Re: initialization vs supervision

From: Laurent Bercot <>
Date: Wed, 23 Jul 2014 22:18:26 +0100

On 23/07/2014 20:16, Wayne Marshall wrote:
> In the best of un!x traditions, a stronger
> system may in fact be one that recognizes the fundamental
> differences between the two functions, and provides purpose-specific
> solutions for each of them.

  I absolutely agree with this, as with all the rest of your message.

  However, an initialization system can strongly benefit from being
tailored to use a supervision system, so close ties between the two are
not surprising.
  Doing all the one-time initialization without having supervision
support is complex: one-time initialization often needs early services,
that the rest of the initialization depends on - I think of a default
logger, and of udevd, for instance.
  The pstrees that are posted in this thread show a nice amount of
supervised services, and also some services that are *not* supervised;
the reason for this is probably that the unsupervised services are
started in /etc/runit/1, when runsvdir isn't yet started. This is a shame:
you want core services to be supervised, even more than non-core ones.

  I believe the right way for an initialization system to boot is:
- do the minimum necessary amount of early init so the supervisor can work
- fork the one-time initialization process, and block it so it can only
run once the supervision tree is active
- exec into the supervision system (so that it is either process 1 itself,
or supervised by process 1).

  This is the approach I have with s6. However, since I wanted to keep s6
system-agnostic and, as you said, initialization is system-dependent, I did
not provide an out-of-the-box /sbin/init - and it put too much work in the
hands of packagers. I intend to work on a s6-init package, which will
unfortunately have to be Linux-specific, to cover this flaw. The forked
one-time initialization process can safely be left to distribution packagers,
just like /etc/runit/1 is; but the tricky /sbin/init has to be provided in
order for an integrated init+supervision system to be usable.

Received on Wed Jul 23 2014 - 21:18:26 UTC

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