Tags: ntpd

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  1. 3 years ago by sox
    service ntp stop
    ntpd -gq -c /etc/ntp.conf
    service ntp start
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  2. 4 years ago by spirit
    > According to www.ntp.org in stanard Linux o.s. (adjtime(2) - http://www.ntp.org/ntpfaq/NTP-s-algo.htm#S-ALGO-BASIC) time adjusting has rate of 0.5ms per second
    That's the _maximum_ slew rate. The actual slew rate depends on a number f factors.
    > to slew time but because do you speak about "maximum" rate of 0.5 ms/sec. ?
    The maximum slew rate is 500ppm; this is the equivalent of half a millisecond per second or 43 seconds per day.
    > Does ntpd use always the same 0.5 as value or it's a variable parameter ?
    500ppm is the _maximum_ slew rate that most kernels can tolerate. The actual slew rate depends on a number of factors.
    > I'm confused because "Rob MacGregor" said about step method (128ms < offset < 1000s) :
    1000 seconds == the default panic threshold. ntpd will abort when it sees an offset greater than the panic threshold
    128ms == the default step/slew threshold. ntpd will slew offsets below this threhold and will step offsets above this threshold
    >Stepping: Time changes in large units, quickly With "Step" method (settimeofday), time is gradually changed with higher rate or time is changes immediately to correct time.
    step == reset the clock to the correct time in _one_ instantaneous step.
    A stepped clock can "move backwards".
    slew == adjust the clock by speeding it up or slowing it down. A slewed clock never "moves backwards"
    > example for use step method : my local clock is 5:00 pm and real time is 5:05 pm, Ntpd set immediately local clock to 5:05 pm or it corrects time gradually ?
    Slewing the clock to correct a 5 minute offset will take 6.97 days at the maximum 500ppm slew rate.
    5 minutes is greater than the default 128ms step/slew threshold. In this case ntpd will _step_ the clock.
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