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xsm - X Session Manager
xsm [-display display] [-session sessionName] [-verbose]
xsm is a session manager. A session is a group of applications, each
of which has a particular state. xsm allows you to create arbitrary
sessions - for example, you might have a "light" session, a "develop-
ment" session, or an "xterminal" session. Each session can have its
own set of applications. Within a session, you can perform a "check-
point" to save application state, or a "shutdown" to save state and
exit the session. When you log back in to the system, you can load a
specific session, and you can delete sessions you no longer want to
Some session managers simply allow you to manually specify a list of
applications to be started in a session. xsm is more powerful because
it lets you run applications and have them automatically become part of
the session. On a simple level, xsm is useful because it gives you
this ability to easily define which applications are in a session. The
true power of xsm, however, can be taken advantage of when more and
more applications learn to save and restore their state.
Causes xsm to connect to the specified X display.
Causes xsm to load the specified session, bypassing the session
Turns on debugging information.
Using xsm requires a change to your .xsession file:
The last program executed by your .xsession file should be xsm. With
this configuration, when the user chooses to shut down the session
using xsm, the session will truly be over.
Since the goal of the session manager is to restart clients when log-
ging into a session, your .xsession file, in general, should not
directly start up applications. Rather, the applications should be
started within a session. When xsm shuts down the session, xsm will
know to restart these applications. Note however that there are some
types of applications that are not "session aware". xsm allows you to
manually add these applications to your session (see the section titled
SM_SAVE_DIR environment variable
If the SM_SAVE_DIR environment variable is defined, xsm will save all
configuration files in this directory. Otherwise, they will be stored
in the user's home directory. Session aware applications are also
encouraged to save their checkpoint files in the SM_SAVE_DIR directory,
although the user should not depend on this convention.
Default Startup Applications
The first time xsm is started, it will need to locate a list of appli-
cations to start up. For example, this list might include a window
manager, a session management proxy, and an xterm. xsm will first look
for the file .xsmstartup in the user's home directory. If that file
does not exist, it will look for the system.xsm file that was set up at
installation time. Note that xsm provides a "fail safe" option when
the user chooses a session to start up. The fail safe option simply
loads the default applications described above.
Each line in the startup file should contain a command to start an
application. A sample startup file might look this:
<start of file>
<end of file>
STARTING A SESSION
When xsm starts up, it first checks to see if the user previously saved
any sessions. If no saved sessions exist, xsm starts up a set of
default applications (as described above in the section titled Default
Startup Applications). If at least one session exists, a session menu
is presented. The [-session sessionName] option forces the specified
session to be loaded, bypassing the session menu.
The session menu
The session menu presents the user with a list of sessions to choose
from. The user can change the currently selected session with the
mouse, or by using the up and down arrows on the keyboard. Note that
sessions which are locked (i.e. running on a different display) can not
be loaded or deleted.
The following operations can be performed from the session menu:
Load Session Pressing this button will load the currently
selected session. Alternatively, hitting the
Return key will also load the currently selected
session, or the user can double click a session
from the list.
Delete Session This operation will delete the currently selected
session, along with all of the application check-
point files associated with the session. After
pressing this button, the user will be asked to
press the button a second time in order to con-
firm the operation.
Default/Fail Safe xsm will start up a set of default applications
(as described above in the section titled Default
Startup Applications). This is useful when the
user wants to start a fresh session, or if the
session configuration files were corrupted and
the user wants a "fail safe" session.
Cancel Pressing this button will cause xsm to exit. It
can also be used to cancel a "Delete Session"
CONTROLLING A SESSION
After xsm determines which session to load, it brings up its main win-
dow, then starts up all applications that are part of the session. The
title bar for the session manager's main window will contain the name
of the session that was loaded.
The following options are available from xsm's main window:
Client List Pressing this button brings up a window containing a
list of all clients that are in the current session.
For each client, the host machine that the client is
running on is presented. As clients are added and
removed from the session, this list is updated to
reflect the changes. The user is able to control how
these clients are restarted (see below).
By pressing the View Properties button, the user can
view the session management properties associated
with the currently selected client.
By pressing the Clone button, the user can start a
copy of the selected application.
By pressing the Kill Client button, the user can
remove a client from the session.
By selecting a restart hint from the Restart Hint
menu, the user can control the restarting of a
client. The following hints are available:
- The Restart If Running hint indicates that the
client should be restarted in the next session if it
is connected to the session manager at the end of the
- The Restart Anyway hint indicates that the client
should be restarted in the next session even if it
exits before the current session is terminated.
