sigset_t newmask;
struct sigaction sa;

sa.sa_handler= handler;   //handler is name of subroutine
sigfillset(&sa.sa_mask);  //set up to block all signals
sigdelset(&sa.sa_mask, SIGPIPE); // allow SIGPIPE to interrupt handler
                                // normally not done
                                // allowing this is non-typical
sa.sa_flags =0;
sigaction(SIGUSR1, &sa, NULL);