ubuntu的版本支持的时间都有限, 如果过了支持的时间，更新源会被停用，那么只能采取old-releases源了。
查看当前系统的版本信息
chs@chs-VirtualBox:~/project/openscada$ sudo lsb_release -a [sudo] password for chs: No LSB modules are available. Distributor ID: Ubuntu Description: Ubuntu 11.04 Release: 11.04 Codename: natty
可以发现当前的系统版本是11.04，代号为natty。
old-releases源信息如下
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
修改更新源，替换成上面的源信息
chs@chs-VirtualBox:~/project/openscada$sudo vim /etc/apt/sources.list
源更新
chs@chs-VirtualBox:~/project/openscada$sudo apt-get update
其他过期版本的old-releases源信息只需替换如上代号（natty）部分即可。
