| NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | CONFORMING TO | NOTES | BUGS | SEE ALSO | COLOPHON | The Linux Programming Interface |
KILL(2) Linux Programmer's Manual KILL(2)
kill - send signal to a process
#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 >= 1 || _XOPEN_SOURCE || _POSIX_SOURCE
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 error checking is still
performed; this can be used to check for the existence of a process
ID or process group ID.
For a process to have permission to send a signal it must either be
privileged (under Linux: have the CAP_KILL capability), 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.
On success (at least one signal was sent), zero is returned. On
error, -1 is returned, and errno is set appropriately.
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 pid or process group does not exist. Note that an
existing process might be a zombie, a process which already
committed termination, but has not yet been wait(2)ed for.
SVr4, 4.3BSD, POSIX.1-2001.
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.1-2001 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.1-2001 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.
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 that of the
receiver, or the real user ID of the sender matched that of the
receiver. 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 receiver. The current rules, which conform
to POSIX.1-2001, were adopted in kernel 1.3.78.
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.
_exit(2), killpg(2), signal(2), tkill(2), exit(3), sigqueue(3),
capabilities(7), credentials(7), signal(7)
This page is part of release 3.51 of the Linux man-pages project. A
description of the project, and information about reporting bugs, can
be found at http://www.kernel.org/doc/man-pages/.
Linux 2013-02-05 KILL(2)
HTML rendering created 2013-05-17 by Michael Kerrisk, author of The Linux Programming Interface, maintainer of the Linux man-pages project
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