~$ do-release-upgrade -m desktop -f kde -d
Checking for a new Ubuntu release
Err Upgrade tool signature
  404  Not Found [IP: 91.189.91.24 80]
Err Upgrade tool
  404  Not Found [IP: 91.189.91.24 80]
Fetched 0 B in 0s (0 B/s)
WARNING:root:file 'quantal.tar.gz.gpg' missing
Failed to fetch
Fetching the upgrade failed. There may be a network problem.