bionic (5) Xsession.5.gz

Provided by: x11-common_7.7+19ubuntu7.1_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)