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NAME
sighold, sigignore, sigpause, sigrelse, sigset — signal management
SYNOPSIS
#include <signal.h>
int sighold(int sig);
int sigignore(int sig);
int sigpause(int sig);
int sigrelse(int sig);
void (*sigset(int sig, void (*disp)(int)))(int);
DESCRIPTION
Use of any of these functions is unspecified in a multi-threaded process.
The sighold(), sigignore(), sigpause(), sigrelse(), and sigset() functions provide
simplified signal management.
The sigset() function shall modify signal dispositions. The sig argument specifies the
signal, which may be any signal except SIGKILL and SIGSTOP. The disp argument specifies
the signal's disposition, which may be SIG_DFL, SIG_IGN, or the address of a signal
handler. If sigset() is used, and disp is the address of a signal handler, the system
shall add 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 sigset()
is used, and disp is equal to SIG_HOLD, sig shall be added to the signal mask of the
calling process and sig's disposition shall remain unchanged. If sigset() is used, and
disp is not equal to SIG_HOLD, sig shall be removed from the signal mask of the calling
process.
The sighold() function shall add sig to the signal mask of the calling process.
The sigrelse() function shall remove sig from the signal mask of the calling process.
The sigignore() function shall set the disposition of sig to SIG_IGN.
The sigpause() function shall remove sig from the signal mask of the calling process and
suspend the calling process until a signal is received. The sigpause() function shall
restore the signal mask of the process to its original state before returning.
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 wait(), waitid(), and waitpid() shall fail and set errno to
[ECHILD].
RETURN VALUE
Upon successful completion, sigset() 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 errno set to indicate the error.
The sigpause() function shall suspend execution of the thread until a signal is received,
whereupon it shall return −1 and set errno to [EINTR].
For all other functions, upon successful completion, 0 shall be returned. Otherwise, −1
shall be returned and errno set to indicate the error.
ERRORS
These functions shall fail if:
EINVAL The sig argument is an illegal signal number.
The sigset() and sigignore() functions shall fail if:
EINVAL An attempt is made to catch a signal that cannot be caught, or to ignore a signal
that cannot be ignored.
The following sections are informative.
EXAMPLES
None.
APPLICATION USAGE
The sigaction() function provides a more comprehensive and reliable mechanism for
controlling signals; new applications should use the sigaction() function instead of the
obsolescent sigset() function.
The sighold() function, in conjunction with sigrelse() or sigpause(), may be used to
establish critical regions of code that require the delivery of a signal to be temporarily
deferred. For broader portability, the pthread_sigmask() or sigprocmask() functions should
be used instead of the obsolescent sighold() and sigrelse() functions.
For broader portability, the sigsuspend() function should be used instead of the
obsolescent sigpause() function.
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 sigprocmask(), which is replaced by
pthread_sigmask()). The sigset() function can be implemented as a simple wrapper for
sigaction(). The sighold() function is equivalent to sigprocmask() or pthread_sigmask()
with SIG_BLOCK set. The sigignore() function is equivalent to sigaction() with SIG_IGN
set. The sigpause() function is equivalent to sigsuspend(). The sigrelse() function is
equivalent to sigprocmask() or pthread_sigmask() with SIG_UNBLOCK set.
FUTURE DIRECTIONS
These functions may be removed in a future version.
SEE ALSO
Section 2.4, Signal Concepts, exec, pause(), pthread_sigmask(), sigaction(), signal(),
sigsuspend(), wait(), waitid()
The Base Definitions volume of POSIX.1‐2008, <signal.h>
COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form from IEEE Std
1003.1, 2013 Edition, Standard for Information Technology -- Portable Operating System
Interface (POSIX), The Open Group Base Specifications Issue 7, Copyright (C) 2013 by the
Institute of Electrical and Electronics Engineers, Inc and The Open Group. (This is
POSIX.1-2008 with the 2013 Technical Corrigendum 1 applied.) 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.unix.org/online.html .
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 .