15-second difference in time - NTP

This is a discussion on 15-second difference in time - NTP ; Hello, I've got a FreeBSD box acting as an ntp server for my local lan. All boxes connect up to it for synchronization of time. I run a network capable backup program called bacula and today while running a backup ...

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Thread: 15-second difference in time

  1. 15-second difference in time

    Hello,
    I've got a FreeBSD box acting as an ntp server for my local lan. All
    boxes connect up to it for synchronization of time. I run a network capable
    backup program called bacula and today while running a backup between two
    machines i got an error that the time between the two differed by 15
    seconds. I realize this isn't a lot of time, but reading the ntp docs i was
    under the impression that ntp would keep all boxes on my lan within
    milliseconds accurate of each other. If this is so i'd appreciate any
    suggestions as to what my issue might be.
    Thanks.
    Dave.



  2. Re: 15-second difference in time

    Dave wrote:
    > Hello,
    > I've got a FreeBSD box acting as an ntp server for my local lan.
    > All boxes connect up to it for synchronization of time. I run a
    > network capable backup program called bacula and today while running
    > a backup between two machines i got an error that the time between
    > the two differed by 15 seconds. I realize this isn't a lot of time,
    > but reading the ntp docs i was under the impression that ntp would
    > keep all boxes on my lan within milliseconds accurate of each other.
    > If this is so i'd appreciate any suggestions as to what my issue
    > might be. Thanks.
    > Dave.


    Dave,

    You say: "All boxes connect up to it for synchronization of time". Do you
    mean that all boxes run the NTP software as a client to the FreeBSD box
    (this is the way in which NTP is normally deployed), or that once every so
    often all boxes go and get the time from the FreeBSD system, and then just
    drift at random? If the latter, then NTP isn't controlling all boxes, if
    the former than you have an issue. What OS is running on "all boxes"?

    David



  3. Re: 15-second difference in time

    Hi, Dave!

    Dave schrieb:
    > Hello,
    > I've got a FreeBSD box acting as an ntp server for my local lan. All
    > boxes connect up to it for synchronization of time. I run a network capable
    > backup program called bacula and today while running a backup between two
    > machines i got an error that the time between the two differed by 15
    > seconds. I realize this isn't a lot of time, but reading the ntp docs i was
    > under the impression that ntp would keep all boxes on my lan within
    > milliseconds accurate of each other. If this is so i'd appreciate any
    > suggestions as to what my issue might be.
    > Thanks.
    > Dave.
    >
    >


    We once had a customer using our LANTIME time servers on his database
    backup servers. Each night the system clock of that server experienced
    30-second-jumps and it turned out that he is using IDE/ATAPI harddisks
    and DMA transfer (IIRC) and his Linux kernel was loosing timer ticks due
    to the heavy I/O caused by nightly update jobs.

    Sounds a little bit like your problem, doesn't it? :-)

    Best regards,
    Heiko




    --
    Meinberg radio clocks: 25 years of accurate time worldwide

    MEINBERG Radio Clocks
    www.meinberg.de

    Stand alone ntp time servers and radio clocks based on GPS, DCF77 and
    IRIG. Rackmount and desktop versions and PCI slot cards.

  4. Re: 15-second difference in time

    Dave wrote:

    > Hello,
    > I've got a FreeBSD box acting as an ntp server for my local lan. All
    > boxes connect up to it for synchronization of time. I run a network capable
    > backup program called bacula and today while running a backup between two
    > machines i got an error that the time between the two differed by 15
    > seconds. I realize this isn't a lot of time, but reading the ntp docs i was
    > under the impression that ntp would keep all boxes on my lan within
    > milliseconds accurate of each other. If this is so i'd appreciate any
    > suggestions as to what my issue might be.
    > Thanks.
    > Dave.
    >
    >


    Without knowing any more than the above, it's not possible to tell!

    What version(s) of ntpd are you running? Which operating systems are
    you running them on? What hardware?

    My first guess would be that ntpd is not running at all on one or more
    machines.

    How about posting the output of "ntpq -p" for the affected machines?


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