Summer time change

[Dmitriy_16]

I use HP cluster in cold standby node which consists of two servers rp5470. Also there is Informix database which runs only on active node.
In my country it is neccessary to modify time to times per year. I want to organize this process automatically. As I understood it is enough to set correct Timezone. Current timezone is GMT-2 but it does not support automatic change time. I want to set correct timezone Europe/Kiev.
can I use set_parms timezone command?
Other question. Is it dangerous for Informix DB if time will be changed automatically for one hour? When I made change to winter time I stopped all application and Informix DB and only after this modify timezone. If time will be changed automaticaly when Informix is in running state can it demage database?

[Kent Ostby]

You can use set_parms.

I have no idea on the DB aspect. Generally it is especially bad to make time run backwards.

[Bill Hassell]

HP-UX is unique in that time NEVER changes internally--it is always GMT. The only 'apparent' time change is when the current value of $TZ has a set of rules for timezones. The supplied list of timezones are located in /usr/lib/tztab and with the man page for tztab, you can construct your own timezone which will display the time for you local area.

Informix should handle the time change just fine unless your version is very old. As I mentioned, the time does not change, only the representation of the GMT time changes. For instance, if you temporarily change the TZ value, you can see how it affects the date command:

TZ=EST5EDT date
TZ=PST8PDT date
date

In the first two cases, the TZ value is set to New York timezone, then to Los Angeles timezone (Eastern and Pacific) and the date is displayed accordingly. The last date command shows your local time. To add your own entry, the man page for tztab will be helpful. Also look at the timezone for Finland (EET-2EETDST) in tztab which is GMT-2 plus rules for when the switch is to occur.

[A. Clay Stephenson]

Bear in mind that you could have many different timezones in effect by users connected to your box all over the world. The database is expected to handle that sort of thing without a hiccup. You should set the set the TZ to an entry in /usr/lib/tztab and then you will never need to do anything again. One common error application programmers make is not allowing for the timezone in the date/time displays. For example, if your time changes at 2:00 AM (as it does in the US) then if the display is simply 02:15 AM then the user has no way of knowing is this is 02:15 AM standard time or daylight/summer time. A better display would be something like 02:15 AM CDT; then the displayed time is not ambiguous.