Some index files failed to download. They have …… or old ones used instead

问题：

平台：Ubuntu12.04

W: Failed to fetch http://us.archive.ubuntu.com/ubuntu/dists/precise/universe/binary-i386/Packages 404 Not Found [IP: 91.189.92.182 80]
E: Some index files failed to download. They have been ignored, or old ones used instead. 

分析：

在安装系统的时候，代理服务器填写错误。 

解决：

创建或编辑/etc/apt/apt.conf文件

sudo vi /etc/apt/apt.conf
    添加如下内容：
    Acquire::http { Proxy "http://192.168.88.10:3142"; }; 
    或
    Acquire::http::Proxy "http://192.168.88.10:3142";  

注：代理服务器可不填写，即把该文件清空；代理服务器填写请根据实际情况填写，以上为本人的个人情况而已。