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

[Adam Borowski <kilobyte@angband.pl>]

On Thu, Dec 04, 2014 at 05:25:26PM +0100, Christian Seiler wrote:
>  - Switchig depends order of init [1]
>    (sysvinit-core before systemd-sysv)
> 
>     -> won't work, because init is Essential, but systemd-sysv isn't,
>        so this change would default the init system to sysvinit for
>        jessie (which is against the TC ruling from earlier this year,
>        so unless you'd want to overrule that... ;-))

That's why in my proposal the installation of systemd-sysv by default is
moved to debootstrap.

In scripts/{unstable,jessie}, function work_out_debs(), you add
"systemd-sysv" to the variable "required".  This can be done
unconditionally, or, preferably, only in the "-" variant, as other variants
either don't use init at all or are unbootable with systemd.  And in some
use cases like pbuilder or non-lvm/btrfs sbuild size gains are important:
it takes longer to unpack the tarball than to build an average package.

I did test the following change:
=====================
work_out_debs () {
        required="$(get_debs Priority: required)"
== to ===
work_out_debs () {
        required="$(get_debs Priority: required) systemd-sysv"
=====================
and it does what you want.

On the other hand, relying on an upload to wheezy is quite fragile.

Also, it is intuitive to keep changes to the default install in debootstrap
rather than in dependencies.  And it makes future changes of the default
easy without breaking existing systems.


As for reasons not to switch, you did not mention the multitude of "breaks
the whole system" (ie, severity:critical) bugs in common configurations.
These include:
* vservers/containers
* chroots that run daemons
* some configurations of encrypted lvm
* custom kernels (including those you can't upgrade)
* nonexistant filesystems in fstab (this one is being worked on)
* etc, etc.

Thus, the potential for breakage is simply too big.  This is similar, but
bigger in scope than the grub1->grub2 switch some years ago.

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