I resolved this problem by modifying my /etc/apt/sources.list to remove the mirror method, and point directly to ubuntu sources. I.e. my old sources.list contained lines like this:
deb mirror://mirrors.ubuntu.com/mirrors.txt xenial main restricted Which I modified to this: deb http://us.archive.ubuntu.com/ubuntu/ xenial main restricted -- You received this bug notification because you are a member of Ubuntu Bugs, which is subscribed to Ubuntu. https://bugs.launchpad.net/bugs/1795207 Title: upgrade to ubuntu-18.04: 'ubuntu-minimal' not found To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/ubuntu-release-upgrader/+bug/1795207/+subscriptions -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs
