The next question was the long-term strategy with systemd: we have 2
approaches

1) mix systemd (PID 1) to use the boot phase (especially one shots)
and later (after system initialization) use s6 to manage all services.

2) just use s6

My question to the list is, what do you use today? Do you use S6 in
mainstream distributions and how?

It is exceedingly difficult to use a distribution using systemd as
its init system and entirely rip out systemd. It is quite possible
to use s6 as the sole init system (and couple it with any service
manager you want, be it s6-rc, anopa, slew, OpenRC...), but to
achieve that, it's much easier to start from a distribution that does
*not* use systemd. (Adélie, Alpine, Void, Gentoo, to name a few.)

If your goal is to be able to use Ubuntu packages out of the box,
then you'll definitely be better off keeping the systemd ecosystem,
which said packages could depend upon, and simply use s6 on top of
it (s6-svscan being supervised by systemd).

It is also possible to keep systemd but reduce its impact, by moving
the boot services from systemd to a service manager running under s6,
one by one. This can be a way to incrementally transition from a
systemd-managed machine to a fully s6-managed machine.

There is a s6-frontend project in the making, which is planned to
be released in 2020 or 2021 (could be much earlier if I got a
sponsor and didn't have to work on unrelated contracts), which aims
to offer a fully integrated init system and interface around the s6
ecosystem (s6, s6-rc, s6-linux-init) including certain policy
decisions: the goal is to make it easier for mainstream distributions
to adopt s6 as a full-featured alternative to systemd. In the
meantime, I am aware that lack of presence and support in mainstream
projects is a major pain point for s6; but you can always write here,
or to the list's sibling, the supervision mailing-list, and our
small but vibrant community will certainly have insights to share.

For informal discussions that don't need a written record, there is
also the #s6 channel on Freenode, where we're usually pretty
reactive.

HTH,

--
Laurent

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