_x_s_m is a session manager. A session is a group of applications, each
of which has a particular state. _x_s_m 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. _x_s_m is more powerful
because it lets you run applications and have them automatically become
part of the session. On a simple level, _x_s_m is useful because it
gives you this ability to easily define which applications are in a session.
The true power of _x_s_m, however, can be taken advantage of when more
and more applications learn to save and restore their state.
The last program executed by your _._x_s_e_s_s_i_o_n file should be _x_s_m. With this configuration, when the user chooses to shut down the session using _x_s_m, 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 _x_s_m shuts down the session, _x_s_m will know to restart these applications. Note however that there are some types of applications that are not "session aware". _x_s_m allows you to manually add these applications to your session (see the section titled _C_l_i_e_n_t _L_i_s_t).
Each line in the startup file should contain a command to start an application. A sample startup file might look this:
The following operations can be performed from the session menu:
The following options are available from _x_s_m's main window:
An application that support the WWMM__SSAAVVEE__YYOOUURRSSEELLFF protocol will receive
a WWMM__SSAAVVEE__YYOOUURRSSEELLFF 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 WWMM__SSAAVVEE__YYOOUURRSSEELLFF protocol, then
the proxy will provide enough information to the session manager to restart
the application (using WWMM__CCOOMMMMAANNDD), but no state will be restored.
twm
smproxy
xterm
STARTING A SESSION
When _x_s_m starts up, it first checks to see if the user previously
saved any sessions. If no saved sessions exist, _x_s_m starts up a set
of default applications (as described above in the section titled
_D_e_f_a_u_l_t _S_t_a_r_t_u_p _A_p_p_l_i_c_a_t_i_o_n_s). If at least one session exists, a
session menu is presented. The [[--sseessssiioonn sseessssiioonnNNaammee]] 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.
CONTROLLING A SESSION
After _x_s_m determines which session to load, it brings up its main
window, 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.
By pressing the VViieeww PPrrooppeerrttiieess
button, the user can view the session management properties associated with
the currently selected client.
By pressing the CClloonnee button, the user can start a copy of the selected
application.
By pressing the KKiillll CClliieenntt button, the user can remove a client from
the session.
By selecting a restart hint from the RReessttaarrtt HHiinntt menu, the user can
control the restarting of a client. The following hints are available:
-
The RReessttaarrtt IIff RRuunnnniinngg 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 RReessttaarrtt AAnnyywwaayy hint indicates that the client should be restarted
in the next session even if it exits before the current session is terminated.
-
The RReessttaarrtt IImmmmeeddiiaatteellyy hint is similar to the RReessttaarrtt AAnnyywwaayy 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 RReessttaarrtt NNeevveerr 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 _T_H_E _P_R_O_X_Y). _x_s_m allows the user to manually add
such applications to the session. The bottom of the _C_l_i_e_n_t _L_i_s_t 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,
_x_s_m will restart these applications in addition to the regular "session
aware" applications.
Pressing the DDoonnee button removes the CClliieenntt LLiisstt 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 SSaavvee TTyyppee
which informs the applications in the session how much state they should save.
The LLooccaall
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 GGlloobbaall
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 BBootthh
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 SSaavvee TTyyppee, the user must specify an
IInntteerraacctt SSttyyllee.
The NNoonnee type indicates that the application should not interact with
the user while saving state.
The EErrrroorrss type indicates that the application may interact with
the user only if an error condition arises.
The AAnnyy type indicates that the application may interact with
the user for any purpose. Note that _x_s_m will only allow one
application to interact with the user at a time.
After the checkpoint is completed, _x_s_m 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.
HOW _X_S_M RESPONDS TO SIGNALS
_x_s_m 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.
_x_s_m 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 PROXY
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
WWMM__CCLLIIEENNTT__LLEEAADDEERR property. This property provides a pointer to
the client leader window which contains the WWMM__CCLLAASSSS, WWMM__NNAAMMEE,
WWMM__CCOOMMMMAANNDD, and WWMM__CCLLIIEENNTT__MMAACCHHIINNEE properties.
or ...
- The application maps a top level window which does not contain the
WWMM__CCLLIIEENNTT__LLEEAADDEERR property. However, this top level window
contains the WWMM__CCLLAASSSS, WWMM__NNAAMMEE, WWMM__CCOOMMMMAANNDD, and
WWMM__CCLLIIEENNTT__MMAACCHHIINNEE properties.
REMOTE APPLICATIONS
_x_s_m requires a remote execution protocol in order to restart
applications on remote machines. Currently, _x_s_m supports the
_r_s_t_a_r_t protocol. In order to restart an application on remote
machine XX, machine XX must have _r_s_t_a_r_t installed. In
the future, additional remote execution protocols may be supported.
SEE ALSO
smproxy(1), rstart(1)
AUTHORS
Ralph Mor, X Consortium
Jordan Brown, Quarterdeck Office Systems