[ntp:questions] how to have offset < 1ms

Richard B. Gilbert rgilbert88 at comcast.net
Mon Apr 12 20:35:46 UTC 2010


lhommedumatch wrote:
> I have my PC clock synchronised with a ntp server (ntpgmtaceb).
> 
> With ntpq -p, I see an offset of 6ms.
> How can I be sure to have an offset < 1ms
> 
> ntpq -p
>      remote           refid      st t when poll reach   delay
> offset  jitter
> ==============================================================================
>  LOCAL(0)        .LOCL.          10 l   61   64  377    0.000
> 0.000   0.001
> *ntpgmtaceb      .1PPS.           1 u  709 1024  377   29.431
> -6.450   0.917
> 
> Here is my ntp.conf:
> # Permit time synchronization with our time source, but do not
> # permit the source to query or modify the service on this system.
> restrict default kod nomodify notrap nopeer noquery
> 
> # Permit all access over the loopback interface.  This could
> # be tightened as well, but to do so would effect some of
> # the administrative functions.
> restrict 127.0.0.1
> restrict -6 ::1
> 
> # Hosts on local network are less restricted.
> #restrict 192.168.1.0 mask 255.255.255.0 nomodify notrap
> 
> # Use public servers from the pool.ntp.org project.
> # Please consider joining the pool (http://www.pool.ntp.org/
> join.html).
> 
> #broadcast 192.168.1.255 key 42         # broadcast server
> #broadcastclient                        # broadcast client
> #broadcast 224.0.1.1 key 42             # multicast server
> #multicastclient 224.0.1.1              # multicast client
> #manycastserver 239.255.254.254         # manycast server
> #manycastclient 239.255.254.254 key 42  # manycast client
> 
> # Undisciplined Local Clock. This is a fake driver intended for backup
> # and when no outside source of synchronized time is available.
> server 127.127.1.0
> fudge   127.127.1.0 stratum 10
> 
> # Drift file.  Put this in a directory which the daemon can write to.
> # No symbolic links allowed, either, since the daemon updates the file
> # by creating a temporary in the same directory and then rename()'ing
> # it to the file.
> driftfile /var/lib/ntp/drift
> 
> # Key file containing the keys and key identifiers used when operating
> # with symmetric key cryptography.
> keys /etc/ntp/keys
> 
> # Specify the key identifiers which are trusted.
> #trustedkey 4 8 42
> 
> # Specify the key identifier to use with the ntpdc utility.
> #requestkey 8
> 
> # Specify the key identifier to use with the ntpq utility.
> #controlkey 8
> server ntpgmtaceb
> restrict ntpgmtaceb mask 255.255.255.255 nomodify notrap noquery
> 
> Regards,
> Ludovic

Read the documentation CAREFULLY!  I think that you will find that 
"offset" is NOT the difference between your clock and the correct time!

There IS a number that does represent the difference between your clock 
and the correct time but I have forgotten what it's called.




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