SUMMARY: Daylight savings

From: Stephanie Lam (MIS) (
Date: Tue Oct 20 1998 - 11:18:32 CDT


Thanks to those who responded. The questions may seem naive - I guess it
is from a newbie like me. I appreciate those who so patiently explained
the daylight savings without insults.

Solaris tracks time in seconds since
Midnite, January 70, 1970.
When you use Solaris libraries to display the date/time, Daylight
savings is calculated
using your timezone info ($TZ).

If Solaris has the correct view of
where you are, ie, U.S. West Coast,
it will "change the clock" at
02:00:00 -7:00 to be
01:00:00 -8:00.

In either case, it is really 09:00:00 GMT.

If you look in the directory /usr/share/lib/zoneinfo, there are some
text files with lower case names which fully explain how the time is
changed. For instance, the file europe gives details of the summer time
(English for daylight savings time) changes in european time zones.

Internally, Solaris uses "unix time", seconds since January 1, 1970,
0:00h, GMT

So it doesn't, in fact, change time at all. It's not until you try to
compute local time (which is what ls, date, etc do) that the dst changes
are noted.

There is no "event" that happens. The rules that govern timezones
just tell the software to use a different offset now that the change
over has passed.

These new rules are in affect typically when the real world timezone
occurs; details can be found in /usr/share/lib/zoneinfo where all the
data is kept.

Mixed answers:
1. Jobs re-run twice
2. Don't get re-run but get skipped during spring

1. Suggestions in handling daylight savings is not to schedule any cron
jobs between 1:59am - 3:01am on Sunday.
2. Some say I don't have to do anything...


Many thanks to:

        Ronald Loftin []
        Seth Rothenberg []
        Matthew Atkinson []
        Sean Quaint []
        Casper Dik [casper@holland.Sun.COM]
        Rothenanger, Juergen []
        Roger Fujii []
        Arthur Darren Dunham []

> Hi,
> I could not find information about how Solaris handles daylight
> Q1. At what time does Solaris changes the time?
> Q2. What happens to cron jobs then? I think they get re-run but I
> like to confirm...
> Q3. What are your recommendations in handling the daylight savings ?

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