sudo apt-get update
the terminal returned:
N: Ignoring file 'getdeb.list.bck' in directory '/etc/apt/sources.list.d/' as it has an invalid filename extension
W: Failed to fetch http://archive.getdeb.net/ubuntu/dis...eb/Release.gpg Something wicked happened resolving 'archive.getdeb.net:http' (-5 - No address associated with hostname)
W: Failed to fetch http://packages.medibuntu.org/dists/...ck/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.
What went wrong?
How do I fix this?
How do I prevent this from happening in the future?