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[gpsd-dev] [PATCH] HOWTO: calculate the average GPS offset
From: |
Beat Bolli |
Subject: |
[gpsd-dev] [PATCH] HOWTO: calculate the average GPS offset |
Date: |
Mon, 21 Oct 2013 23:29:21 +0200 |
---
www/gpsd-time-service-howto.txt | 30 ++++++++++++++++++++++++++++++
1 file changed, 30 insertions(+)
diff --git a/www/gpsd-time-service-howto.txt b/www/gpsd-time-service-howto.txt
index 62aefda..c0592a3 100644
--- a/www/gpsd-time-service-howto.txt
+++ b/www/gpsd-time-service-howto.txt
@@ -459,6 +459,36 @@ 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
--
1.8.4.rc3
- [gpsd-dev] [PATCH] HOWTO: calculate the average GPS offset,
Beat Bolli <=
Re: [gpsd-dev] [PATCH] HOWTO: calculate the average GPS offset, Eric S. Raymond, 2013/10/22