kill

Examples (TL;DR)

• Terminate a program using the default SIGTERM (terminate) signal: kill process_id
• List available signal names (to be used without the SIG prefix): kill -l
• Terminate a background job: kill %job_id
• Terminate a program using the SIGHUP (hang up) signal. Many daemons will reload instead of terminating: kill -1|HUP process_id
• Terminate a program using the SIGINT (interrupt) signal. This is typically initiated by the user pressing Ctrl + C: kill -2|INT process_id
• Signal the operating system to immediately terminate a program (which gets no chance to capture the signal): kill -9|KILL process_id
• Signal the operating system to pause a program until a SIGCONT ("continue") signal is received: kill -17|STOP process_id
• Send a SIGUSR1 signal to all processes with the given GID (group id): kill -SIGUSR1 -group_id

tldr.sh

Synopsis

kill [-signal|-s signal|-p] [-q value] [-a] [--] pid|name...
kill -l [number] | -L

Description

The command kill sends the specified signal to the specified processes or process groups.

If no signal is specified, the TERM signal is sent. The default action for this signal is to terminate the process. This signal should be used in preference to the KILL signal (number 9), since a process may install a handler for the TERM signal in order to perform clean-up steps before terminating in an orderly fashion. If a process does not terminate after a TERM signal has been sent, then the KILL signal may be used; be aware that the latter signal cannot be caught, and so does not give the target process the opportunity to perform any clean-up before terminating.

Most modern shells have a builtin kill command, with a usage rather similar to that of the command described here.  The --all, --pid, and --queue options, and the possibility to specify processes by command name, are local extensions.

If signal is 0, then no actual signal is sent, but error checking is still performed.

Arguments

The list of processes to be signaled can be a mixture of names and PIDs.

pid

Each pid can be one of four things:

n

where n is larger than 0.  The process with PID n is signaled.

0

All processes in the current process group are signaled.

-1

All processes with a PID larger than 1 are signaled.

-n

where n is larger than 1.  All processes in process group n are signaled.  When an argument of the form '-n' is given, and it is meant to denote a process group, either a signal must be specified first, or the argument must be preceded by a '--' option, otherwise it will be taken as the signal to send.

name

All processes invoked using this name will be signaled.

Options

-s, --signal signal

The signal to send.  It may be given as a name or a number.

-l, --list [number]

Print a list of signal names, or convert the given signal number to a name. The signals can be found in /usr/include/linux/signal.h

-L, --table

Similar to -l, but it will print signal names and their corresponding numbers.

-a, --all

Do not restrict the command-name-to-PID conversion to processes with the same UID as the present process.

-p, --pid

Only print the process ID (PID) of the named processes, do not send any signals.

--verbose

Print PID(s) that will be signaled with kill along with the signal.

-q, --queue value

Use sigqueue(3) rather than kill(2). The value argument is an integer that is sent along with the signal.  If the receiving process has installed a handler for this signal using the SA_SIGINFO flag to sigaction(2), then it can obtain this data via the si_sigval field of the siginfo_t structure.

Notes

Although it is possible to specify the TID (thread ID, see gettid(2)) of one of the threads in a multithreaded process as the argument of kill, the signal is nevertheless directed to the process (i.e., the entire thread group). In other words, it is not possible to send a signal to an explicitly selected thread in a multithreaded process. The signal will be delivered to an arbitrarily selected thread in the target process that is not blocking the signal. For more details, see signal(7) and the description of CLONE_THREAD in clone(2).

Return Codes

kill has the following return codes:

0

success

1

failure

64

partial success (when more than one process specified)

See Also

bash(1), tcsh(1), sigaction(2), kill(2), sigqueue(3), signal(7)

Authors

Salvatore Valente
Karel Zak

The original version was taken from BSD 4.4.

Availability

The kill command is part of the util-linux package and is available from Linux Kernel Archive.

Referenced By

3proxy(8), ax25d(8), axfer-transfer(1), biboumi(1), blktrace(8), corosync-vqsim(8), darkstat(8), ezstream(1), forktest(6), fuser(1), kill(2), killall(1), kissattach(8), ldattach(8), lp5250d(1), lsof(1), lxc.container.conf(5), m6pack(8), mkiss(8), nrsdrv(8), o2hbmonitor(8), pgrep(1), pg_top(1), pmsignal(1), posix_spawn(3), povray(1), procenv(1), rigctld(1), rotctld(1), sigaction(2), signal(2), signal(7), skill(1), tcpdump(8), tgif.1x(1), thttpd(8), timeout(1), t-prot(1), uucico(8), vtc(7), whowatch(1), xargs(1).