SLEEP(3) Linux Programmers Manual SLEEP(3)
sleep - Sleep for the specified number of seconds
unsigned int sleep(unsigned int seconds);
sleep() makes the calling process sleep until seconds seconds have
elapsed or 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.
sleep() may be implemented using SIGALRM; 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.
alarm(2), signal(2), signal(7)
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GNU 2008-07-04 SLEEP(3)