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Linux Migration: Page 5 of 9

The mother of all processes is "init." It keeps track of the system's state, and starts or stops processes accordingly. The system's state is also known as the "init state," or the "run level." When you're running in single-user (maintenance) mode, for example, this is init level 1. Multiuser mode with no network is init level 2; multiuser mode with networking is run level 3.

Doing X Windows

The Linux GUI isn't intrinsic to the operating system. This has its advantages. If the GUI isn't available, for instance, you can still get real work done, like recovering a system in a failure.

But it's nice to have a GUI around when you need it. Linux's GUI is made up of an X Windows server, a window manager for the X server and general client programs. X Windows is a client/server system: The X server runs on the host machine and provides a context for clients to display their information. Since there's no tight coupling between where the client program is running and where it displays, X Windows clients don't have to run on the same machines as the server. And they can display and receive their output and input remotely, without special remote-control software. While this does simplify administration, it can also pose a security risk.