sleep - sleep for a specified number of seconds
unsigned int sleep(unsigned int seconds);
sleep() causes the calling thread to sleep either until the number of
real-time seconds specified in seconds have elapsed or until a signal
arrives which is not ignored.
Zero if the requested time has elapsed, or the number of seconds left to sleep,
if the call was interrupted by a signal handler.
For an explanation of the terms used in this section, see attributes(7).
On Linux, sleep() is implemented via nanosleep(2). See the
nanosleep(2) man page for a discussion of the clock used.
On some systems, sleep() may be implemented using alarm(2) and
SIGALRM (POSIX.1 permits this); mixing calls to alarm(2) and
sleep() is a bad idea.
Using longjmp(3) from a signal handler or modifying the
handling of SIGALRM while sleeping will cause undefined results.
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