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Re: How to disable UTC time?

On Tue, Jul 09, 2013 at 09:20:18AM +0200, Ralf Mardorf wrote:
> On Tue, 2013-07-09 at 08:54 +0200, basti wrote:
> > Or set Windows to use UTC, don't know if it still works.
> And what should people do that don't use Windows, but need a correct
> local time for software that does run without an OS or who want the
> local time for saved BIOS settings?

Having the "correct" [local] time in the BIOS is of dubious value
if you're just booting Linux.  It's not like anyone actually looks
at it directly--there's no real need to; the clock is fully
adjustable from within Linux with date/hwclock.  Same for any other
OS.  What's on the BIOS setup screen is not exactly of great
importance; and UTC here is not wrong in any way.  Who on earth is
using software "without an OS". I'm unconvinced that there's a
credible use case there.

> The OP asked how to use local time by the hwclock and not how to use UTC
> with Windows. Does the OP use Windows?

If you /really/ want to configure Linux to use local time, and I'm
not for a moment recommending it, then

  sed -i -e 's:^UTC$:LOCAL:' /etc/adjtime

the UTC= parameter in /etc/default/rcS is no longer used; hwclock
now uses the value in /etc/adjtime (this is the only actual use
of this file).  If you upgraded to wheezy, the UTC setting will
have been automatically migrated to /etc/adjtime; for a new install
it'll have used /etc/adjtime from the start.

> I'm using local time, but I don't care about what ever time settings
> Microsoft should prefer. To chose local or UTC time has nothing to do
> with Windows, especially when Windows isn't installed.

It's almost always an incorrect choice.  If you dual boot, then both
systems will want to do DST adjustments, guaranteeing it will screw up
at least twice per year in all probability, and quite possibly more
than that as the different OSes all try to update the hwclock.  But
even if you single boot it's still possible to screw up over DST
changes.  UTC is *guaranteed* to be reliable by being simple, monotonic
and avoiding pointless dicking around with the clock.  Believe me, I
spent several man days testing hwclock and the init scripts prior to
the release of wheezy including transitioning between every possible
utc/local tz/dst possible.  LOCAL does work, just not 100% reliably.
The system knows which timezone you're in, and the system clock is UTC
irrespective of the hardware clock, so there's really no good reason
not to use UTC for the hardware clock.

I dual boot with Windows; I just disabled DST changes and set the
timezone to UTC (in Windows).  It would have been nicer to tell it
to use a UTC hardware clock, but I didn't care enough about Windows
to bother configuring that; as suggested before, Windows can be
configured to use a UTC hardware clock if you want to dual boot.


  .''`.  Roger Leigh
 : :' :  Debian GNU/Linux    http://people.debian.org/~rleigh/
 `. `'   schroot and sbuild  http://alioth.debian.org/projects/buildd-tools
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