After update zfsutils-linux, the update process tries to mount zfs file in /mnt but since in /mnt there are another disk mount fails with:
Setting up zfsutils-linux (0.8.3-1ubuntu12.5) ...
zfs-import-scan.service is a disabled or a static unit, not starting it.
zfs-import-scan.service is a disabled or a static unit, not starting it.
Job for zfs-mount.service failed because the control process exited with error code.
See "systemctl status zfs-mount.service" and "journalctl -xe" for details.
invoke-rc.d: initscript zfs-mount, action "start" failed.
● zfs-mount.service - Mount ZFS filesystems
Loaded: loaded (/lib/systemd/system/zfs-mount.service; enabled; vendor preset: enabled)
Active: failed (Result: exit-code) since Fri 2020-12-11 21:05:24 CET; 8ms ago
Docs: man:zfs(8)
Process: 177294 ExecStart=/sbin/zfs mount -a (code=exited, status=1/FAILURE)
Main PID: 177294 (code=exited, status=1/FAILURE)
dic 11 21:05:24 serv systemd[1]: Starting Mount ZFS filesystems...
dic 11 21:05:24 serv zfs[177294]: cannot mount '/mnt': directory is not empty
dic 11 21:05:24 serv systemd[1]: zfs-mount.service: Main process exited, code=exited, status=1/FAILURE
dic 11 21:05:24 serv systemd[1]: zfs-mount.service: Failed with result 'exit-code'.
dic 11 21:05:24 serv systemd[1]: Failed to start Mount ZFS filesystems.
ProblemType: Package
DistroRelease: Ubuntu 20.04
Package: zfsutils-linux 0.8.3-1ubuntu12.5
ProcVersionSignature: Ubuntu 5.4.0-56.62-generic 5.4.73
Uname: Linux 5.4.0-56-generic x86_64
NonfreeKernelModules: zfs zunicode zavl icp zcommon znvpair
ApportVersion: 2.20.11-0ubuntu27.13
AptOrdering:
python3-aptdaemon.gtk3widgets:amd64: Install
aptdaemon:amd64: Install
python3-aptdaemon:amd64: Install
NULL: ConfigurePending
Architecture: amd64
CasperMD5CheckResult: skip
Date: Fri Dec 11 20:56:40 2020
ErrorMessage: installed zfsutils-linux package post-installation script subprocess returned error exit status 1
InstallationDate: Installed on 2020-03-24 (261 days ago)
InstallationMedia: Ubuntu 19.10 "Eoan Ermine" - Release amd64 (20191017)
Python3Details: /usr/bin/python3.8, Python 3.8.5, python3-minimal, 3.8.2-0ubuntu2
PythonDetails: /usr/bin/python2.7, Python 2.7.18, python-is-python2, 2.7.17-4
RelatedPackageVersions:
dpkg 1.19.7ubuntu3
apt 2.0.2ubuntu0.1
SourcePackage: zfs-linux
Title: package zfsutils-linux 0.8.3-1ubuntu12.5 failed to install/upgrade: installed zfsutils-linux package post-installation script subprocess returned error exit status 1
UpgradeStatus: Upgraded to focal on 2020-05-19 (206 days ago)
ZFS will refrain from mounting over a currently mounted mount point, so that is expected.
It would be useful to see what zfs expects the mounted file systems are and what you had mounted, e.g.
1. See what zfs expectes as the mounted zfs file systems:
sudo zfs list
2. See what was mounted:
cat /proc/mounts