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Bug#746578: Reasons to keep systemd-sysv as the first alternative

On Thu, Sep 18, 2014 at 11:36:53AM -0700, Josh Triplett wrote:
> On Thu, 18 Sep 2014 11:09:18 -0700 Russ Allbery <rra@debian.org> wrote:
> > I conceptually dislike the user experience of switching init systems
> > because the user upgraded some random package that, from their
> > perspective, doesn't appear related to the init system.  I feel like
> > switching init systems should be a more intentional action than that.
> > There is a variety of local customization that is init-system-specific,
> > and I'm dubious that we're going to be able to catch and warn about all of
> > it.
> > 
> > I've not made up my mind about the merits of switching init systems from
> > sysvinit to systemd during a dist-upgrade, but if we do that, I think we
> > should do it via some more deliberate and obvious method than pulling
> > systemd-sysv in via the dependency tree of some random package.  The
> > partial upgrade UX for that is really bad, IMO.
> I agree completely that it doesn't make sense for the transition from
> sysvinit to systemd to take place via libpam-systemd rather than via
> some core package like "init", not least of which because that would
> mean systems with desktops or certain daemon packages installed would
> get transitioned to systemd but other systems would not.
> However, as far as I can tell, I think we've actually solved that
> problem: wheezy systems with sysvinit installed will upgrade to the
> transitional "sysvinit" package, which depends on "init", which depends
> on "systemd-sysv | sysvinit-core | upstart".  Between that and "init"
> being "Essential: yes" (which causes apt to try to install it on
> all upgrades to jessie), that *should* cause a transition to
> systemd-sysv.
> Now, that's not quite optimal yet.  Michael Biebl is currently working
> on a plan to have fallback boot options available in GRUB that will boot
> to sysvinit when both are installed, and that would require having both
> systemd-sysv and some sysvinit package (not clear which one) installed.
> (This could support other bootloaders as well, and systems not
> explicitly covered could still explicitly boot with
> init=/lib/sysvinit/init on the kernel command line.)

Correction to this part of my mail: /lib/sysvinit/init is provided by
the sysvinit package, which will remain installed in an upgrade from
wheezy to jessie.  So, this already works, apart from the automatic
entries in the grub bootloader.  My apologies for suggesting that there
was more to do there in terms of package dependencies.

I just tested this by installing a wheezy "minbase" chroot with
debootstrap and upgrading it to jessie.  This installed systemd-sysv via
"init", left sysvinit installed, and /lib/sysvinit/init existed for use
as a fallback init.  At no time was libpam-systemd installed.

> Nonetheless, as far as I can tell, libpam-systemd is *not* the package
> driving the systemd transition anymore.  Does that address your concern,
> Russ?
> - Josh Triplett

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