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Re: System time 1 hr ahead of real time



On Mon, 2009-04-06 at 09:56 -0700, Kam Leo wrote:
> On Mon, Apr 6, 2009 at 9:17 AM, suvayu ali <fatkasuvayu+linux gmail com> wrote:
> >
> > I have a strong hunch booting to XP after the DST change caused this
> > mismatch. What is the recommended way of maintaining the system time
> > for dual boot machines?
> 
> When you use a dual/multi-boot system you need to disable one or more
> of your systems from automatically updating for daylight savings. This
> goes whether you are booting multiple versions of Windows or a mixture
> of Windows and Linux.

Linux in UTC will always show the correct time (as long as the hardware
clock is correct UTC), whether on or off at the transition.

Linux in local time will *not* make adjustments for DST if it is not
running when the transition occurs, but it will adjust if it is running
at that time.  

Windows will adjust if it is running or the first time it is turned on
after the change, no matter what.

So you can see that there are various kinds of trouble you can get into
if you try to use local time on a dual-boot machine, depending on which,
if any, system is running at the transition time.

I don't use Windows that much, so I keep the hardware clock in UTC,
Linux running ntpd, Windows in time zone GMT with DST adjustments turned
off (which has to be done for all Windows users separately).  Then the
machine shows the correct local time in Linux, but it shows UTC in
Windows.

I've heard that there is a Windows registry entry that allows one to
keep the hardware clock in UTC on Windows, but I've also heard that it
can break things.

> 
> The other issue is that you need to patch your Windows software.
> Daylight savings began last month.

The other thing that makes this hard is that DST starts on different
dates in different countries, and countries keep changing things...
-- 
                Matthew Saltzman

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


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