Bug#762194: a technical proposal

[Adam Borowski <kilobyte@angband.pl>]

Hi!
As Ansgar requests technical solutions, here's one:

just like systemd-shim|systemd-sysv, switch the "init" package from
  Pre-Depends: systemd-sysv | sysvinit-core | upstart
to
  Pre-Depends: sysvinit-core | systemd-sysv | upstart

The set of packages installed by d-i / debootstrap is steered by hard-coded
scripts, thus new systems can default to whatever is set there.  On the
other hand, during upgrades, the init system is driven by apt's resolution
of the above pre-dependency.  If systemd-sysv or upstart were already
installed, no change is done; if none of these three packages is present,
apt would install sysvinit-core, preserving existing init system.

Just as exim|postfix or xfce|lxde|gnome|... choice is preserved over
upgrades -- even if the default for new installation changes -- it is
inappropriate to override the existing init system.

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