schemes.
    
           DisplayManager.DISPLAY.systemShell
                  Xdm sets the SHELL environment  variable  for  the  startup  and
                  reset  scripts  to the value of this resource.  It is /bin/sh by
                  default.
    
           DisplayManager.DISPLAY.failsafeClient
                  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.
    
           DisplayManager.DISPLAY.grabServer
    
           DisplayManager.DISPLAY.grabTimeout
                  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
    
           DisplayManager.DISPLAY.authName
                  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,
                  ''XDM-AUTHORIZATION-1 MIT-MAGIC-COOKIE-1.''
    
           DisplayManager.DISPLAY.authFile
                  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.
    
           DisplayManager.DISPLAY.authComplain
                  If set to ''false,'' disables the use of the unsecureGreeting in
                  the  login  window.  See the section Authentication Widget.  The
                  default is ''true.''
    
           DisplayManager.DISPLAY.resetSignal
                  The number of the signal xdm sends to reset the server.  See the
                  section Controlling the Server.  The default is 1 (SIGHUP).
    
           DisplayManager.DISPLAY.termSignal
                  The number of the signal xdm sends to terminate the server.  See
                  the  section  Controlling  the  Server.   The  default   is   15
                  (SIGTERM).
    
           DisplayManager.DISPLAY.resetForAuth
                  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.
    
           DisplayManager.DISPLAY.userAuthDir
                  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.
    
                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-
           sion.
    
    
    

    XDMCP ACCESS CONTROL

           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
           queries.
    
           An Indirect entry also contains a host name or pattern, but follows  it
           with a list of host names or macros to which indirect queries should be
           sent.
    
           A macro definition contains a macro name and a list of host  names  and
           other  macros  that  the  macro expands to.  To distinguish macros from
           hostnames, macro names start with  a  '%'  character.   Macros  may  be
           nested.
    
           Indirect  entries  may  also specify to have xdm run chooser to offer a
           menu of hosts to connect to.  See the section Chooser.
    
           When checking access for a  particular  display  host,  each  entry  is
           scanned  in  turn and the first matching entry determines the response.
           Direct and Broadcast entries are ignored when scanning for an  Indirect
           entry and vice-versa.
    
           !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.
    
           Examples:
    
           rincewind.sample.net ff02::1                 #IPv6 Multicast to ff02::1
                                                        #with a hop count of 1
           ponder.sample.net    CHOOSER 239.192.1.1/16  #Offer a menu of hosts
                                                        #who respond to IPv4 Multicast
                                                        # to 239.192.1.1 with a TTL of 16
    
    
    

    CHOOSER

           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-
    
    
    

    LISTEN

           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.
    
           Examples:
           LISTEN * ff02::1    # Listen on all interfaces and to the
                               # ff02::1 IPv6 multicast group.
           LISTEN 10.11.12.13  # Listen only on this interface, as long
                               # as no other listen directives appear in
                               # file.
    
    
    

    IPv6 MULTICAST ADDRESS SPECIFICATION

           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.
    
    
    

    LOCAL SERVER SPECIFICATION

           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
           '':0 Sun-CG3 local /usr/bin/X :0''  instead  of  ''localhost:0  Sun-CG3
           local  /usr/bin/X  :0'' if your other resources are specified as ''Dis-
           playManager._0.session'').  The display class portion is also  used  in
           the  display-specific resources, as the class of the resource.  This is
           useful if you have a large collection of similar displays  (such  as  a
           corral  of  X  terminals) and would like to set resources for groups of
           them.  When using XDMCP, the display is required to specify the display
           class, so the manual for your particular X terminal should document the
           display class string for your device.  If it doesn't, you can  run  xdm
           in  debug  mode and look at the resource strings which it generates for
           that device, which will include the class string.
    
           When xdm starts a session,  it  sets  up  authorization  data  for  the
           server.   For  local  servers,  xdm  passes  ''-auth  filename'' on the
           server's command line to point it at its authorization data.  For XDMCP
           servers, xdm passes the authorization data to the server via the Accept
           XDMCP request.
    
    
    

    RESOURCES FILE

           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
                #endif
    
           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.
    
    
    

    SETUP PROGRAM

           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.
    
    
           Here is a sample Xsetup script:
    
                #!/bin/sh
                # Xsetup_0 - setup script for one workstation
                xcmsdb < /etc/X11/xdm/monitors/alex.0
                xconsole -geometry 480x130-0-0 -notify -verbose -exitOnFail &
    
    
    

    AUTHENTICATION WIDGET

           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.
    
           xlogin.Login.foreground
                  The color used to display the input typed by the user.
    
           xlogin.Login.face
                  The  face used to display the input typed by the user when built
                  with Xft support.  The default is ''Serif-18''.
    
           xlogin.Login.font
                  The font used to display the input typed by the  user  when  not
                  built with Xft support.
    
           xlogin.Login.greeting
                  A  string which identifies this window.  The default is ''X Win-
                  dow System.''
    
           xlogin.Login.unsecureGreeting
                  When X authorization is requested in the configuration file  for
    
           xlogin.Login.namePrompt
                  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:  ''
    
           xlogin.Login.passwdPrompt
                  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:  ''
    
           xlogin.Login.promptFace
                  The face used to display prompts when built  with  Xft  support.
                  The default is ''Serif-18:bold''.
    
           xlogin.Login.promptFont
                  The  font  used  to display prompts when not built with Xft sup-
                  port.
    
