Unable to upgrade from LTS to normal release: unresolvable error

[Charles Faulkner]

I have recently reinstalled my Ubuntu system using the ISO from 22.04 LTS. I decided to upgrade from 22.04 LTS to a regular release, so modified my config to use the normal setting. I installed all the current updates and everything that I was requested to do, then rebooted.

Following the reboot, I opened a terminal and sent "do-release-upgrade". The system gave me all the information about updating to lunar, and then proceeded to get all the necessary sources. Subsequently, the upgrade failed with the following text:

Checking package manager
Reading package lists... Done
Building dependency tree... Done
Reading state information... Done

Calculating the changes

Calculating the changes

Could not determine the upgrade

An unresolvable problem occurred while calculating the upgrade.

If none of this applies, then please report this bug using the
command 'ubuntu-bug ubuntu-release-upgrader-core' in a terminal. If
you want to investigate this yourself the log files in
'/var/log/dist-upgrade' will contain details about the upgrade.
Specifically, look at 'main.log' and 'apt.log'.

Restoring original system state

Aborting

I have no idea what caused this, and can find no clues within the data generated and collected by the ubuntu-bug application, the data from which is attached to this bug.

Thanks for your help :)

ProblemType: Bug
DistroRelease: Ubuntu 22.04
Package: ubuntu-release-upgrader-core 1:22.04.17
ProcVersionSignature: Ubuntu 6.2.0-35.35~22.04.1-generic 6.2.16
Uname: Linux 6.2.0-35-generic x86_64
ApportVersion: 2.20.11-0ubuntu82.5
Architecture: amd64
CasperMD5CheckResult: pass
CrashDB: ubuntu
CrashReports:
 640:1000:124:21692707:2023-10-18 18:27:39.652267217 +0100:2023-10-18 18:27:40.652267217 +0100:/var/crash/_usr_bin_nautilus.1000.crash
 640:1000:124:57993195:2023-10-19 14:29:25.350192151 +0100:2023-10-19 14:28:50.553713686 +0100:/var/crash/_usr_bin_plasmashell.1000.crash
CurrentDesktop: KDE
Date: Thu Oct 19 15:48:57 2023
InstallationDate: Installed on 2023-10-18 (1 days ago)
InstallationMedia: Ubuntu 22.04 LTS "Jammy Jellyfish" - Release amd64 (20220419)
PackageArchitecture: all
SourcePackage: ubuntu-release-upgrader
UpgradeStatus: Upgraded to jammy on 2023-10-19 (0 days ago)
mtime.conffile..etc.update-manager.release-upgrades: 2023-10-19T13:44:33.896170

[Launchpad Janitor (janitor)]

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