The concept of a process is fundamental to any multiprogramming operating system. A process is usually defined as an instance of a program in execution; thus, if 16 users are running vi at once, there are 16 separate processes (although they can share the same executable code). Processes are often called tasks or threads in the Linux source code.

In this chapter, we discuss static properties of processes and then describe how process switching is performed by the kernel. The last two sections describe how processes can be created and destroyed. We also describe how Linux supports multithreaded applications — as mentioned in Chapter 1, it relies on so-called lightweight processes (LWP).