SIGBLOCK(3) | Library Functions Manual | SIGBLOCK(3)

# NAME

`sigblock`, `sigmask` — block signals

# SYNOPSIS

`#include <signal.h>`

int
`sigblock`(int mask);

int
`sigmask`(int signum);

# DESCRIPTION

This interface is made obsolete by sigprocmask(2).

`sigblock`() adds the signals specified in mask to the set of signals currently being blocked from delivery. Signals are blocked if the corresponding bit in mask is a 1; the macro `sigmask`() is provided to construct the mask for a given signum.

It is not possible to block `SIGKILL` or `SIGSTOP`; this restriction is silently imposed by the system.

# RETURN VALUES

The previous set of masked signals is returned.

# EXAMPLES

The following example utilizing `sigblock`():

    int omask;

    omask = sigblock(sigmask(SIGINT) | sigmask(SIGHUP));

Becomes:

    sigset_t set, oset;

    sigemptyset(&set);
    sigaddset(&set, SIGINT);
    sigaddset(&set, SIGHUP);
    sigprocmask(SIG_BLOCK, &set, &oset);

Another use of `sigblock`() is to get the current set of masked signals without changing what is actually blocked. Instead of:

    int set;

    set = sigblock(0);

Use the following:

    sigset_t set;

    sigprocmask(SIG_BLOCK, NULL, &set);

# SEE ALSO

kill(2), sigaction(2), sigprocmask(2), sigaddset(3), sigsetmask(3)

# HISTORY

A `sigblock`() system call first appeared in 4.2BSD. In 4.3BSD-Reno, it was reimplemented as a wrapper around sigprocmask(2). The old system call was kept for compatibility until OpenBSD 4.9.

December 13, 2022 | Debian