Xsession - initialize X session
Xsession [ session-type
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
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
(5) configuration file easier to deal with than
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
(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
. To change this for xdm,
‘DisplayManager*session’ resource in the
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
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.
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
be called explicitly with a path, as in startx /etc/X11/Xsession
. 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 Xsession.options.
- 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
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.
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.
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
(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
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 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
- 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.
- 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
- 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
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
$HOME/.Xsession (note the difference in case). The first one found
is used. If the script is not executable, it is marked to be executed with
the Bourne shell interpreter, sh. Finally, if none of the above
succeeds, the following programs are searched for:
/usr/bin/x-session-manager, /usr/bin/x-window-manager, and
/usr/bin/x-terminal-emulator. The first one found is used. If none
are found, Xsession aborts with an error.
- Start ssh-agent(1), if needed. If the line
‘use-ssh-agent’ is present in Xsession.options, and
no SSH agent process appears to be running already, ssh-agent is
marked to be used to execute the startup program determined previously.
Note: this functionality may move to the ssh package in the
- Start the X session. The startup program is executed,
inside a Bourne shell if it is not executable, and inside an ssh-agent if
necessary. The shell's exec command is used to spare a slot in the
Of course, any of the existing files can be edited in place.
Because the order in which the various scripts in /etc/X11/Xsession.d
executed is important, files to be added to this directory should have a
well-formed name. The following format is recommended:
* a two-digit number denoting sequence;
* the name of the package providing the script (or ‘custom’ for
* an underscore;
* a description of the script's basic function, using only characters allowed by
Here is an example of how one might write a script, named
, to invoke xmodmap
if [ -x /usr/bin/X11/xmodmap ]; then
if [ -f "$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.
is used for communicating with the user. It is a wrapper for the
(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.
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
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
- specifies the user's home directory; various files are
searched for here.
- 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 using
- contains configuration options for the
/etc/X11/Xsession script. See Xsession.options(5) for more
- 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
- 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.
- is where standard output and standard error for
Xsession script and all X client processes are directed by
- 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).
Stephen Early, Mark Eichin, and Branden Robinson developed Debian's X session
handling scripts. Branden Robinson wrote this manual page.