问题描述：
每次我尝试为我的操作系统 (Ubuntu 12.04) 下载更新时，我都会收到以下错误消息列表：
W:Failed to fetch http://extras.ubuntu.com/ubuntu/dists/precise/Release.gpg Something wicked happened resolving 'extras.ubuntu.com:http' (-5 - No address associated with hostname)
, W:Failed to fetch http://ppa.launchpad.net/deluge-team/ppa/ubuntu/dists/precise/Release.gpg Something wicked happened resolving 'ppa.launchpad.net:http' (-5 - No address associated with hostname)
, W:Failed to fetch http://packages.medibuntu.org/dists/precise/Release.gpg Something wicked happened resolving 'packages.medibuntu.org:http' (-5 - No address associated with hostname)
, W:Failed to fetch http://archive.canonical.com/ubuntu/dists/precise/Release.gpg Something wicked happened resolving 'archive.canonical.com:http' (-5 - No address associated with hostname)
, W:Failed to fetch http://ppa.launchpad.net/tualatrix/ppa/ubuntu/dists/precise/Release.gpg Something wicked happened …