[chrony-users] Defaulting to stepping the clock

[Pedro Côrte-Real <pedro@xxxxxxxxxxx>]

Hi,

I'm a user of Ubuntu both on servers and desktops/laptops. With Ubuntu
18.04 switching to chrony by default I decided to use that on all
machines. When setting up the roll-out to all machines using puppet I
checked the default config to see if I neded to do any changes. Two
lines stood out:

maxupdateskew 100.0
makestep 1 3

If I'm reading the documentation correctly this means "step the clock
in the first three corrections if the step is above one second but
below 100"

It seems at least the second line is a recommended config:

https://chrony.tuxfamily.org/faq.html#_what_is_the_minimum_recommended_configuration_for_an_ntp_client

This seems very strange to me as a default for an NTP tool. I have two
main use cases that I assume are common:

1) For a server never step the clock and if the drift is large
complain loudly because something has gone very wrong. Servers are
always on and should be always syncing so if their clock drifts a lot
something has gone wrong.
2) In a desktop/laptop stepping the clock is probably always ok if
going forward but may be bad if going back. So just accept frequency
adjustments both going forward and backwards. Machines are turned
on/off, suspend/resume and so it's less important to complain loudly.
Instead maintain monotonic clocks that are synchronized quickly even
if their frequency needs to shift a log.

Given all this why were these defaults chosen? Are there recommended
settings to approximate 1) and 2)? Is the recommendation to do
something else?

Thanks,

Pedro

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