FAQ
Suppose you have server A and server B. Server B is running 60
seconds too fast, while server A is accurate. Is there a way to
gradually move server B's time back into sync with server A, without
making a drastic, immediate change to the clock? In other words, we
would like to 'smear' the difference across several hours or days to
ensure there are no drastic changes in timestamps, etc.

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  • Brian Mathis at Sep 4, 2012 at 1:17 pm

    On Tue, Sep 4, 2012 at 12:17 PM, Sean Carolan wrote:
    Suppose you have server A and server B. Server B is running 60
    seconds too fast, while server A is accurate. Is there a way to
    gradually move server B's time back into sync with server A, without
    making a drastic, immediate change to the clock? In other words, we
    would like to 'smear' the difference across several hours or days to
    ensure there are no drastic changes in timestamps, etc.

    This is already how ntpd works. When you first start the service
    (usually upon reboot), it will use 'ntpdate' to do a hard set of the
    clock, then ntpd picks up and adjusts the clock back and forth to keep
    it correct.


    ? Brian Mathis
  • Sean Carolan at Sep 4, 2012 at 1:24 pm

    This is already how ntpd works. When you first start the service
    (usually upon reboot), it will use 'ntpdate' to do a hard set of the
    clock, then ntpd picks up and adjusts the clock back and forth to keep
    it correct.
    My understanding was that ntpd will use "slewing" for adjustments of
    less than ~120ms or so, but for adjustments between 120ms and 17
    minutes it will use "stepping" instead, making an abrupt and immediate
    adjustment of the entire delta.

    What I'm trying to avoid is abruptly resetting the clock from 12:06 to
    12:05 all at once. Instead we want to slowly turn the clock back that
    one minute, but spread the changes across several hours or days.
  • Sean Carolan at Sep 4, 2012 at 1:33 pm

    What I'm trying to avoid is abruptly resetting the clock from 12:06 to
    12:05 all at once. Instead we want to slowly turn the clock back that
    one minute, but spread the changes across several hours or days.
    I think the "-x" option may be our solution; I R'd the FM and it says:

    "...If the -x option is included on the command line, the clock will
    never be stepped and only slew corrections will be used."

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