Re: Scary bugs
Henrique M Holschuh wrote:
> The hwclock man page makes it very clear that if, for example, you have NTP
> running in your machine (implies "11 minute mode" for the kernel), you must
> *never* call --hctosys or --adjust, and shouldn't even call hwclock
> --systohc as that disables 11 minute mode. This isn't documented in the
> README.Debian of either ntp or util-linux.
Hmm, I've seen this mentioned in various places but have never observed
I run a simple NTP server locally and the CMOS does still drift.
> Here's a possible (and probably broken somewhere :-) ) strategy to do this.
> It is not implementation-complete. For example, one would need to invalidate
> the drift file, as well as implement the idea of a drift file that only has
> the systematic drift stored, but not when it was last applied (I guess, I
> didn't study the hwclock code).
Gosh. Have you evver installed adjtimex? Have you looked at the --log
> 1. Train hwclock so that it learns the RTC's drift without tampering. I'll
> call this a "training period" where the user is strongly advised (in a
> bothersome, impossible not to notice way) not to touch the RTC, and told
> to deal with the crap himself if he does change the RTC.
> 2. The RTC drift is reasonably constant (otherwise the RTC is useless).
> hwclock should refuse to change the RTC drift too much unless in training
> mode. How much is 'too much' must be found by some careful testing, and
> should probably be configurable.
> If the drift is too big, warn the user and do not change the sistematic
> drift in the drift file.
> 3. hwclock should refuse to run --adjust if the drift to be applied to the
> RTC is "too big" (quite likely after a few days of downtime), warn the
> user that the clock has gained/lost too many seconds/hours/days (just
> like Solaris does), and maybe request the user to verify and run
> something like hwclock --adjust --force-adjust; hwclock --hctosys
Here is an example of an adjtimex --log being run out of cron. Then
adjtimex -r produces:
hecate root/~>adjtimex -r |tail -5
cmos_error = -8.41455 +- 0.00008 ppm suggested adjustment =
sys_error = -13.07469 +- 0.00007 ppm suggested tick = 10000
freq = 856863
note: clock variations and unstated data errors may mean that the
least squares solution has a bigger uncertainty than estimated here
There were a lot of measurements to get this result. It's quite accurate