ein@ein-desktop:~$ sudo apt-get update
Trovato:1 http://ubuntu.mirror.garr.it/mirrors/ubuntu-archive xenial InRelease
Trovato:2 http://ppa.launchpad.net/ubuntu-wine/ppa/ubuntu xenial InRelease     
Trovato:3 http://archive.canonical.com/ubuntu xenial InRelease                 
Trovato:4 https://repo.skype.com/deb stable InRelease 
Scaricamento di:5 https://download.01.org/gfx/ubuntu/16.04/main xenial InRelease [3.651 B]
Ign:5 https://download.01.org/gfx/ubuntu/16.04/main xenial InRelease
Trovato:6 http://ubuntu.mirror.garr.it/mirrors/ubuntu-archive xenial-updates InRelease
Trovato:7 http://ubuntu.mirror.garr.it/mirrors/ubuntu-archive xenial-security InRelease
Trovato:8 http://ubuntu.mirror.garr.it/mirrors/ubuntu-archive xenial-backports InRelease
Recuperati 3.651 B in 3s (1.130 B/s)
Lettura elenco dei pacchetti... Fatto
W: Errore GPG: https://download.01.org/gfx/ubuntu/16.04/main xenial InRelease: Le seguenti firme non sono state verificate perché la chiave pubblica non è disponibile: NO_PUBKEY 56A3DEF863961D39
W: The repository 'https://download.01.org/gfx/ubuntu/16.04/main xenial InRelease' is not signed.
N: Data from such a repository can't be authenticated and is therefore potentially dangerous to use.
N: See apt-secure(8) manpage for repository creation and user configuration details.
ein@ein-desktop:~$