Sunday, October 11, 2009

Why Process required

As You know Linux is multi-user, multitasking Os. It means you can run more than two process simultaneously if you wish. For e.g. To find how many files do you have on your system you may give command like:

$ ls / -R | wc -l

This command will take lot of time to search all files on your system. So you can run such command in Background or simultaneously by giving command like

$ ls / -R | wc -l &

The ampersand (&) at the end of command tells shells start process (ls / -R | wc -l) and run it in background takes next command immediately.

Process & PID defined as:
"An instance of running command is called process and the number printed by shell is called process-id (PID), this PID can be use to refer specific running process."

Linux Command Related with Process

Following tables most commonly used command(s) with process:

For this purpose Use this Command Examples*
To see currently running process ps $ ps
To stop any process by PID i.e. to kill process
kill {PID} $ kill 1012
To stop processes by name i.e. to kill process killall {Process-name} $ killall httpd
To get information about all running process ps -ag $ ps -ag
To stop all process except your shell kill 0 $ kill 0
For background processing (With &, use to put particular command and program in background) linux-command & $ ls / -R | wc -l &
To display the owner of the processes along with the processes ps aux $ ps aux
To see if a particular process is running or not. For this purpose you have to use ps command in combination with the grep command

ps ax | grep process-U-want-to see

For e.g. you want to see whether Apache web server process is running or not then give command

$ ps ax | grep httpd

To see currently running processes and other information like memory and CPU usage with real time updates. top
See the output of top command.

$ top


Note
that to exit from top command press q.
To display a tree of processes pstree $ pstree

* To run some of this command you need to be root or equivalnt user.

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