Re: [chrony-users] meaning of +/- error in sources cmd?

[Matthew Eshleman <matthew@xxxxxxxxxxxxxxxxxxxxxxxx>]

Thank you very much, this was very helpful.

Best regards,

Matthew

On Mon, Jan 31, 2022 at 2:46 AM Miroslav Lichvar <mlichvar@xxxxxxxxxx> wrote:

On Sat, Jan 29, 2022 at 11:58:48AM -0600, Matthew Eshleman wrote:
> I am curious about the source of the +/- error, which is described in the
> docs as:
> "The number following the +/- indicator shows the margin of error in the
> measurement."
>
> How is the value determined and what impacts it? How does one make this
> smaller? I'm happy to review source code or such if necessary, I'm just not
> sure where to look beyond the chronyc doc.

It's the NTP root distance, which is an estimate of the maximum error.
It contains half of the root delay, which is the sum of all round trip
times on the path to the reference clock on the primary server
(stratum 1) and root dispersion, which estimates the sum of errors on
the path due to instability of clocks (increasing at a minimum rate
configured by the maxclockerror directive).

Use the chronyc ntpdata command to see the server's root delay and
dispersion. From that you should see how much of the distance comes
from the server and client.

On the server you might be able to configure a shorter polling
interval of the reference clock to reduce its root dispersion.

If most of the distance is from the network delay, you would need to
move the server closer to the client and reduce the number of
routers/switches on the path.

On the client you can do some changes, but their impact would be tens
of microseconds at most: enable hardware timestamping if supported on
the NICs and enable the F323 extension field if both server and client
are running chrony-4.2.

--
Miroslav Lichvar


--
To unsubscribe email chrony-users-request@xxxxxxxxxxxxxxxxxxxx
with "unsubscribe" in the subject.
For help email chrony-users-request@xxxxxxxxxxxxxxxxxxxx
with "help" in the subject.
Trouble?  Email listmaster@xxxxxxxxxxxxxxxxxxxx.