| SIGPROCMASK(2) | System Calls Manual | SIGPROCMASK(2) | 
sigprocmask —
#include <signal.h>
int
  
  sigprocmask(int
    how, const sigset_t *
    restrict set, sigset_t *
    restrict oset);
sigprocmask() function examines and/or changes the
  current signal mask (those signals that are blocked from delivery). Signals
  are blocked if they are members of the current signal mask set.
If set is not null, the action of
    sigprocmask() depends on the value of the parameter
    how. The signal mask is changed as a function of the
    specified set and the current mask. The function is
    specified by how using one of the following
  values:
SIG_BLOCKSIG_UNBLOCKSIG_SETMASKIf oset is not null, it is set to the previous value of the signal mask.
When set is null, the value of how is insignificant and the mask remains unset providing a way to examine the signal mask without modification.
The system quietly disallows SIGKILL or
    SIGSTOP to be blocked.
sigprocmask() call will fail and the signal mask
  will be unchanged if one of the following occurs:
EINVAL]sigprocmask() function conforms to
  IEEE Std 1003.1-1990 (“POSIX.1”).
| June 4, 1993 | NetBSD 9.4 |