Ubuntu Unleashed 2015 Edition: Covering 14.10 and 15.04, Tenth Edition

Using the kill Command to Control Processes

The kill command is a basic UNIX system command. You can communicate with a running process by entering a command into its interface, such as when you type into a text editor. But some processes (usually system processes rather than application processes) run without such an interface, and you need a way to communicate with them as well, so you use a system of signals. The kill system accomplishes that by sending a signal to a process, and you can use it to communicate with any process. The general format of the kill command is as follows:

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matthew@seymour:~$ kill option PID

Note that if you are using kill on a process you do not own, you need to have super user privileges ...