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[gpsd-dev] Final revisions to the Time Service HOWTO


From: Eric S. Raymond
Subject: [gpsd-dev] Final revisions to the Time Service HOWTO
Date: Wed, 20 Nov 2013 00:37:19 -0500 (EST)

I'm walking through the process in the HOWTO.  Some questions that are
coming up:

1. ntpd versus chronyd.  What criteria suggest one, what the other?
   What should the HOWTO say about the tradeoffs?  Even if it's as
   simple as "chrony fans like it because X" and "ntpd fans like it
   because Y", we need to say *something* to explain why both
   exist and help the reader make an informed choice.

   I have added some trial text:

      Of these two, ntpd is the older and more popular choice - thus, the
      one with the best-established peer community if you need help in
      unusual situations.  On the other hand, chrony has a reputation for
      being easier to set up and configure, and is better in situations
      where your machine has to be disconnected from the Internet for long
      periods of time.

      A feature comparison, part of the chrony documentation, is at
      <<CHRONY-COMPARE>>. If you don't already know enough about time
      service to have a preference, the functional differences between them
      are unlikely to be significant to you; flip a coin.

   If anyone feels they can improve on this, please do.

2. The text now asserts that chrony (like ntpd) uses a short drift
   history and autoadjusts its drift sampling interval.  It does this
   for two reasons.  (a) I want to separate the discussion of crystal
   drift - which is a general phenomenon - from the specifics of
   either ntpd or chronyd implementation.  (b) Thinking about the
   underlying statistics it's not easy to see how chrony could be
   doing anything else unless it has jumped to something *very*
   sophisticated like Kalman filtering.

   The chrony documentation strongly hints at a short drift history
   but is silent about interval autoadjustment.  Can anyone confirm
   or refute that this is what it does?

More generally, please look for FIXME comments in the document and
fill in what you can.
-- 
                <a href="http://www.catb.org/~esr/";>Eric S. Raymond</a>

Democracy is two wolves and a lamb voting on what to have for lunch. Liberty is
a well-armed lamb contesting the vote!
        -- Benjamin Franklin



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