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Date:      Fri, 21 Dec 2007 10:44:42 -0800
From:      John Webster <jwebster@es.net>
To:        Bill Moran <wmoran@potentialtech.com>
Cc:        questions@freebsd.org, "Michael W. Lucas" <mwlucas@blackhelicopters.org>, shinny knight <sh1nny_kn1ght@yahoo.com>
Subject:   Re: timekeeping on jail servers
Message-ID:  <62F8888810A130657FBCAF47@vortex.es.net>
In-Reply-To: <20071221132440.31ded74f.wmoran@potentialtech.com>
References:  <20071218165521.GA37529@bewilderbeast.blackhelicopters.org>	<343753.78466.qm@web44811.mail.sp1.yahoo.com>	<20071221112303.19619c39.wmoran@potentialtech.com>	<7BEE288E7C218E96DB9E8AA0@jw-laptop.dhcp.lbnl.us> <20071221132440.31ded74f.wmoran@potentialtech.com>

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--On Friday, December 21, 2007 13:24:40 -0500 Bill Moran <wmoran@potentialtech.com> wrote:

> In response to John Webster <jwebster@es.net>:
>> 
>> --On December 21, 2007 11:23:03 AM -0500 Bill Moran <wmoran@potentialtech.com> wrote:
>> 
>> > In response to shinny knight <sh1nny_kn1ght@yahoo.com>:
>> > 
>> > The reason that is not recommended is that it results in sudden steps
>> > of the clock.  Occasionally, these steps go backwards.  Software that
>> > is very sensitive to time changes (make processes, database servers,
>> > anything doing calculations WRT time) can break, crash, or work
>> > inaccurately.
>> 
>> ntpdate -B should slew the time slowly.  (According to the manpage.)
> 
> Not generally suitable for cron because it can take longer to slew
> than it does for the next cron execution to occur, which would then
> result in multiple ntpdate programs fighting each other (not sure
> what the effect of this would be).
> 

If I were doing it I would write a script with locking in order
to ensure multiple jobs don't fight.  Simple.


Happy Holidays!




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