sleep —
suspend process execution for interval of seconds
Standard C Library (libc, -lc)
#include <unistd.h>
unsigned int
  
  sleep(unsigned
    int seconds);
The sleep() function suspends execution of the calling
  process until either the number of seconds specified by
  seconds have elapsed or a signal is delivered to the
  calling process and its action is to invoke a signal-catching function or to
  terminate the process. The suspension time may be longer than requested due to
  the scheduling of other activity by the system.
If the sleep() function returns because the requested
  time has elapsed, the value returned will be zero. If the
  sleep() function returns due to the delivery of a
  signal, the value returned will be the unslept amount (the request time minus
  the time actually slept) in seconds.
The sleep() function conforms to IEEE
  Std 1003.1-1990 (“POSIX.1”).
A sleep() function appeared in
  Version 7 AT&T UNIX.