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.Dd June 4, 1993
.Dt SLEEP 3
.Os
.Sh NAME
.Nm sleep
.Nd suspend process execution for interval of seconds
.Sh SYNOPSIS
.Fd #include <unistd.h>
.Ft unsigned int
.Fn sleep "unsigned int seconds"
.Sh DESCRIPTION
The
.Fn sleep
function suspends execution of the calling process until either the
number of seconds specified by
.Fa seconds
have elapsed or a signal is delivered to the calling 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 ;
it requires one system call each time it is invoked.
A similar but less compatible function can be obtained with a single
.Xr select 2 ;
such a function would not restart after signals, and also does not interfere
with other uses of
.Xr setitimer 2
(not that
.Fn sleep
interferes with interval timers anymore).
.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 nanosleep 2 ,
.Xr select 2 ,
.Xr setitimer 2 ,
.Xr sigaction 2 ,
.Xr sigsuspend 2 ,
.Xr alarm 3 ,
.Xr pause 3 ,
.Xr usleep 3
.Sh STANDARDS
The
.Fn sleep
function conforms to
.St -p1003.1-90 .
.Sh HISTORY
A
.Fn sleep
function appeared in
.At v7 .