I'm trying to upgrade from 16.04 to 18.04 LTS. When I go to do-release-upgrade, though, I get a message "no new release found."
I've tried editing (or not editing) /update-manager/release-upgrades; I've tried do-release-upgrade -d; I've tried everything I could find on the internet.
One twist to this is that the server I'm trying to upgrade is behind a local mirror; that is, instead of downloading from ubuntu directly, it's downloading from this local mirror; the server is behind a firewall of sorts. Are there special servers that need to be in sources.list for do-release-upgrade? I'm at a loss.