Content-type: text/html; charset=UTF-8 Man page of KILL

KILL

Section: User Commands (1)
Updated: October 2011
Index Return to Main Contents

NAME

kill - send a signal to a process

SYNOPSIS

kill [options] <pid> [...]

DESCRIPTION

The default signal for kill is TERM. Use -l or -L to list available signals. Particularly useful signals include HUP, INT, KILL, STOP, CONT, and 0. Alternate signals may be specified in three ways: -9, -SIGKILL or -KILL. Negative PID values may be used to choose whole process groups; see the PGID column in ps command output. A PID of -1 is special; it indicates all processes except the kill process itself and init.

OPTIONS

<pid> [...]: Send signal to every <pid> listed.
-<signal>: -s <signal> --signal <signal> Specify the signal to be sent. The signal can be specified by using name or number. The behavior of signals is explained in signal(7) manual page.
-l, --list [signal]: List signal names. This option has optional argument, which will convert signal number to signal name, or other way round.
-L, --table: List signal names in a nice table.

NOTES

Your shell (command line interpreter) may have a built-in kill command. You may need to run the command described here as /bin/kill to solve the conflict.

EXAMPLES

kill -9 -1: Kill all processes you can kill.
kill -l 11: Translate number 11 into a signal name.
kill -L: List the available signal choices in a nice table.
kill 123 543 2341 3453: Send the default signal, SIGTERM, to all those processes.

STANDARDS

This command meets appropriate standards. The -L flag is Linux-specific.

AUTHOR

Albert Cahalan wrote kill in 1999 to replace a bsdutils one that was not standards compliant. The util-linux one might also work correctly.

REPORTING BUGS

Please send bug reports to

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Time: 04:45:19 GMT, September 16, 2022 Content-type: text/html; charset=UTF-8 Man page of KILL

KILL

Section: Linux Programmer's Manual (2)
Updated: 2017-09-15
Index Return to Main Contents

NAME

kill - send signal to a process

SYNOPSIS

#include <sys/types.h>
#include <signal.h>

int kill(pid_t pid, int sig);

Feature Test Macro Requirements for glibc (see feature_test_macros(7)):

kill(): _POSIX_C_SOURCE

DESCRIPTION

The kill() system call can be used to send any signal to any process group or process.

If pid is positive, then signal sig is sent to the process with the ID specified by pid.

If pid equals 0, then sig is sent to every process in the process group of the calling process.

If pid equals -1, then sig is sent to every process for which the calling process has permission to send signals, except for process 1 (init), but see below.

If pid is less than -1, then sig is sent to every process in the process group whose ID is -pid.

If sig is 0, then no signal is sent, but existence and permission checks are still performed; this can be used to check for the existence of a process ID or process group ID that the caller is permitted to signal.

For a process to have permission to send a signal, it must either be privileged (under Linux: have the CAP_KILL capability in the user namespace of the target process), or the real or effective user ID of the sending process must equal the real or saved set-user-ID of the target process. In the case of SIGCONT, it suffices when the sending and receiving processes belong to the same session. (Historically, the rules were different; see NOTES.)

RETURN VALUE

On success (at least one signal was sent), zero is returned. On error, -1 is returned, and errno is set appropriately.

ERRORS

EINVAL: An invalid signal was specified.
EPERM: The process does not have permission to send the signal to any of the target processes.
ESRCH: The process or process group does not exist. Note that an existing process might be a zombie, a process that has terminated execution, but has not yet been wait(2)ed for.

CONFORMING TO

POSIX.1-2001, POSIX.1-2008, SVr4, 4.3BSD.

NOTES

The only signals that can be sent to process ID 1, the init process, are those for which init has explicitly installed signal handlers. This is done to assure the system is not brought down accidentally.

POSIX.1 requires that kill(-1,sig) send sig to all processes that the calling process may send signals to, except possibly for some implementation-defined system processes. Linux allows a process to signal itself, but on Linux the call kill(-1,sig) does not signal the calling process.

POSIX.1 requires that if a process sends a signal to itself, and the sending thread does not have the signal blocked, and no other thread has it unblocked or is waiting for it in sigwait(3), at least one unblocked signal must be delivered to the sending thread before the kill() returns.

Linux notes

Across different kernel versions, Linux has enforced different rules for the permissions required for an unprivileged process to send a signal to another process. In kernels 1.0 to 1.2.2, a signal could be sent if the effective user ID of the sender matched effective user ID of the target, or the real user ID of the sender matched the real user ID of the target. From kernel 1.2.3 until 1.3.77, a signal could be sent if the effective user ID of the sender matched either the real or effective user ID of the target. The current rules, which conform to POSIX.1, were adopted in kernel 1.3.78.

BUGS

In 2.6 kernels up to and including 2.6.7, there was a bug that meant that when sending signals to a process group, kill() failed with the error EPERM if the caller did not have permission to send the signal to any (rather than all) of the members of the process group. Notwithstanding this error return, the signal was still delivered to all of the processes for which the caller had permission to signal.

COLOPHON

This page is part of release 4.15 of the Linux man-pages project. A description of the project, information about reporting bugs, and the latest version of this page, can be found at https://www.kernel.org/doc/man-pages/.