I used do-release-upgrade to move from 14.04 to 16.04. It seemed to go through, although there were a number of packages listed afterwards that were not upgraded successfully.
Booting straight into 16.04 the system halts with: "Failed to start Load Kernel Modules See 'systemctl status systemd-modules-load.service' [OK] Started Journal Service ..... [ OK ] Created slice system-systemd\x2dbacklight.slice"
I went to try "dpkg --configure -a" from Recovery Mode, following What to do after Failed to start Load Kernel Modules
This failed because I have no network access (ping gives "Network is unreachable")
This is when I have a network cable connection, that works fine when I boot a live image on the same laptop