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Date:      Mon, 28 Feb 2005 03:36:41 -0800
From:      "Loren M. Lang" <lorenl@alzatex.com>
To:        Ian Smith <smithi@nimnet.asn.au>
Cc:        freebsd-questions@freebsd.org
Subject:   Re: Received mail timestamp is off by 7 hours
Message-ID:  <20050228113641.GG1672@alzatex.com>
In-Reply-To: <Pine.BSF.3.96.1050228001404.7219I-100000@gaia.nimnet.asn.au>
References:  <20050227120022.F3FEA16A5AC@hub.freebsd.org> <Pine.BSF.3.96.1050228001404.7219I-100000@gaia.nimnet.asn.au>

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On Mon, Feb 28, 2005 at 12:58:17AM +1100, Ian Smith wrote:
> On Sun, 27 Feb 2005 03:10:12 -0700 Pat Maddox <pergesu@gmail.com> wrote: 
> 
>  > Alright, I got it all working now.  Not sure how to change the time
>  > zone with config files, so I just used sysinstall to change it to MST
>  > (time zone is arbitrary, but since this is the zone I live in, it's
>  > convenient for me).  Then I used ntpdate to sync it, and it's working
>  > well now.
>  > 
>  > Thanks for pointing that out to me.  I just thought that CET was central time :)
> 
> Yes sysinstall's as good a way as any, it'll set your timezone and also
> let you choose between running with a UTC or local time CMOS clock.  Or
> you can manually tun tzsetup(8) and create (or not) /etc/wall_cmos_clock
> .. see adjkerntz(8) 
> 
> Take little notice of people opining that you must or even should run
> CMOS UTC time; that's entirely up to you.  I've always preferred local
> time CMOS clocks personally; sysinstall creates /etc/wall_cmos_clock and
> cron runs 'adjkerntz -a' halfhourly at times when daylight savings time
> might come or go in your zone, and that's always worked fine here. 

The reason using UTC for the cmos clock is that it never changes like US
daylight savings does.  Now if your timezone doesn't ever need to be
pushed forward or backwards then it won't be a problem, but otherwise
evertime the system boots up, it has to determine if the cmos time is
correct or needs to be adjusted.  A UTC time will always be correct and
can be turned exactly into the correct time at the moment.  I think that
if FreeBSD crashed just after it booted up and adjusted the hour forward,
then on the next reboot, it would adjust it another hour forward.  In
general, it is just harder to manage.  Even worse would be my Quad boot
system with Gentoo Linux, FreeBSD, OpenBSD, NetBSD.  If I used local
time for my cmos clock then every daylight savings change, each os would
adjust the clock independently and I'd be 3 hours off.

> 
> The only thing to watch running wall_cmos_clock is that if you boot to
> single user mode, before /etc/rc has run 'adjkerntz -i' the system will
> assume CMOS is UTC, so any files then modified show timestamps in UTC
> (discovered the hard way in Jan 2000 on a box with a broken y2k BIOS :)
> 
> Cheers, Ian
> 
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-- 
I sense much NT in you.
NT leads to Bluescreen.
Bluescreen leads to downtime.
Downtime leads to suffering.
NT is the path to the darkside.
Powerful Unix is.

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