[Bug 1987679] Re: os-prober leaves filesystems (lvm-thin, lvm snap) mounted

[Heitor Alves de Siqueira]

Hey mikeaa, thanks for chiming in!

I'm not sure I agree there actually, by looking at the current code. We
only get to the point where grub-probe exits with a non-zero status due
to grub-mount succeeding before (in the previous if condition). This is
also the original report of the bug, as I understood it: filesystems are
left mounted due to grub-mount succeeding, but grub-probe exploding the
script prematurely (due to set -e and non-zero exit status).

Given the other 50mounted-tests script under os-probes/, I think we are meant to run tests if grub-mount succeeds, regardless of whether grub-probe fails (or returns an empty string). That's already the case for grub-probe exiting with zero but not printing out anything, which we currently address by forcing $type=fuseblk.
My understanding is that if grub-mount succeeds, we do want to run the tests so that we can pick up any bootable OSes (i.e. just because we let the tests run, doesn't mean that a GRUB entry is going to be created; one of the OS tests needs to succeed for that).

What do you think?

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Title:
  os-prober leaves filesystems (lvm-thin, lvm snap) mounted

Status in os-prober package in Ubuntu:
  In Progress
Status in os-prober source package in Focal:
  In Progress
Status in os-prober source package in Jammy:
  In Progress
Status in os-prober source package in Kinetic:
  Won't Fix
Status in os-prober source package in Noble:
  In Progress
Status in os-prober source package in Oracular:
  In Progress
Status in os-prober source package in Plucky:
  In Progress

Bug description:
  If one happens to have by accident (or on purpose) a thick LVM snapshot, or a thin-LV with a copy of a system on it, update-grub reports
  /sbin/grub-probe: error: unknown filesystem.
  Found Ubuntu 22.04.1 LTS on /dev/mapper/vgxubuntu-s22.04
  and
  /sbin/grub-probe: error: disk `lvmid/X7waXv-rMDA-5fQA-aw6l-ei1I-8Gz3-pQl3lr/k3Ze1u-Mfwc-pxUt-7fXa-FjSZ-7IkX-HAxf3b' not found.
  Found Ubuntu 22.04.1 LTS (22.04) on /dev/mapper/vgxubuntu-XR22.04.1U

  and leaves the systems mounted rw on /var/lib/os-prober/mount.
  On subsequent invocations update-grub spews out multiple
  mdir: failed to remove '/var/lib/os-prober/mount': Device or resource busy

  I'm pretty sure this also causes a new install to hang (though a
  power-reset seems to load the new system - not sure if it is complete
  or not.)

  The missing umounts should be relatively easy to fix, but the thick
  snapshot error is particularly vague as most users (I think) would
  take the "unknown filesystem" to refer to the previous entry.

  I have been playing with grub2-common-2.06-2ubuntu7 on xubuntu
  22.04.1, though I am sure this has been around a while

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