[Bug 1909911] [NEW] Upgrade to 20.04.1 fails

[Siddhartha Ghosh]

Public bug reported:

I am trying to upgrade from Ubuntu 18.04 to Ubuntu 20.04.1 using the
"software updater" which prompts me that there is a new LTS release.

Here is the error message:
==
Could not calculate 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'.
==
And last few lines from /var/log/dist-upgrade/main.log
==
2021-01-03 21:07:30,440 DEBUG need_server_mode(): run in 'desktop' mode, (because of pkg 'ubuntu-desktop')
2021-01-03 21:07:30,440 DEBUG quirks: running PreDistUpgradeCache
2021-01-03 21:07:30,440 DEBUG running Quirks.PreDistUpgradeCache
2021-01-03 21:07:30,441 INFO checking for python-dbg
2021-01-03 21:07:30,441 INFO checking for python-doc
2021-01-03 21:07:30,441 INFO checking for python-minimal
2021-01-03 21:07:30,441 INFO installing python-is-python2 because python-minimal was installed
2021-01-03 21:07:30,441 DEBUG Installing 'python-is-python2' (python-minimal was installed on the system)
2021-01-03 21:07:30,441 INFO removing python-minimal because python-is-python2 is being installed
2021-01-03 21:07:30,441 DEBUG Removing 'python-minimal' (python-is-python2 is being installed on the system)
==

Thanks

ProblemType: Bug
DistroRelease: Ubuntu 18.04
Package: ubuntu-release-upgrader-core 1:18.04.41
ProcVersionSignature: Ubuntu 4.15.0-128.131-generic 4.15.18
Uname: Linux 4.15.0-128-generic x86_64
ApportVersion: 2.20.9-0ubuntu7.21
Architecture: amd64
CrashDB: ubuntu
CurrentDesktop: ubuntu:GNOME
Date: Sun Jan  3 21:07:55 2021
InstallationDate: Installed on 2018-08-04 (883 days ago)
InstallationMedia: Ubuntu 18.04.1 LTS "Bionic Beaver" - Release amd64 (20180725)
PackageArchitecture: all
SourcePackage: ubuntu-release-upgrader
UpgradeStatus: Upgraded to bionic on 2021-01-03 (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/1909911

Title:
  Upgrade to 20.04.1 fails

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

Bug description:
  I am trying to upgrade from Ubuntu 18.04 to Ubuntu 20.04.1 using the
  "software updater" which prompts me that there is a new LTS release.

  Here is the error message:
  ==
  Could not calculate 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'.
  ==
  And last few lines from /var/log/dist-upgrade/main.log
  ==
  2021-01-03 21:07:30,440 DEBUG need_server_mode(): run in 'desktop' mode, (because of pkg 'ubuntu-desktop')
  2021-01-03 21:07:30,440 DEBUG quirks: running PreDistUpgradeCache
  2021-01-03 21:07:30,440 DEBUG running Quirks.PreDistUpgradeCache
  2021-01-03 21:07:30,441 INFO checking for python-dbg
  2021-01-03 21:07:30,441 INFO checking for python-doc
  2021-01-03 21:07:30,441 INFO checking for python-minimal
  2021-01-03 21:07:30,441 INFO installing python-is-python2 because python-minimal was installed
  2021-01-03 21:07:30,441 DEBUG Installing 'python-is-python2' (python-minimal was installed on the system)
  2021-01-03 21:07:30,441 INFO removing python-minimal because python-is-python2 is being installed
  2021-01-03 21:07:30,441 DEBUG Removing 'python-minimal' (python-is-python2 is being installed on the system)
  ==

  Thanks

  ProblemType: Bug
  DistroRelease: Ubuntu 18.04
  Package: ubuntu-release-upgrader-core 1:18.04.41
  ProcVersionSignature: Ubuntu 4.15.0-128.131-generic 4.15.18
  Uname: Linux 4.15.0-128-generic x86_64
  ApportVersion: 2.20.9-0ubuntu7.21
  Architecture: amd64
  CrashDB: ubuntu
  CurrentDesktop: ubuntu:GNOME
  Date: Sun Jan  3 21:07:55 2021
  InstallationDate: Installed on 2018-08-04 (883 days ago)
  InstallationMedia: Ubuntu 18.04.1 LTS "Bionic Beaver" - Release amd64 (20180725)
  PackageArchitecture: all
  SourcePackage: ubuntu-release-upgrader
  UpgradeStatus: Upgraded to bionic on 2021-01-03 (0 days ago)
  VarLogDistupgradeTermlog:

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