[ntp:questions] ntpd -g option

unruh unruh at invalid.ca
Wed Feb 15 20:22:48 UTC 2012

On 2012-02-15, Dave Hart <hart at ntp.org> wrote:
> On Tue, Feb 14, 2012 at 16:54, Echols Jr, Thomas <tommy.echols at cubic.com> wrote:
>> Does anyone know why this would occur? ?Will a -g option not work with a
>> Shared memory time source, or is there something else that needs to be
>> done in tandem. Below is my ntp.conf file:
> ntpd -g behavior is the same for reference clocks and upstream NTP
> servers.  The timeout happens when the shared memory segment's valid
> field is zero.  Bad time is triggered by incredible date or time
> values.
> I wonder if gpsd is requiring the time be close before sharing it with
> ntpd.  Miroslav Lichvar has a patch pending to add support to

I think it depends. If it is pps that gpsd is reading, then I think the
answer is yes. It either uses the nmea from the gps system to set the
seconds of the pps or waits. I know the shmpps code does exactly that--
waits for the ntpq to report that the clock is synced with an offset of
less than about 1.4 sec before sending pps pulses ( since it uses the
system clock to determine the seconds part of the pps time)

> refclock_shm.c to report a timecode string in response to ntpq's cv,
> you might give that a whirl:
> http://bugs.ntp.org/2048
> Cheers,
> Dave Hart

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