Xsession(5)							File Formats Manual						       Xsession(5)

NAME

       Xsession - initialize X session

SYNOPSIS

       Xsession [ session-type ]

DESCRIPTION

       /etc/X11/Xsession  is a Bourne shell (sh(1)) script which is run when an X Window System session is begun by startx(1) or a display manager
       such as xdm(1).	(Some display managers only invoke Xsession when specifically directed to so by the user; see the documentation  for  your
       display	manager to find out more.)  Administrators unfamiliar with the Bourne shell will likely find the Xsession.options(5) configuration
       file easier to deal with than Xsession itself.

       Xsession is not intended to be invoked directly by the user; to be effective it needs to run in a special  environment  associated  with  X
       server initialization.  startx, xdm, xinit(1), and other similar programs handle this.

       By  default on a Debian system, Xsession is used by both common methods of starting the X Window System, xdm (or another X display manager)
       and startx.  To change this for xdm, edit the 'DisplayManager*session' resource in the /etc/X11/xdm/xdm-config file --  for  other  display
       managers,  consult  their documentation.  To stop startx from using Xsession by default, replace the contents of the /etc/X11/xinit/xinitrc
       file.

       The Xsession script is quite flexible, and extensive customization of the X startup procedure is  possible  without  modifying  the  script
       itself.	See "CUSTOMIZING THE STARTUP PROCEDURE" below.

   SESSION TYPES
       Xsession may optionally be passed a single argument indicating the type of X session to be started.  It is up to the display manager to set
       the argument. To pass Xsession an argument from startx or xinit, /etc/X11/Xsession (or /etc/X11/xinit/xinitrc) must  be	called	explicitly
       with a path, as in startx /etc/X11/Xsession failsafe.  By default, three different arguments are supported:

       failsafe
	      invokes  a  session consisting solely of an x-terminal-emulator(1) (no window manager is launched).  If the x-terminal-emulator pro-
	      gram cannot be found, the session exits.	The 'failsafe' argument  is  ignored  if  there  is  no  'allow-failsafe'  line  in  Xses-
	      sion.options.

       default
	      produces the same behavior as if no session type argument had been given at all.

       program
	      starts  program if it can be found in the $PATH.	This is usually a session manager or a very featureful window manager.	If program
	      is not found, the Xsession script proceeds with its default behavior.  This argument is ignored if there is no 'allow-user-xsession'
	      line  in	Xsession.options.   (If  the administrator does not want users writing their own .xsession files, it makes little sense to
	      permit them to specify the names of arbitrary programs to run.)  Note that the restriction may be easy to bypass, e.g.  by  using  a
	      .gnomerc file instead.

   DEFAULT STARTUP PROCEDURE
       Initially,  Xsession  performs some housekeeping.  It declares a set of built-in functions (see "BUILT-IN SHELL FUNCTIONS" below) and vari-
       ables, then attempts to create a log file for the X session, or append to an existing one.  Historically this is called	an  'error'  file,
       but it catches all sorts of diagnostic output from various X clients run in the user's session, not just error messages.  If it is impossi-
       ble to write to an error file, the script (and thus the X session) aborts.  For convenience, once the error file  is  successfully  opened,
       Xsession  reports  the  fact  that the session has started, the invoking username, and the date to the error file.  This makes it easier to
       discern which X session produced a particular line of output in the file.

       Xsession next confirms that its script directory, Xsession.d, exists.  If it does not, the script aborts.  After the  script  directory	is
       confirmed  to  be  present, Xsession uses run-parts(1) to identify files in that directory that should be sourced (executed) in the shell's
       environment.  Only files named in a certain way are sourced; see the run-parts manual page for a description of	valid  characters  in  the
       filename.  (This restriction enables the administrator to move experimental or problematic files out of the way of the script but keep them
       in an obvious place, for instance by renaming them with '.old' or '.broken' appended to the filename.)

   SUPPLIED SCRIPTS
       Five shell script portions are supplied by default to handle the details of the session startup procedure.

       /etc/X11/Xsession.d/20x11-common_process-args
	      Arguments are processed as described in "SESSION TYPES" above.  The startup program, if one is identified at this point,	is  merely
	      stored for later reference, and not immediately executed.

       /etc/X11/Xsession.d/30x11-common_xresources
	      X  resources  are  merged.  run-parts is again used, this time to identify files in the /etc/X11/Xresources directory that should be
	      processed with 'xrdb -merge'.  Next, if the line 'allow-user-resources' is present in Xsession.options, the user's $HOME/.Xresources
	      file is merged in the same way.

       /etc/X11/Xsession.d/35x11-common_xhost-local
	      Give  access  to	the  X	server to the same user on the local host.  If the xhost command is available, it will use it to allow any
	      process of the same user running on the local host to access the X server.

       /etc/X11/Xsession.d/40x11-common_xsessionrc
	      Source global environment variables.  This script will source anything in $HOME/.xsessionrc if the file is present. This allows  the
	      user to set global environment variables for their X session, such as locale information.

