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time change

 
Highlighted
Advisor

time change

Hi,
I have a lot of hp9000 running hpux 11.11 & 11.23 situated in Morroco.
We have concerned by the change of summer timme at 1st June 00:00 to 01:00.
What do you suggest me :change the system time or just the timezone(TZ=WAT0).(Note that tztab is not updated for Morroco).
Other question:What is the impact on the running processes(database and applications)during the modification.Shall we stop all processes before change?
thanks
5 REPLIES 5
Highlighted
Acclaimed Contributor

Re: time change

Hi:

Do not change your system time. Use an appropriate TZ (timezone) setting as defined in '/usr/lib/tztab'.

In addition, implement NTP to synchronize yuor server's with a reliable external time source.

NTP works in UTC (GMT). Time always advances. It is your definition of *local* time that can change --- the positive or negative offset from UTC. This is what the 'TZ' variable is designed to do based on the rules defined in '/usr/lib/tztab'. See the manpages for 'tztab(4)' and for 'cron' [particularly the section titled "Spring and Autumn Time Transitions"].

For example:

# TZ=UTC date
Wed May 23 11:55:53 UTC 2008
# TZ=EST5EDT date
Wed May 23 07:55:55 EDT 2008
# TZ=EST-10EDT date
Wed May 23 21:55:58 EST 2008

Thus, every process could have its own idea of what constitutes the correct time. Do *not* increment or decrement the real time on your server without stopping critical processes like databases!

Moving time forward is generally benign. Moving time backwards can cause havoc with a database.

Regards!

...JRF...
Highlighted
Advisor

Re: time change

thanks for your reply,
I understand that we must stop all process before change.
I don't use Ntp and i want to automate the change on all servers by using the file tztab,here is the lines added for testing:

WAT0WATDST
47 14 22 5 2002-2040 4 WATDST-1
59 8 18-25 5 2008 5 WAT0

and TZ=WAT0WATDST in /etc/TIMEZONE.
the first line works fine,but when i want to go back the second line doesn't work.
regards
Highlighted
Acclaimed Contributor

Re: time change

Hi (again):

Either your post scrambed something or your 'tzlib' format is wrong. Please re-examine the 'tzlib' manpages and/or the '/usr/lib/tztab' file.

Once you have correctly modified the file, you should plan a reboot sometime before the new rules will apply. In this way, all processes will have a chance to read and cache the new rules.

If I recall correctly, once you have modified your 'tztab' any application of a standard 'tzlib' patch wiht 'swinstall' will *not* overlay your version, but rather leave the new version in the ' /usr/newconfig/etc' directory.

Regards!

...JRF...
Highlighted
Acclaimed Contributor

Re: time change

>I want to automate the change on all servers by using the file tztab, here are the lines added for testing:
WAT0WATDST
47 14 22 5 2002-2040 4 WATDST-1
59 08 18-25 5 2008 5 WAT0
>and TZ=WAT0WATDST in /etc/TIMEZONE.
>the first line works fine, but when i want to go back the second line doesn't work.

These transition times are sure odd. Do you have a link to some official document that mentions the exact times of the changes?
Friday May 22 at 14:47 on 2002 thru 2040.
(This is wrong.)
Stop on Sat May 18-25 at 0859 only in 2008.
This range is also wrong.

This is full of undocumented format errors. See:
http://forums.itrc.hp.com/service/forums/questionanswer.do?threadId=1225597

You should also test this with Clay's dst.pl script:
http://forums.itrc.hp.com/service/forums/questionanswer.do?threadId=1231438

>JRF: Either your post scrambled something or your tztab format is wrong. Please re-examine the tztab manpages and/or the /usr/lib/tztab file.

It doesn't look too scrambled, just hard to read and incorrect. Unfortunately tztab(4) doesn't have enough info.

>once you have modified your tztab any application of a standard tztab patch with swinstall will *not* overlay your version, but rather leave the new version in the /usr/newconfig/etc directory.

Right, see:
http://forums.itrc.hp.com/service/forums/questionanswer.do?threadId=1214435
Highlighted
Advisor

Re: time change

thanks all for your replys
I'll try to correct the entry in tztab file

best regards