Re: DST Changes

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Date:         Wed, 25 Feb 2004 11:19:44 -0800
To: aix-l@Princeton.EDU

I'm confused.

If I change the TZ using smitty chtz, and then select "yes" for "use
daylight savings time?", and then select "PST8PDT" for pacific US, according
to the help for each additional option, all I have to do is leave all
options blank since I'm in the US and the defaults are correct?

That leaves me with 'TZ=PST8PDT" in the environment file. So this is enough
to handle daylight savings time?

If I wanted to hardcode it, I'm not sure how to answer "Day Light Savings
Time Offset from CUT"? The help says "If the field is blank, the value will
match the default value, which is one hour ahead of the standard time."

Would it simply be +01, so hardcoded it would be
"TZ=PST8PDT+01,M4.1.0/02,M10.5.0/02"?

The above value would be equal to TZ=PST8PDT in the US?

I can see I will be waking up at 2:00am on the first Sunday in April.

I have always relied on our corporate times server via NTP to keep our
clocks in synch, but a few weeks ago they were wrong and we ended up with
the wrong date and time, so now we don't use them.

Thus the paranoia!

Thanks,
Kevin Adams
PacifiCare Behavioral Health
Principal Systems Analyst
AIX CATE

-----Original Message-----
From: IBM AIX Discussion List [mailto:aix-l@Princeton.EDU]On Behalf Of
Green, Simon
Sent: Wednesday, February 25, 2004 9:19 AM
To: aix-l@Princeton.EDU
Subject: Re: [aix-l] DST Changes

Provided your Timezone is set correctly, (TZ in /etc/environment) there
should not be any problem and there is no need to take any further action.
It's worth remembering that ideally you should re-boot your system if you
have to make a change to TZ, but it's not always strictly necessary: I made
a lot of changes recently and all I've done is restart the cron daemon and
ensure that the applications, (mostly SAP and Data Warehouse systems) are
re-started - not actually a full reboot of the systems.

Any half-way decent application will use the actual system clock for
critical things like database log timestamps, so there is no problem there.

It's possible that you'll see overlapping time-stamps in text logs, but that
won't do any harm in itself. Technical personnel should be aware of it.

Scheduling - through crontab or actual scheduling packages - may have some
issues, with jobs getting missed in the spring, or running twice in the
autumn. However, that's highly dependent on the particular scheduling
system. Crontab's very basic, obviously, but a good scheduler should handle
the situation cleanly.

Personally, I haven't taken any special actions for DST in several years.
We did have some problems last autumn because TZ was not identical on all of
our servers, in particular there were difference between some SAP
Application servers and their Database servers. This arose because of
differences in when the time change occurred:-

Some of the servers had TZ=CET-1CEST,M3.5.0/02,M10.5.0/03, others only had
CET-1CEST,M3.5.0,M10.5.0. In the second case, the time for the change
defaults to the US standard, which is 2am local time in both cases. In
Europe, the standard is for 01:00 GMT, which equates to 02:00 CET in the
spring, or 03:00 CET in the autumn.

In fact, this doesn't really matter very much in most cases, provided you
are consistent.

The correct TZ for the UK is "GMT0BST,M3.5.0/01,M10.5.0/02". You can either
edit /etc/environment, or use the chtz command.

--
Simon Green
Altria ITSC Europe Ltd
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> -----Original Message-----
> From: Kumar, Praveen (cahoot) [mailto:Praveen.Kumar@CAHOOT.COM]
> Sent: 25 February 2004 16:32
> To: aix-l@Princeton.EDU
> Subject: DST Changes
>
>
> Hi All,
>
>         Can someone let me know what are the issues to be
> taken care during
> DayLight Saving Time changes. My aix boxes have Websphere and
> HTTP Server
> running on them..
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• Previous message: Kumar, Praveen (cahoot): "Re: DST Changes"
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