root@server:~# do-release-upgrade
Checking for a new Ubuntu release
Get:1 Upgrade tool signature [198 B]
Get:2 Upgrade tool [1205 kB]
Fetched 1205 kB in 0s (0 B/s)
authenticate 'raring.tar.gz' against 'raring.tar.gz.gpg'
extracting 'raring.tar.gz'
Traceback (most recent call last):
  File "/tmp/ubuntu-release-upgrader-z46ggn/raring", line 6, in <module>
    from DistUpgrade.DistUpgradeMain import main
  File "/tmp/ubuntu-release-upgrader-z46ggn/DistUpgrade/DistUpgradeMain.py", line 27, in <module>
    import apt
ImportError: No module named apt