Xsession - initialize X session
Xsession [ session-type ]
/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 pro
grams 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 man
agers, 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.
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:
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
produces the same behavior as if no session type argument had
been given at all.
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-user-xsession line in Xsession.options. (If the admin
istrator 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 users session, not just error messages. If it is
impossible to write to an error file, the script (and thus the X ses
sion) 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 eas
ier to discern which X session produced a particular line of output in
Xsession next confirms that its script directory, Xsession.d, exists.
If it does not, the script aborts. After the script directory is con
firmed to be present, Xsession uses run-parts(1) to identify files in
that directory that should be sourced (executed) in the shells envi
ronment. 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 experi
mental 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 shell script portions are supplied by default to handle the
details of the session startup procedure.
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.
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
users $HOME/.Xresources file is merged in the same way.
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.
Determine startup program. The X client to launch as the con
trolling 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 $HOME/.Xsession (note the
difference in case). The first one found is used. If the
script is not executable, it is marked to be executed with the
Bourne shell interpreter, sh. Finally, if none of the above
succeeds, the following programs are searched for:
/usr/bin/x-session-manager, /usr/bin/x-window-manager, and
/usr/bin/x-terminal-emulator. The first one found is used. If
none are found, Xsession aborts with an error.
Start ssh-agent(1), if needed. If the line use-ssh-agent is
present in Xsession.options, and no SSH agent process appears to
be running already, ssh-agent is marked to be used to execute
the startup program determined previously. Note: this function
ality may move to the ssh package in the future.
Start the X session. The startup program is executed, inside a
Bourne shell if it is not executable, and inside an ssh-agent if
necessary. The shells exec command is used to spare a slot in
the process table.
CUSTOMIZING THE STARTUP PROCEDURE
Of course, any of the existing files can be edited in place.
Because the order in which the various scripts in /etc/X11/Xsession.d
are executed is important, files to be added to this directory should
have a well-formed name. The following format is recommended:
* a two-digit number denoting sequence;
* the name of the package providing the script (or custom for
* an underscore;
* a description of the scripts basic function, using only characters
allowed by run-parts.
Here is an example of how one might write a script, named 40cus
tom_load-xmodmap, to invoke xmodmap(1x):
if [ -x /usr/bin/X11/xmodmap ]; then
if [ -f "$SYSMODMAP" ]; then
if [ -x /usr/bin/X11/xmodmap ]; then
if [ -f "$USRMODMAP" ]; then
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 users 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.
The following environment variables affect the execution of Xsession:
HOME specifies the users home directory; various files are searched
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.
indicates the width of terminal device in character cells. This
value is used for formatting diagnostic messages.
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.
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
contains configuration options for the /etc/X11/Xsession script.
See Xsession.options(5) for more information.
contains X resources specific to the invoking users environ
ment. 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 depre
cated for over ten years at the time of this writing. .Xre
sources should be used instead.
is a sequence of commands invoking X clients (or a session man
ager such as xsm(1x)). See the manual page for xinit for tips
on writing an .xsession file.
is where standard output and standard error for Xsession script
and all X client processes are directed by default.
is where the X session error file is placed if $HOME/.xses
sion-errors cannot be opened. For security reasons, the exact
filename is randomly generated by tempfile(1).
Stephen Early, Mark Eichin, and Branden Robinson developed Debians X
session handling scripts. Branden Robinson wrote this manual page.
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)
Debian Project 2004-11-04 Xsession(5)