usleep — suspend execution for microsecond intervals


#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


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

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



Interrupted by a signal; see signal(7).


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


For an explanation of the terms used in this section, see attributes(7).

Interface Attribute Value
usleep() Thread safety MT-Safe

Conforming to

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

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.


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

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


This page is part of release 5.04 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

clock_nanosleep(2), cpipe(1), dgenrc(5), free(1), freecolor(1), gawk(1), getitimer(2), nanosleep(2), __ppc_get_timebase(3), pthsem(3), select_tut(2), signal(7), time(7), ualarm(3).

2017-09-15 Linux Programmer's Manual