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Daylight Saving patch for New Zealand

 
 
David Empson
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      09-27-2007
New Zealand is changing its daylight saving rules from Sunday 30th
September (starting a week earlier, and finishing two or three weeks
later, next March).

Apple haven't done anything about supplying a patch for Mac OS X, so a
friend of mine wrote his own one, which requires Mac OS X 10.4.9 or
10.4.10. He's also done a version for 10.3.9, and has a program which
can manually edit the daylight saving rules for Mac OS 9. (There is no
solution that I know of for 10.0 through 10.2.8.)

I've written a detailed article about the problem on my user group's web
site:

http://www.welmac.org.nz/nzdst2007.php

The patch can be downloaded here:

http://www.mactcp.org.nz/nzdt.html

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David Empson
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David Empson
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      09-27-2007
Lawrence D'Oliveiro <(E-Mail Removed)_zealand> wrote:

> In message <1i53n40.z2rjflxidmqjN%(E-Mail Removed)>, David Empson
> wrote:
>
> > Apple haven't done anything about supplying a patch for Mac OS X, so a
> > friend of mine wrote his own one, which requires Mac OS X 10.4.9 or
> > 10.4.10. He's also done a version for 10.3.9...

>
> Doesn't OS X use the standard /usr/share/zoneinfo files like other *nix
> systems?


Not entirely. It does use zoneinfo for anything which uses POSIX
standards or the standard C library calls such as localtime(). This
includes almost all of the BSD or GPL open source sofware included with
Mac OS X.

Mac OS X also uses IBM's ICU mechanism (a database with Unicode and
country-specfic information), which includes another copy of the time
zone tables. This database is installed in a standard location and used
by the CoreFoundation framework, which is in turn used by most GUI
applications which are aware of time zones. The main example is iCal,
which is the standard calendar application on Mac OS X.

This means that to update Mac OS X for daylight saving rule changes, it
is necessary to patch both the zoneinfo files and the global ICU data
files. If you patch one and not the other, some applications (including
iCal) get very confused because they are using both the CoreFoundation
calls and the C standard library calls. Observed symptoms include iCal
thinking that October 2007 is also called September.

Apple did a patch which updated all the global rules in February 2007
(including the US changes for March), but they haven't done one since
then, and two system updates later they still have the February rules.

The New Zealand rule change was officially announced in April or May, so
Apple has been tardy in getting its time zone rules back in sync. They
will probably have updated rules in 10.4.11 and 10.5, but neither of
those will be available before September 30th, so an unpatched Mac will
think New Zealand is an hour earlier for a week.

The patch I referenced only covers these two parts of the system
(zoneinfo and global ICU). It doesn't update Java (which has its own
copy of the timezone rules), or anything else which has its own rules
(WebObjects is another example). Other open source or cross-platform
software might include its own copy of the ICU database (or the timezone
rules in some other form). I don't know of any other specific examples.

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David Empson
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David Empson
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      09-27-2007
Jonathan Walker <(E-Mail Removed)> wrote:

> On Thu, 27 Sep 2007 12:44:30 +1200, David Empson wrote:
>
> > Apple haven't done anything about supplying a patch for Mac OS X, so a
> > friend of mine wrote his own one, which requires Mac OS X 10.4.9 or
> > 10.4.10. He's also done a version for 10.3.9, and has a program which
> > can manually edit the daylight saving rules for Mac OS 9. (There is no
> > solution that I know of for 10.0 through 10.2.8.)

>
> What about the solution of simply restarting that PC and manually changing
> the time in the BIOS, or Apple equivalent?


Not a good idea.

If you set the clock manually ahead by an hour, it will result in the
entire world appearing to be an hour ahead. If you do anything involving
overseas communication, you will have to remember that your computer is
showing times for other countries that are out by an hour.

It will also affect things like timestamps on e-mail, resulting in
sorting errors when sorting by date (both mail you send and mail you
receive).

If you later install a patch to fix the daylight saving rules (either
official or unofficial) then any files saved during that week you had
the clock set ahead will move an extra hour ahead, which might stuff up
things like backups.


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David Empson
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