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.\"     @(#)usleep.3	8.1 (Berkeley) 6/4/93
.\"
.Dd April 22, 2024
.Dt USLEEP 3
.Os
.Sh NAME
.Nm usleep
.Nd suspend execution for interval of microseconds
.Sh LIBRARY
.Lb libc
.Sh SYNOPSIS
.In unistd.h
.Ft int
.Fn usleep "useconds_t microseconds"
.Sh DESCRIPTION
.Bf -symbolic
This interface is obsoleted by
.Xr nanosleep 2 .
.Ef
.Pp
The
.Fn usleep
function
suspends execution of the calling process
until either the number of microseconds specified by
.Fa microseconds
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.
.Sh RETURN VALUES
On successful completion,
.Fn usleep
returns 0.
Otherwise, it returns \-1 and sets
.Va errno
to indicate the error.
.Sh ERRORS
The
.Fn usleep
function may fail if:
.Bl -tag -width Er
.It Bq Er EINTR
.Nm
was interrupted by the delivery of a signal.
.El
.Sh SEE ALSO
.Xr nanosleep 2 ,
.Xr sleep 3
.Sh STANDARDS
The
.Fn usleep
function conforms to
.St -xpg4.2 .
It later appeared in the
.Tn POSIX
standard, but in
.St -p1003.1-2004
it was marked as legacy and the use of
.Xr nanosleep 2
was recommended instead.
The
.St -p1003.1-2008
revision removed
.Fn usleep
from the specification.
.Sh HISTORY
The
.Fn usleep
function appeared in
.Bx 4.3 .
.Sh CAVEATS
In
.St -p1003.1-2004 ,
.Nm
was limited to values of
.Fa microseconds
less than one million.
Some implementations, including
.Nx
before 10.1, fail immediately with
.Er EINVAL
\(em and don't sleep at all \(em if
.Fa microseconds
is one million or greater.