[Bug 1929025] [NEW] upgrade from 18.04.5 LTS to 20.4 LTS failed: Could not calculate the upgrade

[Sebastien DESERT]

Public bug reported:

automatic upgrade from 18.04.6 LTS to 20.04 LTS was done, but not successfull. 
Error message "Could not calculate the upgrade"

last lines in /var/log/dist-upgrade$ cat main.log :

2021-05-20 08:11:42,504 INFO removing python-minimal because python-is-python2 is being installed
2021-05-20 08:11:42,504 DEBUG Removing 'python-minimal' (python-is-python2 is being installed on the system)
2021-05-20 08:11:42,504 INFO failed to remove python-minimal
2021-05-20 08:11:42,504 INFO checking for python-dev (auto_inst=True)
2021-05-20 08:11:42,504 INFO checking for libpython-dev (auto_inst=True)
2021-05-20 08:11:42,504 INFO checking for libpython-stdlib (auto_inst=True)
2021-05-20 08:11:42,504 INFO removing libpython-stdlib because None is being installed
2021-05-20 08:11:42,504 DEBUG Removing 'libpython-stdlib' (None is being installed on the system)
2021-05-20 08:11:42,504 INFO failed to remove libpython-stdlib
2021-05-20 08:11:42,505 INFO checking for libpython-dbg (auto_inst=True)

ProblemType: Bug
DistroRelease: Ubuntu 18.04
Package: ubuntu-release-upgrader-core 1:18.04.44
ProcVersionSignature: Ubuntu 4.15.0-143.147-generic 4.15.18
Uname: Linux 4.15.0-143-generic x86_64
ApportVersion: 2.20.9-0ubuntu7.23
Architecture: amd64
CrashDB: ubuntu
CurrentDesktop: ubuntu:GNOME
Date: Thu May 20 09:00:34 2021
InstallationDate: Installed on 2013-02-06 (3024 days ago)
InstallationMedia: Ubuntu 12.04 LTS "Precise Pangolin" - Release amd64 (20120425)
PackageArchitecture: all
SourcePackage: ubuntu-release-upgrader
UpgradeStatus: Upgraded to bionic on 2021-05-20 (0 days ago)
VarLogDistupgradeTermlog:

** Affects: ubuntu-release-upgrader (Ubuntu)
     Importance: Undecided
         Status: New


** Tags: amd64 apport-bug bionic dist-upgrade third-party-packages

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https://bugs.launchpad.net/bugs/1929025

Title:
  upgrade from 18.04.5 LTS to 20.4 LTS failed: Could not calculate the
  upgrade

Status in ubuntu-release-upgrader package in Ubuntu:
  New

Bug description:
  automatic upgrade from 18.04.6 LTS to 20.04 LTS was done, but not successfull. 
  Error message "Could not calculate the upgrade"

  last lines in /var/log/dist-upgrade$ cat main.log :

  2021-05-20 08:11:42,504 INFO removing python-minimal because python-is-python2 is being installed
  2021-05-20 08:11:42,504 DEBUG Removing 'python-minimal' (python-is-python2 is being installed on the system)
  2021-05-20 08:11:42,504 INFO failed to remove python-minimal
  2021-05-20 08:11:42,504 INFO checking for python-dev (auto_inst=True)
  2021-05-20 08:11:42,504 INFO checking for libpython-dev (auto_inst=True)
  2021-05-20 08:11:42,504 INFO checking for libpython-stdlib (auto_inst=True)
  2021-05-20 08:11:42,504 INFO removing libpython-stdlib because None is being installed
  2021-05-20 08:11:42,504 DEBUG Removing 'libpython-stdlib' (None is being installed on the system)
  2021-05-20 08:11:42,504 INFO failed to remove libpython-stdlib
  2021-05-20 08:11:42,505 INFO checking for libpython-dbg (auto_inst=True)

  ProblemType: Bug
  DistroRelease: Ubuntu 18.04
  Package: ubuntu-release-upgrader-core 1:18.04.44
  ProcVersionSignature: Ubuntu 4.15.0-143.147-generic 4.15.18
  Uname: Linux 4.15.0-143-generic x86_64
  ApportVersion: 2.20.9-0ubuntu7.23
  Architecture: amd64
  CrashDB: ubuntu
  CurrentDesktop: ubuntu:GNOME
  Date: Thu May 20 09:00:34 2021
  InstallationDate: Installed on 2013-02-06 (3024 days ago)
  InstallationMedia: Ubuntu 12.04 LTS "Precise Pangolin" - Release amd64 (20120425)
  PackageArchitecture: all
  SourcePackage: ubuntu-release-upgrader
  UpgradeStatus: Upgraded to bionic on 2021-05-20 (0 days ago)
  VarLogDistupgradeTermlog:

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