[Bug 1982486] [NEW] update-motd-fsck-at-reboot: exclude nbd devices

[Launchpad Bug Tracker]

You have been subscribed to a public bug by Matthieu Clemenceau (mclemenceau):

[Impact]

* update-motd-fsck-at-reboot will block shutdown if a broken NBD device
is present in the system when it executes.  In some configurations (e.g.
when sudo authorisation is provided via sssd, which stops before this
task completes), this can result in a hard power cycle being required to
return a machine to service.

* Users with NBD devices will erroneously see them reported as devices
that will be fsck'd at next boot.

[Test Plan]

* Get a QEMU image containing an ext4 partition (e.g. https://cloud-images.ubuntu.com/releases/focal/release/ubuntu-20.04-server-cloudimg-amd64.img)
* `qemu-nbd -c /dev/nbd0 <that image>`
* `mount /dev/nbd0p2 /mnt` (partition number may vary depending on your image)
* Execute `update-motd-fsck-at-reboot`
* Observe NBD device not included

[Where problems could occur]

If the one-line fix is incorrect, users may not receive notification of
fsck'ing that is going to happen, which they may rely on.

[Original Report]

I've ended up in a situation where a machine's /dev/nbd* devices are in
a broken state: the easiest way for me to fix this is to reboot the
system.  However, the reboot is blocked by update-motd-fsck-at-reboot
trying to run dumpe2fs against one of the broken partitions:

$ ps faux
...
root      191396  0.0  0.2  37864  8672 ?        Ss   12:37   0:00 sshd: dwatkins [priv]
root      191421  0.0  0.0   2608   480 ?        S    12:37   0:00  \_ sh -c /usr/bin/env -i PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin run-parts --ls
root      191422  0.0  0.0   2496   508 ?        S    12:37   0:00      \_ run-parts --lsbsysinit /etc/update-motd.d
root      191455  0.0  0.0   2608  1748 ?        S    12:37   0:00          \_ /bin/sh /usr/lib/update-notifier/update-motd-fsck-at-reboot
root      191483  0.0  0.0   3480   944 ?        D    12:37   0:00              \_ dumpe2fs -h /dev/nbd0p2
...

These NBD devices will not be present after a reboot, so I think the
script would probably be more correct if it omitted operating on these
devices.

** Affects: update-notifier (Ubuntu)
     Importance: High
     Assignee: Dan Watkins (oddbloke)
         Status: Fix Released

** Affects: update-notifier (Ubuntu Focal)
     Importance: Undecided
         Status: New

** Affects: update-notifier (Ubuntu Jammy)
     Importance: Undecided
         Status: New

** Affects: update-notifier (Ubuntu Kinetic)
     Importance: High
     Assignee: Dan Watkins (oddbloke)
         Status: Fix Released


** Tags: fr-2579
-- 
update-motd-fsck-at-reboot: exclude nbd devices
https://bugs.launchpad.net/bugs/1982486
You received this bug notification because you are a member of Ubuntu Foundations Bugs, which is subscribed to the bug report.