           xlogin.Login.promptColor
                  The color used to display prompts.
    
           xlogin.Login.changePasswdMessage
                  A message  which  is  displayed  when  the  users  password  has
                  expired.  The default is ''Password Change Required''
    
           xlogin.Login.fail
                  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''
    
           xlogin.Login.failFace
                  The face used to display the failure message when built with Xft
                  support.  The default is ''Serif-18:bold''.
    
           xlogin.Login.failFont
                  The font used to display the failure message when not built with
                  Xft support.
    
           xlogin.Login.failColor
                  The color used to display the failure message.
    
           xlogin.Login.failTimeout
                  The  number  of  seconds  that the failure message is displayed.
                  The default is 10.
    
           xlogin.Login.logoFileName
                  Name of an XPM format pixmap to display in the  greeter  window,
                  if built with XPM support.   The default is no pixmap.
    
           xlogin.Login.logoPadding
                  is  the  shadow color, used on the bottom and right sides of the
                  frame, and the top and left sides  of  text  input  areas.   The
                  default  for  both  is  the  foreground  color, providing a flat
                  appearance.
    
           xlogin.Login.frameWidth
                  frameWidth is the width in pixels of the area around the greeter
                  frame drawn in hiColor and shdColor.
    
           xlogin.Login.innerFramesWidth
                  innerFramesWidth  is the width in pixels of the area around text
                  input areas drawn in hiColor and shdColor.
    
           xlogin.Login.sepWidth
                  sepWidth is the width in pixels of the bezeled line between  the
                  greeting and input areas drawn in hiColor and shdColor.
    
           xlogin.Login.allowRootLogin
                  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.
    
           xlogin.Login.allowNullPasswd
                  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.
    
           xlogin.Login.echoPasswd
                  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''.
    
           xlogin.Login.echoPasswdChar
                  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.
    
           xlogin.Login.translations
                  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\
    
           delete-character
                  Erases the character after the cursor.
    
           move-backward-character
                  Moves the cursor backward.
    
           move-forward-character
                  Moves the cursor forward.
    
           move-to-begining
                  (Apologies  about  the spelling error.)  Moves the cursor to the
                  beginning of the editable text.
    
           move-to-end
                  Moves the cursor to the end of the editable text.
    
           erase-to-end-of-line
                  Erases all text after the cursor.
    
           erase-line
                  Erases the entire text.
    
           finish-field
                  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.
    
           abort-session
                  Terminates and restarts the server.
    
           abort-display
                  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.
    
           restart-session
                  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.
    
           insert-char
                  Inserts the character typed.
    
           set-session-argument
                  Specifies  a single word argument which is passed to the session
                  at startup.  See the section Session Program.
    
           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:
    
                #!/bin/sh
                #
                # 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
                fi
                sessreg -a -l $DISPLAY -x /etc/X11/xdm/Xservers $LOGNAME
                /etc/X11/xdm/GiveConsole
                exit 0
    
    
    

    SESSION PROGRAM

           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
    
           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.
    
                #!/bin/sh
                #
                # Xsession
                #
                # This is the program that is run as the client
                # for the display manager.
    
                case $# in
                1)
                     case $1 in
                     failsafe)
                          exec xterm -geometry 80x24-0-0
                          ;;
                     esac
                esac
    
                startup=$HOME/.xsession
                resources=$HOME/.Xresources
    
                if [ -f "$startup" ]; then
                     exec "$startup"
                else
                     if [ -f "$resources" ]; then
                          xrdb -load "$resources"
                     fi
                     twm &
                     xman -geometry +10-10 &
                     exec xterm -geometry 80x24+10+10 -ls
                fi
    
           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
                #
                sessreg -d -l $DISPLAY -x /etc/X11/xdm/Xservers $LOGNAME
                /etc/X11/xdm/TakeConsole
                exit 0
    
    
    

    CONTROLLING THE SERVER

           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.
    
    
    

    CONTROLLING XDM

           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.
    
    
    

    ADDITIONAL LOCAL DISPLAYS

           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.
    
    
    

    OTHER POSSIBILITIES

           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:
           See the section Controlling Xdm for a description of using  signals  to
           enable  and disable these terminals in a manner reminiscent of init(8).
    
    
    

    LIMITATIONS

           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.
    
    
    

    ASYNCHRONOUS EVENTS

           xdm uses SIGALRM and SIGUSR1 for its  own  inter-process  communication
           purposes,  managing the relationship between the parent xdm process and
           its children.  Sending these signals to any xdm process may  result  in
           unexpected behavior.
    
           SIGHUP causes  xdm to rescan its configuration files and reopen its log
                  file.
    
           SIGTERM
                  causes xdm to terminate its children and shut down.
    
           SIGUSR2
                  causes xdm to reopen its log file.  This is useful if log  rota-
                  tion is desired, but SIGHUP is too disruptive.
    
    
    

    FILES

           /etc/X11/xdm/xdm-config
                               the default configuration file
    
           $HOME/.Xauthority   user  authorization  file where xdm stores keys for
                               clients to read
    
           /usr/lib/X11/xdm/chooser
                               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
    
           /var/lib/xdm/A<display>-<suffix>
                               the default place for authorization files
    
           /tmp/K5C<display>   Kerberos credentials cache
    
    
    

    SEE ALSO

           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.
    
    
    

    AUTHOR

    
    
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