Comment 9 for bug 65587

I'd argue that

/etc/inti.d/avahi-daemon start

should start it unconditionally and then the toggling on and off should be done with the addition or removal of symlinks. That's how rcX.d works and it looks like that's how dbus works too.

rcX.d comes with a tool for creating a removing the symlinks update-rc.d, if dbus or upstart don't come with equivalent tools then that's a bug. In fact update-rc.d should just work whether the system actually uses rcX.d or something else.

If you want to stick with enable_avahi then I suggest you have it make/remove symlinks instead of sedding /etc/default/avahi-daemon.

If you want to have it turned off by defualt then at install you just don't make the link in the dbus directory.

I think that leaves everyone with things working as they'd expect them but you still have the ability to enable/disable the boot behaviour and leave it off by default.