do-release-upgrade brakes system on network failure

[Karl Kastner]

On a friends computer the release upgrade was interrupted due to a power out. On reboot, the system could not be fixed with an apt-get -f install and then apt-get dist-upgrade, because some packages were not yet downloaded and the system was in a state were the network was not functioning. I solved this problem by means of live usb stick, chroot and then continuing the upgrade. Such a situations should be prevented by first downloading all packages before the release upgrade begins. If the system has to be upgraded in stages, then the packages for each stage should be downloaded entirely such that the user is never left with a broken system.

ProblemType: Bug
DistroRelease: Ubuntu 16.04
Package: ubuntu-release-upgrader-core 1:16.04.14
ProcVersionSignature: Ubuntu 4.4.0-31.50-generic 4.4.13
Uname: Linux 4.4.0-31-generic x86_64
ApportVersion: 2.20.1-0ubuntu2.1
Architecture: amd64
CrashDB: ubuntu
CurrentDesktop: GNOME-Classic:GNOME
Date: Wed Aug 24 21:58:57 2016
InstallationDate: Installed on 2015-11-05 (293 days ago)
InstallationMedia: Ubuntu 14.04.3 LTS "Trusty Tahr" - Beta amd64 (20150805)
PackageArchitecture: all
SourcePackage: ubuntu-release-upgrader
UpgradeStatus: No upgrade log present (probably fresh install)