---
name: "usleep"
section: "3"
platform: "linux"
package: "man-pages"
version: "6.19-1"
release: "Arch Linux 2026-11-01"
platforms: ["linux", "freebsd", "macos"]
url: "https://new.carta.tech/usleep"
---

# usleep(3)

suspend execution for microsecond intervals

## NAME

usleep - suspend execution for microsecond intervals

## LIBRARY

Standard C library (*libc*, *-lc*)

## SYNOPSIS

```
#include <unistd.h>
```

**int usleep(useconds\_t** *usec***);**

Feature Test Macro Requirements for glibc (see [**feature\_test\_macros**(7)](/feature_test_macros/7.md)):

**usleep**():

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

## DESCRIPTION

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 error.

## ERRORS

- **EINTR**

  Interrupted by a signal; see [**signal**(7)](/signal/7.md).

- **EINVAL**

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

## ATTRIBUTES

For an explanation of the terms used in this section, see [**attributes**(7)](/attributes/7.md).

| | | |
| --- | --- | --- |
| **Interface** | **Attribute** | **Value** |
| **usleep**() | Thread safety | MT-Safe |

## STANDARDS

None.

## HISTORY

4\.3BSD, POSIX.1-2001. POSIX.1-2001 declares it obsolete, suggesting [**nanosleep**(2)](/nanosleep/2.md) instead. Removed in POSIX.1-2008.

On the original BSD implementation, and before glibc 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.

## CAVEATS

The interaction of this function with the **SIGALRM** signal, and with other timer functions such as [**alarm**(2)](/alarm/2.md), [**sleep**(3)](/sleep/3.md), [**nanosleep**(2)](/nanosleep/2.md), [**setitimer**(2)](/setitimer/2.md), [**timer\_create**(2)](/timer_create/2.md), [**timer\_delete**(2)](/timer_delete/2.md), [**timer\_getoverrun**(2)](/timer_getoverrun/2.md), [**timer\_gettime**(2)](/timer_gettime/2.md), [**timer\_settime**(2)](/timer_settime/2.md), [**ualarm**(3)](/ualarm/3.md) is unspecified.

## SEE ALSO

[**alarm**(2)](/alarm/2.md), [**getitimer**(2)](/getitimer/2.md), [**nanosleep**(2)](/nanosleep/2.md), [**select**(2)](/select/2.md), [**setitimer**(2)](/setitimer/2.md), [**sleep**(3)](/sleep/3.md), [**ualarm**(3)](/ualarm/3.md), [**useconds\_t**(3type)](/useconds_t/3type.md), [**time**(7)](/time/7.md)