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Date:      Thu, 1 Oct 1998 11:51:51 +0100
From:      "Andy.Robb" <Robb.Andy@x-tension.com>
To:        "'freebsd-questions@FreeBSD.ORG'" <freebsd-questions@FreeBSD.ORG>
Subject:   training timeofday clock with ntpdate
Message-ID:  <B766A4A0DB0BD2119BF40000F824778EE42F@mailhost.x-tension.co.uk>

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Request:

Please can you allow adjtime() calls to trim the system clock?
Preferably, accumulate the adjustments in a file (probably ignoring
large adjustments).  This file could be read at bootup to trim the
system clock.

Background:

I understand that the kernel includes code to trim the clock frequency
when using xntpd.  However, xntpd raises the ISDN line to our ISP every
few minutes.

I would like to be able to use the accumulated error from ntpdate (say)
to train the kernel's clock to be within 0.5 sec/day (typically 0.1
sec/day) and use ntpdate just once a day.

I know that Irix from SGI supports this kind of technique with both
"timed" and "timeslave" daemons - albeit through special system calls.
I have written programs using ICMP TIMESTAMP messages to synchronise
both Linux (using adjtime) and HP-UX 9 systems (hacking the kernel) to a
group of SGI systems that co-operated with timed.

Many thanks for a great system,
Andy Robb.

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