+++ /dev/null
-.\" Copyright (c) 2000 Andries Brouwer <aeb@cwi.nl>
-.\" and Copyright (c) 2007 Michael Kerrisk <mtk.manpages@gmail.com>
-.\" and Copyright (c) 2008, Linux Foundation, written by Michael Kerrisk
-.\" <mtk.manpages@gmail.com>
-.\" based on work by Rik Faith <faith@cs.unc.edu>
-.\" and Mike Battersby <mike@starbug.apana.org.au>.
-.\"
-.\" %%%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.
-.\"
-.\" Permission is granted to copy and distribute modified versions of this
-.\" manual under the conditions for verbatim copying, provided that the
-.\" entire resulting derived work is distributed under the terms of a
-.\" permission notice identical to this one.
-.\"
-.\" Since the Linux kernel and libraries are constantly changing, this
-.\" manual page may be incorrect or out-of-date. The author(s) assume no
-.\" responsibility for errors or omissions, or for damages resulting from
-.\" the use of the information contained herein. The author(s) may not
-.\" have taken the same level of care in the production of this manual,
-.\" which is licensed free of charge, as they might when working
-.\" professionally.
-.\"
-.\" Formatted or processed versions of this manual, if unaccompanied by
-.\" the source, must acknowledge the copyright and authors of this work.
-.\" %%%LICENSE_END
-.\"
-.\" Modified 2004-11-19, mtk:
-.\" added pointer to sigaction.2 for details of ignoring SIGCHLD
-.\" 2007-06-03, mtk: strengthened portability warning, and rewrote
-.\" various sections.
-.\" 2008-07-11, mtk: rewrote and expanded portability discussion.
-.\"
-.TH SIGNAL 2 2014-08-19 "Linux" "Linux Programmer's Manual"
-.SH NAME
-signal \- ANSI C signal handling
-.SH SYNOPSIS
-.B #include <signal.h>
-.sp
-.B typedef void (*sighandler_t)(int);
-.sp
-.BI "sighandler_t signal(int " signum ", sighandler_t " handler );
-.SH DESCRIPTION
-The behavior of
-.BR signal ()
-varies across UNIX versions,
-and has also varied historically across different versions of Linux.
-\fBAvoid its use\fP: use
-.BR sigaction (2)
-instead.
-See \fIPortability\fP below.
-
-.BR signal ()
-sets the disposition of the signal
-.I signum
-to
-.IR handler ,
-which is either
-.BR SIG_IGN ,
-.BR SIG_DFL ,
-or the address of a programmer-defined function (a "signal handler").
-
-If the signal
-.I signum
-is delivered to the process, then one of the following happens:
-.TP 3
-*
-If the disposition is set to
-.BR SIG_IGN ,
-then the signal is ignored.
-.TP
-*
-If the disposition is set to
-.BR SIG_DFL ,
-then the default action associated with the signal (see
-.BR signal (7))
-occurs.
-.TP
-*
-If the disposition is set to a function,
-then first either the disposition is reset to
-.BR SIG_DFL ,
-or the signal is blocked (see \fIPortability\fP below), and then
-.I handler
-is called with argument
-.IR signum .
-If invocation of the handler caused the signal to be blocked,
-then the signal is unblocked upon return from the handler.
-.PP
-The signals
-.B SIGKILL
-and
-.B SIGSTOP
-cannot be caught or ignored.
-.SH RETURN VALUE
-.BR signal ()
-returns the previous value of the signal handler, or
-.B SIG_ERR
-on error.
-In the event of an error,
-.I errno
-is set to indicate the cause.
-.SH ERRORS
-.TP
-.B EINVAL
-.I signum
-is invalid.
-.SH CONFORMING TO
-C89, C99, POSIX.1-2001.
-.SH NOTES
-The effects of
-.BR signal ()
-in a multithreaded process are unspecified.
-.PP
-According to POSIX, the behavior of a process is undefined after it
-ignores a
-.BR SIGFPE ,
-.BR SIGILL ,
-or
-.B SIGSEGV
-signal that was not generated by
-.BR kill (2)
-or
-.BR raise (3).
-Integer division by zero has undefined result.
-On some architectures it will generate a
-.B SIGFPE
-signal.
-(Also dividing the most negative integer by \-1 may generate
-.BR SIGFPE .)
-Ignoring this signal might lead to an endless loop.
-.PP
-See
-.BR sigaction (2)
-for details on what happens when
-.B SIGCHLD
-is set to
-.BR SIG_IGN .
-.PP
-See
-.BR signal (7)
-for a list of the async-signal-safe functions that can be
-safely called from inside a signal handler.
