Re: Why touch the CMOS clock?

Steven S. Dick (
Tue, 14 May 96 04:04 EDT

In article <19960512144353.16753.qmail@Mail.UTexas.EDU>,
lilo <alfred!ucf-cs!!TaRDiS> wrote:
>On Sat, 11 May 1996, Herbert Rosmanith wrote:
>> If you dont have the chance to update your clock via ntp, then the
>> RTC is *much more* accurate than the internal, interrupt driven timer-clock.
>You've tried using adjtime to correct the problem?

Actually, I spent about a month or two calibrating my system's interrupt driven
clock. I wrote a command line utility that calls adjtimex directly to set
the system tick length.

My system's clock is accurate within one or two seconds a MONTH.
As long as it is on and running Linux, the clock doesn't drift significantly!

Prior to calibration, it drifted by as much as 30 seconds a day. The
RTC doesn't drift quite that much when the system is off, but it does
drift enough that I have to check the clock if I have the system off for
more than a few hours.

I don't adjust my clock with an external source, but the calibration
done with adjtimex seems to trigger the kernel updating the RTC.
I'm perfectly happy with this. I'd be unhappy if it was changed.

If you don't like the RTC fiddled with unexpectedly, either don't
synchronize your system clock, or add a flag to the adjtimex stuff
to not update the clock... Don't just remove the code because you
personally have no use for it.