Comment 0 for bug 1990907

With u-a-t 27.11, currently on -proposed, upgrading from Xenial to Bionic fails when unattached.

The reason is: Bionic has some updates available in esm-apps, and the repositories are present due to the postinst script seeing that the service is not beta anymore.

However, the preferences file only pins esm for Xenial, and do-release-upgrade:
1. Sees the packages in the Bionic ESM repository
2. Ignores the pinning to 'never'
3. Fails to get those packages - all of them are 401ed
4. Fail to calculate the diffs and exits 1.

Although found and reproducible when upgrading from Xenial to Bionic, this bug may affect any upgrade across releases where the system is unattached, and has any given package installed which is present in the ESM repository of the next release.