package zfsutils-linux 0.8.3-1ubuntu12.12 failed to install/upgrade: installed zfsutils-linux package post-installation script subprocess returned error exit status 1

[Lawrence MacIntyre]

system update failed

ProblemType: Package
DistroRelease: Ubuntu 20.04
Package: zfsutils-linux 0.8.3-1ubuntu12.12
ProcVersionSignature: Ubuntu 5.4.0-77.86-generic 5.4.119
Uname: Linux 5.4.0-77-generic x86_64
NonfreeKernelModules: zfs zunicode zavl icp zcommon znvpair nvidia_modeset nvidia
ApportVersion: 2.20.11-0ubuntu27.18
Architecture: amd64
CasperMD5CheckResult: skip
Date: Fri Aug 20 16:56:14 2021
ErrorMessage: installed zfsutils-linux package post-installation script subprocess returned error exit status 1
Python3Details: /usr/bin/python3.8, Python 3.8.10, python3-minimal, 3.8.2-0ubuntu2
PythonDetails: N/A
RelatedPackageVersions:
 dpkg 1.19.7ubuntu3
 apt 2.0.6
SourcePackage: zfs-linux
Title: package zfsutils-linux 0.8.3-1ubuntu12.12 failed to install/upgrade: installed zfsutils-linux package post-installation script subprocess returned error exit status 1
UpgradeStatus: No upgrade log present (probably fresh install)
mtime.conffile..etc.logrotate.d.apport: 2021-07-05T13:03:06.049681

[Launchpad Janitor (janitor)]

Status changed to 'Confirmed' because the bug affects multiple users.

[Simon Déziel (sdeziel)]

@Lawrence, it seems the problem is when zfs-mount tries to mount /boot/grub it meets a directory with some content:

  Aug 20 16:56:14 nautique zfs[163828]: cannot mount '/boot/grub': directory is not empty

It could be that it was umount'ed before some command populated /boot/grub? But maybe there is more to it as `dmesg` has many such messages:

  zfs-mount-generator: boot-grub.mount already exists

To recover from this you can probably simply move the content to some temporary directory, make sure nothing's left in /boot/grub, zfs mount it and then move the content back in.