-.\" Hey Emacs! This file is -*- nroff -*- source.
-.\"
.\" Copyright (c) 1992 Drew Eckhardt (drew@cs.colorado.edu), March 28, 1992
.\"
+.\" %%%LICENSE_START(VERBATIM)
.\" Permission is granted to make and distribute verbatim copies of this
.\" manual provided the copyright notice and this permission notice are
.\" preserved on all copies.
.\"
.\" Formatted or processed versions of this manual, if unaccompanied by
.\" the source, must acknowledge the copyright and authors of this work.
+.\" %%%LICENSE_END
.\"
.\" Modified by Michael Haardt <michael@moria.de>
.\" Modified by Thomas Koenig <ig25@rz.uni-karlsruhe.de>
.\" Modified 1996-07-21 by Andries Brouwer <aeb@cwi.nl>
.\" Modified 1997-01-17 by Andries Brouwer <aeb@cwi.nl>
.\" Modified 2001-12-18 by Andries Brouwer <aeb@cwi.nl>
-.\" Modified 2002-07-24 by Michael Kerrisk <mtk-manpages@gmx.net>
+.\" Modified 2002-07-24 by Michael Kerrisk <mtk.manpages@gmail.com>
.\" Added note on historical rules enforced when an unprivileged process
.\" sends a signal.
-.\" Modified 2004-06-16 by Michael Kerrisk <mtk-manpages@gmx.net>
+.\" Modified 2004-06-16 by Michael Kerrisk <mtk.manpages@gmail.com>
.\" Added note on CAP_KILL
.\" Modified 2004-06-24 by aeb
.\" Modified, 2004-11-30, after idea from emmanuel.colbus@ensimag.imag.fr
.\"
-.TH KILL 2 2004-06-24 "Linux 2.6.7" "Linux Programmer's Manual"
+.TH KILL 2 2016-03-15 "Linux" "Linux Programmer's Manual"
.SH NAME
kill \- send signal to a process
.SH SYNOPSIS
.sp
.BI "int kill(pid_t " pid ", int " sig );
.fi
+.sp
+.in -4n
+Feature Test Macro Requirements for glibc (see
+.BR feature_test_macros (7)):
+.in
+.sp
+.ad l
+.BR kill ():
+_POSIX_C_SOURCE
+.ad b
.SH DESCRIPTION
The
.BR kill ()
system call
can be used to send any signal to any process group or process.
.PP
-If \fIpid\fP is positive, then signal \fIsig\fP is sent to \fIpid\fP.
+If \fIpid\fP is positive, then signal \fIsig\fP is sent to the
+process with the ID specified by \fIpid\fP.
.PP
If \fIpid\fP equals 0, then \fIsig\fP is sent to every process in the
-process group of the current process.
+process group of the calling process.
.PP
If \fIpid\fP equals \-1, then \fIsig\fP is sent to every process
for which the calling process has permission to send signals,
-except for process 1 (init), but see below.
+except for process 1 (\fIinit\fP), but see below.
.PP
If \fIpid\fP is less than \-1, then \fIsig\fP is sent to every process
-in the process group \fI\-pid\fP.
+in the process group whose ID is \fI\-pid\fP.
.PP
-If \fIsig\fP is 0, then no signal is sent, but error checking is still
-performed.
+If \fIsig\fP 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
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
+In the case of
+.B SIGCONT
+it suffices when the sending and receiving
processes belong to the same session.
-.SH "RETURN VALUE"
+(Historically, the rules were different; see NOTES.)
+.SH RETURN VALUE
On success (at least one signal was sent), zero is returned.
On error, \-1 is returned, and
.I errno
has not yet been
.BR wait (2)ed
for.
+.SH CONFORMING TO
+POSIX.1-2001, POSIX.1-2008, SVr4, 4.3BSD.
.SH NOTES
-The only signals that can be sent process ID 1, the
+The only signals that can be sent to process ID 1, the
.I init
process, are those for which
.I init
This is done to assure the
system is not brought down accidentally.
.LP
-POSIX.1-2001 requires that \fIkill(\-1,sig)\fP send \fIsig\fP
-to all processes that the current process may send signals to,
+POSIX.1 requires that \fIkill(\-1,sig)\fP send \fIsig\fP
+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
-\fIkill(\-1,sig)\fP does not signal the current process.
+\fIkill(\-1,sig)\fP does not signal the calling process.
.LP
-POSIX.1-2001 requires that if a process sends a signal to itself,
+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 \fIsigwait\fP(3), at least one
+has it unblocked or is waiting for it in
+.BR sigwait (3),
+at least one
unblocked signal must be delivered to the sending thread before the
-\fIkill\fP().
-.SH 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,
.BR kill ()
-failed with the error
-.B EPERM
-if the caller did have permission to send the signal to \fIany\fP (rather
-than \fIall\fP) 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.
-.SH "LINUX HISTORY"
+returns.
+.SS 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 the 0.* kernels things chopped and changed quite
.\" a bit - MTK, 24 Jul 02
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.
+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 receiver.
-The current rules, which conform to POSIX.1-2001, were adopted
+user ID of the target.
+The current rules, which conform to POSIX.1, were adopted
in kernel 1.3.78.
-.SH "CONFORMING TO"
-SVr4, 4.3BSD, POSIX.1-2001
-.SH "SEE ALSO"
+.SH 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,
+.BR kill ()
+failed with the error
+.B EPERM
+if the caller did not have permission to send the signal to \fIany\fP (rather
+than \fIall\fP) 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.
+.SH SEE ALSO
.BR _exit (2),
.BR killpg (2),
.BR signal (2),
-.BR sigqueue (2),
.BR tkill (2),
.BR exit (3),
+.BR sigqueue (3),
.BR capabilities (7),
+.BR credentials (7),
.BR signal (7)
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