/etc/X11/Xsession is a Bourne shell
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 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 , 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 (oqDisplayManager*session(cq 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, and there is no way to
pass
Xsession an argument from
startx or
xinit . 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 (oqfailsafe(cq argument is ignored if there is no
(oqallow-failsafe(cq 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 (oqallow-user-xsession(cq 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.)
"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 (oqerror(cq 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 (oq.old(cq or (oq.broken(cq
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/20xfree86-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/30xfree86-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 (oqxrdb -merge(cq.
Next, if the line (oqallow-user-resources(cq is present in
Xsession.options , the user's
$HOME/.Xresources file is merged in the same way.
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 (oqallow-user-xsession(cq 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
$HOME/.Xsession (note the difference in case).
The first one found is used.
If the script is not executable, it is marked to be executed with the
Bourne shell interpreter,
sh . Finally, if none of the above succeeds, the following programs are searched
for:
/usr/bin/x-session-manager , /usr/bin/x-window-manager , and
/usr/bin/x-terminal-emulator . The first one found is used.
If none are found,
Xsession aborts with an error.
/etc/X11/Xsession.d/90xfree86-common_ssh-agent
Start
ssh-agent(1) , if needed.
If the line (oquse-ssh-agent(cq is present in
Xsession.options , and no SSH agent process appears to be running already,
ssh-agent is marked to be used to execute the startup program determined previously.
Note: this functionality may move to the ssh package in the future.
/etc/X11/Xsession.d/99xfree86-common_start
Start the X session.
The startup program is executed, inside a Bourne shell if it is not
executable, and inside an ssh-agent if necessary.
The shell's
exec command is used to spare a slot in the process table.
"CUSTOMIZING THE STARTUP PROCEDURE" Of course, any of the existing files can be edited in place.
Because the order in which the various scripts in
/etc/X11/Xsession.d are executed is important, files to be added to this directory should
have a well-formed name.
The following format is recommended:
* a two-digit number denoting sequence;
* the name of the package providing the script (or (oqcustom(cq for
locally-created scripts);
* an underscore;
* a description of the script's basic function, using only characters allowed
by
run-parts .
Here is an example of how one might write a script, named
40custom_load-xmodmap , to invoke
xmodmap (1x):
SYSMODMAP="/etc/X11/Xmodmap"
USRMODMAP="$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
source d, 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 and/or
/usr/share/doc/xfree86-common/examples/xsession 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.
