[gentoo-dev] Re: Re: rfc: locations of binaries and separate /usr

[Steven J Long]

Rich Freeman wrote:

> On Wed, Jan 4, 2012 at 8:50 AM, Steven J Long
> <slong@××××××××××××××××××.uk> wrote:
>> The thing I don't understand is why it is necessary to move stuff from
>> /bin to /usr/bin. After all, if you're running the "approved" setup you
>> don't have a separate /usr so all the binaries are available from the
>> get-go.
>
> Where is this approved setup documented?

I could swear we were told in prior discussions on this list that a separate 
/usr partition is not considered supported by upstream udev, but searching 
all I can find is that an initramfs is required.[1]

Having read the other page[2] that has been pointed out, the answer to my 
question "what does this enable that we can't do currently?" is: 
snapshotting the OS by backing up just the /usr partition.

I can see the attraction in that, especially for organisations. Though it 
does make me smile that it depends on having a separate /usr partition to 
work. ;)

The whole saga has just seemed confused to me: one minute a separate /usr is 
a terrible idea, the next we have to move every binary to /usr in order to 
snapshot a separate /usr. Loath as I am to agree with him, I have to concur 
with Ciaran McCreesh that this is "a case of carelessly letting the horse 
escape and then trying to convince everyone that no-one needs a horse 
anyway."[3]

> Well, it is hard to think of a meaningful raid+lvm configuration that
> doesn't require an initramfs of some sort with the dependence on files
> in /usr during boot.  So, getting our initramfs options improved and
> supporting this configuration just makes sense regardless before we
> unmask newer versions of udev.
>
I was under the impression that anyone using lvm+raid (+luks) on root 
already has an initramfs, and there are docs out there about that, but sure, 
improving those docs and the software is always a good idea.
 
> Raid+lvm isn't exactly an unusual use-case.  Many distros actually use
> at least lvm by default now.
>
Yeah I've been using lvm for several years now, with a separate /usr and no 
initramfs, though not on root. For the last few months, I've been running 
with the tweaked udev startup scripts I mentioned before, so /usr is mounted 
before udev starts (which is possible since I don't have any requirement on 
udev-initialised hardware to mount local drives.)

Regardless of the ability to backup just /usr, I'm still not convinced about 
moving every binary there. It certainly isn't necessary, in that the 
packages we install respect prefix, and there's no need to change the 
ebuilds to make packages work; further most admins already have their own 
backup scripts in-place.

I for one, would like to be able to run in single-user mode off just the 
rootfs, in case for instance, something goes wrong with lvm and /usr won't 
mount; and I don't want to duplicate all those utilities in an initramfs. If 
that's not going to be possible, fair enough: that's life.

[1] http://www.freedesktop.org/wiki/Software/systemd/separate-usr-is-broken
[2] http://fedoraproject.org/wiki/Features/UsrMove
[3] http://article.gmane.org/gmane.linux.gentoo.devel/72130
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