[ntp:questions] Linux 11-minute mode (RTC update)
root at localhost.invalid
Fri Apr 4 12:25:12 UTC 2008
Serge Bets wrote:
> Noob wrote:
>> STA_UNSYNC (0x0040, clock unsynchronized) is 0. [...] Thus the kernel
>> should write the system time to the RTC every 11 minutes; but it does
> Fine! Don't touch anything, happy man, or it might well "tomber en
Hello Serge, I was hoping you'd comment!
If I don't want the kernel to update the RTC, I can always undef
> Real men don't want the eleven-minutes mode.
> It is not only extremely inaccurate by itself, but it also steps on
> the toes of those tools that are able to manage the RTC properly.
Our equipment is supposed to run 24/7 for months / years.
I need to keep the RTC synchronized, in case of power failure.
Do you believe that running hwclock --systohc periodically is better
than using the kernel's 11-minute mode?
> I previously posted some figures, comparing the accuracy of writing the
> RTC (not counting drift). Mean offset and dispersion:
> - eleven-minutes mode: -2150 µs +-5000
> - hwclock util-linux-ng 2.13.1: -2500 µs +-170
> - hwclock 2.32 from BJH: 0 µs +-10
( I use http://giraffe-data.com/software/about_hwclock.html )
If I use hwclock to update the RTC, how often should I do it?
What do you think about the following script?
sleep 660 # or some other value?
hwclock --utc --systohc
> Furthermore both hwclocks are able to evaluate and compensate the drift
> of the RTC. The eleven-minutes mode cannot do that, and instead it can
> perturbate hwclock's calculations.
Is the crystal of the RTC supposed to be more stable than the crystal
of the CPU?
More information about the questions