Provided by: x11-common_7.4~5ubuntu18_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(1x)  or  a  display  manager
       such  as  xdm(1x).   (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(1x),  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/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(1x):

       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(1x) 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(1x)).  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(7x),  run-parts(1),  ssh-agent(1),  startx(1x),
       tempfile(1), xdm(1x), xmessage(1x), xmodmap(1x), xrdb(1x), sh(1)