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Manpage of Xsession

Xsession

Section: File Formats (5)
Updated: 2001-11-08
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NAME

Xsession - initialize X session  

SYNOPSIS

Xsession [ session-type ]  

DESCRIPTION

/etc/X11/Xsession is a Bourne shell (sh(1)) script which is run every time 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 unfamilar 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(1), xdm(1), 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 and startx. To change this for xdm, edit the "DisplayManager*session" resource in the /etc/X11/xdm/xdm-config file; for startx, 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. By default, three different arguments are supported:
failsafe
invokes a session consisting solely of /usr/bin/x-terminal-emulator (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. (The reason being, 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.)
 

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. 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 creation of an error file is impossible, the script (and thus the X session) aborts.

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 an internal implementation of 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(1) 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.)

Five scripts are provided by default:

1) Argument processing. 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.

2) Merging of X resources. run-parts(1) 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.

3) 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 the line "allow-user-xsession" is present in Xsession.options, a user-specified session program or script is used. If a program or failsafe argument was given and is allowed (see above), it is used instead. Otherwise, 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(1). If "allow-user-xsession" is not specified, or no user X session program can be located, and no failsafe session is to be run, 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.

4) Start ssh-agent, 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(1) is marked to be used to execute the startup program determined previously. Note: this functionality may move to the ssh package in the future.

5) Start the X session. Finally, the startup program is executed, inside a Bourne shell if necessary, 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

* an underscore

* a description of the script's basic function, using only characters allowed by run-parts(1).

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 may be given an arbitrarily long message string. It is formatted to the user's terminal width (breaking lines at whitespace) and sent to standard error.

message_nonl is used for communicating with the user when a trailing newline is undesirable. It may be given an arbitrarily long message string. It is formatted to the user's terminal width (breaking lines at whitespace) and sent to standard error.

errormsg is used for indicating an error condition and aborting the script. It can be used as message above. After displaying the message to standard error, it will exit Xsession with status 1.  

ENVIRONMENT

The following environment variables affect the execution of Xsession:
HOME
The user's home directory; various files are searched for here.
TMPDIR
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
Width of terminal device, in character cells. 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(1) 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(1).
/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 and/or /usr/share/doc/xfree86-common/examples/xsession for tips on writing an .Xsession file.
 

OUTPUT FILES

$HOME/.xsession-errors
Where standard output and standard error for Xsession script and all X client processes are directed by default.
$TMPDIR
Where the X session error file is placed if $HOME/.xsession-errors cannot be opened. The filename is provided by tempfile(1).
 

SEE ALSO

Xsession.options(5), X(1), run-parts(1), ssh-agent(1), startx(1), tempfile(1), xdm(1), xmodmap(1), xrdb(1), sh(1)  

AUTHOR

/etc/X11/Xsession and its associated files in /etc/X11/Xsession.d were written by Stephen Early, Mark Eichin, and Branden Robinson.


 

Index

NAME
SYNOPSIS
DESCRIPTION
SESSION TYPES
DEFAULT STARTUP PROCEDURE
CUSTOMIZING THE STARTUP PROCEDURE
BUILT-IN SHELL FUNCTIONS
ENVIRONMENT
INPUT FILES
OUTPUT FILES
SEE ALSO
AUTHOR

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