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.\" Copyright (c) 2007 Michael Kerrisk <mtk.manpages@gmail.com>
.\"
.\" 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.
.\"
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.\" manual under the conditions for verbatim copying, provided that the
.\" entire resulting derived work is distributed under the terms of a
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.\"
.\" 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.\" manual page may be incorrect or out-of-date.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.
.\"
.TH SYSV_SIGNAL 3 2007-05-04 "" "Linux Programmer's Manual"
.SH NAME
sysv_signal \- signal handling with System V semantics
.SH SYNOPSIS
.BR "#define _GNU_SOURCE" "         /* See feature_test_macros(7) */"
.br
.B #include <signal.h>
.sp
.B typedef void (*sighandler_t)(int);
.sp
.BI "sighandler_t sysv_signal(int " signum ", sighandler_t " handler );
.SH DESCRIPTION
The
.BR sysv_signal ()
function takes the same arguments, and performs the same task, as
.BR signal (2).

However
.BR sysv_signal ()
provides the System V unreliable signal semantics, that is:
a) the disposition of the signal is reset to the default
when the handler is invoked;
b) delivery of further instances of the signal is not blocked while
the signal handler is executing; and
c) if the handler interrupts (certain) blocking system calls,
then the system call is not automatically restarted.
.SH RETURN VALUE
The
.BR sysv_signal ()
function returns the previous value of the signal handler, or
.B SIG_ERR
on error.
.SH ERRORS
As for
.BR signal (2).
.SH CONFORMING TO
This function is nonstandard.
.SH NOTES
Use of
.BR sysv_signal ()
should be avoided; use
.BR sigaction (2)
instead.

On older Linux systems,
.BR sysv_signal ()
and
.BR signal (2)
were equivalent.
But on newer systems,
.BR signal (2)
provides reliable signal semantics; see
.BR signal (2)
for details.

The use of
.I sighandler_t
is a GNU extension;
this type is only defined if
the
.B _GNU_SOURCE
feature test macro is defined.
.SH SEE ALSO
.BR sigaction (2),
.BR signal (2),
.BR bsd_signal (3),
.BR signal (7)