Process API¶

Key Terms

• Each process has a name; in most systems, that name is a number known as a process ID (PID).

• The fork() system call is used in UNIX systems to create a new process. The creator is called the parent; the newly created process is called the child. As sometimes occurs in real life [J16], the child process is a nearly identical copy of the parent.

• The wait() system call allows a parent to wait for its child to complete execution.

• The exec() family of system calls allows a child to break free from its similarity to its parent and execute an entirely new program.

• A UNIX shell commonly uses fork(), wait(), and exec() to launch user commands; the separation of fork and exec enables features like input/output redirection, pipes, and other cool features, all without changing anything about the programs being run.

• Process control is available in the form of signals, which can cause jobs to stop, continue, or even terminate.

• Which processes can be controlled by a particular person is encapsulated in the notion of a user; the operating system allows multiple users onto the system, and ensures users can only control their own processes.

• A superuser can control all processes (and indeed do many other things); this role should be assumed infrequently and with caution for security reasons.