Re: [chrony-users] Running chrony inside container

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On Thu, Mar 21, 2019 at 11:12:34PM +0100, Sedrubal wrote:
> > It is not recommended to run chronyd (with or without -x) when another 
> process is controlling the system clock.
> But this would be the case.
> Can you explain the reason for this warning? Do you have a better idea?

chronyd assumes it's the only process controlling the system clock. If
it's not, any adjustments outside its knowledge will disrupt the
stability of its control loop. If the adjustments are small, or not
too frequent, it may work ok. The -x option doesn't change this,
except chronyd won't touch the clock.

> We have multiple identical container hosts (each running chrony as ntp client, 
> which should use the containered chrony as ntp server). We want to be able to 
> start the container dynamically on any of our container hosts, so we can't 
> choose one host and stop chrony there and run the container with the correct 
> privileges to be able to modify the system clock.

It's not very clear to me which instances are controlling the clock
and which are not.

If an instance controlling the clock is using another instance running
on the same host as a server (which uses -x), that probably won't work
very well. Any adjustment made by the client would be messing with the
server's time in a feedback loop.

Miroslav Lichvar

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