'\" et
.TH SIGHOLD "3P" 2017 "IEEE/The Open Group" "POSIX Programmer's Manual"
.\"
.SH PROLOG
This manual page is part of the POSIX Programmer's Manual.
The Linux implementation of this interface may differ (consult
the corresponding Linux manual page for details of Linux behavior),
or the interface may not be implemented on Linux.
.\"
.SH NAME
sighold,
sigignore,
sigpause,
sigrelse,
sigset
\(em signal management
.SH SYNOPSIS
.LP
.nf
#include <signal.h>
.P
int sighold(int \fIsig\fP);
int sigignore(int \fIsig\fP);
int sigpause(int \fIsig\fP);
int sigrelse(int \fIsig\fP);
void (*sigset(int \fIsig\fP, void (*\fIdisp\fP)(int)))(int);
.fi
.SH DESCRIPTION
Use of any of these functions is unspecified in a multi-threaded
process.
.P
The
\fIsighold\fR(),
\fIsigignore\fR(),
\fIsigpause\fR(),
\fIsigrelse\fR(),
and
\fIsigset\fR()
functions provide simplified signal management.
.P
The
\fIsigset\fR()
function shall modify signal dispositions. The
.IR sig
argument specifies the signal, which may be any signal except SIGKILL
and SIGSTOP. The
.IR disp
argument specifies the signal's disposition, which may be SIG_DFL,
SIG_IGN, or the address of a signal handler. If
\fIsigset\fR()
is used, and
.IR disp
is the address of a signal handler, the system shall add
.IR sig
to the signal mask of the calling process before executing the signal
handler; when the signal handler returns, the system shall restore the
signal mask of the calling process to its state prior to the delivery
of the signal. In addition, if
\fIsigset\fR()
is used, and
.IR disp
is equal to SIG_HOLD,
.IR sig
shall be added to the
signal mask of the calling process and
.IR sig 's
disposition shall remain unchanged. If
\fIsigset\fR()
is used, and
.IR disp
is not equal to SIG_HOLD,
.IR sig
shall be removed from the signal mask of the calling process.
.P
The
\fIsighold\fR()
function shall add
.IR sig
to the signal mask of the calling process.
.P
The
\fIsigrelse\fR()
function shall remove
.IR sig
from the signal mask of the calling process.
.P
The
\fIsigignore\fR()
function shall set the disposition of
.IR sig
to SIG_IGN.
.P
The
\fIsigpause\fR()
function shall remove
.IR sig
from the signal mask of the calling process and suspend the calling process
until a signal is received. The
\fIsigpause\fR()
function shall restore the signal mask of the process to its original
state before returning.
.P
If the action for the SIGCHLD signal is set to SIG_IGN, child processes
of the
calling processes shall not be transformed into zombie processes when
they terminate. If the calling process subsequently waits for its
children, and the process has no unwaited-for children that were
transformed into zombie processes, it shall block until all of its
children terminate, and
\fIwait\fR(),
\fIwaitid\fR(),
and
\fIwaitpid\fR()
shall fail and set
.IR errno
to
.BR [ECHILD] .
.SH "RETURN VALUE"
Upon successful completion,
\fIsigset\fR()
shall return SIG_HOLD if the signal had been blocked and the signal's
previous disposition if it had not been blocked. Otherwise, SIG_ERR
shall be returned and
.IR errno
set to indicate the error.
.P
The
\fIsigpause\fR()
function shall suspend execution of the thread until a signal is
received, whereupon it shall return \-1 and set
.IR errno
to
.BR [EINTR] .
.P
For all other functions, upon successful completion, 0 shall be returned.
Otherwise, \-1 shall be returned and
.IR errno
set to indicate the error.
.SH ERRORS
These functions shall fail if:
.TP
.BR EINVAL
The
.IR sig
argument is an illegal signal number.
.P
The
\fIsigset\fR()
and
\fIsigignore\fR()
functions shall fail if:
.TP
.BR EINVAL
An attempt is made to catch a signal that cannot be caught, or to
ignore a signal that cannot be ignored.
.LP
.IR "The following sections are informative."
.SH EXAMPLES
None.
.SH "APPLICATION USAGE"
The
\fIsigaction\fR()
function provides a more comprehensive and reliable mechanism for
controlling signals; new applications should use the
\fIsigaction\fR()
function instead of the obsolescent
\fIsigset\fR()
function.
.P
The
\fIsighold\fR()
function, in conjunction with
\fIsigrelse\fR()
or
\fIsigpause\fR(),
may be used to establish critical regions of code that require the
delivery of a signal to be temporarily deferred. For broader
portability, the
\fIpthread_sigmask\fR()
or
\fIsigprocmask\fR()
functions should be used instead of the obsolescent
\fIsighold\fR()
and
\fIsigrelse\fR()
functions.
.P
For broader portability, the
\fIsigsuspend\fR()
function should be used instead of the obsolescent
\fIsigpause\fR()
function.
.SH RATIONALE
Each of these historic functions has a direct analog in the other
functions which are required to be per-thread and thread-safe (aside
from
\fIsigprocmask\fR(),
which is replaced by
\fIpthread_sigmask\fR()).
The
\fIsigset\fR()
function can be implemented as a simple wrapper for
\fIsigaction\fR().
The
\fIsighold\fR()
function is equivalent to
\fIsigprocmask\fR()
or
\fIpthread_sigmask\fR()
with SIG_BLOCK set. The
\fIsigignore\fR()
function is equivalent to
\fIsigaction\fR()
with SIG_IGN set. The
\fIsigpause\fR()
function is equivalent to
\fIsigsuspend\fR().
The
\fIsigrelse\fR()
function is equivalent to
\fIsigprocmask\fR()
or
\fIpthread_sigmask\fR()
with SIG_UNBLOCK set.
.SH "FUTURE DIRECTIONS"
These functions may be removed in a future version.
.SH "SEE ALSO"
.IR "Section 2.4" ", " "Signal Concepts",
.IR "\fIexec\fR\^",
.IR "\fIpause\fR\^(\|)",
.IR "\fIpthread_sigmask\fR\^(\|)",
.IR "\fIsigaction\fR\^(\|)",
.IR "\fIsignal\fR\^(\|)",
.IR "\fIsigsuspend\fR\^(\|)",
.IR "\fIwait\fR\^(\|)",
.IR "\fIwaitid\fR\^(\|)"
.P
The Base Definitions volume of POSIX.1\(hy2017,
.IR "\fB<signal.h>\fP"
.\"
.SH COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.1-2017, Standard for Information Technology
-- Portable Operating System Interface (POSIX), The Open Group Base
Specifications Issue 7, 2018 Edition,
Copyright (C) 2018 by the Institute of
Electrical and Electronics Engineers, Inc and The Open Group.
In the event of any discrepancy between this version and the original IEEE and
The Open Group Standard, the original IEEE and The Open Group Standard
is the referee document. The original Standard can be obtained online at
http://www.opengroup.org/unix/online.html .
.PP
Any typographical or formatting errors that appear
in this page are most likely
to have been introduced during the conversion of the source files to
man page format. To report such errors, see
https://www.kernel.org/doc/man-pages/reporting_bugs.html .