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xdm(1)                                                                  xdm(1)




NAME

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


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
       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.


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.  /usr/X11/lib/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.
              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.  As XDMCP uses the registered well-known UDP port 177,
              this resource should not be changed except for debugging. If set
              to 0 xdm will not listen for XDMCP or Chooser requests.

       -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.


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 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.

       DisplayManager.debugLevel
              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.

       DisplayManager.daemonMode
              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
              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
              /usr/X11/lib/X11/xdm.   Can  be overridden for specific displays
              by DisplayManager.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
              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.

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

       DisplayManager.randomFile
              A file to checksum to generate the seed of  authorization  keys.
              This  should  be a file that changes frequently.  The default is
              /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.greeterLib
              On systems that support a dynamically-loadable greeter  library,
              the name of the library.  The default is
               /usr/X11/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
              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
               /usr/X11/lib/X11/xdm/Xresources is the conventional name.

       DisplayManager.DISPLAY.chooser
              Specifies the program run to offer  a  host  menu  for  Indirect
              queries redirected to the special host name CHOOSER.
               /usr/X11/lib/X11/xdm/chooser  is the default.  See the sections
              XDMCP Access Control and Chooser.

       DisplayManager.DISPLAY.xrdb
              Specifies the program used to load the resources.   By  default,
              xdm uses  /usr/X11/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/X11/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
              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 default values
              are 5 for openDelay, 5 for openRepeat, 30 for openTimeout and  4
              for startAttempts.

       DisplayManager.DISPLAY.pingInterval

       DisplayManager.DISPLAY.pingTimeout
              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.

       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.
              ``:/bin:/usr/bin:/usr/X11/bin:/usr/ucb''  is  a  common setting.
              The default value can be specified at build time in the X system
              configuration file with DefaultUserPath.

       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  specified  at  build time by the DefaultSystemPath
              entry      in      the      system      configuration      file;
              ``/etc:/bin:/usr/bin:/usr/X11/bin:/usr/ucb'' is a common choice.
              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/X11/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
              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.

       DisplayManager.DISPLAY.authorize

       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.


CONFIGURATION FILE

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

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


            DisplayManager.servers:            /usr/X11/lib/X11/xdm/Xservers
            DisplayManager.errorLogFile:       /var/log/xdm.log
            DisplayManager*resources:          /usr/X11/lib/X11/xdm/Xresources
            DisplayManager*startup:            /usr/X11/lib/X11/xdm/Xstartup
            DisplayManager*session:            /usr/X11/lib/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-
       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.

       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.

       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-
       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-
       Manager.DISPLAY.resources.

       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.


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 addresss representing  a  net-
              work  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 Node-Local, 2 for Link-Local, 5 for
       Site-Local, and so on.  (See IETF RFC 2373 or its replacement for  fur-
       ther  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
       to start the server.  A typical entry for local display number 0  would
       be:

         :0 Digital-QV local /usr/X11/bin/X :0

       The display types are:

       local     local display: xdm must run the server
       foreign   remote display: xdm opens an X connection to a running server


       The  display  name must be something that can be passed in the -display
       option to an X program.  This string is used to generate  the  display-
       specific  resource  names,  so be careful to match the names (e.g., use
       ``:0 Sun-CG3 local /usr/X11/bin/X :0'' instead of ``localhost:0 Sun-CG3
       local  /usr/X11/bin/X  :0''  if  your  other resources are specified as
       ``DisplayManager._0.session'').  The display class portion is also used
       in  the display-specific resources, as the class of the resource.  This
       is useful if you have a large collection of similar displays (such as a
       corral  of  X  terminals) and would like to set resources for groups of
       them.  When using XDMCP, the display is required to specify the display
       class, so the manual for your particular X terminal should document the
       display class string for your device.  If it doesn't, you can  run  xdm
       in  debug  mode and look at the resource strings which it generates for
       that device, which will include the class string.

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


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: #overrideCtrl<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.

       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:

            #!/bin/sh
            # Xsetup_0 - setup script for one workstation
            xcmsdb < /usr/X11/lib/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 format
       described in the Font Names section of  fonts.conf(5).   If  not,  then
       fonts  are specified using the resources with names ending in "font" in
       the traditional X Logical Font Description format described in the Font
       Names section of X(7).

       xlogin.Login.width, xlogin.Login.height, xlogin.Login.x, xlogin.Login.y
              The  geometry of the Login widget is normally computed 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
              this  display  and  none  is  in use, this greeting replaces the
              standard greeting.  The default is ``This is  an  unsecure  ses-
              sion''

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

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

       xlogin.Login.greetColor
              The color used to display the greeting.

       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
              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.

       xlogin.Login.useShape
              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
              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''.

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

       The actions which are supported by the widget are:

       delete-previous-character
              Erases the character before the cursor.

       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 current name/password pair.  If
              the name/password pair is valid, xdm
              starts the session.  Otherwise the failure message is displayed and
              the user is prompted again.

       abort-session
              Terminates and restarts the server.

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

       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.

       allow-all-access
              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.


STARTUP PROGRAM

       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 /etc/utmp (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 /usr/X11/lib/X11/xdm/Xservers $LOGNAME
            /usr/X11/lib/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
            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.

            #!/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


RESET PROGRAM

       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, removing entries from /etc/utmp or
       unmounting directories from file servers.   The  environment  variables
       that were passed to Xstartup are also passed to Xreset.

       A sample Xreset script:
            #!/bin/sh
            #
            # Xreset
            #
            # This program is run as root after the session ends
            #
            sessreg -d -l $DISPLAY -x /usr/X11/lib/X11/xdm/Xservers $LOGNAME
            /usr/X11/lib/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:

            xdm -server ":0 SUN-3/60CG4 local /usr/X11/bin/X :0"


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

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


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


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.


FILES

       /usr/X11/lib/X11/xdm/xdm-config
                           the default configuration file

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

       /usr/X11/lib/X11/xdm/chooser
                           the default chooser

       /usr/X11/bin/xrdb   the default resource database loader

       /usr/X11/bin/X      the default server

       /usr/X11/bin/xterm  the default session program and failsafe client

       /usr/X11/lib/X11/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), fonts.conf(5).
       X Display Manager Control Protocol


AUTHOR

       Keith Packard, MIT X Consortium



X Version 11                       xdm 1.1.8                            xdm(1)

Mac OS X 10.6 X11 - Generated Sun Mar 7 12:28:58 CST 2010