Daylight Savings Time

Matthew Saltzman mjs at
Wed Nov 4 01:28:30 UTC 2009

On Tue, 2009-11-03 at 15:32 -0500, Clyde E. Kunkel wrote: 
> On 11/03/2009 11:02 AM, Clyde E. Kunkel wrote:
> > Should rawhide have set US East Coast Daylight Saving Time back one hour
> > on Nov 1 to Standard Time?
> >
> OK, I see I am I wonder why?  The bios on this machine 
> DOES NOT use UTC and the UTC box was unchecked during installation. Does 
> that make a difference?

Yes.  If you use UTC for the hardware clock, then the right thing is
always done with regard to DST.  

If you use localtime, then Linux assumes that the hardware clock
contains the correct local time at boot.  The DST adjustment will take
place if the machine is running at the time of the transition, and the
correct time will be saved if the machine is rebooted after that.  If
the machine is off at the time of the transition and you don't set the
hardware clock, the time will be an hour off at boot.

> I also see that since setting the time correctly about 5 hours ago, time 
> has gained 5 minutes.  I recall msgs sometime ago on this list about the 
> clock gaining time in rawhide, so all I may have been seeing was time 
> creep and not an erroneous EDST -> EST.

If the machine is connected to the Internet, you should consider using
NTP to keep your clock in line.

                Matthew Saltzman

Clemson University Math Sciences
mjs AT clemson DOT edu

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