Este é o erro que recebo quando tento atualizar qualquer coisa.
Ign cdrom://Ubuntu 12.10 _Quantal Quetzal_ - Release amd64 (20121017.5) quantal InRelease
Ign cdrom://Ubuntu 12.10 _Quantal Quetzal_ - Release amd64 (20121017.5) quantal Release.gpg
Ign cdrom://Ubuntu 12.10 _Quantal Quetzal_ - Release amd64 (20121017.5) quantal Release
Err cdrom://Ubuntu 12.10 _Quantal Quetzal_ - Release amd64 (20121017.5) quantal/main amd64 Packages
Please use apt-cdrom to make this CD-ROM recognized by APT. apt-get update cannot be used to add new CD-ROMs
Err cdrom://Ubuntu 12.10 _Quantal Quetzal_ - Release amd64 (20121017.5) quantal/restricted amd64 Packages
Please use apt-cdrom to make this CD-ROM recognized by APT. apt-get update cannot be used to add new CD-ROMs
Err cdrom://Ubuntu 12.10 _Quantal Quetzal_ - Release amd64 (20121017.5) quantal/main i386 Packages
Please use apt-cdrom to make this CD-ROM recognized by APT. apt-get update cannot be used to add new CD-ROMs
Err cdrom://Ubuntu 12.10 _Quantal Quetzal_ - Release amd64 (20121017.5) quantal/restricted i386 Packages
Please use apt-cdrom to make this CD-ROM recognized by APT. apt-get update cannot be used to add new CD-ROMs
Ign cdrom://Ubuntu 12.10 _Quantal Quetzal_ - Release amd64 (20121017.5) quantal/main Translation-en_US
Ign cdrom://Ubuntu 12.10 _Quantal Quetzal_ - Release amd64 (20121017.5) quantal/main Translation-en
Ign cdrom://Ubuntu 12.10 _Quantal Quetzal_ - Release amd64 (20121017.5) quantal/restricted Translation-en_US
Ign cdrom://Ubuntu 12.10 _Quantal Quetzal_ - Release amd64 (20121017.5) quantal/restricted Translation-en
Ign http://archive.ubuntu.com quantal InRelease
Get:1 http//repo.steampowered.com precise InRelease [2,840 B]
Err http//archive.ubuntu.com quantal-updates/main Sources
404 Not Found [IP: 91.189.91.13 80]
Err http://archive.ubuntu.com quantal-updates/restricted Sources
Ign http//archive.ubuntu.com quantal-security/main Translation-en_US
W: Failed to fetch cdrom://Ubuntu 12.10 _Quantal Quetzal_ - Release amd64 (20121017.5)/dists/quantal/main/binary-amd64/Packages Please use apt-cdrom to make this CD-ROM recognized by APT. apt-get update cannot be used to add new CD-ROMs
W: Failed to fetch http:/archive.ubuntu.com/ubuntu/dists/quantal/main/source/Sources 404 Not Found [IP: 91.189.91.13 80]
E: Some index files failed to download. They have been ignored, or old ones used instead.
FYI: Eu tive que apagar um monte de coisas porque isso não me deixava postar todos os links ou o que quer que fosse no relatório.
12.10 é uma versão não suportada. Você não pode mais depender dos repositórios de software que estão sendo mantidos.
Seu único caminho de atualização válido a partir de 12.04 seria diretamente para o 14.04 - o próximo lançamento do LTS.
Edite /etc/update-manager/release-upgrades e defina Prompt=lts
Execute do-release-upgrade em um terminal.