Re: ntp and hwclock
On Tue, 23 Jan 2007, Ken Heard wrote:
> >Linux kernel updates CMOS (hardware clock) time every 11 minutes.
Only when in ntp sync mode, AFAIK. Maybe the new RTC class lets one change
this easily, but then the "CMOS RTC" port to the new RTC class ain't in
Linux mainline yet.
> >In-kernel clock, that uses various CPU/Chipset hardware and is stable
> >enough. Its precision is as good as CPU frequency high (mostly). Any big
> >drift may be caused by bugs in the kernel, low precision of CMOS while
> >computer is powered off.
Plus low stability on the kernel clock sources in the presence of cpu freq
changes, sleep to ram or to disk, spread-spectrum clock modulation, and
general bogon activity.
> Does the foregoing mean that Etch does not need ntp or ntpdate to
> maintain reasonable clock stability?
No. On a standard consumer peecee(snort!), you will really need ntpdate to
be sure the clock is not set to anything dumb during system bootstrap, and
if you really need clock stability for real, a proper ntp setup (which is a
lot more than just ntpd running!) is also a requirement.
--
"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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