How to repair/reinstall guix on foreign distro

[Thorsten Wilms <t_w_@freenet.de>]

Hi! It seems every few weeks i’m thrown into a initramfs prompt, as
root got mounted read-only. The way out is always running fsck, which
reports errors and offers fixes that I either can’t map to anything, or
that refer to paths that belong to guix. Usually only below /gnu/store,
but this time also var/guix.

Now `guix pull` fails with:
```
;;; WARNING: loading compiled
file /gnu/store/8bsnz1fk330qbn1p8k18i0j11vld4jxd-guix-module-union/lib/guile/3.0/site-ccache/guix/build-system/gnu.go
failed: ;;; In procedure load-thunk-from-memory: not an ELF file
Updating channel 'guix' from Git repository at
'https://git.savannah.gnu.org/git/guix.git'... guix pull: error: Git
error: invalid data in index - incorrect header signature
```

At first, I focused on the warning (sorry, leoprikler) ... the same git
error happens when using an older guix.

Now a fix for that would be great, but independent of that, I have to
wonder how one should go about reinstalling guix on a foreign distro. I
cannot umount or remount and remove /gnu/store!

Even after `sudo systemctl stop gnu-store.mount`, /gnu/store is busy.
`fuser -kim /gnu/store/` will throw me out of the session, even though
I would think everything that belongs to it is part of the host (Ubuntu
Unity 20.10). No sudo umount or remount or rm -rf allowed, /gnu/store
remains ro and busy. Short of booting another system (say an USB
stick), is there a way to clear /gnu/store? Or to safely replace its
content?


-- 
Thorsten Wilms <t_w_@freenet.de>