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Re: daylight savings time: POSIX vs real world



liw@iki.fi (Lars Wirzenius)  wrote on 02.05.97 in <m0wNMJp-000AiDC@liw.clinet.fi>:

> If Linux set the BIOS clock itself, things would still break. This
> seems to happen if you use both Windows95 and Windows NT -- both
> will ask you if it is OK to set the clock after daylight savings
> time has begun or ended. So your clock will be off by one hour.

True. But for people that only use other systems that don't reset the  
clock, and still want to have the clock at local time to keep the other  
systems happy, there is a solution.

I'm running xntpd to synchronize my clock, so I can assume that the  
running clock is "always" ok (well, after it has been able to sync with  
the net).

This doesn't set the hardware clock, though.

No problem - make a cron job that does "clock -w" every hour or so, to set  
the hardware clock from the system clock.

Now Linux _does_ set the hardware clock to the correct variant of local  
time (according to the time zone that the cron job sees).

If Linux is not active at the start or end of summer time, then it will  
correct the clock once it gets active (assuming that the xntpd package is  
configured so approximately-one-hour corrections will actually be made -  
this is usually done with /et/xntpd start).

There's only one problem - the Linux system time must be kept correct. I  
get it from the net with xntpd; you can get it from a local clock with  
xntpd; otherwise you must set it manually.

MfG Kai


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