       /etc/X11/Xsession.d/50x11-common_determine-startup
	      Determine  startup  program.   The X client to launch as the controlling process (the one that, upon exiting, causes the X server to
	      exit as well) is determined next.  If a program or failsafe argument was given and is allowed (see above), it is used  as  the  con-
	      trolling	process.  Otherwise, if the line 'allow-user-xsession' is present in Xsession.options, a user-specified session program or
	      script is used.  In the latter case, two historically popular names for user X session scripts are searched for: $HOME/.xsession and
	      $HOME/.Xsession  (note  the  difference in case).  The first one found is used.  If the script is not executable, it is marked to be
	      executed with the Bourne shell interpreter, sh.  Finally, if none of the above succeeds, the following programs  are  searched  for:
	      /usr/bin/x-session-manager,  /usr/bin/x-window-manager, and /usr/bin/x-terminal-emulator.  The first one found is used.  If none are
	      found, Xsession aborts with an error.

       /etc/X11/Xsession.d/90x11-common_ssh-agent
	      Start ssh-agent(1), if needed.  If the line 'use-ssh-agent' is present in Xsession.options, and no SSH agent process appears  to	be
	      running  already, ssh-agent is marked to be used to execute the startup program determined previously.  Note: this functionality may
	      move to the ssh package in the future.

       /etc/X11/Xsession.d/99x11-common_start
	      Start the X session.  The startup program is executed, inside a Bourne shell if it is not executable, and  inside  an  ssh-agent	if
	      necessary.  The shell's exec command is used to spare a slot in the process table.

   CUSTOMIZING THE STARTUP PROCEDURE
       Of course, any of the existing files can be edited in place.

       Because the order in which the various scripts in /etc/X11/Xsession.d are executed is important, files to be added to this directory should
       have a well-formed name.  The following format is recommended:

       * a two-digit number denoting sequence;

       * the name of the package providing the script (or 'custom' for locally-created scripts);

       * an underscore;

       * a description of the script's basic function, using only characters allowed by run-parts.

       Here is an example of how one might write a script, named 40custom_load-xmodmap, to invoke xmodmap(1):

       SYSMODMAP="/etc/X11/Xmodmap"
       USRMODMAP="$HOME/.Xmodmap"

       if [ -x /usr/bin/X11/xmodmap ]; then
	   if [ -f "$SYSMODMAP" ]; then
	       xmodmap "$SYSMODMAP"
	   fi
       fi

       if [ -x /usr/bin/X11/xmodmap ]; then
	   if [ -f "$USRMODMAP" ]; then
	       xmodmap "$USRMODMAP"
	   fi
       fi

       Those writing scripts for Xsession to execute should avail themselves of its built-in shell functions, described below.

   BUILT-IN SHELL FUNCTIONS
       message is used for communicating with the user.  It is a wrapper for the echo(1) command and relies upon echo for its argument processing.
       This  function  may  be given an arbitrarily long message string, which is formatted to the user's terminal width (breaking lines at white-
       space) and sent to standard error.  If the DISPLAY environment variable is set and the xmessage(1) program is available, xmessage  is  also
       used to display the message.

       message_nonl  is  used for communicating with the user when a trailing newline is undesirable; it omits a trailing newline from the message
       text.  It otherwise works as message.

       errormsg is used for indicating an error condition and aborting the script.  It works as message, above, except that after  displaying  the
       message, it will exit Xsession with status 1.

ENVIRONMENT

       The following environment variables affect the execution of Xsession:

       HOME   specifies the user's home directory; various files are searched for here.

       TMPDIR names  a	default  directory  for  temporary  files; if the standard X session error file cannot be opened, this variable is used to
	      locate a place for one.

       COLUMNS
	      indicates the width of terminal device in character cells.  This value is used for formatting diagnostic messages.

INPUT FILES

       /etc/X11/Xsession.d/
	      is a directory containing Bourne shell scripts to be executed by Xsession.  Files in this directory are matched using run-parts  and
	      are sourced, not executed in a subshell.

       /etc/X11/Xresources/
	      is  a directory containing files corresponding to Debian package names, each of which contains system-wide X resource settings for X
	      clients from the corresponding package.  The settings are loaded with xrdb -merge.   Files  in  this  directory  are  matched  using
	      run-parts.

       /etc/X11/Xsession.options
	      contains configuration options for the /etc/X11/Xsession script.	See Xsession.options(5) for more information.

       $HOME/.Xresources
	      contains	X resources specific to the invoking user's environment.  The settings are loaded with xrdb -merge.  Note that $HOME/.Xde-
	      faults is a relic from X Version 10 (and X11R1) days, before app-defaults files were implemented.  It has been deprecated  for  over
	      ten years at the time of this writing.  .Xresources should be used instead.

       $HOME/.xsession
	      is a sequence of commands invoking X clients (or a session manager such as xsm(1)).  See the manual page for xinit for tips on writ-
	      ing an .xsession file.

OUTPUT FILES

       $HOME/.xsession-errors
	      is where standard output and standard error for Xsession script and all X client processes are directed by default.

       $TMPDIR/filename
	      is where the X session error file is placed if $HOME/.xsession-errors cannot be opened.  For security reasons, the exact filename is
	      randomly generated by tempfile(1).

AUTHORS

       Stephen Early, Mark Eichin, and Branden Robinson developed Debian's X session handling scripts.	Branden Robinson wrote this manual page.

SEE ALSO

       Xsession.options(5), X(7), run-parts(1), ssh-agent(1), startx(1), tempfile(1), xdm(1), xmessage(1), xmodmap(1), xrdb(1), sh(1)

Debian Project							    2004-11-04							       Xsession(5)