NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | CONFORMING TO | NOTES | BUGS | SEE ALSO | COLOPHON
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 || _XOPEN_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().
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 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), sigqueue(2), tkill(2), exit(3),
capabilities(7), credentials(7), signal(7)
This page is part of release 3.08 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 2008-04-18 KILL(2)