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| author | Beat Bolli <bbolli@ewanet.ch> | 2013-10-21 23:29:21 +0200 |
|---|---|---|
| committer | Eric S. Raymond <esr@thyrsus.com> | 2013-10-22 13:45:43 -0400 |
| commit | c01b8f571c0b6b9d8db27f6e11304bf259a01b7e (patch) | |
| tree | 47705b9df6c0ae6168e7120b2f4269b139fa4635 /www | |
| parent | 653e45624182b11bc349fe5f1c4d70690b1edbf5 (diff) | |
| download | gpsd-c01b8f571c0b6b9d8db27f6e11304bf259a01b7e.tar.gz | |
HOWTO: calculate the average GPS offset
Diffstat (limited to 'www')
| -rw-r--r-- | www/gpsd-time-service-howto.txt | 30 |
1 files changed, 30 insertions, 0 deletions
diff --git a/www/gpsd-time-service-howto.txt b/www/gpsd-time-service-howto.txt index 6bdc7c36..fc793050 100644 --- a/www/gpsd-time-service-howto.txt +++ b/www/gpsd-time-service-howto.txt @@ -528,6 +528,36 @@ If the offset is positive, reduce the time1 value and vice versa. A more detailed description of the output is available at <<NTPQ-OUTPUT>>. +In order to determine the correct GPS offset, do the following: + +1. Add these lines to ntp.conf: + +----------------------------------------------------------------------------- +statsdir /var/log/ntpstats/ +statistics peerstats +filegen peerstats file peerstats type day enable +----------------------------------------------------------------------------- + +This enables logging of the peer server statistics. + +2. Start ntpd and let it run for at least four hours. + +3. Calculate the average GPS offset: + +----------------------------------------------------------------------------- +awk ' + /127\.127\.28\.0/ { sum += $5 * 1000; cnt++; } + END { print sum / cnt; } +' </var/log/ntpstats/peerstats +----------------------------------------------------------------------------- + +This prints the average offset. + +5. Adjust the "time1" value in ntp.conf by subtracting the average + offset from step 4. + +6. Restart ntpd. + == Providing public NTP service == <<NTP-FAQ>> has good advice on things to be sure you have done - and |