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.TH SYSV_SIGNAL 2 2007-05-04 "" "Linux Programmer's Manual"
.SH NAME
sysv_signal \- signal handling with System V semantics
.SH SYNOPSIS
.B #define _GNU_SOURCE
.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 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
.B sighandler_t
is a GNU extension;
this type is only defined if 
the _GNU_SOURCE feature test macro is defined.
.SH "CONFORMING TO"
This function is non-standard.
.SH "SEE ALSO"
.BR sigaction (2),
.BR signal (2),
.BR bsd_signal (3),
.BR feature_test_macros (7),
.BR signal (7)