How to determine whether the OS has the latest DST rules

Edwin Groothuis edwin at
Fri Nov 7 16:10:27 UTC 2008

 <yoshito_umaoka <at>> writes:

> > I am working on an issue related to Brazil timezone. Our code reads 
> > the DST rules from windows registry instead of tzdata.
> > 
> > My question is -- how do I determine whether the windows system has 
> > applied the latest timezone DST rules from the following registry? I
> > don't know how to interpret the binary data
> To access time zone rules used by Windows, you can use the API below -

For "freebsd-update" (binary FreeBSD base system patch and migration) I have
been asked if it was possible to determine of which timezone the current
installed file in /etc/localtime was, so people could have non-interactive
updates with regarding to that. The timezone given by date(1) doesn't always
give a good enough hint, specially not for me in Australia where EST is often
confused by programs with the US version of EST...

Also, being able to compare the old /etc/localtime with the newly to be
installed one gives a hint on whether or not this is an important one for this
machine, i.e. if you have to restart long-running services (syslog, cron) which
otherwise will not notice the DST change.

Consider it a feature request :-)


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