[Bug 1786039] Re: Upgrade from 16.04.5 to 18.04.1 crashes with message unable to resolve upgrade

[Ubuntu Foundations Team Bug Bot]

** Tags added: xenial2bionic

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https://bugs.launchpad.net/bugs/1786039

Title:
  Upgrade from 16.04.5 to 18.04.1 crashes with message unable to resolve
  upgrade

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

Bug description:
  On running update-manager -c no new upgrades are seen. But with the -d
  option, the upgrade to 18.04.1 becomes available. On choosing to
  upgrade, it finishes the first step ("preparing to upgrade"). A pop up
  appears saying that third party sources are disabled, and can be re
  enabled later on. However, on the next step ("Setting new software
  channels") it crashes with the message: "Could not calculate the
  upgrade, an unresolvable error occurred while calculating the
  upgrade".

  Ubuntu release description:
  Description:	Ubuntu 16.04.5 LTS
  Release:	16.04

  Update-manager version info:
  update-manager:
    Installed: 1:16.04.13
    Candidate: 1:16.04.13
    Version table:
   *** 1:16.04.13 500
          500 http://archive.ubuntu.com/ubuntu xenial-updates/main amd64 Packages
          500 http://archive.ubuntu.com/ubuntu xenial-updates/main i386 Packages
          100 /var/lib/dpkg/status
       1:16.04.12 500
          500 http://archive.ubuntu.com/ubuntu xenial-security/main amd64 Packages
          500 http://archive.ubuntu.com/ubuntu xenial-security/main i386 Packages
       1:16.04.3 500
          500 http://archive.ubuntu.com/ubuntu xenial/main amd64 Packages
          500 http://archive.ubuntu.com/ubuntu xenial/main i386 Packages

  ProblemType: Bug
  DistroRelease: Ubuntu 16.04
  Package: ubuntu-release-upgrader-core 1:16.04.25
  ProcVersionSignature: Ubuntu 4.15.0-30.32~16.04.1-generic 4.15.18
  Uname: Linux 4.15.0-30-generic x86_64
  ApportVersion: 2.20.1-0ubuntu2.18
  Architecture: amd64
  CrashDB: ubuntu
  CurrentDesktop: Unity
  Date: Wed Aug  8 18:58:23 2018
  InstallationDate: Installed on 2017-06-24 (409 days ago)
  InstallationMedia: Ubuntu 16.04.2 LTS "Xenial Xerus" - Release amd64 (20170215.2)
  PackageArchitecture: all
  SourcePackage: ubuntu-release-upgrader
  Symptom: ubuntu-release-upgrader
  UpgradeStatus: Upgraded to xenial on 2018-08-08 (0 days ago)
  VarLogDistupgradeTermlog:

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