Re: [gentoo-dev] Warn users not to do separate /usr partition without proper initramfs in the handbook?

[Michał Górny]

On Sat, 30 Jul 2011 10:27:27 +0300
Samuli Suominen <ssuominen@g.o> wrote:

> Since running separate /usr without mounting it from initramfs on top
> of / before init is and has been broken with udev for a long time
> now[1][2][3]
>
> [1] http://bugs.gentoo.org/show_bug.cgi?id=364235
> [2] http://fedoraproject.org/wiki/Features/UsrMove#Move_all_to_.2Fusr
> [3]
> http://www.freedesktop.org/wiki/Software/systemd/separate-usr-is-broken
>
> Can we warn users about not doing the separate /usr mistake in the
> handbook?

So, let's sum up a little.

The most common argument against separate /usr requiring a proper
initramfs is 'it works now, thus it's great'. That is practically
understandable that people don't like to switch things upside down like
that, especially when machines are not locally reachable.

What's the exact differences between an initramfs and an early bootup
setup in rootfs? As I see it:
- initramfs is a small fs which is used for a short while on boot, to
  setup the system necessarily for the early bootup sequence,
- while initial rootfs is a rather large piece of fs which is supposed
  to contain random stuff necessary for the early bootup to be able to
  proceed and mount the necessary remaining stuff before the actual
  bootup begins. And we're mostly stuck with it for the whole runtime.

As I see it, I see no reason to keep forcing things like complete glibc,
ncurses and the whole other lot of libraries for the early bootup if
all needed is some kind of minimal 'mount' program (for instance).

In the ol' days I tried building a NFS-shared system and the main
problem was that some of early run tools relied heavily on the local
system libs and files before they were replaced by NFS mounts. And I
had to keep them in sync manually which is not the most comfortable
thing.

I don't see how trying to fit the best set of libs and files into
rootfs can solve it. You either want for the system to be clean or
weirdly split to support various possible configurations. And decide
which are not 'weird enough' not to support.

And really, most of the things about separate /usr are hacks which were
introduced because the system was incapable of a proper rootfs.
Read-only /usr should be read-only rootfs with writable mounts on top
of it. NFS-mounted /usr should be the whole system part network-mounted
(which would be easier if everything went into /usr rather than being
split).

-- 
Best regards,
Michał Górny