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.\" Copyright (c) 2003 Tom Rhodes
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.\" $FreeBSD: src/lib/libc/sys/ntp_adjtime.2,v 1.1.2.1 2003/04/22 17:31:18 trhodes Exp $
.\"
.Dd April 25, 2012
.Dt NTP_ADJTIME 2
.Os
.Sh NAME
.Nm ntp_adjtime
.Nd NTP daemon application interface
.Sh LIBRARY
.Lb libc
.Sh SYNOPSIS
.In sys/types.h
.In sys/timex.h
.Ft int
.Fn ntp_adjtime "struct timex *tp"
.Sh DESCRIPTION
The
.Fn ntp_adjtime
system call is used as a kernel interface
for Network Time Protocol daemons like
.Xr dntpd 8
and
.Xr ntpd 8 .
Certain fields of the
.Vt timex
structure are interpreted in either
microseconds or nanoseconds, according to the state of the
.Dv STA_NANO
bit in the
.Va status
word.
.Pp
In the
.Dx
kernel, the
.Fn ntp_adjtime
and
.Xr ntp_gettime 2
system calls can be used to determine which
resolution is in use, and to select either one at any time.
The resolution selected affects the scaling of certain fields in the
.Fn ntp_gettime
and
.Fn ntp_adjtime
system calls.
.Pp
Take note that this
.Tn API
is extremely complex and stateful.
Users should not attempt modification without first
reviewing the
.Xr ntpd 8
sources in depth.
.Bd -literal
/*
 * NTP daemon interface (ntp_adjtime()) - used to discipline CPU clock
 * oscillator and determine status.
 *
 * Note: The offset, precision and jitter members are in microseconds if
 * STA_NANO is zero and nanoseconds if not.
 */
struct timex {
	unsigned int modes;	/* clock mode bits (wo) */
	long	offset;		/* time offset (ns/us) (rw) */
	long	freq;		/* frequency offset (scaled PPM) (rw) */
	long	maxerror;	/* maximum error (us) (rw) */
	long	esterror;	/* estimated error (us) (rw) */
	int	status;		/* clock status bits (rw) */
	long	constant;	/* poll interval (log2 s) (rw) */
	long	precision;	/* clock precision (ns/us) (ro) */
	long	tolerance;	/* clock frequency tolerance (scaled
				 * PPM) (ro) */
	/*
	 * The following read-only structure members are implemented
	 * only if the PPS signal discipline is configured in the
	 * kernel. They are included in all configurations to insure
	 * portability.
	 */
	long	ppsfreq;	/* PPS frequency (scaled PPM) (ro) */
	long	jitter;		/* PPS jitter (ns/us) (ro) */
	int	shift;		/* interval duration (s) (shift) (ro) */
	long	stabil;		/* PPS stability (scaled PPM) (ro) */
	long	jitcnt;		/* jitter limit exceeded (ro) */
	long	calcnt;		/* calibration intervals (ro) */
	long	errcnt;		/* calibration errors (ro) */
	long	stbcnt;		/* stability limit exceeded (ro) */
};
.Ed
.Pp
Upon successful completion,
.Fn ntp_adjtime
will fill the
.Fa tp
argument with the current clock state.
.Sh RETURN VALUES
.Rv -std ntp_adjtime
.Pp
Possible states of the clock are:
.Pp
.Bl -tag -compact -width ".Dv TIME_ERROR"
.It Dv TIME_OK
Everything okay, no leap second warning.
.It Dv TIME_INS
insert leap second warning.
.It Dv TIME_DEL
delete leap second warning.
.It Dv TIME_OOP
Leap second in progress.
.It Dv TIME_WAIT
Leap second has occurred.
.It Dv TIME_ERROR
Clock not synchronized.
.El
.Sh ERRORS
The
.Fn ntp_adjtime
system call may return
.Er EPERM
if the caller
does not have sufficient permissions.
.Sh SEE ALSO
.Xr ntp_gettime 2 ,
.Xr dntpd 8 ,
.Xr ntpd 8 Pq Pa net/openntpd
.Sh AUTHORS
This manual page was written by
.An Tom Rhodes Aq Mt trhodes@FreeBSD.org .