f1fe8d5bac
TAI is a timescale, just like UTC. The tai field returns the offset between the two, and isn't really used for precision time keeping. Explain in brief what a positive and a negative leap seconds are. Add some URLs to very useful web pages about time and time keeping for more information on using this API. Reviewed by: phk
115 lines
3.6 KiB
Groff
115 lines
3.6 KiB
Groff
.\"
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.\" Copyright (c) 2003 Tom Rhodes
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.\" All rights reserved.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
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.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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.\" ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
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.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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.\" SUCH DAMAGE.
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.\"
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.\" $FreeBSD$
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.\"
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.Dd June 21, 2003
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.Dt NTP_GETTIME 2
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.Os
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.Sh NAME
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.Nm ntp_gettime
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.Nd NTP user application interface
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.Sh SYNOPSIS
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.In sys/timex.h
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.Ft int
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.Fn ntp_gettime "struct ntptimeval *ntv"
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.Sh DESCRIPTION
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The time returned by
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.Fn ntp_gettime
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is in a
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.Vt timespec
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structure, but may be in either microsecond
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(seconds and microseconds) or nanosecond (seconds and nanoseconds) format.
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The particular format in use is determined by the
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.Dv STA_NANO
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bit of the status
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word returned by the
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.Fn ntp_adjtime
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system call.
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.Fn ntp_gettime
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has as argument a pointer to the
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.Vt ntptimeval
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structure with the following members:
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.Bd -literal
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struct ntptimeval {
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struct timespec time; /* current time (ns) (ro) */
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long maxerror; /* maximum error (us) (ro) */
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long esterror; /* estimated error (us) (ro) */
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long tai; /* TAI-UTC offset */
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int time_state; /* time status */
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};
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.Ed
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.Pp
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These are understood as:
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.Bl -tag -width ".Va time_state"
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.It Va time
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Current time (read-only).
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.It Va maxerror
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Maximum error in microseconds (read-only).
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.It Va esterror
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Estimated error in microseconds (read-only).
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.It Va tai
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Offset in seconds between the TAI and UTC time scales.
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This offset is published twice a year and is an integral number of
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seconds between TAI (which does not have leap seconds) and UTC (which
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does).
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.Xr ntpd 8
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or some other agent maintains this value.
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A value of 0 means unknown.
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As of the date of the manual page, the offset is 32 seconds.
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.It Va time_state
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Current time status.
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.El
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.Sh RETURN VALUES
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.Rv -std ntp_gettime
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.Pp
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Possible states of the clock are:
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.Pp
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.Bl -tag -compact -width ".Dv TIME_ERROR"
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.It Dv TIME_OK
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Everything okay, no leap second warning.
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.It Dv TIME_INS
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Positive leap second warning.
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At the end of the day, an additional second will be inserted after 23:59:59.
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.It Dv TIME_DEL
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Negative leap second warning.
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At the end of the day, 23:59:59 is skipped.
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.It Dv TIME_OOP
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Leap second in progress.
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.It Dv TIME_WAIT
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Leap second has occurred.
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.It Dv TIME_ERROR
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Clock not synchronized.
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.El
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.Sh SEE ALSO
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.Xr ntp_adjtime 2 ,
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.Xr ntpd 8 ,
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.Dq Li http://www.bipm.fr/enus/5_Scientific/c_time/time_1.html ,
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.Dq Li http://www.boulder.nist.gov/timefreq/general/faq.htm ,
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.Dq Li ftp://time.nist.gov/pub/leap-seconds.list
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.Sh AUTHORS
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This manual page was written by
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.An Tom Rhodes Aq trhodes@FreeBSD.org .
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