int sigprocmask(int how, const sigset_t *set, sigset_t *oset);- Indicates how a signal should be modified
SIG_BLOCK: add to currently blockedSIG_UNBLOCK: delete from currently blockedSIG_SETMASK: set collection of signals from being blocked
int sigprocmask(int how, const sigset_t *set, sigset_t *oset);SIG_BLOCK: add to currently blockedSIG_UNBLOCK: delete from currently blockedSIG_SETMASK: set collection of signals from being blocked