1. process

An instance of a running program is called a process. Every time you run a shell command, a program is run and a process is created for it.

In any modern operating system there can be more than one instance of a program loaded in memory at the same time.

2. Linux process management

Operating systems need some ways to create processes.

  • In a very simple system designed for running only a single application (e.g., the controller in a microwave oven), it may be possible to have all the processes that will ever be needed be present when the system comes up.

  • In general-purpose systems, however, some way is needed to create and terminate processes as needed during operation.

There are four principal events that cause a process to be created:

  • System initialization.

  • Execution of process creation system call by a running process.

  • A user request to create a new process.

  • Initiation of a batch job.

Process creation in UNIX and Linux are done through fork() or clone() system calls.

There are several steps involved in process creation.

  • process scheduling,

  • interrupt handling,

  • signaling,

  • process prioritization,

  • process switching,

  • process state,

  • process memory

2.1. Life cycle of a process

1→ creation 2→ execution 3→ termination 4→ removal