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 "development" session, or an "xterminal" session.
Each session can have its own set of applications. Within a session, you
can perform a "checkpoint" 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 keep.
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.
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 logging 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 Client List).
Each line in the startup file should contain a command to start an application. A sample startup file might look this:
<start of file>
twm
smproxy
xterm
<end of file>
The following operations can be performed from the session menu:
The following options are available from xsm's main window:
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 current session.
- 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 session.
- 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 commands 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 applications in addition to the regular "session aware" applications.
Pressing the Done button removes the Client List window.
If the session being checkpointed was never assigned a name, the user will
be required to specify a session 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 overwrite the
already existing session. Note that a session which is locked can not be
overwritten.
When performing a checkpoint, the user must specify a Save Type which informs
the applications in the session 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 editing buffer, the location of the
cursor, etc...
The Global type indicates that the application should commit all of its
data to permanent, globally accessible 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, etc...
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 arises.
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 necessary, display a window containing the list of applications which did not report a successful save of state.
The user may choose to shutdown the session with our without performing a checkpoint.
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.
- 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.
or ...
- 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 restored.