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Bug#762194: Automatic switch to systemd on wheezy->jessie upgrades

On Fri, 19 Sep 2014 13:44:43 +0100 Ian Jackson <ijackson@chiark.greenend.org.uk> wrote:
> Package: tech-ctte
> At the risk of generating confusion due to a duplication of threads:

On the contrary, thank you for moving this to a separate thread.

I would like to propose that, if the TC addresses this point at all, it
does so sequentially rather than in parallel.  I think it's worth
addressing 746578 first, which (assuming apt does the right thing in the
various install/upgrade scenarios) can be solved rather easily and
hopefully uncontroversially.

> It appears that the answer to #746578 (libpam-systemd dependency) does
> not depend on whether users upgrading should be switched to systemd by
> default.  The current state in jessie is that users are switched by
> default.  This is controversial.

I don't think this is as controversial as you think.  The current setup,
including the sysvinit transitional package and new essential init
package, was discussed and implemented by maintainers of sysvinit,
systemd, and upstart, and cleanly supports all three, while reflecting
the systemd default.

Furthermore, to quote Steve Langasek's mail:
> For the record, this is not my position.  I understand Russ's
> concerns, but I also think the grub transition is as much an example
> of the *problems* with such an approach as it is of the successes,
> because at the end of the day users are still left to manually switch
> away from grub1 - many of whom never have, and have wound up with more
> bugs over the long term as a result of using EOLed software.  We
> should take care that our users' upgrade experience is a good one, but
> there are downsides to a policy of never making a change on upgrade
> that we haven't 100% proven won't result in boot regressions.

Returning to your mail:
> There are also of course important practical problems with
> automatically switching.  There have been suggestions that these
> should be dealt with by automatically detecting problem cases.  But we
> do not yet have a coherent design for such an approach, let alone an
> implementation.  It is IMO too late in the jessie release cycle for us
> to be developing and introducing such a thing.  This is particularly
> true given that the details are likely to be contested.

I disagree with your characterization here.

The sysvinit transitional package provides one fallback, which allows
users to boot sysvinit via init=/lib/sysvinit/init.  Michael Biebl is
currently working on automatically adding GRUB menu options to boot
sysvinit, to make that even easier.

Apart from that, I expect the problematic cases to be quite obvious and
uncontested (other than by those who consider "installing systemd at
all" a problematic case).  And we can add additional checks quite
easily.  The most obvious cases are:

- /etc/inittab entries other than the default.
- Hand-edited /etc/init.d/* scripts from packages that will be
  overridden by .service files.

> The alternative would be:
>     Users upgrading to jessie should, by default, be automatically
>     switched from sysvinit to systemd, where feasible.
>     A straightforward mechanism for avoiding the switch should be
>     provided and documented.

I agree with documenting this: we should have a very clear statement in
the release notes documenting the new default init system, and stating
that anyone wishing to continue using sysvinit should install
sysvinit-core and systemd-shim.  We should also have a NEWS entry in an
appropriate package, for the benefit of users with apt-listchanges

I would also propose introducing a separate alternative requesting an
explicit unconditional prompt on upgrade; while not optimal, it would be
easy enough to add, and still preferable to having a different default
for upgrades than for new installs.

- Josh Triplett

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