sleep() - suspend process execution for interval of seconds
#include <unistd.h>
u_int sleep (u_int seconds)
The sleep(3) function suspends execution of the calling process for at least seconds of time, or until a signal is delivered to the calling process which invokes a signal-catching function or terminates the process. System activity or time spent in processing the call may lengthen the sleep.
sleep(3) returns 0 if its sleep was completed, or it returns the number of seconds left unslept if it was interrupted by a signal.