-g broken

Gary E. Miller gem at rellim.com
Sat Mar 24 00:23:28 UTC 2018

Yo Hal!

On Fri, 23 Mar 2018 17:15:51 -0700
Hal Murray via devel <devel at ntpsec.org> wrote:

> Gary said:
> > The raspberry pi has no RTC.  When it starts cold, the time may
> > well be in 1969.  Somehow, not sure how, that becomes 2134.  Then
> > gpsd uses that as the GPS epoch, and things go downhill from
> > there...   
> So gpsd does something stupid and you expect ntpd to figure out how
> to recover?

Yup.  It is the job of ntpd to remove false chimers.  And in my case,
it does so, but still sets the wrong time.

> This is a good example of the sort of heuristic I was talking about.
> If the time really is in 2134, then gpsd might be doing the right
> thing.  But how likely is that?

Sadly GPS time is in weeks, modulo 1024.  So 2134 just one of many

> Do we know how a Raspberry Pi sets its clock during boot?

It has no RTC, so nothing to set the clock from.  There are a few
heuristics that various distros apply.  None very good.

> I just rebooted a Pi with ntpd disabled.  It came up with a sensible
> time.  I powered it off for several minutes and it came up with the
> time when I powered it off.

Yeah, depends on your distro.  They usually get it right, I'm worried
about the corner cases when it does not.  Like on first boot from a
raw install.

Gary E. Miller Rellim 109 NW Wilmington Ave., Suite E, Bend, OR 97703
	gem at rellim.com  Tel:+1 541 382 8588

	    Veritas liberabit vos. -- Quid est veritas?
    "If you can’t measure it, you can’t improve it." - Lord Kelvin
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