topic Re: xntpd and "daylight saving time" in Operating System - HP-UX

xntpd and "daylight saving time"

Andreas Bechtle_1 — Tue, 22 Mar 2005 05:30:20 GMT

Hi,

please forgive me, I`m sure that question was asked a hundred times but I cannot find anything in the web.

I`ve some HP-UX 11.23 servers with daylight saving time and "xntp -x" (slew).

If I understand the man-pages correct xntpd will shut down if the timedifference is bigger than 1000 seconds. So what to do when we switch to daylight saving time? ntpdate (manually or by cron)? Or better a reboot (especially if the time switches from 03:00 to 02:00)?

Or is there a parameter I can use so xntpd do it all by itself? I'd prefer if the system can do all by itself and the application people just stop their stuff for some time.

Best Regards

Andreas

Re: xntpd and "daylight saving time"

Pete Randall — Tue, 22 Mar 2005 06:00:27 GMT

You have to remember that the time doesn't actually change for daylight savings time, just the way the time is displayed. You don't need to reboot or change any parameters or anything. Just leave it alone.

Pete

Re: xntpd and "daylight saving time"

Kent Ostby — Tue, 22 Mar 2005 08:11:37 GMT

Because this time change is predictable, all of the HP programs that are dependent will handle the time change either by using the system clock (and hence ignoring the "displayed time") or by compensating for the displayed time.

xntp and Serviceguard do the first.

cron does the second.

Re: xntpd and "daylight saving time"

Patrick Wallek — Tue, 22 Mar 2005 09:40:42 GMT

All time on HP-UX machines is actually kept in GMT, which never changes.

The time you see when you use the 'date' command is determined according to the TZ environment variable, or if that isn't set /etc/TIMEZONE or /etc/default/tz. The TZ variable looks something like: CST6CDT, which means Central Standard Time (GMT -6) Central Daylight Time.

If you look at the /usr/lib/tztab file that will show exactly when the time will change for almost all timezones defined.

Don't worry about changing the time on your machine. It will happen automagically.

Re: xntpd and "daylight saving time"

A. Clay Stephenson — Tue, 22 Mar 2005 09:54:01 GMT

Remember, this is UNIX; it's possible that you could have users connected all over the world in many different timezones and the system has to be able to cope with that. The system simply counts seconds since 1-Jan-1970 00:00:00 UTC and that never changes. How the time is displayed is determined by the TZ setting but how the time is kept internally remains constant. UNIX boxes connected around the world that were the members of a common NTP network would have (very nearly) the same internal time values although the way the time data might be displayed might be widely divergent. In short, you don't need to do anything about DST because nothing really happens.

Re: xntpd and "daylight saving time"

Andreas Bechtle_1 — Wed, 23 Mar 2005 05:49:28 GMT

OK, thanks. This helps

The problem are the applications (SAP/oracle). They will be shut down during the "switch". As the (displayed) time on the unix system switch immediatly (as you explained) this is only an application-task.

Thanks all

Andreas