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Re: Scary bugs

On Fri, 04 Feb 2000, Edmund GRIMLEY EVANS wrote:
> Henrique M Holschuh <hmh+debianml@rcm.org.br>:
> > 3. --systohc on shutdown (without --adjust, and with --hctosys on startup)
> >    is needed to allow users to use the "one clock" approach. It is also
> >    needed for correct NTP operation. It is probably desired by anyone using
> >    ntpdate as well.
> My experience was that NTP did not work until I edited hwclock.sh to
> remove the --systohc.

NTP "did not work" ? This sounds _very_ strange. --systohc in shutdown, as
long as there is no --adjust on startup (and right now there isn't) simply
cannot interfere with a running NTP, because NTP has been already shutdown
by the time --systohc is run. Was there a --adjust on startup? Does your
computer do weird things to the processor speed (APM power conservation, APM

The --systohc is there because it is a sensible default, mostly. It will
work well for the majority of users _and_ computers AFAIK.

> I also found the --systohc rather annoying when I wasn't using NTP: it
> caused the clock to drift much faster than it used to.

It looks like your system clock is very badly out of sync. This could very
well cause weird clock hoppings across reboots (eg. when you just did a fast
reboot to change kernels) which could cause time screwups in your logs, for
example. IMHO your problem isn't with --systohc... it is far worse. adjtimex
might help you, I think.

> I think the --systohc was introduced in Debian 2.1; Debian 2.0 didn't
> have it, and my clock was fairly reliable then ...

Your RTC was reliable. Your system clock wasn't and still isn't even without
--systohc. --systohc just caused you to notice a bad problem that was
already there and probably needs to be addressed IMHO.

> to the Internet every day, but not always for long enough for NTP to
> synchronise itself. I don't want the hardware clock to be adjusted

I'd like to humbly suggest you have a look at ntpdate and chrony, as well as
adjtimex. APM can cause system clock weirdness as well.

> unless the system clock has been set by NTP. As I understand it, NTP
> causes the hardware clock to be adjusted anyway, so --systohc is
> unnecessary. I don't think my situation is unique. Other Debian users

There's a bad kludge in the kernel RTC auto-update "11 minute" mode which
screws up with adjustments above 30 minutes. --systohc on shutdown is still
necessary if you want to be *sure* the RTC is not left operating in a wrong

  "One disk to rule them all, One disk to find them. One disk to bring
  them all and in the darkness grind them. In the Land of Redmond
  where the shadows lie." -- The Silicon Valley Tarot
  Henrique Holschuh 

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