Ok, the upgrade does appear to get off the ground (it's still running as I write this) if I create a /etc/update-manager/release-upgrades.d/DistUpgrade.cfg containing the following 2 lines:
[Sources] AllowThirdParty = true
Ok, the upgrade does appear to get off the ground (it's still running as I write this) if I create a /etc/update- manager/ release- upgrades. d/DistUpgrade. cfg containing the following 2 lines:
[Sources]
AllowThirdParty = true