The Gnome desktop uses several important components to function, most function in the background. The Gnome session manager is one of those many components. If you are using the Gnome desktop you are most likely using the Gnome session manager as well.
Gnome Session Functions
The Gnome session manager is used to start the Gnome desktop. The session manager is started by the login or display manager and will load a user session when you login to your desktop.
More Gnome Session Functions
The Gnome session manager is able to save user sessions and restore them to the same point including all open windows. The user has the ability to choose which session is loaded. If you load a saved user session all running applications will also be remembered and restarted. You can also choose to load a new default session every time you login.
Gnome Session Administration
The average desktop user will have very little reason to manually interact with the session manager. You can simple let it perform its functions in the background. But of course, like me, some users will feel the need to mess with everything. Thankfully the session manager offers many options that you can customize to change the functionality.
After logging into your system using the graphical login screen the session manager will then take over.
When the session manager first starts it will load many of the required services. After the basic services are loaded the session manager will then automatically move on.
Window Manager Startup
The Gnome session manager will then load the specified window manager more required services.
The session manager will then continue to load all of your default startup applications, or the applications from your previous session. This also includes your panels and other desktop tools.
When the Gnome session manager is finished loading your desktop it will go to sleep, it will become active again when used.
The session manager will take over again when you logout of your system. The session manager will also prompt you if anything required you attention before logging out. If everything is in order the session manager will end all applications including the desktop and window manager. You will then be returned to the login screen, or the system will shutdown if told to do so.
The Gnome control center also provides for easy configuration of these options, just look for your session settings. The session manager settings may also be found in the system settings window depending on your version of Gnome.
Launching Gnome Session Settings
You can also lanch the Gnome session manager settings dialog with the command below.
The Gnome session manager can also be launched manually from the command line with the following syntax.
$ gnome-session --option
Use the command below if you would like to specify a session to load.
$ gnome-session --choose-session=SESSION
The next command will toggle failsafe mode, meaning sessions will be read from the defauls sessions file.
$ gnome-session --failsafe
With the command below you can set the time delay that the Gnome session manager will wait for clients to register. Set the number in milliseconds, the defailt is 30,000.
$ gnome-session --purge-delay=NUMBER
Set the amount of time the Gnome session manager will wait for clients to respong, the default is 10,000.
$ gnome-session --warn-delay=NUMBER
Next you can set the amount of time the Gnome session manager will wait for clients to die, the default is 10,000.
$ gnome-session --suicide-delay=NUMBER