'\" t
.\" Copyright (c) 2007 Michael Kerrisk <mtk.manpages@gmail.com>
.\"
.\" SPDX-License-Identifier: Linux-man-pages-copyleft
.\"
.TH sysv_signal 3 2023-07-20 "Linux man-pages 6.05.01"
.SH NAME
sysv_signal \- signal handling with System V semantics
.SH LIBRARY
Standard C library
.RI ( libc ", " \-lc )
.SH SYNOPSIS
.nf
.BR "#define _GNU_SOURCE" "         /* See feature_test_macros(7) */"
.B #include <signal.h>
.PP
.B typedef void (*sighandler_t)(int);
.PP
.BI "sighandler_t sysv_signal(int " signum ", sighandler_t " handler );
.fi
.SH DESCRIPTION
The
.BR sysv_signal ()
function takes the same arguments, and performs the same task, as
.BR signal (2).
.PP
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 ATTRIBUTES
For an explanation of the terms used in this section, see
.BR attributes (7).
.TS
allbox;
lbx lb lb
l l l.
Interface	Attribute	Value
T{
.na
.nh
.BR sysv_signal ()
T}	Thread safety	MT-Safe
.TE
.sp 1
.SH VERSIONS
Use of
.BR sysv_signal ()
should be avoided; use
.BR sigaction (2)
instead.
.PP
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.
.PP
The use of
.I sighandler_t
is a GNU extension;
this type is defined only if
the
.B _GNU_SOURCE
feature test macro is defined.
.SH STANDARDS
None.
.SH SEE ALSO
.BR sigaction (2),
.BR signal (2),
.BR bsd_signal (3),
.BR signal (7)