alarm - set an alarm clock for delivery of a signal
#include <unistd.h>
unsigned int alarm(unsigned int seconds);
alarm() returns the number of seconds remaining until any previously scheduled alarm was due to be delivered, or zero if there was no previously scheduled alarm.
gettimeofday(2), pause(2), select(2), setitimer(2), sigaction(2), signal(2), timer_create(2), timerfd_create(2), sleep(3), time(7)