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Processes are not the same as programs; in addition to the machine instructions (often called ``text''), they have additional components (mainly data that is being processed in memory) that are not part of the program itself.
Several processes being scheduled for ``simultaneous'' execution by the kernel may in fact be instances of a single program. For example, on a multiuser system, several users may use the cat utility: this is held as a single program in /bin/cat.
For an explanation of how the system manages processes, see ``An overview of the system''. See also ``Understanding the UNIX system''.
You may need to destroy runaway processes, or processes that have finished running but have not been removed from the system (``zombies''). You may also need to find out what processes are running, cause processes to run after you log off, and execute groups of processes (piping the output of one to the input of another). These tasks are explained below.
There are two methods for managing processes; process control and job control. Process control allows you to interact with all the processes on the system. Job control allows you to move jobs between the background and foreground using the shell.