我一直尝试从 18.10 升级到至少 19.04，例如使用此处的说明
每当我打字do-release-upgrade时，我都会得到
Checking for a new Ubuntu release
Your Ubuntu release is not supported anymore.
For upgrade information, please visit:
http://www.ubuntu.com/releaseendoflife
Please install all available updates for your release before upgrading.
我不知道在这个节骨眼上我们能做什么。