Comment 17 for bug 1438612

(In reply to Martin Pitt from comment #4)
> I'm not sure if root on NFS was ever attempted/supported. You'd basically
> need half an OS in your initramfs then? :-)

Yes it is/was, with or without an initramfs:

https://www.kernel.org/doc/Documentation/filesystems/nfs/nfsroot.txt
https://anonscm.debian.org/cgit/kernel/initramfs-tools.git/tree/scripts/nfs

> > The fewer constraints we have to apply to startup, the better [...]
> > So I would
> > be OK with giving dbus.service DefaultDependencies=no, but I would not
> > necessarily encourage requiring it to start before basic.target.
>
> Why not before basic.target? This would make it a basic system service which
> everyone could rely on. It's already kind of that through dbus.socket? It
> could lead to a more serialized boot of course, as non-dbus services would
> have to wait for dbus.service then.

If dbus.service *on a particular system configuration* is After something that is After basic.target, and basic.target is After dbus.service, then we have a cyclic dependency on that system configuration. (This is regardless of whether it works without cyclic dependencies for the relevant distribution's dbus maintainers, who presumably know enough to avoid bizarre boot orderings.)

Notable examples of things that dbus might need:

* NIS and other sources of users
* networking and other non-trivial infrastructure to get /usr

Debian and Ubuntu have traditionally run dbus as a rc2.d service, so there is nothing to stop it having such dependencies.