Re: timezones

[Clive Menzies <clive@clivemenzies.co.uk>]

On (06/04/05 00:28), Bruno Hertz wrote:
> michael <linux@networkingnewsletter.org.uk> writes:
> 
> > Here in the UK we recently went to British Summer Time, putting the
> > clocks +1hr from GMT. On my dual boot (Debian + WinXP) it now seems I
> > have a problem. WinXP reports the correct BST time, whereas Debian is an
> > additional hour in front (ie GMT+2 instead of GMT+1) but I can't work
> > out why. A quick Internet search didn't throw anything up.
> >
> > I'm running:
> > michael@manchester-campaigns:~$ uname -a;cat /etc/apt/sources.list
> > Linux manchester-campaigns 2.4.18-bf2.4 #1 Son Apr 14 09:53:28 CEST 2002
> > i686 GNU/Linux
> >
> > deb ftp://ftp.uk.debian.org/debian/ unstable main non-free contrib
> >
> > with Real Time Clock Driver v1.10e
> >
> > Not sure what other info to add (I thought there were msgs about
> > hardware clock at boot but not sure how to access these - not in dmesg)
> >
> > Ta for any advice!
> 
> Don't use Windows myself, but I seem to recall that this is a classic
> dual boot problem with Linux/Windows. More specifically, the default
> (and reasonable) Linux setup suggests and assumes that your hardware
> clock is set to UTC (or GMT, if you will, although those are not strictly
> equivalent), while Windows not only assumes that you use local time, but
> actually sets your hardware clock this way.
> 
> What does that mean? During winter, your local time is UTC + 0, so
> when Windows sets the hardware clock to local time, it is still UTC + 0,
> and Linux won't be disturbed. When changing to summer time though,
> Windows sets the hardware clock to UTC + 1. Linux on the other hand
> still assumes it is UTC + 0, and adds another hour for BST, not on the
> hardware clock but as system time, which is then hardware clock time + 1.
> That's the problem :)
> 
> Afaik, there's nothing to correct this on the Windows side. You can
> however choose localtime as your default Linux hardware clock time
> also with hwclock (cf. man hwclock). In this case, the glibc timezone
> library will _not_ add another hour for BST, and Windows and Linux time
> should be in sync again. This might have the drawback however that Linux
> itself won't change any more from GMT to BST or vice versa. At least that's
> the last I heard of, it might have changed in the meantime. So when that
> changes occur (last Sunday in March and October), you have to set the
> hardware clock either yourself on Linux or, hehe, by booting into Windows :)
Good explanation - I just knew it that they didn't play well together ;)

Thanks

Clive

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