sigset(3)

NAME

sigset, sighold, sigrelse, sigignore - System V signal API

SYNOPSIS

#define _XOPEN_SOURCE 500
#include <signal.h>
typedef void (*sighandler_t)(int);
sighandler_t sigset(int sig, sighandler_t disp);
int sighold(int sig);
int sigrelse(int sig);
int sigignore(int sig);

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 This API is obsolete: new applications should use the POSIX signal API (sigaction(2), sigprocmask(2), etc.)

The sigset() function modifies the disposition of the signal sig. The disp argument can be the address of a signal handler function, or one of the following constants:

SIG_DFL

Reset the disposition of sig to the default.

SIG_IGN

Ignore sig.

SIG_HOLD

Add sig to the process's signal mask, but leave the disposition of sig unchanged.

If disp specifies the address of a signal handler, then sig is added to the process's signal mask during execution of the handler.

If disp was specified as a value other than SIG_HOLD, then sig is removed from the process's signal mask.

The dispositions for SIGKILL and SIGSTOP cannot be changed.

The sighold() function adds sig to the calling process's signal mask.

The sigrelse() function removes sig from the calling process's signal mask.

The sigignore() function sets the disposition of sig to SIG_IGN.

RETURN VALUE

On success, sigset() returns SIG_HOLD if sig was blocked before the call, or the signal's previous disposition if it was not blocked before the call. On error, sigset() returns -1, with errno set to indicate the error. (But see BUGS below.)

The sighold(), sigrelse(), and sigignore() functions return 0 on success; on error, these functions return -1 and set errno to indicate the error.

ERRORS

For sigset() see the ERRORS under sigaction(2) and sigprocmask(2).

For sighold() and sigrelse() see the ERRORS under sigprocmask(2).

For sigignore(), see the errors under sigaction(2).

CONFORMING TO

SVr4, POSIX.1-2001. These functions are obsolete: do not use them in new programs. POSIX.1-2008 marks sighold(), sigignore(), sigpause(), sigrelse(), and sigset() as obsolete, recommending the use of sigaction(2), sigprocmask(2), pthread_sigmask(3), and sigsuspend(2) instead.

NOTES

These functions appeared in glibc version 2.1.

The sighandler_t type is a GNU extension; it is only used on this page to make the sigset() prototype more easily readable.

The sigset() function provides reliable signal handling semantics (as when calling sigaction(2) with sa_mask equal to 0).

On System V, the signal() function provides unreliable semantics (as when calling sigaction(2) with sa_mask equal to SA_RESETHAND | SA_NODEFER). On BSD, signal() provides reliable semantics. POSIX.1-2001 leaves these aspects of signal() unspecified. See signal(2) for further details.