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Re: [gpsd-dev] PPS and privilege-dropping

From: Harlan Stenn
Subject: Re: [gpsd-dev] PPS and privilege-dropping
Date: Thu, 17 Oct 2013 20:11:08 +0000

"Eric S. Raymond" writes:
> The JSON PPS messages were designed with a specific purpose in mind -
> to track the skew between NTP-adjusyed system clock and GPS+PPS time
> so Dave Taht and I can benchmark NTP.

And there was much rejoicing.

> A brief tutorial on how to choose NTPd offset parameters would be good
> to have in the HOWTO, too.  Basically I want this to be a primer for
> the relatively ignorant - like, er, me.
> Also I think the table of NTP offsets that's now on the hardware page
> should move to the HOWTO.

I'd love to have (links to) all this content somewhere on both NTP and
NTF websites.  I'd be curious to see how this could be used to
illuminate system behavior for PTP and RADclock solutions as well.

>> ALL ntpd prefers root for initialization.  There is serious loss of
>> functionality when not initialized as root.
> The HOWTO should explain this.  There's a reference to it in a comment
> in ntpshm.c, but it didn't tell me enough to understand *why*.

I'm not sure what is meant here.  Some of the things ntpd needs root for
include opening port 123, sometimes updating the time, and there may
also be an issue for shmget() units 0 and 1 (which are 0600 perms, while
units 2 and 3 are 0666).  There may be other cases.


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