fstab cleanup of / does not work

[vrothberg]

It looks like we regressed after commit d46b072 since the fstab cleanup does not work (anymore).

The systemd-remount-fs.service fails with

mount: /: fsconfig system call failed: overlay: No changes allowed in reconfigure.
dmesg(1) may have more information after failed mount system call.
/usr/bin/mount for / exited with exit status 32.

/etc/fstab includes

UUID=d457c96a-3adb-48aa-9bb3-3c34ba1c338b / btrfs subvol=root,compress=zstd:1,ro 0 0

[cgwalters]

What generated that /etc/fstab? How did you install this system? Was it with Anaconda or not?

The reason we don't change that fstab line today is it already contains the ro option which is not expected here.

Hmm, I'm guessing this didn't come from Anaconda, but I did find osbuild/bootc-image-builder@c609003 and while that wasn't wrong I really should have taken the next step and fixed it to not emit a fstab entry at all.

[vrothberg]

Was it with Anaconda or not?

Yes, I installed the system with an anaconda-iso produced by BIB.

[cgwalters]

Umm so much technical debt in this area. AFAICS bib still uses this code for that case which is really suboptimal in so many ways because it uses the wrong filesystem type by default across different distros...not even honoring the bootc default filesystem.

More generally default partitioning can differ by OS/distro or desired base image too...again ideally we support embedding this in the container image and in this embedded ISO case Anaconda could read that (ref rhinstaller/anaconda#5197 more generally).

There is a big sub-thread here though that on the bootc side here we really do need to give guidance for people on how to use /etc/fstab correctly...composefs basically breaks the historical concept of /. The baseline guidance would probably just be to recommend root flags as a kernel argument and don't write an /etc/fstab entry for / at all.

[cgwalters]

➡ #972

[cgwalters]

• anaconda: https://bugzilla.redhat.com/show_bug.cgi?id=2332319
• bib: switch from /etc/fstab to root flags karg osbuild/bootc-image-builder#756