[Bug 1868315] Re: I tried upgrading from 16.04 to 18.04 using terminal commands and it says "couldnt calculate upgrade" & "use ppa-purge tool"

[Ubuntu Foundations Team Bug Bot]

*** This bug is a duplicate of bug 1611737 ***
    https://bugs.launchpad.net/bugs/1611737

** Tags added: xenial2bionic

** This bug has been marked a duplicate of bug 1611737
   Can't upgrade from a release if ros packages are  installed from ROS servers

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https://bugs.launchpad.net/bugs/1868315

Title:
  I tried upgrading from 16.04 to 18.04 using terminal commands and it
  says "couldnt calculate upgrade" & "use ppa-purge tool"

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

Bug description:
  Description:	Ubuntu 16.04.6 LTS
  Release:	16.04

  ProblemType: Bug
  DistroRelease: Ubuntu 16.04
  Package: ubuntu-release-upgrader-core 1:16.04.29
  ProcVersionSignature: Ubuntu 4.15.0-91.92~16.04.1-generic 4.15.18
  Uname: Linux 4.15.0-91-generic x86_64
  ApportVersion: 2.20.1-0ubuntu2.22
  Architecture: amd64
  CrashDB: ubuntu
  CurrentDesktop: Unity
  Date: Sat Mar 21 01:23:25 2020
  InstallationDate: Installed on 2019-10-15 (157 days ago)
  InstallationMedia: Ubuntu 16.04.5 LTS "Xenial Xerus" - Release amd64 (20180731)
  PackageArchitecture: all
  SourcePackage: ubuntu-release-upgrader
  UpgradeStatus: Upgraded to xenial on 2020-03-20 (0 days ago)
  VarLogDistupgradeTermlog:

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