[arch-projects] [mkinitcpio] mounting /usr from the initrd

[Tom Gundersen]

Hi guys,

I have been thinking about sorting out /usr being a separate
mountpoint. Mainly because I keep getting bug reports that turn out to
be caused by this.

The current status is that we move some tools from /usr to / in the
hope that this will allow us to boot without /usr being mounted. This
mostly works, but not quite, as there are still stuff left in /usr
that are used by early boot (and mostly just fails silently).

This website created by the systemd folks sums it up nicely (just
replace "systemd" with "initscripts" everywhere):
<http://www.freedesktop.org/wiki/Software/systemd/separate-usr-is-broken>.

The solution they propose, and which I agree with, is to mount /usr
from the initrd just as we mount / (an alternative solution is to just
declare separate /usr as not supported, but I guess that would not
make us popular).

Before working up a patch, I wanted to hear if there are any
objections to this approach, and in particular that Thomas agrees that
it is the right way to go.

The interface I suggest is to allow two new kernel options "usr" and
"rootflags" that correspond to "root" and "rootflags". The pivot_root
stuff I submitted recently will already take care of unmounting. The
syntax could obviously be discussed, and I suggest getting in touch
with the dracut guys to make sure we choose the same syntax (I don't
think they yet have support for this, but I might be wrong).

Any thoughts?

Cheers,

Tom

PS

A nice sideeffect is that once we have this we can simplify a lot of
our PKGBUILDS as they never need to put stuff in / any more, and
eventually /bin, /sbin and /lib will be empty and can just be
symlinked to /usr/{{,s}bin,lib}.