Bug#746577: closed by Michael Biebl <biebl at debian.org> (Re: Bug#746577: systemd-sysv: for upgrade safety, systemd-sysv and sysvinit-core must be coinstallable)

[Zack Weinberg]

I don't wish to play bug tracker ping-pong here, but I feel that you
are still missing the point.  This is not about the default for new
installations, this is not about opt-out versus opt-in to the switch.

This is about *upgrade safety*.

Upgrade safety, IMNSHO, requires a stabilization point in between the
package upgrades and the change of active init.  A point where both
the old and the new init providers are fully installed, and the system
can easily, without installing or removing anything, be switched *back
and forth* between the two, so that the changeover can be *tested*.
This is like keeping an older kernel in the bootloader menu just in
case the new kernel doesn't work correctly.

The release notes should describe the process something like this:

1. apt-get dist-upgrade will install systemd but will not activate it.
 If you reboot at this point your system will still come up under
sysvinit.
2. Now is a good time to check over all local customizations to make
sure they are compatible with systemd; known issues include X, Y, and
Z.
3. To activate systemd, execute the command 'update-init-system
--select systemd' and then reboot.
4. If the system fails to boot after step 3, or if it is not fully
operational in some way (e.g. failing to provide all expected network
services), you can revert to sysvinit by booting with init=/bin/sh and
executing 'update-init-system --select sysvinit' (you may need to
mount filesystems first).  See [wiki page on troubleshooting systemd]
for more troubleshooting advice.
5. Once you are satisfied that the system operates correctly under
systemd, you can remove the sysvinit implementation with 'dpkg --purge
sysvinit-core'.  Note that many packages will still be managed using
sysvinit *scripts* for the jessie release.

Does this give you a clearer understanding of what I am asking for and why?

zw