Session Management

The state of the desktop can be remembered. At a later time, and perhaps at a different X display station, the state of the desktop can be re-created. A session is a snapshot of the state of a user's desktop at a point in time. The Common Desktop Environment supports two sessions from which the user can choose:

• Home session--A snapshot of the desktop state that reassembles in the same way each time it is started.

• Current session--The state of a desktop saved at logout time.

The Common Desktop Environment Session Manager coordinates these activities, but applications are responsible for saving their own state.

The desktop uses the X11R5 Interclient Communication Conventions style of session management. This consists mostly of conventions for setting properties on top-level windows. The desktop extends this by providing a facility that allocates specific files into which applications can store their state. A command-line flag then points to this file when the application is restarted. Applications that maintain multiple top-level windows must save the state of each of them.

A session is associated with a particular user. In the Common Desktop Environment, the Login Manager is responsible for initial user login. The Login Manager is an alternative GUI for the UNIX login program. Normally, it checks the entered password with the user's registered password. However, vendors can provide authentication schemes tuned to their platform.

The Login Manager is network-aware. When faced with an X display that is normally served by host A, the user can log into the user's desktop by running a session from host B that has full access to the user's normal set of files and services on host B. This is possible by Login Manager acting as the desktop's X11 Display Manager (XDM). The XDM Control Protocol (XDMCP) is used between X11 window servers and XDMs on the network. The Login Manager displays its login window or host chooser window on any X11 server requesting either XDM service. This makes the Common Desktop Environment a good match for use with XDMCP-aware X terminals.

For connections to the X server, the desktop uses the X magic cookie scheme to control access. If a user on some host machine can read a certain file within a session owner's home directory, then access to the X server is granted. An alternative to this per-user authorization is per-host authorization. This is useful for installations supporting pre-X11R4 clients, which will be unable to connect to X servers using the X magic cookie scheme.

X resource files are handled in the context of Common Desktop Environment sessions as follows: a set of Common Desktop Environment default resources is merged with a host version of this file, followed by the user's $HOME/.Xdefaults file, followed by a session-specific file of resources that have changed through user interaction with the Style Manager. The result is stored in the RESOURCE_MANAGER property of the root window. To enable fine-grain customization, the C preprocessor is run on resource files.