[ntp:questions] Q: Disabling "11 minute mode"

Dean S. Messing deanm at sharplabs.com
Fri Jan 25 20:40:13 UTC 2008


Serge Bets wrote:
>  On Tuesday, January 22, 2008 at 19:02:23 +0000, Dean S. Messing wrote:
> 
> > Is it possible to disable "11 minute mode" from "ntp.conf"?
> 
> No. You have to tweak the kernel. If you have the PPSkit:
> 
> | $ echo 0 > /proc/sys/kernel/time/rtc_update
> 
> Otherwise you have to patch time.c in the kernel. Dead easy, just a
> matter of commenting out a line or two. I'm so patching all my kernels,
> reading and writing the RTC exclusively with hwclock 2.31, and am
> getting a far better accuracy.
> 
> The main purpose of an RTC is to initialise the system time at powerup,
> isn't it? Most people startup in the morning at around half a second of
> the true time, and later ntpd has to step this to UTC. I routinely
> startup at some low milliseconds of the true time, offset quickly
> slewed. My last step event was years ago.

Thanks Serge.  I looked up PPSkit.  Looks good, but I'm going to have
to learn how to patch the Fedora kernel to install PPSkit.

But I'm discovering that I have rather deeper problems on my machine
(a Dell 490 Precision).  Using adjtimex --compare to track the drift
between system and cmos clock (ntpd not running), I see that the RTC
is behaving _very_ strangely.  It will begin to return screwy values
after several hours of doing "adjtimex --compare" and then get to the
point where "hwclcok --show" hangs.  So my desire to turn off "11
minute mode" is  mute when ntp is running is mute.

For your amusement, here's a snippet of the output of
"adjtime --compare" with an interval of 60 seconds:

1200982902     0.001784       -2.0  10001   3929312   10001   4060301
1200982962     0.001792        0.1  10001   3929312   10001   3920719
1200983022     0.002051        4.3  10001   3929312   10001   3646240
1200983082     0.001828       -3.7  10001   3929312   10001   4173062
1200983142     0.001756       -1.2  10001   3929312   10001   4007957
1200983202     0.002025        4.5  10001   3926656   10001   3632906
1200983261     0.500370     8305.8  10001   3926288    9918   3549307
1200983281    40.001689   658355.3  10001   3926288    3418    301130
1200983341    40.001931        4.0  10001   3926288   10001   3661966
1200983407    34.001894  -100000.6  10001   3926288   11001   3966652
1200983461    40.001646    99995.9  10001   3926288    9001   4197121
1200983521    40.001890        4.1  10001   3926288   10001   3659882
1200983609    12.001763  -466668.8  10001   3924640   14668   1878649
1200983641    40.001606   466664.0  10001   3924640    5334   6280787
1200983741     0.001726  -666664.7  10001   3924640   16668   1609118
1200983761    40.001911   666669.8  10001   3924640    3334   5907090
1200983821    40.001553       -6.0  10001   3924640   10001   4315525
1200983921     0.001748  -666663.4  10001   3924640   16668   1527086
1200983941    40.001894   666669.1  10001   3924640    3334   5949798
1200984001    40.001554       -5.7  10001   3924640   10001   4295994
1200984101     0.001700  -666664.2  10001   3921488   16668   1577580
1200984161     0.001291       -6.8  10001   3921104   10001   4367718
1200984221     0.001532        4.0  10001   3921104   10001   3657823
1200984275     6.001806   100004.6  10001   3921104    9001   3621886
1200984301    40.001722   566665.3  10001   3920368    4334   6196568
1200984361    40.001974        4.2  10001   3920368   10001   3645108
1200984427    34.001868  -100001.8  10001   3920368   11001   4036253
1200984481    40.001679    99996.8  10001   3920368    9001   4126878

Things got so bad that the output eventually became:

199345540  1001658696.064552  1592732.9  10001   3879376   -5926   1725431
199345717  1001658600.500585 -1592732.8  10001   3879376   25928   6027853
199345718  1001658696.023830  1592054.1  10001   3879376   -5919    335126
199345896  1001658600.500586 -1592054.1  10001   3879376   25922    868985
199345897  1001658696.045414  1592413.8  10001   3879376   -5923   2975047


Before it went crazy, it had run smoothly for 5 or 6 hours.
When I rebooted into the BIOS and looked at the RTC it was off by
several years.

This has now happened thrice, but only when adjtimex is running in the
compare mode for long periods.  I have no idea what this means.  The
cmos battery does not appear to be the problem since, after a reboot,
the RTC remains at proper time indefinitely (modulo drift), unless
and until I run adjtimex --compare for several hours.

Anyway, thanks for the info. on "11 minute mode".  Wish I could fix my
RTC problem

Dean



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