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.Dd $Mdocdate: February 8 2020 $
.Dt SLEEP 3
.Os
.Sh NAME
.Nm sleep
.Nd suspend process execution for interval measured in 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 process until either
.Fa seconds
seconds have elapsed or a signal is delivered to the process and its
action is to invoke a signal-catching function or to terminate the
process.
The suspension time may be longer than requested due to the
scheduling of other activity by the system.
.Pp
This function is implemented using
.Xr nanosleep 2
by pausing for
.Fa 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
.Dv SIGALRM .
.Sh RETURN VALUES
If the
.Fn sleep
function returns because the requested time has elapsed, the value
returned will be zero.
If the
.Fn sleep
function returns due to the delivery of a signal, the value returned
will be the unslept amount (the request time minus the time actually
slept) in seconds.
.Sh SEE ALSO
.Xr sleep 1 ,
.Xr nanosleep 2
.Sh STANDARDS
The
.Fn sleep
function conforms to
.St -p1003.1-90 .
.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.