Process management is one of the important aspects of System Administration in Linux, and it includes the killing of processes using the kill command.


What is a Process in Linux?


A process on a Linux system can be a running occurrence of an application or program. You can also refer to processes as tasks executing in the operating system.


When a process is running, it keeps on shifting from one state to another and a process can in one of the following states:

  • Running: meaning the process is either executing or it is just set to be executed.
  • Waiting: meaning that the process is waiting for an event or for a system resource to carry out a task.


There are two types of waiting process under Linux namely interruptible and uninterruptible.


A waiting process that can be interrupted by signals is called Interruptible, while a waiting process that is directly waiting on hardware conditions and cannot be interrupted under any conditions is called uninterruptible.

  • Stopped: meaning that the process has been stopped, using a signal.
  • Zombie: meaning the process has been stopped abruptly and is dead.


When killing processes, the kill command is used to send a named signal to a named process or groups of processes. The default signal is the TERM signal.


Remember that the kill command can be a built-in function in many modern shells or external located at /bin/kill.


How to Find Process PID in Linux


In Linux, every process on a system has a PID (Process Identification Number) which can be used to kill the process.


You can identify the PID of any process by using the pidof command as follows:

$ pidof firefox
$ pidof chrome
$ pidof gimp-2.8


How to Kill Processes in Linux


Once you find the process PID, let us now look at how to kill processes. In this first example, I am going to first get the PID of the process and then send a signal to it.


I want to kill gimp process, so I will do it as follows:

$ pidof gimp-2.8
$ kill 9378


To verify that the process has been killed, run the pidof command and you will not be able to view the PID.

$ pidof gimp-2.8


You can also send a named signal to the process by using the signal name or numbers as follows:

$ pidof vlc
$ kill -SIGTERM 9541
$ pidof vlc


Using the signal number to kill a process:

$ pidof banshee
$ kill -9 9647
$ pidof banshee


In the above example, the number 9 is the signal number for the SIGKILL signal.


How to Kill Multiple Process PID’s in Linux


To kill more than one process, pass the PID(s) to the kill command as follows:

$ pidof gimp-2.8
$ pidof vlc
$ pidof banshee
$ kill -9 9734 9747 9762


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