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Date: Wed, 21 Oct 2020 15:14:45 -0400
From: Steve Litt <slitt@troubleshooters.com>
To: supervision@list.skarnet.org
Subject: Re: Dependencies in S6
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On Wed, 21 Oct 2020 13:26:25 +0000
"Laurent Bercot" <ska-supervision@skarnet.org> wrote:

>   "A is ready" means:
>    - if A is a oneshot: when the script has completed
>    - if A is a longrun:
>      * if there is a notification-fd file in the service definition
> directory: when the daemon has notified readiness
>      * if there is no such file: as soon as the run script has started
> (which is not a good readiness indicator; it is akin to starting B
> _right after A_, essentially in parallel, so you may have race
> conditions here - which is why you should always use readiness
> notifications.)

I seem to remember that s6 also has specially named shellscript to
determine dependency readiness. So, for instance, process B requires a
functioning network, the shellscript would contain a ping command or an
ip command. I do this all the time, informally.
 
SteveT

Steve Litt 
Autumn 2020 featured book: Thriving in Tough Times
http://www.troubleshooters.com/thrive