$ do-release-upgrade -d
Checking for a new ubuntu release
Err Upgrade tool signature
  404  Not Found [IP: 91.189.92.169 80]
Get:1 Upgrade tool [1550 kB]
Fetched 1550 kB in 0s (0 B/s)
WARNING:root:file 'precise.tar.gz.gpg' missing
Failed to fetch
Fetching the upgrade failed. There may be a network problem.