sleep man page

sleep — sleep for a specified number of seconds


#include <unistd.h>

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.

Return Value

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).

Interface Attribute Value
sleep() Thread safety MT-Unsafe sig:SIGCHLD/linux

Conforming to

POSIX.1-2001, POSIX.1-2008.


On Linux, sleep() is implemented via nanosleep(2). See the nanosleep(2) man page for a discussion of the clock used.

Portability notes

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.

See Also

sleep(1), alarm(2), nanosleep(2), signal(2), signal(7)


This page is part of release 4.10 of the Linux man-pages project. A description of the project, information about reporting bugs, and the latest version of this page, can be found at

Referenced By

aio(7), alarm(2), clock_nanosleep(2), dnscap(1), dskutil(1), explain(1), explain(3), explain_sleep(3), explain_sleep_or_die(3), getitimer(2), nanosleep(2), pth(3), pthsem(3), signal(7), signal-safety(7), sleep(1), stress-ng(1), time(7), ualarm(3), upslog(8), usleep(3).

2017-03-13 GNU Linux Programmer's Manual