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SubjectRe: Linux timekeeping plans
On Thu, 3 Dec 1998, Brandon S. Allbery KF8NH wrote:
>
> PC RTCs are horrible. For all that it lost up to 15 seconds a day, my
> 486DX2/66 kept better time in Linux (or OS/2, etc.) than its RTC did. My
> P200 dosesn't appear to be much better.
>

Here is a log of my Linux file-server's time referenced to NIST at
one-hour intervals.

Script started on Thu Dec 3 11:30:48 1998
# while gettime time-a.timefreq.bldrdoc.gov ; do sleep 3600 ; done

Reference time = Thu Dec 3 11:31:37 1998
My time = Thu Dec 3 11:31:37 1998
Difference = 0
Reference time = Thu Dec 3 12:31:38 1998
My time = Thu Dec 3 12:31:38 1998
Difference = 0
Reference time = Thu Dec 3 13:31:38 1998
My time = Thu Dec 3 13:31:38 1998
Difference = 0
Reference time = Thu Dec 3 14:31:38 1998
My time = Thu Dec 3 14:31:38 1998
Difference = 0
Reference time = Thu Dec 3 15:31:38 1998
My time = Thu Dec 3 15:31:38 1998
Difference = 0
Reference time = Thu Dec 3 16:31:37 1998
My time = Thu Dec 3 16:31:37 1998
Difference = 0
Reference time = Thu Dec 3 17:31:37 1998
My time = Thu Dec 3 17:31:37 1998
Difference = 0
Reference time = Thu Dec 3 18:31:37 1998
My time = Thu Dec 3 18:31:37 1998
Difference = 0
Reference time = Thu Dec 3 19:31:37 1998
My time = Thu Dec 3 19:31:37 1998
Difference = 0
Reference time = Thu Dec 3 20:31:36 1998
My time = Thu Dec 3 20:31:33 1998
Difference = -3 seconds
Reference time = Thu Dec 3 21:31:36 1998
My time = Thu Dec 3 21:31:33 1998
Difference = -3 seconds
Reference time = Thu Dec 3 22:31:35 1998
My time = Thu Dec 3 22:31:34 1998
Difference = -1 seconds
gettime connect(): Connection timed out
# exit
exit

Script done on Fri Dec 4 08:24:22 1998

You can see that the time was quite stable until 20:31:36 where it
took a jump of a few seconds, then by 22:31:35 it had gotten close
to the original.

I find that most all PCs are quite stable, but do suffer a long-term
drift, mostly because of the unidirectional jog shown above. If the
time would slowly vary about a mean value, the adjtime mechanism would
on, the average, keep the time quite close to NIST.

Instead, I fix by resetting the time to NIST once each morning using
a crond script.

Cheers,
Dick Johnson
***** FILE SYSTEM WAS MODIFIED *****
Penguin : Linux version 2.1.128 on an i686 machine (400.59 BogoMips).
Warning : It's hard to remain at the trailing edge of technology.


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