NAME

sigblock — block signals

LIBRARY

Standard C Library (libc, -lc)

SYNOPSIS

#include <signal.h>

int
sigblock(int mask);

int
sigmask(signum);

DESCRIPTION

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 using 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), sigsetmask(3), sigsetops(3)

HISTORY

The sigblock() function call appeared in 4.2BSD and has been deprecated.