Blocking

A global signal mask defines the set of signals that are blocked from being delivered to a process. A process's signal mask copies its initial state from the signal mask of the parent process. The mask can be changed with calls to sigaction(2), sigblock(3B), sigsetmask(3B), sigprocmask(2), sigsetops(3C), sighold(3C), or sigrelse(3C) (see signal(3C)).