Re: Reason for s6-svscan -X

From: Paul Sopka <psopka_at_sopka.ch>
Date: Mon, 3 Mar 2025 19:46:32 +0100

>
> 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

Received on Mon Mar 03 2025 - 19:46:32 CET

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