- The Restart Immediately hint is similar to the
Restart Anyway hint, but in addition, the client is
meant to run continuously. If the client exits, the
session manager will try to restart it in the current
- The Restart Never hint indicates that the client
should not be restarted in the next session.
Note that all X applications may not be "session
aware". Applications that are not session aware are
ones that do not support the X Session Management
Protocol or they can not be detected by the Session
Management Proxy (see the section titled THE PROXY).
xsm allows the user to manually add such applications
to the session. The bottom of the Client List window
contains a text entry field in which application com-
mands can be typed in. Each command should go on its
own line. This information will be saved with the
session at checkpoint or shutdown time. When the
session is restarted, xsm will restart these applica-
tions in addition to the regular "session aware"
Pressing the Done button removes the Client List win-
Session Log... The Session Log window presents useful information
about the session. For example, when a session is
restarted, all of the restart commands will be dis-
played in the log window.
Checkpoint By performing a checkpoint, all applications that are
in the session are asked to save their state. Not
every application will save its complete state, but
at a minimum, the session manager is guaranteed that
it will receive the command required to restart the
application (along with all command line options). A
window manager participating in the session should
guarantee that the applications will come back up
with the same window configurations.
If the session being checkpointed was never assigned
a name, the user will be required to specify a ses-
sion name. Otherwise, the user can perform the
checkpoint using the current session name, or a new
session name can be specified. If the session name
specified already exists, the user will be given the
opportunity to specify a different name or to over-
write the already existing session. Note that a ses-
sion which is locked can not be overwritten.
When performing a checkpoint, the user must specify a
Save Type which informs the applications in the ses-
sion how much state they should save.
The Local type indicates that the application should
save enough information to restore the state as seen
by the user. It should not affect the state as seen
by other users. For example, an editor would create
a temporary file containing the contents of its edit-
ing buffer, the location of the cursor, etc...
The Global type indicates that the application should
commit all of its data to permanent, globally acces-
sible storage. For example, the editor would simply
save the edited file.
The Both type indicates that the application should
do both of these. For example, the editor would save
the edited file, then create a temporary file with
information such as the location of the cursor,
In addition to the Save Type, the user must specify
an Interact Style.
The None type indicates that the application should
not interact with the user while saving state.
The Errors type indicates that the application may
interact with the user only if an error condition
The Any type indicates that the application may
interact with the user for any purpose. Note that
xsm will only allow one application to interact with
the user at a time.
After the checkpoint is completed, xsm will, if nec-
essary, display a window containing the list of
applications which did not report a successful save
Shutdown A shutdown provides all of the options found in a
checkpoint, but in addition, can cause the session to
exit. Note that if the interaction style is Errors
or Any, the user may cancel the shutdown. The user
may also cancel the shutdown if any of the applica-
tions report an unsuccessful save of state.
The user may choose to shutdown the session with our
without performing a checkpoint.
HOW XSM RESPONDS TO SIGNALS
xsm will respond to a SIGTERM signal by performing a shutdown with the
following options: fast, no interaction, save type local. This allows
the user's session to be saved when the system is being shutdown. It
can also be used to perform a remote shutdown of a session.
xsm will respond to a SIGUSR1 signal by performing a checkpoint with
the following options: no interaction, save type local. This signal
can be used to perform a remote checkpoint of a session.
Since not all applications have been ported to support the X Session
Management Protocol, a proxy service exists to allow "old" clients to
work with the session manager. In order for the proxy to detect an
application joining a session, one of the following must be true:
- The application maps a top level window containing the
WM_CLIENT_LEADER property. This property provides a pointer to the
client leader window which contains the WM_CLASS, WM_NAME, WM_COMMAND,
and WM_CLIENT_MACHINE properties.
- The application maps a top level window which does not contain the
WM_CLIENT_LEADER property. However, this top level window contains the
WM_CLASS, WM_NAME, WM_COMMAND, and WM_CLIENT_MACHINE properties.
An application that support the WM_SAVE_YOURSELF protocol will receive
a WM_SAVE_YOURSELF client message each time the session manager issues
a checkpoint or shutdown. This allows the application to save state.
If an application does not support the WM_SAVE_YOURSELF protocol, then
the proxy will provide enough information to the session manager to
restart the application (using WM_COMMAND), but no state will be
xsm requires a remote execution protocol in order to restart applica-
tions on remote machines. Currently, xsm supports the rstart protocol.
In order to restart an application on remote machine X, machine X must
have rstart installed. In the future, additional remote execution pro-
tocols may be supported.
Ralph Mor, X Consortium
Jordan Brown, Quarterdeck Office Systems
X Version 11 XSM(1)