`kill`

Terminate or signal processes (POSIX)

Syntax:

kill [-n nid] [-signal_name | -signal_number] pid...

kill -l

Options:

-signal_name: The name of the signal to be sent to the specified process. Values of signal_name are recognized in case-independent fashion, with or without the SIG prefix.
-signal_number: (Deprecated) A non-negative decimal integer representing the signal to be sent to the specified process.
-l: ("el") Don't send signals. List possible values for signal_name.
-n nid: Kill the process on the specified node. This option is not available in the shell builtin version of kill.
pid: A decimal integer specifying a process or process group to be signaled. A positive number pid is simply a process ID. A negative number pid has its absolute value taken as a process group ID. The signal is sent to all processes belonging to the group.
A pid of zero sends the signal to all processes owned by the user in the current shell's process group.

Don't use a pid of zero when logged on as root. Signalling all the background processes owned by superuser and any current superuser foreground processes (e.g. backups in progress) may produce unpredictable results.

Description:

The kill utility sends a signal to the process(es) specified by each pid operand. By default, kill sends the SIGTERM signal, but you may override this default by naming a signal to be sent.

To print out the list of signals that may be sent, use kill with the -l option:

    kill -l

The kill command is available both as a standalone utility and as a shell builtin. To make sure that you're using the utility, specify the full path.

Examples:

Any of the commands:

    kill -9 100 -16

    kill -sigkill 100 -16

    kill -KILL 100 -16

sends the SIGKILL signal to the process whose process ID is 100 and to all processes whose process group ID is 16, assuming the sending process has permission to send that signal to the specified processes, and that they exist.

Exit status:

0: At least one matching process was found for each pid option, and the specified signal was successfully sent to each matching process.
>0: An error occurred.

Caveats:

Some shells include a builtin kill command. To make sure you're using the kill utility, specify the the full path to it.