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KILL(1) General Commands Manual KILL(1)

kill — terminate or signal a process

kill [-s signal_name] pid ...

kill -l [exit_status]

kill -signal_name pid ...

kill -signal_number pid ...

The kill utility sends a signal to the process(es) specified by the pid operand(s). If no signal is specified, SIGTERM is used.

Only the superuser may send signals to other users' processes.

The options are as follows:

[exit_status]
Display the name of the signal corresponding to exit_status. exit_status may be the exit status of a command killed by a signal (see the special sh(1) parameter ‘?’) or a signal number.

If no operand is given, display the names of all the signals.

signal_name
A symbolic signal name specifying the signal to be sent instead of the default SIGTERM.
-signal_name
A symbolic signal name specifying the signal to be sent instead of the default SIGTERM.
-signal_number
A non-negative decimal integer specifying the signal to be sent instead of the default SIGTERM.

The following PIDs have special meanings:

-1
If superuser, broadcast the signal to all processes; otherwise, broadcast to all processes belonging to the user.
0
Send the signal to all processes whose group ID is equal to the process group ID of the sender, and for which the process has permission.
-pgid
Send the signal to all processes within the specified process group.

Some of the more commonly used signals:

1
HUP (hang up)
2
INT (interrupt)
3
QUIT (quit)
6
ABRT (abort)
9
KILL (non-catchable, non-ignorable kill)
14
ALRM (alarm clock)
15
TERM (software termination signal)

For a more complete list, consult the sigaction(2) manual page.

A signal number of 0 (kill -0 pid) checks the validity of a certain PID, to see if it exists. An exit code of 0 means that the specified process exists.

The kill utility exits 0 on success, and >0 if an error occurs.

Forcibly terminate process ID 1234:

$ kill -9 1234

Send the init(8) process the hangup signal, instructing it to re-read ttys(5):

# kill -HUP 1

csh(1), ksh(1), pkill(1), ps(1), kill(2), sigaction(2)

The kill utility is compliant with the IEEE Std 1003.1-2008 (“POSIX.1”) specification.

The -signal_name and -signal_number syntax is marked by IEEE Std 1003.1-2008 (“POSIX.1”) as being an X/Open System Interfaces option.

kill also exists as a built-in to csh(1) and ksh(1), though with a different syntax.

A kill command appeared in Version 3 AT&T UNIX.

February 9, 2020 OpenBSD-6.8