man > Xsession(5)

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 ses‐
       sion 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 it‐
       self.

       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 Win‐
       dow  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, re‐
       place 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” be‐
       low.

   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  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  pro‐
              ceeds  with  its  default  behavior.   This  argument  is  ignored if there is no ‘al‐
              low-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 spec‐
              ify 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 re‐
       ports 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 im‐
              mediately 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/.Xre‐
              sources 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 lo‐
              cal host to access the X server.

       /etc/X11/Xsession.d/40x11-common_xsessionrc
              Source global environment variables.  This script will source anything in $HOME/.xses‐
              sionrc if the file is present. This allows the user to set  global  environment  vari‐
              ables 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 Xses‐
              sion.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,  Xses‐
              sion 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.op‐
              tions,  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  functional‐
              ity 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 impor‐
       tant, files to be added to this directory should have a well-formed name.  The following for‐
       mat 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 xmes‐
       sage(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 mes‐
       sage, 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  sub‐
              shell.

       /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.op‐
              tions(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 temp‐
              file(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), xmes‐
       sage(1), xmodmap(1), xrdb(1), sh(1)

Debian Project                               2004-11-04                                  Xsession(5)