do-release-upgrade 
Checking for a new Ubuntu release
Get:1 Upgrade tool signature [836 B]                                                                                                             
Get:2 Upgrade tool [1266 kB]                                                                                                                     
Fetched 1267 kB in 0s (0 B/s)                                                                                                                    
authenticate 'xenial.tar.gz' against 'xenial.tar.gz.gpg' 
extracting 'xenial.tar.gz'