ubuntu minimal not found

[Tanmay Singal]

While performing an upgrade from ubuntu 16.04 lts to 18.04 lts, some third party entries in the source.list are initially disabled, and thereafter ubuntu minimal isn't found. And this stops the upgrading procedure.

ProblemType: Bug
DistroRelease: Ubuntu 16.04
Package: ubuntu-release-upgrader-core 1:16.04.29
ProcVersionSignature: Ubuntu 4.15.0-70.79~16.04.1-generic 4.15.18
Uname: Linux 4.15.0-70-generic x86_64
NonfreeKernelModules: nvidia_uvm nvidia wl
ApportVersion: 2.20.1-0ubuntu2.21
Architecture: amd64
CrashDB: ubuntu
Date: Sat Nov 16 03:45:20 2019
InstallationDate: Installed on 2018-01-10 (674 days ago)
InstallationMedia: Ubuntu 16.04.3 LTS "Xenial Xerus" - Release amd64 (20170801)
PackageArchitecture: all
SourcePackage: ubuntu-release-upgrader
UpgradeStatus: Upgraded to xenial on 2019-11-15 (0 days ago)
VarLogDistupgradeAptlog:
 Log time: 2019-11-16 03:43:56.447292
 Log time: 2019-11-16 03:44:05.115197
 Log time: 2019-11-16 03:45:20.381433
 Log time: 2019-11-16 03:45:23.462588