Re: Guidance on PHC refclock validity/stratum handling in chrony

On Wed, Feb 04, 2026 at 04:23:40PM +0100, MOUHOUNE Samir wrote:
> Dear chrony-users,
> 
>   I’m looking for guidance on how chrony should ideally handle validity and
> stratum when using a PHC refclock. I’m working on an embedded Linux
>   system where the local time source is a PHC exposed via /dev/ptp0, and
> chrony is configured with refclock PHC /dev/ptp0.
> 
>   We can detect source validity and stratum (from our upstream time system)
> and expose those values in sysfs, but chrony’s PHC refclock doesn’t
>   appear to consume that information. As a result, chrony keeps reporting a
> low stratum even when the upstream time is invalid or stratum >= 16.
> 
>   Questions:
> 
>   1. Is there a recommended mechanism in chrony to convey refclock
> validity/unsync state when the source is a PHC?

I think the only option is to disable the selection of the source by
the "chronyc selectopts PHC0 +noselect" command.

>   2. Is there any supported way for a PHC refclock to influence the
> effective stratum in chrony, without patching chrony?

No.

>   As an alternative, we can feed chrony via SHM. That lets us set leap =
> LEAP_Unsynchronised when invalid, which chrony understands, but SHM
>   doesn’t carry stratum (at least in the standard structure), so the
> stratum still can’t be made dynamic.
> 
>   Given these constraints, what approach would you recommend to correctly
> represent both validity and stratum for a PHC-based source?

Currently, there is no way to do that.

-- 
Miroslav Lichvar


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