Provided by: x11-common_7.6+12ubuntu1_all bug

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  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 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 variables, 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  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  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 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 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 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/.Xdefaults 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 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/.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)