NTPD unable to adjust local clock

Matthew Dillon dillon at apollo.backplane.com
Tue Apr 5 17:35:24 PDT 2005

:I'm in securelevel 0.
:> Does anyone else have this problem?
:Yes, I'm seeing this as well.  Without a thorough analysis, it looks like
:once it gets under 1s of error (my clock runs pretty fast) it seems to be
:able to adjust it okay.

    I've run some basic tests and ntpd seems to work with adjustments
    both less then and greater then 1 second.

    If your clock naturally runs very fast or very slow there could be
    a problem.  adjtime() only adjusts 30ms per 60 seconds when the 
    time delta is less then one second, and 300ms per 60 seconds when
    the time delta is greater then one second.  If your clock naturally
    runs beyond the 30ms per 60 seconds limit then the time is going to
    constantly be > 1 second off because adjtime() won't be able to
    compensate for the broken clock.

    It looks like the OpenBSD ntpd that we are using now is no where near
    as sophisticated as the original ntpd we had.  It has no capability
    to make PLL adjustments.  All it does is call adjtime().  adjtime() is 
    a very poor substitute for ntp_adjtime().


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