This is due to your use of mirror://mirrors.ubuntu.com/mirrors.txt in your /etc/apt/sources.list. When ubuntu-release-upgrader checks if your current mirror is reachable, it does not know how to check mirror:// URIs.
As a workaround, please use a single mirror (e.g. http://no.archive.ubuntu.com/ubuntu) in your /etc/apt/sources.list, and then do the upgrade. You should be able to switch back to mirrors://mirrors.ubuntu.com/mirrors.txt after the upgrade.
Hi Lars,
This is due to your use of mirror: //mirrors. ubuntu. com/mirrors. txt in your /etc/apt/ sources. list. When ubuntu- release- upgrader checks if your current mirror is reachable, it does not know how to check mirror:// URIs.
As a workaround, please use a single mirror (e.g. http:// no.archive. ubuntu. com/ubuntu) in your /etc/apt/ sources. list, and then do the upgrade. You should be able to switch back to mirrors: //mirrors. ubuntu. com/mirrors. txt after the upgrade.