Re: possible to transform signals sent by s6-svc?

From: Laurent Bercot <>
Date: Sat, 15 Oct 2016 05:09:16 +0000

>So what I'd like to do is have "s6-svc -d" result in the process
>SIGINT and SIGCONT to the supervised process, rather than SIGTERM and
>It doesn't seem like there's a way to do this. Or am I missing

  No, you can't remap s6-svc -d. This is a feature that runit has and s6
doesn't: if it's important to you, runit can do it.

  The problem with custom control is that unlike runsv, s6-supervise is
implemented as a full DFA over an asynchronous loop (which is a good
thing, because it guarantees consistency of state and responsiveness),
spawning a user-controlled customized control script would completely
with the design. A bad script could make s6-supervise unresponsive and
useless. I thought it was too much of a risk for the benefit it brings.

  As you found out, s6-svc -Oic is the way to down the service with a
(and a SIGCONT for safety).

>It looks like there is a mechanism to do that kind of signal remapping
>s6-svscan, using the -s option, but the documentation for servicedirs
>doesn't mention anything like that.

  It's different for s6-svscan, because spawning the custom signal
for s6-svscan does not mess with its internal state. If the custom
handlers do something crazy like stalling forever, s6-svscan is still
responsive and performing its job. That's not possible with

>If I'm right and there's no easy way to do that, it's not necessarily a
>huge problem -- currently I'm just using "s6-svc -iO" to shut down
>PostgreSQL, and I can keep doing that; or, alternatively, I can patch
>PostgreSQL to switch the behavior of TERM and INT. But if there *is* a
>to get s6-svc to behave differently, I'm interested!

  s6-svc, no - at least not yet. Apparently there's some demand for that
functionality, so I'll probably think about a way to implement it
in a future version of s6.

  But there's a way to trap and convert signals in your run script
  If your run script is written in shell, you can achieve more or less
same effect with a script akin to the one described here:
(this is the very discussion that led me to write the "trap" execline
  It's a dirty workaround, it uses one more process, but what can you do
when daemons don't use SIGTERM as you would want them to. :)

For PostgreSQL, though, the semantics are arguably correct: SIGTERM for
a really clean shutdown and SIGINT for a forced (but still clean)
shutdown; you just don't want to wait for all client sessions to
so you use a different s6-svc command. Seems to me like everything is
working as intended. :)

Received on Sat Oct 15 2016 - 05:09:16 UTC

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