kill.2: Clarify the meaning if sig==0

[thirdparty/man-pages.git] / man2 / kill.2

diff --git a/man2/kill.2 b/man2/kill.2
index b5fa14c32a2d64ad66e0b74bbd40dd7278eb149d..acd53fe47a188af7a0182f738b6ac113e65ab6a1 100644 (file)
--- a/man2/kill.2
+++ b/man2/kill.2
@@ -1,7 +1,6 @@
-.\" 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.
@@ -21,6 +20,7 @@
 .\"
 .\" 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>
@@ -41,7 +41,7 @@
 .\" Modified 2004-06-24 by aeb
 .\" Modified, 2004-11-30, after idea from emmanuel.colbus@ensimag.imag.fr
 .\"
-.TH KILL 2 2008-04-18 "Linux" "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
@@ -58,8 +58,10 @@ Feature Test Macro Requirements for glibc (see
 .BR feature_test_macros (7)):
 .in
 .sp
+.ad l
 .BR kill ():
-_POSIX_C_SOURCE || _XOPEN_SOURCE
+_POSIX_C_SOURCE
+.ad b
 .SH DESCRIPTION
 The
 .BR kill ()
@@ -79,10 +81,10 @@ except for process 1 (\fIinit\fP), but see below.
 If \fIpid\fP is less than \-1, then \fIsig\fP is sent to every process
 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.
+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
@@ -94,7 +96,8 @@ 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
@@ -115,8 +118,8 @@ a process which already committed termination, but
 has not yet been
 .BR wait (2)ed
 for.
-.SH "CONFORMING TO"
-SVr4, 4.3BSD, POSIX.1-2001.
+.SH CONFORMING TO
+POSIX.1-2001, POSIX.1-2008, SVr4, 4.3BSD.
 .SH NOTES
 The only signals that can be sent to process ID 1, the
 .I init
@@ -126,33 +129,34 @@ has explicitly installed signal handlers.
 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
+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 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
 .BR sigwait (3),
 at least one
 unblocked signal must be delivered to the sending thread before the
-.BR kill ().
-.SS "Linux Notes"
+.BR kill ()
+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 BUGS
 In 2.6 kernels up to and including 2.6.7,
@@ -160,17 +164,17 @@ 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
+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"
+.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)