[Bug 1928498] Re: An unknown error is causing the upgrade from 16.04 to 18.04 to fail. No specific error name displayed. It only points out that it is unresolvable

[Prabhat Telidevara]

** Attachment added: "main.log"
   https://bugs.launchpad.net/ubuntu/+source/ubuntu-release-upgrader/+bug/1928498/+attachment/5497635/+files/main.log

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https://bugs.launchpad.net/bugs/1928498

Title:
  An unknown error is causing the upgrade from 16.04 to 18.04 to fail.
  No specific error name displayed. It only points out that it is
  unresolvable

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

Bug description:
  Calculating the changes

  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'.

  ProblemType: Bug
  DistroRelease: Ubuntu 16.04
  Package: ubuntu-release-upgrader-core 1:16.04.32
  ProcVersionSignature: Ubuntu 4.15.0-142.146~16.04.1-generic 4.15.18
  Uname: Linux 4.15.0-142-generic x86_64
  ApportVersion: 2.20.1-0ubuntu2.30
  Architecture: amd64
  CrashDB: ubuntu
  CurrentDesktop: Unity
  Date: Fri May 14 11:13:05 2021
  InstallationDate: Installed on 2017-12-16 (1245 days ago)
  InstallationMedia: Ubuntu 16.04.3 LTS "Xenial Xerus" - Release amd64 (20170801)
  PackageArchitecture: all
  SourcePackage: ubuntu-release-upgrader
  UpgradeStatus: Upgraded to xenial on 2021-05-14 (0 days ago)

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