Time difference between Win98 and Fedora

[Matthew Saltzman]

On Wed, 22 Sep 2004, Jeff Vian wrote:

> On Wed, 2004-09-22 at 07:43, James Wilkinson wrote:
> > Rob "Hairysocks" wrote:
> > > I have a dual-boot PC and notice that I can't get the time
> > > correct on both Win98 and Fedora. When the Win98 time is correct
> > > then the time on Fedora is one hour ahead.
> > >
> > > I'm sure its got something to do with British Summer Time / GMT,
> > > and that we are currently in BST, but I can't see how to get it
> > > correct.
> >
> > Jeff Vian wrote:
> > > IMHO, you can suffer with the difference, or do not use DST.
> > >
> > > Windows resets system time with the daylight savings time changes (twice
> > > a year).  Linux leaves system time alone and makes the change in
> > > software to display DST.  When you do dual boot in an environment where
> > > DST is used you will see this discrepancy.
> >
> > As others have noted, this is not necessarily correct. Linux expects
> > that it might be run on a dual-booting system, and will convert from
> > the hardware clock to UTC for its own internal use. It expects that
> > the clock will be reset at the beginning and end of daylight savings.
> >
> > Use system-config-time to set this.
> >
> > James.
>
> Please provide details on how this is accomplished to keep both OSes
> happy with the time.

You can't keep both OS's happy under all circumstances without setting the
hardware clock in the BIOS or from the OS in some cases.

>
> I have been unable to find the details for what you say, and I am one of
> those affected by my occasional boot to Win98 and the time change.
>
> The only solution I have found is to tell windows to not reset time for
> DST. Then it has the correct time half the year and is an hour off the
> other half year.
>
> As I said earlier, this is because M$ resets system time and Linux does
> a software adjustment for the DST time change and always expects the
> hardware clock to have a consistent offset from UCT.

This isn't quite correct.  Fedora reads the hardware clock on boot to set
the system clock and sets the hardware clock to the system clock on
shutdown.  If the hardware clock is specified as UTC, then it is read as
UTC and the system clock set to the correct time for the current timezone
(DST included).  If the hardware clock is specified as LOCAL, then on
boot, Linux assumes that the hardware clock contains the correct current
time (DST included).  If the time is correct on boot, it will be set
correctly on shutdown.

See my other post in this thread for the implications for interaction with
Windows.

-- 
		Matthew Saltzman

Clemson University Math Sciences
mjs AT clemson DOT edu
http://www.math.clemson.edu/~mjs