Re: Have an external script wait for a oneshot service
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> On 5 Dec 2024, at 01:58, Laurent Bercot <ska-supervision_at_skarnet.org> wrote:
>
>
>>
>> Although it would be nicer to have a standard way to do this
>
> There is a standard way to block until a oneshot has completed:
> depend on that oneshot.
>
> Duh.
>
> The thing is, s6-rc wasn't designed to have external scripts
> interacting in this way with this engine, because if you have programs
> depending on intermediary s6-rc states, they should be managed by s6-rc
> as well. The point is to have a predictable machine state when s6-rc
> exits; if you have random other stuff doing things in parallel, that
> defeats the purpose.
>
> And with an s6-linux-init setup, at boot time there is no other
> process than s6-rc managing your services. You have the supervision
> tree, and the stage 2 script, and that's it. And if you're going to
> spawn stuff in your rc.init that waits for oneshot X in the s6-rc db,
> then... why? Why not have said stuff as another service?
>
> If you cannot, for whatever reason, maybe bring your services up in
> two steps?
> s6-rc change X && stuff & s6-rc change default
>
> And if all else fails, the generic solution would be to have a oneshot
> Y depending on X (so, that would run once X is done) that sends a
> notification to a place of your choice via a mechanism of your choice,
> you could use a fifodir and s6-ftrig-notify for this. You would still
> have to deal with the race conditions around setting up the listener etc.
>
> The cleanest way to achieve what you want, without support in the
> service set itself, is to s6-rc change X first, then s6-rc change the
> rest of your services. That way, you avoid breaking abstraction with
> hacks of questionable aesthetic value.
>
> --
> Laurent
>
Received on Thu Dec 05 2024 - 06:59:50 CET
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: Thu Dec 05 2024 - 07:00:35 CET