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.Dd $Mdocdate: March 31 2022 $
.Dt SLEEP 3
.Os
.Sh NAME
.Nm sleep
.Nd suspend execution for an interval of seconds
.Sh SYNOPSIS
.In unistd.h
.Ft unsigned int
.Fn sleep "unsigned int seconds"
.Sh DESCRIPTION
The
.Fn sleep
function suspends execution of the calling thread until at least the
given number of
.Fa seconds
have elapsed or an unmasked signal is delivered to the calling thread.
.Pp
This version of
.Fn sleep
is implemented with
.Xr nanosleep 2 ,
so delivery of any unmasked signal will terminate the sleep early,
even if
.Dv SA_RESTART
is set with
.Xr sigaction 2
for the interrupting signal.
.Sh RETURN VALUES
If
.Fn sleep
sleeps for the full count of
.Fa seconds ,
it returns 0.
Otherwise,
.Fn sleep
returns the number of seconds remaining from the original request.
.Sh ERRORS
The
.Fn sleep
function sets
.Va errno
to
.Dv EINTR
if it is interrupted by the delivery of a signal.
.Sh SEE ALSO
.Xr sleep 1 ,
.Xr nanosleep 2 ,
.Xr sigaction 2
.Sh STANDARDS
The
.Fn sleep
function conforms to
.St -p1003.1-2008 .
.Pp
Setting
.Va errno
is an extension to that specification.
.Sh HISTORY
A
.Fn sleep
system call first appeared in
.At v2 .
In
.At v7 ,
it was removed and replaced by a C library implementation based on
.Xr signal 3
and
.Xr alarm 3 .
For
.Ox 2.1 ,
it was reimplemented as a wrapper around the
.Xr nanosleep 2
system call.