Ubuntu – How to get Ubuntu Update Manager to nag me only about the current version

The other answers aren't quite right, but combining them put me on the right track.

/etc/update-manager/release-upgrades controls what updates you'll be notified about. /usr/lib/update-manager/release-upgrade-motd generates the "update available" message. The problem is that release-upgrade-motd caches the message, which means that once it's been generated, changing /etc/update-manager/release-upgrades doesn't get rid of the message.

So the answer is:

1. Tell Update Manager what releases you want to be notified about.

2. sudo rm /var/lib/update-notifier/release-upgrade-available to get rid of the cached message.

Note: For version 13.04 (and later), the path has changed. So point 2. to get rid of the cached message is now:

sudo rm /var/lib/ubuntu-release-upgrader/release-upgrade-available

Your update process ought to give you a complete log of what is being downloaded, unpacked, installed and configured. If it doesn't, there is something wrong, but at this point we can only speculate what. However, you can simply interrupt the upgrade with Ctrl + C. Then do sudo apt install -f to see where you were.

One thing may have gone wrong though. If the upgrade process was running, then early on your Ubuntu version string was changed (in your case from xenial to bionic) in /etc/apt/sources.list. You may need to change that back before retrying the upgrade.