Linux Server Hacks, Volume Two

Hack #75. Kill Processes the Right Way

The Linux kill command enables you to terminate processes normally or by using a sledgehammer.

If you spend much time as a Linux user or administrator, sooner or later you're going to have to end a process (often simply a program that no longer responds to user input or that just won't seem to go away). The safest way to kill a process is to simply use the kill command, with no modifiers or flags. First use the ps –ef command to determine the process ID (PID) of the process you want to kill, and then simply type this command:

	# kill -pid

The standard kill command usually works just fine, terminating the offending process and returning its resources to the system. However, if your process has started child processes, simply killing the parent can potentially leave the child processes running, and therefore still consuming system resources. In order to prevent such so-called "zombie processes," you should make sure that you kill any and all child processes before you kill their respective parent processes.

Killing Processes in the Right Order

You can identify child process and their parents by using the Linux ps -ef command and examining each entry, looking at the column labeled PPID (parent process ID). However, if you're only interested in a specific family of processes, using the grep command makes life easier.

Let's look at an example. If we're trying to kill the httpd process, we'll need to kill its child processes before we can kill the parent. ...