Meu comando todo apt-get termina com algo assim:
Err http://security.ubuntu.com quantal-security Release.gpg
Temporary failure resolving 'security.ubuntu.com'
Err http://rs.archive.ubuntu.com quantal Release.gpg
Temporary failure resolving 'rs.archive.ubuntu.com'
Err http://rs.archive.ubuntu.com quantal-updates Release.gpg
Temporary failure resolving 'rs.archive.ubuntu.com'
Err http://rs.archive.ubuntu.com quantal-backports Release.gpg
Temporary failure resolving 'rs.archive.ubuntu.com'
Reading package lists... Done
W: Failed to fetch http://rs.archive.ubuntu.com/ubuntu/dists/quantal/Release.gpg Temporary failure resolving 'rs.archive.ubuntu.com'
W: Failed to fetch http://rs.archive.ubuntu.com/ubuntu/dists/quantal-updates/Release.gpg Temporary failure resolving 'rs.archive.ubuntu.com'
W: Failed to fetch http://rs.archive.ubuntu.com/ubuntu/dists/quantal-backports/Release.gpg Temporary failure resolving 'rs.archive.ubuntu.com'
W: Failed to fetch http://security.ubuntu.com/ubuntu/dists/quantal-security/Release.gpg Temporary failure resolving 'security.ubuntu.com'
W: Some index files failed to download. They have been ignored, or old ones used instead.
Eu tentei --fix-missing, update, autoremove ... mas o problema permanece