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processes

summary

����This subchapter looks at UNIX (and Linux) processes.

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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.

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