On 2020-07-07 12:20, Steve Litt wrote:

> You need certain executables, pre-mount, before a separate /usr can be
> mounted. These went in /sbin, which is on the root and always
> available. If you could mount the root partition, you could proceed.
>
> But now, if you mount /usr somewhere off the root, and simply have
> /sbin symlink to it, those executables aren't available right away.
> Imagine if you need the mount executable to mount /usr, but the mount
> executable *is* on /usr. Buried shovel. The only way around it is to
> do the mounts in initramfs.

Of course I know all of this. And I guess strictly speaking it *is* an
answer to my question: if you had this setup and suddenly, without
notice, you got switched to a "merged" world, you'd be hosed until you
built an initramfs.

But that is not how in fact it happens: you have plenty of notice, and
plenty of time to change to a scheme with /usr within the root
filesystem. And then you don't need an initramfs again, at least not for
the above reason.

So maybe the real question is, in the merged world, do you have a reason
to insist on /usr being a mount point, other than tradition? I know that
people used to do rescue tasks via a single-user boot with only the
rootfs mounted, but for a long time now it is far easier to do such
things by booting into some kind of "live" system on a USB stick. One
can make the live system minimal if so inclined, and in fact the minimal
Devuan live system is just about perfect for this purpose.

--
Ian