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[gpsd-dev] A detail in your ntpoffset script

From: Eric S. Raymond
Subject: [gpsd-dev] A detail in your ntpoffset script
Date: Tue, 22 Oct 2013 18:17:29 -0400 (EDT)

awk '
     /127\.127\.28\.0/ { sum += $5 * 1000; cnt++; }
     END { print sum / cnt; }
' </var/log/ntpstats/peerstats

Should that be .1 rather than .0?  

I'm thinking of this coment in ntpshm.c:

 * Segments 0 and 1: permissions 0600, i.e. other programs can only
 *                   read and write as root.
 * Segments 2 and 3: permissions 0666, i.e. other programs can read
 *                   and write as any user.  I.e.: if ntpd has been
 *                   configured to use these segments, any
 *                   unpriviliged user is allowed to provide data
 *                   for synchronisation.
 * As gpsd can be started as both root and non-root, this behaviour is
 * mimicked by:
 * Started as root: do as ntpd when attaching (creating) the segments.
 * (In contrast to ntpd, which only attaches (creates) configured
 * segments, gpsd creates all segments.)
 * Started as non-root: only attach (create) segments 2 and 3 with
 * permissions 0666.  As the permissions are for any user, the creator
 * does not matter.
 * For each GPS module gpsd controls, it will use the attached ntpshm
 * segments in pairs (for coarse clock and pps source, respectively)
 * starting from the first found segments.  I.e. started as root, one
 * GPS will deliver data on segments 0 and 1, and as non-root data
 * will be delivered on segments 2 and 3.

This seems to imply that the PPS unit is .1 rather than .0.
                <a href="";>Eric S. Raymond</a>

No matter how one approaches the figures, one is forced to the rather
startling conclusion that the use of firearms in crime was very much
less when there were no controls of any sort and when anyone,
convicted criminal or lunatic, could buy any type of firearm without
restriction.  Half a century of strict controls on pistols has ended,
perversely, with a far greater use of this weapon in crime than ever
        -- Colin Greenwood, in the study "Firearms Control", 1972

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