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SLEEP(3) Linux Programmer's Manual SLEEP(3)

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.

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

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.

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.

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

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2017-09-15 GNU