processes

summary

This subchapter looks at UNIX (and Linux) processes.

processes

This subchapter looks at UNIX (and Linux) processes.

The UNIX term process is pretty much the same as the terms job or task on other operating systems.

multi-tasking

UNIX is a multi-processing operating system. This means that it runs more than one task (or job or process) at a time. On a multi-processor computer it is possible for UNIX to literally run multiple processes at the exact same time. On a single processor computer different processes are swapped into the main CPU (central processing unit) so fast that it gives the illusion that multiple processes are running simultaneously.

One of the reasons that multitasking works is that the processor runs much faster than input/output or mass storage devices (and on modern computers often runs much faster than main memory). Whenever a process has to stop for input, output, or mass storage, there is a convenient moment for the operating system to switch to a different process that is ready to run rather than leave the CPU sitting idle waiting for the I/O to occur.

init

The first process to start running on a traditional UNIX computer is init. Some modern variations, such as Linux, may have a few other processes run first, especially.if the computer or server supports multiple operating systems.

init starts a series of other processes (in UNIX, this is called spawning). Some of these processes only run during boot-up, while others are intended to run as long as the computer is running.

By the time a human user can login to the system, many processes are running.

init is ultimate ancestor process of all other processes in a UNIX system.

process ID

Every process on UNIX (or Linux) has a unique process identification number, called the process ID.

A system administrator uses the process IDs to control the processes.

kill

One useful command available for the system administrator is the kill command, which stops a process and removes it from the system.

An ordinary user can only kill his or her own processes.

A system administrator running as root (including using sudo) can use kill on any process on the entire system.

See the subchapter on kill for more information.