usleep(3) — Linux manual page


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

NAME         top

       usleep - suspend execution for microsecond intervals

SYNOPSIS         top

       #include <unistd.h>

       int usleep(useconds_t usec);

   Feature Test Macro Requirements for glibc (see feature_test_macros(7)):

           Since glibc 2.12:
               (_XOPEN_SOURCE >= 500) && ! (_POSIX_C_SOURCE >= 200809L)
                   || /* Glibc since 2.19: */ _DEFAULT_SOURCE
                   || /* Glibc versions <= 2.19: */ _BSD_SOURCE
           Before glibc 2.12:
               _BSD_SOURCE || _XOPEN_SOURCE >= 500

DESCRIPTION         top

       The usleep() function suspends execution of the calling thread for
       (at least) usec microseconds.  The sleep may be lengthened slightly
       by any system activity or by the time spent processing the call or by
       the granularity of system timers.

RETURN VALUE         top

       The usleep() function returns 0 on success.  On error, -1 is
       returned, with errno set to indicate the cause of the error.

ERRORS         top

       EINTR  Interrupted by a signal; see signal(7).

       EINVAL usec is greater than or equal to 1000000.  (On systems where
              that is considered an error.)

ATTRIBUTES         top

       For an explanation of the terms used in this section, see

       │Interface Attribute     Value   │
       │usleep()  │ Thread safety │ MT-Safe │

CONFORMING TO         top

       4.3BSD, POSIX.1-2001.  POSIX.1-2001 declares this function obsolete;
       use nanosleep(2) instead.  POSIX.1-2008 removes the specification of

       On the original BSD implementation, and in glibc before version
       2.2.2, the return type of this function is void.  The POSIX version
       returns int, and this is also the prototype used since glibc 2.2.2.

       Only the EINVAL error return is documented by SUSv2 and POSIX.1-2001.

NOTES         top

       The type useconds_t is an unsigned integer type capable of holding
       integers in the range [0,1000000].  Programs will be more portable if
       they never mention this type explicitly.  Use

           #include <unistd.h>
               unsigned int usecs;

       The interaction of this function with the SIGALRM signal, and with
       other timer functions such as alarm(2), sleep(3), nanosleep(2),
       setitimer(2), timer_create(2), timer_delete(2), timer_getoverrun(2),
       timer_gettime(2), timer_settime(2), ualarm(3) is unspecified.

SEE ALSO         top

       alarm(2), getitimer(2), nanosleep(2), select(2), setitimer(2),
       sleep(3), ualarm(3), time(7)

COLOPHON         top

       This page is part of release 5.09 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

                                 2017-09-15                        USLEEP(3)

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