.\"	$OpenBSD: adjfreq.2,v 1.5 2013/08/14 06:32:29 jmc Exp $
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.\" Copyright (c) 2006 Otto Moerbeek
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.Dd $Mdocdate: August 14 2013 $
.Dt ADJFREQ 2
.Os
.Sh NAME
.Nm adjfreq
.Nd correct the rate of the system clock
.Sh SYNOPSIS
.Fd #include <sys/types.h>
.Fd #include <sys/time.h>
.Ft int
.Fn adjfreq "const int64_t *freq" "int64_t *oldfreq"
.Sh DESCRIPTION
.Fn adjfreq
adjusts the rate in which time progresses if
.Fa freq
is non-null.
The unit of the rate of adjustment is nanoseconds per second,
shifted left 32 bits to allow for fractional values.
.Pp
If
.Fa oldfreq
is non-null, the current value is returned.
.Pp
Only the superuser may adjust the frequency.
.Sh RETURN VALUES
A return value of 0 indicates that the call succeeded.
A return value of \-1 indicates that an error occurred, and in this
case an error code is stored in the global variable
.Va errno .
.Sh ERRORS
.Fn adjfreq
will fail if:
.Bl -tag -width Er
.It Bq Er EFAULT
Either of the arguments point outside the process's allocated address space.
.It Bq Er EPERM
The
.Fa freq
argument is non-null and the process's effective user ID is not that
of the superuser.
.El
.Sh SEE ALSO
.Xr date 1 ,
.Xr adjtime 2 ,
.Xr gettimeofday 2 ,
.Xr ntpd 8
.Sh HISTORY
The
.Fn adjfreq
function call first appeared in
.Ox 4.0 .