SLEEP(3) BSD Programmer's Manual SLEEP(3)
sleep - suspend process execution for interval of seconds
#include <unistd.h> unsigned int sleep(unsigned int seconds);
The sleep() function suspends execution of the calling process until ei- ther 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 sys- tem. This function is implemented using nanosleep(2); it requires one system call each time it is invoked. A similar but less compatible function can be obtained with a single select(2); such a function would not restart after signals, and also does not interfere with other uses of setitimer(2) (not that sleep() interferes with interval timers anymore).
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.
nanosleep(2), select(2), setitimer(2), sigaction(2), sigsuspend(2), alarm(3), pause(3), usleep(3)
The sleep() function conforms to IEEE Std 1003.1-1990 ("POSIX.1").
A sleep() function appeared in Version 7 AT&T UNIX. MirBSD #10-current June 4, 1993 1