---
name: "sleep"
section: "3"
platform: "macos"
package: "Libc"
version: "1752.120.2"
release: "macOS 26.5"
platforms: ["linux", "freebsd", "macos"]
url: "https://new.carta.tech/sleep/3"
---

# sleep(3)

suspend thread execution for an interval measured in seconds

## NAME

**sleep** – suspend thread execution for an interval measured in seconds

## LIBRARY

Standard C Library (libc, -lc)

## SYNOPSIS

**#include \<unistd.h\>**

*unsigned* *int*\

**sleep**(*unsigned int seconds*);

## DESCRIPTION

The **sleep**() function suspends execution of the calling thread until either *seconds* seconds have elapsed or a signal is delivered to the thread and its action is to invoke a signal-catching function or to terminate the thread or process. System activity may lengthen the sleep by an indeterminate amount.

This function is implemented using [nanosleep(2)](/nanosleep/2.md) by pausing for *seconds* seconds or until a signal occurs. Consequently, in this implementation, sleeping has no effect on the state of process timers, and there is no special handling for SIGALRM.

## RETURN VALUES

If the **sleep**() function returns because the requested time has elapsed, the value returned will be zero. If the **sleep**() function returns due to the delivery of a signal, the value returned will be the unslept amount (the requested time minus the time actually slept) in seconds.

## SEE ALSO

[nanosleep(2)](/nanosleep/2.md), [usleep(3)](/usleep/3.md)

## STANDARDS

The **sleep**() function conforms to ISO/IEC 9945-1:1990 (“POSIX.1”).

## HISTORY

A **sleep**() function appeared in Version 7 AT&T UNIX.