Re: [chrony-users] Root delay and Root dispersion values in `chronyc ntpdata'

[Horia Muntean <horia.muntean@xxxxxxxxx>]

AFAIK in measurements.log there is no info that points to the source clock
so if one has more sources you would have to look at tracking.log to
see whats the current source.

Second in measurements.log there are no records if the source clock is
a reference clock.

Third 'System Time' from 'chronyc tracking' command is  the difference
between the
 chronyd's estimate of the current true time and the system time. This
difference together with root delay and
dispersion can give you the estimated maximum error from UTC.

At least this is my understanding - it might be wrong.

See https://www.mail-archive.com/chrony-users@xxxxxxxxxxxxxxxxxxxx/msg01196.html

<quote>
I think a better way to monitor the maximum error of the system clock

is to use the values from the chronyc tracking command:
abs(System_time) + Root_delay / 2 + Root_dispersion <= target
</quote>

On Tue, Aug 8, 2017 at 6:50 PM, Bill Unruh <unruh@xxxxxxxxxxxxxx> wrote:
> Isn't that information all there already in the "measurements" log?
>
>
> William G. Unruh __| Canadian Institute for|____ Tel: +1(604)822-3273
> Physics&Astronomy _|___ Advanced Research _|____ Fax: +1(604)822-5324
> UBC, Vancouver,BC _|_ Program in Cosmology |____ unruh@xxxxxxxxxxxxxx
> Canada V6T 1Z1 ____|____ and Gravity ______|_ www.theory.physics.ubc.ca/
>
>
> On Tue, 8 Aug 2017, Horia Muntean wrote:
>
>> On Tue, Aug 8, 2017 at 5:07 PM, Miroslav Lichvar <mlichvar@xxxxxxxxxx>
>> wrote:
>>>
>>> Ok. I agree it could be useful.
>>>
>>> Do you think it would be better to write there the delay and
>>> dispersion as was estimated right before the update of the clock to
>>> get the maximum value of dispersion, or rather use the new values from
>>> the update, assuming the user will calculate the amount of dispersion
>>> that accumulated till the next update?
>>>
>>> --
>>> Miroslav Lichvar
>>>
>>
>> How would one compute the estimated error of the system time from UTC
>> at any point in time from information given by 'chronyc tracking' ?
>> Is 'System Time' + 'Root Delay' / 2  + 'Root Dispersion' the correct
>> formula ?
>> If yes then then all these 3 values would be helpful to be put in
>> tracking.log (or maybe other log) regardless
>> they are before or after an update as long as they are consistent
>> (they refer to the state of time from the same moment).
>>
>> For consistency maybe they should be the values 'chronyc tracking'
>> would display after the last update.
>>
>> --
>
>
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