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Bug#1000239: Rescue system won't find root partition, but insists on /usr

On Sat, Dec 4, 2021, 6:45 AM Simon McVittie <smcv@debian.org> wrote:
(Speaking only on my own behalf, not on behalf of the TC, here)

On Fri, 03 Dec 2021 at 16:08:24 -0500, Nicholas D Steeves wrote:
> 1. Debian isn't yet ready for usrmerge

Merged /usr is not actually the problem here, although it exacerbates what
appears to be a pre-existing bug in the rescue mode[0]. The root cause is
that since Debian 9 [1][2], the "/usr-like" parts of the root filesystem
are no longer guaranteed to be self-contained: important shared libraries[3]
and executables have been gradually moving into /usr for a while, and
stretch was the point at which this was declared to be officially allowed.

Merged /usr makes this very noticeable because it's the most extreme
version of that process, where *literally everything* "/usr-like" (most
notably /bin/sh) moves into /usr. When /usr is a separate filesystem, that
leaves a root filesystem that potentially contains only /etc, symlinks and
mount points, which is certainly not enough to be useful to chroot into.

> 2. Reassign to src:rescue, and fix the rescue system.

I think this will have to be the answer. See also [0].

> 3. Disallow configuring of a mount for "/usr"

That would be unfortunate, since one of the things enabled by merged
/usr is the ability to keep all "/usr-like" content on a separate /usr
filesystem that is mounted read-only during normal operation, remounting
it rw only for system updates[4], while leaving /etc and /var rw (and
potentially offering the ability to reformat the partition with /etc
and /var, and then repopulate it via systemd-tmpfiles or similar, as a
"factory reset" mechanism).

I would like to add myself to the Testing part of this process. 

Some may have noticed some "static" from me Yesterday, when I, somehow messed up the "Install Desktop from Network" options, on two qemu Installs of Bookworm. 

I assume that, Bookworm would be the earliest place where most of the Changes would be made to the Rescue System? (Though I have one or two Bullseye Systems that are Expendable also). 
[0] https://bugs.debian.org/769738 (opened in 2014)
[1] https://www.debian.org/releases/stretch/amd64/release-notes/ch-information.en.html#late-mounting-usr
[2] and possibly earlier: that release note was documenting current practice
    rather than describing a new change
[3] for example about half the libraries in `ldd /sbin/cryptsetup`
[4] which potentially happen atomically across a reboot, as seen in ostree,
    or while rebooted into a special boot mode, as with

Speaking of SystemD, are there, yet any good "SystemD for Dummies" books out there?  That is something I would pay Money for. 


Kenneth Parker 

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