sleep(3) — Linux manual page

sleep(3)                 Library Functions Manual                sleep(3)

NAME         top

       sleep - sleep for a specified number of seconds

LIBRARY         top

       Standard C library (libc, -lc)

SYNOPSIS         top

       #include <unistd.h>

       unsigned int sleep(unsigned int seconds);

DESCRIPTION         top

       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         top

       Zero if the requested time has elapsed, or the number of seconds
       left to sleep, if the call was interrupted by a signal handler.

ATTRIBUTES         top

       For an explanation of the terms used in this section, see
       attributes(7).
       ┌──────────────────┬───────────────┬─────────────────────────────┐
       │ Interface        │ Attribute     │ Value                       │
       ├──────────────────┼───────────────┼─────────────────────────────┤
       │ sleep()          │ Thread safety │ MT-Unsafe sig:SIGCHLD/linux │
       └──────────────────┴───────────────┴─────────────────────────────┘

VERSIONS         top

       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.

STANDARDS         top

       POSIX.1-2008.

HISTORY         top

       POSIX.1-2001.

CAVEATS         top

       Using longjmp(3) from a signal handler or modifying the handling
       of SIGALRM while sleeping will cause undefined results.

SEE ALSO         top

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

COLOPHON         top

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Linux man-pages 6.15            2025-05-17                       sleep(3)

Pages that refer to this page: sleep(1),  alarm(2),  clock_nanosleep(2),  getitimer(2),  nanosleep(2),  ualarm(3),  usleep(3),  signal(7),  signal-safety(7),  time(7)

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