upgrade 18.04.04 LTS to 20.04 LTS

[Russ]

Getting this error when upgrade Lubuntu 18.04.04 LTS to the latest 20.04.

alculating the changes

Calculating the changes

Could not calculate the upgrade

An unresolvable problem occurred while calculating the upgrade.

This was likely caused by:
* Unofficial software packages not provided by Ubuntu
Please use the tool 'ppa-purge' from the ppa-purge
package to remove software from a Launchpad PPA and
try the upgrade again.

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

ProblemType: Bug
DistroRelease: Ubuntu 18.04
Package: ubuntu-release-upgrader-core 1:18.04.37
ProcVersionSignature: Ubuntu 5.3.0-51.44~18.04.2-generic 5.3.18
Uname: Linux 5.3.0-51-generic x86_64
ApportVersion: 2.20.9-0ubuntu7.14
Architecture: amd64
CrashDB: ubuntu
CurrentDesktop: GNOME
Date: Fri May 1 19:55:38 2020
InstallationDate: Installed on 2020-04-09 (22 days ago)
InstallationMedia: Lubuntu 18.04.4 LTS "Bionic Beaver" - Release amd64 (20200203)
PackageArchitecture: all
SourcePackage: ubuntu-release-upgrader
UpgradeStatus: Upgraded to bionic on 2020-05-01 (0 days ago)

[Launchpad Janitor (janitor)]

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

[Florian Obradovic (florian-obradovic)]

Same issue here... any idea how I can work around it manually?

[Dwiva Hardijaya (dwiva)]

Here the workaround i use to pass this problem. We need to use app called Synaptic to remove all packages that is considered as unofficial.
Steps:
1. install synaptic with “sudo apt-get install synaptic”
2. open synaptic app and find the list of obsolete packages by clicking on the “Status” button and selecting “Installed (local or obsolete)”.
3. select all of the obsolete packages and mark them for removal, then click on Apply button. (Note: Your important apps my listed as obsolete packages, so make sure to backup the app data if posible. You my also need to keep the list by using screenshot,so you can install them back later after upgrade).

[Saad Ahmad (milta1024)]

How to find the absolute packages, i.en whether it is local or absolute?