Upgrade from 18.04.5 LTS to 20.04.1 LTS fails apparmor missing files

[Dariusz.Ostolski]

Yesterday I've tried to upgrade Ubuntu 18.04.5 LTS to 20.04.1 LTS and upgrade was done but with errors. After rebooting I've got a number of errors which most annoying was:
 appstreamcli: undefined symbol: AS_APPSTREAM_METADATA_PATHS

When trying to use apt, so it wasn't possible to proceed any further.
The upgrade was done in terminal not in X Server.

Commands that I've executed. Before upgrade:

sudo apt-get update && sudo apt-get dist-upgrade
sudo apt autoremove
sudo reboot

After reboot:

do-release-upgrade -m desktop
reboot

I've tried to execute:
apt dist-upgradeapt --fix-broken install

after reboot but it also failed.

As it turned out all those problems were related to the fact that two configuration files were missing after upgrade for app-armor:

/etc/apparmor.d/tunables/home
/etc/apparmor.d/tunables/proc

After creating them I was able to continue and fix upgrade errors. Nevertheless I would expect that going from one LTS to another is smooth process.

For those who also have similar problems those are contents of those files:

root@desktop-ninja-daro:~# cat /etc/apparmor.d/tunables/proc
# Copyright (C) 2012 Canonical Ltd.
#
# This program is free software; you can redistribute it and/or
# modify it under the terms of version 2 of the GNU General Public
# License published by the Free Software Foundation.
#
# ------------------------------------------------------------------

# @{PROC} is the location where proc is mounted.
@{PROC}=/proc/

root@desktop-ninja-daro:~# cat /etc/apparmor.d/tunables/home
# ------------------------------------------------------------------
#
# Copyright (C) 2006-2009 Novell/SUSE
# Copyright (C) 2010 Canonical Ltd.
#
# This program is free software; you can redistribute it and/or
# modify it under the terms of version 2 of the GNU General Public
# License published by the Free Software Foundation.
#
# ------------------------------------------------------------------

# @{HOME} is a space-separated list of all user home directories. While
# it doesn't refer to a specific home directory (AppArmor doesn't
# enforce discretionary access controls) it can be used as if it did
# refer to a specific home directory
@{HOME}=@{HOMEDIRS}/*/ /root/

# @{HOMEDIRS} is a space-separated list of where user home directories
# are stored, for programs that must enumerate all home directories on a
# system.
@{HOMEDIRS}=/home/

# Also, include files in tunables/home.d for site-specific adjustments to
# @{HOMEDIRS}.
#include <tunables/home.d>