一直使用11.04版本，但是官方停止維護已經很長時間了，而目前有更新apt源的需求。通過搜索資料，發現瞭如下解決方法：
1. 標準動作：備份原source.list
sudo mv /etc/apt/source.list /etc/apt/source.list.bk
2.編輯source.list爲如下內容，以11.04版本（代號natty）爲例：
deb http://old-releases.ubuntu.com/ubuntu/ natty main restricted universe multiversedeb http://old-releases.ubuntu.com/ubuntu/ natty-security main restricted universe multiversedeb http://old-releases.ubuntu.com/ubuntu/ natty-updates main restricted universe multiversedeb http://old-releases.ubuntu.com/ubuntu/ natty-proposed main restricted universe multiversedeb http://old-releases.ubuntu.com/ubuntu/ natty-backports main restricted universe multiversedeb-src http://old-releases.ubuntu.com/ubuntu/ natty main restricted universe multiversedeb-src http://old-releases.ubuntu.com/ubuntu/ natty-security main restricted universe multiversedeb-src http://old-releases.ubuntu.com/ubuntu/ natty-updates main restricted universe multiversedeb-src http://old-releases.ubuntu.com/ubuntu/ natty-proposed main restricted universe multiversedeb-src http://old-releases.ubuntu.com/ubuntu/ natty-
backports main restricted universe multiverse
然後sudo apt-get update即可
參考資料：
http://www.dwhd.org/2013/02/03/1971.html
wzw0114
2013.07.15