Re: s6-svscan - controlling terminal semantics and stdin use

From: Colin Booth <>
Date: Tue, 2 Jan 2018 05:06:22 +0000

On Mon, Jan 01, 2018 at 07:53:39PM -0800, Earl Chew via skaware wrote:
> Thanks for the s6-* family of programs.
> I've just started using s6-svscan for some deployments.
> In one of the scenarios, I was prototyping the behaviour of s6-svscan
> over a supervision tree directly at the interactive terminal for use in
> a cron-based scenario.
> ...
> Has this scenario (ie starting s6-svscan from an interactive terminal)
> been considered previously?
I believe this particular failure mode has been considered and decided
an edge-enough case to not be worried about. Laurent will have to say
for sure though.
> My second observation is that stdin of s6-svscan is inherited by all its
> s6-supervise children. I'm wondering if there is anything to be gained
> by that, and whether it would be less surprising to set stdin to
> /dev/null after fork() since having a herd of processes attempting to
> read from the same stdin does not seem to lead anywhere useful.
stdin, stdout, and stderr are inherited when a process is forked,
there's nothing special going on here. Since s6-svscan and s6-svscanctl
ignore stdin, keeping it open shouldn't impact anything. If you want to
close stdin, do it before execing into s6-svscan (or as part of the call
if using shell).
> What do you think?
> Earl

Colin Booth
Received on Tue Jan 02 2018 - 05:06:22 UTC

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