-.PP
-The use of
-.I sighandler_t
-is a GNU extension, exposed if
-.B _GNU_SOURCE
-is defined;
-.\" libc4 and libc5 define
-.\" .IR SignalHandler ;
-glibc also defines (the BSD-derived)
-.I sig_t
-if
-.B _BSD_SOURCE
-is defined.
-Without use of such a type, the declaration of
-.BR signal ()
-is the somewhat harder to read:
-.in +4n
-.nf
-
-.BI "void ( *" signal "(int " signum ", void (*" handler ")(int)) ) (int);"
-.fi
-.in
-.SS Portability
-The only portable use of
-.BR signal ()
-is to set a signal's disposition to
-.BR SIG_DFL
-or
-.BR SIG_IGN .
-The semantics when using
-.BR signal ()
-to establish a signal handler vary across systems
-(and POSIX.1 explicitly permits this variation);
-.B do not use it for this purpose.
-
-POSIX.1 solved the portability mess by specifying
-.BR sigaction (2),
-which provides explicit control of the semantics when a
-signal handler is invoked; use that interface instead of
-.BR signal ().
-
-In the original UNIX systems, when a handler that was established using
-.BR signal ()
-was invoked by the delivery of a signal,
-the disposition of the signal would be reset to
-.BR SIG_DFL ,
-and the system did not block delivery of further instances of the signal.
-This is equivalent to calling
-.BR sigaction (2)
-with the following flags:
-
- sa.sa_flags = SA_RESETHAND | SA_NODEFER;
-
-System\ V also provides these semantics for
-.BR signal ().
-This was bad because the signal might be delivered again
-before the handler had a chance to reestablish itself.
-Furthermore, rapid deliveries of the same signal could
-result in recursive invocations of the handler.
-
-BSD improved on this situation, but unfortunately also
-changed the semantics of the existing
-.BR signal ()
-interface while doing so.
-On BSD, when a signal handler is invoked,
-the signal disposition is not reset,
-and further instances of the signal are blocked from
-being delivered while the handler is executing.
-Furthermore, certain blocking system calls are automatically
-restarted if interrupted by a signal handler (see
-.BR signal (7)).
-The BSD semantics are equivalent to calling
-.BR sigaction (2)
-with the following flags:
-
- sa.sa_flags = SA_RESTART;
-
-The situation on Linux is as follows:
-.IP * 2
-The kernel's
-.BR signal ()
-system call provides System\ V semantics.
-.IP *
-By default, in glibc 2 and later, the
-.BR signal ()
-wrapper function does not invoke the kernel system call.
-Instead, it calls
-.BR sigaction (2)
-using flags that supply BSD semantics.
-This default behavior is provided as long as the
-.B _BSD_SOURCE
-feature test macro is defined.
-By default,
-.B _BSD_SOURCE
-is defined;
-it is also implicitly defined if one defines
-.BR _GNU_SOURCE ,
-and can of course be explicitly defined.
-.IP *
-On glibc 2 and later, if the
-.B _BSD_SOURCE
-feature test macro is not defined, then
-.BR signal ()
-provides System\ V semantics.
-(The default implicit definition of
-.B _BSD_SOURCE
-is not provided if one invokes
-.BR gcc (1)
-in one of its standard modes
-.RI ( -std=xxx " or " -ansi )
-or defines various other feature test macros such as
-.BR _POSIX_SOURCE ,
-.BR _XOPEN_SOURCE ,
-or
-.BR _SVID_SOURCE ;
-see
-.BR feature_test_macros (7).)
-.\"
-.\" System V semantics are also provided if one uses the separate
-.\" .BR sysv_signal (3)
-.\" function.
-.\" .IP *
-.\" The
-.\" .BR signal ()
-.\" function in Linux libc4 and libc5 provide System\ V semantics.
-.\" If one on a libc5 system includes
-.\" .I <bsd/signal.h>
-.\" instead of
-.\" .IR <signal.h> ,
-.\" then
-.\" .BR signal ()
-.\" provides BSD semantics.
-.SH SEE ALSO
-.BR kill (1),
-.BR alarm (2),
-.BR kill (2),
-.BR killpg (2),
-.BR pause (2),
-.BR sigaction (2),
-.BR signalfd (2),
-.BR sigpending (2),
-.BR sigprocmask (2),
-.BR sigsuspend (2),
-.BR bsd_signal (3),
-.BR raise (3),
-.BR siginterrupt (3),
-.BR sigqueue (3),
-.BR sigsetops (3),
-.BR sigvec (3),
-.BR sysv_signal (3),
-.BR signal (7)
-.SH COLOPHON
-This page is part of release 3.79 of the Linux
-.I man-pages
-project.
-A description of the project,
-information about reporting bugs,
-and the latest version of this page,
-can be found at
-\%http://www.kernel.org/doc/man\-pages/.
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