linux-sudo apt-get update

 Ubuntu 11.04 (Natty) 已经停止支持,但可以使用old-releases源了,先备份源列表文件:

sudo cp /etc/apt/sources.list /etc/apt/sources.list.backup

sudo gedit /etc/apt/sources.list

把里面的内容替换为以下内容:

deb http://old-releases.ubuntu.com/ubuntu/ natty main restricted universe multiverse

deb http://old-releases.ubuntu.com/ubuntu/ natty-security main restricted universe multiverse

deb http://old-releases.ubuntu.com/ubuntu/ natty-updates main restricted universe multiverse

deb http://old-releases.ubuntu.com/ubuntu/ natty-proposed main restricted universe multiverse

deb http://old-releases.ubuntu.com/ubuntu/ natty-backports main restricted universe multiverse

deb-src http://old-releases.ubuntu.com/ubuntu/ natty main restricted universe multiverse

deb-src http://old-releases.ubuntu.com/ubuntu/ natty-security main restricted universe multiverse

deb-src http://old-releases.ubuntu.com/ubuntu/ natty-updates main restricted universe multiverse

deb-src http://old-releases.ubuntu.com/ubuntu/ natty-proposed main restricted universe multiverse

deb-src http://old-releases.ubuntu.com/ubuntu/ natty-backports main restricted universe multiverse

重载源列表,使配置生效:
sudo apt-get update