Description:

I just upgraded to 0.9.0. Here is what various sources have to say on the 'usr' hook.

- mkinitcpio.install's post_upgrade

If your /usr is on a separate partition, you must add the "usr" hook
to /etc/mkinitcpio.conf and regenerate your images before rebooting

- /etc/mkinitcpio.conf

NOTE: If you have /usr on a separate partition, you MUST include the
fsck and shutdown hooks.

- https://wiki.archlinux.org/index.php/Mkinitcpio#.2Fusr_as_a_separate_partition

Add the shutdown hook.
Add the fsck hook.
As of mkinitcpio 0.9.0: Add the usr hook.

First I read the post_upgrade output and then mkinitcpio.conf. I thought that mkinitcpio.conf is most likely outdated, and the usr hook _supersedes_ the need for the fsck and shutdown hooks. The wiki entry can also be interpreted that way. But from reading the source it seems that the usr hook is needed in _addition_ to the shutdown and fsck hooks.

I think this should be more clearly stated in all three places above.