-extern int sigaction (int sig, sigaction_t * sigact, sigaction_t * osigact);
-extern int sigprocmask (int how, sigset_t *mask, sigset_t *omask);
-extern int sigemptyset (sigset_t *mask);
-extern int sigsuspend (sigset_t *mask);
-extern int sigdelset (sigset_t *mask, int sig);
-extern int sigaddset (sigset_t *mask, int sig);