1.3. Processes and the Shell

A process is a program in execution and can be identified by its unique PID (process identification) number. The kernel controls and manages processes. A process consists of the executable program, its data and stack, program and stack pointer, registers, and all the information needed for the program to run. When you start the shell, it is a process. The shell belongs to a process group identified by the group's PID. Only one process group has control of the terminal at a time and is said to be running in the foreground. When you log on, your shell is in control of the terminal and waits for you to type a command at the prompt.

The shell can spawn other processes. In fact, when you enter a command at the prompt or ...

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