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Xsession(5) File Formats Manual Xsession(5)

NAME
Xsession - initialize X session

SYNOPSIS
Xsession [ session-type ]

DESCRIPTION
/etc/X11/Xsession is a Bourne shell (sh(1)) script which is run when an X Window System ses‐
sion 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 unfamiliar with the Bourne shell will
likely find the Xsession.options(5) configuration file easier to deal with than Xsession it‐
self.

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(1), and
other similar programs handle this.

By default on a Debian system, Xsession is used by both common methods of starting the X Win‐
dow 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
managers, consult their documentation. To stop startx from using Xsession by default, re‐
place 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” be‐
low.

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. 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:

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 ‘failsafe’ argument is ignored if there is no ‘allow-failsafe’ line in Xses‐
sion.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 pro‐
ceeds with its default behavior. This argument is ignored if there is no ‘al‐
low-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 spec‐
ify 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 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 re‐
ports 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 ‘.old’ or ‘.broken’ 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/20x11-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 im‐
mediately executed.

/etc/X11/Xsession.d/30x11-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 ‘xrdb -merge’. Next, if
the line ‘allow-user-resources’ is present in Xsession.options, the user's $HOME/.Xre‐
sources file is merged in the same way.

/etc/X11/Xsession.d/35x11-common_xhost-local
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 lo‐
cal host to access the X server.

/etc/X11/Xsession.d/40x11-common_xsessionrc
Source global environment variables. This script will source anything in $HOME/.xses‐
sionrc if the file is present. This allows the user to set global environment vari‐
ables for their X session, such as locale information.

/etc/X11/Xsession.d/50x11-common_determine-startup
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 Xses‐
sion.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, Xses‐
sion aborts with an error.

/etc/X11/Xsession.d/90x11-common_ssh-agent
Start ssh-agent(1), if needed. If the line ‘use-ssh-agent’ is present in Xsession.op‐
tions, 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 functional‐
ity may move to the ssh package in the future.

/etc/X11/Xsession.d/99x11-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 impor‐
tant, files to be added to this directory should have a well-formed name. The following for‐
mat is recommended:

* a two-digit number denoting sequence;

* the name of the package providing the script (or ‘custom’ 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(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 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 white‐
space) and sent to standard error. If the DISPLAY environment variable is set and the xmes‐‐
sage(1) 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 mes‐‐
sage, 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 sourced, not executed in a sub‐
shell.

/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.op‐‐
tions(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 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 pro‐
cesses 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 temp‐‐
file(1).

AUTHORS
Stephen Early, Mark Eichin, and Branden Robinson developed Debian's X session handling
scripts. Branden Robinson wrote this manual page.

SEE ALSO
Xsession.options(5), X(7), run-parts(1), ssh-agent(1), startx(1), tempfile(1), xdm(1), xmes‐‐
sage(1), xmodmap(1), xrdb(1), sh(1)

Debian Project 2004-11-04 Xsession(5)