Re: Reason for s6-svscan -X

Paul Sopka <[email protected]> Mon, 3 Mar 2025 19:46:32 +0100

Newsgroups	gmane.comp.sysutils.supervision.general
Message-ID	<Z8X5CBoC9E_6qA6C@NANDERTY>

> 
>   The reason for -X is that s6-svscan and the s6-supervise process for
> s6-svscan-log need to keep an fd to the real console as well (we cannot
> hardcode /dev/console because on some systems it has another name).
> 
With my scripted approach I need to do "... redirfd -a 3 /dev/console s6-svscan -X3 ...",
so I need to write a special "compatible" script for all kernels anyway.

>   s6-svscan needs to restore its stdout and stderr to the real console
> if it exits/panic. It also needs to spawn the supervisor for 
> s6-svscan-log
> with stderr pointing to the real console, because that supervisor cannot
> assume that the s6-svscan-log fifo is always open for reading (and in
> fact, at spawn time, it is not) so this s6-supervise instance also needs
> to write its error messages to the real console.
> 
>   In short: the catch-all logger isn't the only process that needs to 
> know
> the real console, all its ancestors in the supervision tree do as well,
> because they're "lower level" than the catch-all logger.
> 
> --
>   Laurent
> 
Thank you for explaining,
Paul

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