I am new to Ubuntu and when I execute
sudo apt-get update
I get the following errors and warnings
W: GPG error: http://ppa.launchpad.net quantal Release: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 5A9A06AEF9CB8DB0 W: Failed to fetch http://security.ubuntu.com/ubuntu/dists/quantal-security/Release.gpg Something wicked happened resolving 'security.ubuntu.com:http' (-5 - No address associated with hostname) W: Failed to fetch http://extras.ubuntu.com/ubuntu/dists/quantal/Release.gpg Something wicked happened resolving 'extras.ubuntu.com:http' (-5 - No address associated with hostname) W: Failed to fetch http://packages.medibuntu.org/dists/quantal/Release.gpg Something wicked happened resolving 'packages.medibuntu.org:http' (-5 - No address associated with hostname) E: Some index files failed to download. They have been ignored, or old ones used instead.
Can anyone tell me what is wrong?