Re: [tlug] Ubuntu 13.10 clock problems

[Bruno Raoult <braoult@example.com>]

On Thu, Oct 31, 2013 at 5:58 AM, Stephen J. Turnbull <stephen@example.com> wrote:

Bruno Raoult writes:

 > As I live in France, where there is DST change, localtime is
 > absolutely a no-go.

So there's really no problem here.  DST is irrelevant.  By the time
boot has proceeded far enough to worry about these issues, the
timezone library is available.  It will handle DST and such blips
(leap seconds, anyone?) based on the (integer) number of seconds since
the appropriate epoch.  (Note that in the U.S., where the practice of
localtime clocks originated, there were no times zones observing DST
on January 1, 1970, so there aren't any blips in the 24 hours that
matter, and there never will be.)

You missed my point: The *huge* difference between using a localtime and UTC

HW clock is that in case of DST change you have to *change* the HW clock

twice a year (either by +1 or -1 hour). And you have no way to know if it has been

done or not.

Example: Next night, at 3:00. it will be 2:00.

My computer goes to 3:00, changes the HW clock to 2:00.

Then I just reboot. It will get the time from the clock, let say 2:01 (let's dream :-)

So it will go again to the 3:00 and do again the job. We are one hour off.

This is the difference.

Would the CMOS clock not reflect the localtime, we would not have the issue.

So yes, UTC is very different, as it follows what you say: A number of <units>

since the epoch.

In case of a DST country, with the HW clock giving the localtime, this is no more valid,
as half of the year the clock will give a number of <units> equivalent to 1 hour ahead of the epoch.

Bruno.

PS. What I mean by "changing the clock" is: when you reboot, go to the BIOS, it shows

really the local time. If you reboot in my case at 2:29, the BIOS will show 2:30.

1 hour later, you reboot at 2:29, the BIOS will show 2:30.

--
2 + 2 = 5, for very large values of 2.