Comment 2 for bug 1422681

just copying description from my duplicate bug as i think its probably / possibly useful

As seen in the failed systemd adt test at [1], installing 'upstart-bin' and then booting a system with 'init=/sbin/upstart' does not result in a fully functional system. The problem is that there are many upstart jobs provided by 'upstart' package that are essential to Ubuntu system boot.

To recreate the problem, just launch a cloud-instance, or fresh install with systemd, then:
  sudo apt-get install upstart-bin
  set /etc/default/grub up appropriately and run 'update-grub' (adding 'init=/sbin/upstart to GRUB_CMDLINE_LINUX_DEFAULT). Alternatively, you can just edit /bo
ot/grub/grub.cfg directly.
  reboot

System will not completely come up.

Installation of 'upstart' package *does* provide working boot, but conflicts and forces uninstallation of systemd-sysv, which is not desireable.

For reference, there is discussion in ubuntu-release between infinity, didrocks, smoser and cjwatson on 2015-03-18 [2] and 2015-03-19 [3].

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[1] https://jenkins.qa.ubuntu.com/job/vivid-adt-systemd/ARCH=amd64,label=adt/121/consoleFull
[2] http://irclogs.ubuntu.com/2015/03/18/%23ubuntu-release.html
[3] http://irclogs.ubuntu.com/2015/03/19/%23ubuntu-release.html