Xsession - initialize X session
Xsession [ session-type ]
/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 [Toc] [Back]
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-emu-
lator (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 pro-
gram is not found, the Xsession script proceeds with its default
behavior. This argument is ignored if there is no "allow-userxsession"
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 [Toc] [Back]
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
$HOME/.Xsession (note the difference in case). The first one found is
used. If the script is not executable, it is marked to be executed
with the Bourne shell interpreter, sh(1). If "allow-user-xsession" is
not specified, or no user X session program can be located, and no
failsafe session is to be run, the following programs are searched for:
/usr/bin/x-session-manager, /usr/bin/x-window-manager, and /usr/bin/x-
terminal-emulator. The first one found is used. If none are found,
Xsession aborts with an error.
4) Start ssh-agent, if needed. If the line "use-ssh-agent" is present
in Xsession.options, and no ssh agent process appears to be running
already, ssh-agent(1) is marked to be used to execute the startup program
determined previously. Note: this functionality may move to the
ssh package in the future.
5) Start the X session. Finally, the startup program is executed,
inside a Bourne shell if necessary, and inside an ssh-agent if necessary.
The shell's exec command is used to spare a slot in the process
table.
CUSTOMIZING THE STARTUP PROCEDURE [Toc] [Back]
Of course, any of the existing files can be edited in-place.
Because the order in which the various scripts in /etc/X11/Xsession.d
are executed is important, files to be added to this directory should
have a well-formed name. The following format is recommended:
* a two-digit number denoting sequence
* the name of the package providing the script
* an underscore
* a description of the script's basic function, using only characters
allowed by run-parts(1).
Here is an example of how one might write a script, named 40cus-
tom_load-xmodmap, to invoke xmodmap(1):
SYSMODMAP=/etc/X11/Xmodmap
USRMODMAP=$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 [Toc] [Back]
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.
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.
/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. .Xre-
sources 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.
$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 temp-
file(1).
Xsession.options(5), X(1), run-parts(1), ssh-agent(1), startx(1), temp-
file(1), xdm(1), xmodmap(1), xrdb(1), sh(1)
/etc/X11/Xsession and its associated files in /etc/X11/Xsession.d were
written by Stephen Early, Mark Eichin, and Branden Robinson.
Debian GNU/Linux 2001-11-08 Xsession(5)
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