[LinuxPPS] offset 0 etc

[Dave Hart]

On Sun, Mar 18, 2012 at 07:59, Udo van den Heuvel <udovdh at xs4all.nl> wrote:
> On 2012-03-17 14:51, Dave Hart wrote:
>> On Sat, Mar 17, 2012 at 07:15, Udo van den Heuvel <udovdh at xs4all.nl> wrote:
>>> I added a GPS18 to the box with the DCF clock.
>>> Works well, except:
>>> Offset, ppm etc remain at zero.
>>> Why is that?
>>
>> Presumably because those machines are using the daemon loop discipline
>> rather than kernel loop discipline.
[...]
>> Are you passing -x or --slew to
>> ntpd?  Does your ntp.conf "tinker step" or "disable kernel"?
>
> /usr/sbin/ntpd -n -u ntp:ntp -g -x
>
> all machines are on 24/24 for 99.9something % of the year.
> So these do not have much impact.

-x
Normally, the time is slewed if the offset is less than the step
threshold, which is 128 ms by default, and stepped if above the
threshold. This option sets the threshold to 600 s, which is well
within the accuracy window to set the clock manually. Note: Since the
slew rate of typical Unix kernels is limited to 0.5 ms/s, each second
of adjustment requires an amortization interval of 2000 s. Thus, an
adjustment as much as 600 s will take almost 14 days to complete. This
option can be used with the -g and -q options. See the tinker command
for other options. Note: The kernel time discipline is disabled with
this option.

http://www.eecis.udel.edu/~mills/ntp/html/ntpd.html

Cheers,
Dave Hart