'\" t
.\" Copyright (c) 2005 by Michael Kerrisk <mtk.manpages@gmail.com>
.\"
.\" SPDX-License-Identifier: Linux-man-pages-copyleft
.\"
.TH sigset 3 2023-03-30 "Linux man-pages 6.04"
.SH NAME
sigset, sighold, sigrelse, sigignore \- System V signal API
.SH LIBRARY
Standard C library
.RI ( libc ", " \-lc )
.SH SYNOPSIS
.nf
.B #include <signal.h>
.PP
.B typedef void (*sighandler_t)(int);
.PP
.BI "[[deprecated]] sighandler_t sigset(int " sig ", sighandler_t " disp );
.PP
.BI "[[deprecated]] int sighold(int " sig );
.BI "[[deprecated]] int sigrelse(int " sig );
.BI "[[deprecated]] int sigignore(int " sig );
.fi
.PP
.RS -4
Feature Test Macro Requirements for glibc (see
.BR feature_test_macros (7)):
.RE
.PP
.BR sigset (),
.BR sighold (),
.BR sigrelse (),
.BR sigignore ():
.nf
    _XOPEN_SOURCE >= 500
.\"    || _XOPEN_SOURCE && _XOPEN_SOURCE_EXTENDED
.fi
.SH DESCRIPTION
These functions are provided in glibc as a compatibility interface
for programs that make use of the historical System V signal API.
This API is obsolete: new applications should use the POSIX signal API
.RB ( sigaction (2),
.BR sigprocmask (2),
etc.)
.PP
The
.BR sigset ()
function modifies the disposition of the signal
.IR sig .
The
.I disp
argument can be the address of a signal handler function,
or one of the following constants:
.TP
.B SIG_DFL
Reset the disposition of
.I sig
to the default.
.TP
.B SIG_IGN
Ignore
.IR sig .
.TP
.B SIG_HOLD
Add
.I sig
to the process's signal mask, but leave the disposition of
.I sig
unchanged.
.PP
If
.I disp
specifies the address of a signal handler, then
.I sig
is added to the process's signal mask during execution of the handler.
.PP
If
.I disp
was specified as a value other than
.BR SIG_HOLD ,
then
.I sig
is removed from the process's signal mask.
.PP
The dispositions for
.B SIGKILL
and
.B SIGSTOP
cannot be changed.
.PP
The
.BR sighold ()
function adds
.I sig
to the calling process's signal mask.
.PP
The
.BR sigrelse ()
function removes
.I sig
from the calling process's signal mask.
.PP
The
.BR sigignore ()
function sets the disposition of
.I sig
to
.BR SIG_IGN .
.SH RETURN VALUE
On success,
.BR sigset ()
returns
.B SIG_HOLD
if
.I sig
was blocked before the call,
or the signal's previous disposition
if it was not blocked before the call.
On error,
.BR sigset ()
returns \-1, with
.I errno
set to indicate the error.
(But see BUGS below.)
.PP
The
.BR sighold (),
.BR sigrelse (),
and
.BR sigignore ()
functions return 0 on success; on error, these functions return \-1 and set
.I errno
to indicate the error.
.SH ERRORS
For
.BR sigset ()
see the ERRORS under
.BR sigaction (2)
and
.BR sigprocmask (2).
.PP
For
.BR sighold ()
and
.BR sigrelse ()
see the ERRORS under
.BR sigprocmask (2).
.PP
For
.BR sigignore (),
see the errors under
.BR sigaction (2).
.SH ATTRIBUTES
For an explanation of the terms used in this section, see
.BR attributes (7).
.ad l
.nh
.TS
allbox;
lbx lb lb
l l l.
Interface	Attribute	Value
T{
.BR sigset (),
.BR sighold (),
.BR sigrelse (),
.BR sigignore ()
T}	Thread safety	MT-Safe
.TE
.hy
.ad
.sp 1
.SH STANDARDS
POSIX.1-2008.
.TP
.I sighandler_t
GNU.
POSIX.1 uses the same type but without a
.IR typedef .
.SH HISTORY
glibc 2.1.
SVr4, POSIX.1-2001.
POSIX.1-2008 marks these functions
as obsolete, recommending the use of
.BR sigaction (2),
.BR sigprocmask (2),
.BR pthread_sigmask (3),
and
.BR sigsuspend (2)
instead.
.SH NOTES
The
.BR sigset ()
function provides reliable signal handling semantics (as when calling
.BR sigaction (2)
with
.I sa_mask
equal to 0).
.PP
On System V, the
.BR signal ()
function provides unreliable semantics (as when calling
.BR sigaction (2)
with
.I sa_mask
equal to
.IR "SA_RESETHAND | SA_NODEFER" ).
On BSD,
.BR signal ()
provides reliable semantics.
POSIX.1-2001 leaves these aspects of
.BR signal ()
unspecified.
See
.BR signal (2)
for further details.
.PP
In order to wait for a signal,
BSD and System V both provided a function named
.BR sigpause (3),
but this function has a different argument on the two systems.
See
.BR sigpause (3)
for details.
.SH BUGS
Before glibc 2.2,
.BR sigset ()
did not unblock
.I sig
if
.I disp
was specified as a value other than
.BR SIG_HOLD .
.PP
Before glibc 2.5,
.BR sigset ()
does not correctly return the previous disposition of the signal
in two cases.
First, if
.I disp
is specified as
.BR SIG_HOLD ,
then a successful
.BR sigset ()
always returns
.BR SIG_HOLD .
Instead, it should return the previous disposition of the signal
(unless the signal was blocked, in which case
.B SIG_HOLD
should be returned).
Second, if the signal is currently blocked, then
the return value of a successful
.BR sigset ()
should be
.BR SIG_HOLD .
Instead, the previous disposition of the signal is returned.
These problems have been fixed since glibc 2.5.
.\" See http://sourceware.org/bugzilla/show_bug.cgi?id=1951
.SH SEE ALSO
.BR kill (2),
.BR pause (2),
.BR sigaction (2),
.BR signal (2),
.BR sigprocmask (2),
.BR raise (3),
.BR sigpause (3),
.BR sigvec (3),
.BR signal (7)