Changing to Daylight Saving TIme

Changing to Daylight Saving TIme

Post by David Hen » Fri, 10 Apr 1998 04:00:00



Is there an automatic mechanism for changing the date, or TZ, to and
from Daylight Saving Time?
I ask because I have 2 Solaris systems, one changed its date all by
itself and the other didn't and for the life of me I can't figure out
how.
There isn't a crontab action that I can see and I've scanned man pages
and Answerbook, but to no avail.

 
 
 

Changing to Daylight Saving TIme

Post by Casper H.S. Dik - Network Security Engine » Fri, 10 Apr 1998 04:00:00


[[ PLEASE DON'T SEND ME EMAIL COPIES OF POSTINGS ]]


>Is there an automatic mechanism for changing the date, or TZ, to and
>from Daylight Saving Time?

Unix systems don't change time.  They keep time in UTC.

Only the way time is represented changes.  (So until someone types
"date" you won't notice that DST has started)

Quote:>I ask because I have 2 Solaris systems, one changed its date all by
>itself and the other didn't and for the life of me I can't figure out
>how.

Check patch level of the stuff under /usr/share/lib/zoneinfo.

Same $TZ value, but perhaps different timezone files.

Quote:>There isn't a crontab action that I can see and I've scanned man pages
>and Answerbook, but to no avail.

No, cron is not involved as, to the OS, "nothing happens"

Casper
--
Expressed in this posting are my opinions.  They are in no way related
to opinions held by my employer, Sun Microsystems.
Statements on Sun products included here are not gospel and may
be fiction rather than truth.

 
 
 

Changing to Daylight Saving TIme

Post by Maurizio Codog » Sat, 11 Apr 1998 04:00:00



% Unix systems don't change time.  They keep time in UTC.

And this is a Good Thing. But ...

% No, cron is not involved as, to the OS, "nothing happens"

Yup, but *for cron* something does happen. What's the exact behaviour?
Does cron wake up each minute, checks date, and makes actions? This would
mean that an action scheduled for 2:30 each Sunday night was not executed
when DST started (because cron found that after 1:59 there was 3:00) and
will be executed twice when it will end?

.mau.

 
 
 

Changing to Daylight Saving TIme

Post by Casper H.S. Dik - Network Security Engine » Sat, 11 Apr 1998 04:00:00


[[ PLEASE DON'T SEND ME EMAIL COPIES OF POSTINGS ]]


>Yup, but *for cron* something does happen. What's the exact behaviour?
>Does cron wake up each minute, checks date, and makes actions? This would
>mean that an action scheduled for 2:30 each Sunday night was not executed
>when DST started (because cron found that after 1:59 there was 3:00) and
>will be executed twice when it will end?

No, cron keeps a list of actions and whenever an action is started it will
schedule also the next event.

The DST changes are never handled very well in cron, though.

Different things should happen to jobs that:

        run every n minutes (no problem there)
        run every hour      (should run twice at 2:00 am when summertime ends?,
                              and only 23 times in a day when DST starts)

        run every day/week/month during the "lost hour"
                            (should be run exactly once, even when DST changes)

I don't think cron does all that, nor do I know what standards say on this.

What cron typically does is compute the time for the next run/

Then when a job is being run, cron checks whether it's permitted to
run at the time it wakes up; if not, it reschedules.

Casper

--
Expressed in this posting are my opinions.  They are in no way related
to opinions held by my employer, Sun Microsystems.
Statements on Sun products included here are not gospel and may
be fiction rather than truth.

 
 
 

1. Daylight saving time auto change

Is there any command which will show the day and time at which the
system will change to daylight saving time?

We have two machines running AIX 4.1.5. They are located in the
Netherlands (Europe). The change to daylight saving time has changed
in the Netherlands from September to October.

The current setting voor the TZ variable in the file /etc/environment
is as follows:  TZ=NFT-1DFT

We changed this variable today, 21 Sep 1999, to:
TZ=NFT-1DFT,M3.4.0,M10.4.0

To activate this change we need to reboot the system. The next reboot
is planned for the end of next week.
The problem now is that we suspect that the old setting (TZ=NFT-1DFT)
will change to daylight saving time next weekend (before reboot).

We can plan an extra reboot but this is not preferred.

Regards,

Michel Verbraak
Serac b.v.

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