Xsession man page on Debian

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Xsession(5)							   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 specifi‐
       cally directed to so by the user; see the documentation for  your  dis‐
       play  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 pro‐
       grams 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 man‐
       agers, 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
	      program cannot be found,	the  session  exits.   The  ‘failsafe’
	      argument	is  ignored  if	 there	is no ‘allow-failsafe’ line in
	      Xsession.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  pro‐
	      gram 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 admin‐
	      istrator 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	impossible  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  con‐
       firmed  to  be present, Xsession uses run-parts(1) to identify files in
       that directory that should be sourced (executed) in the	shell's	 envi‐
       ronment.	  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 experi‐
       mental 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/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  con‐
	      trolling	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  controlling  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 function‐
	      ality 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	40cus‐
       tom_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 whitespace)
       and sent to standard error.  If the DISPLAY environment variable is set
       and the xmessage(1) program is available, xmessage is also used to dis‐
       play 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 environ‐
	      ment.  The settings are loaded  with  xrdb  -merge.   Note  that
	      $HOME/.Xdefaults	is a relic from X Version 10 (and X11R1) days,
	      before app-defaults files were implemented.  It has been	depre‐
	      cated  for  over	ten  years at the time of this writing.	 .Xre‐
	      sources should be used instead.

       $HOME/.xsession
	      is a sequence of commands invoking X clients (or a session  man‐
	      ager such as xsm(1)).  See the manual page for xinit for tips on
	      writing 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/.xses‐
	      sion-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), temp‐
       file(1), xdm(1), xmessage(1), xmodmap(1), xrdb(1), sh(1)

Debian Project			  2004-11-04			   Xsession(5)
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