当使用apt-get update更新源时，出现下面“Hash Sum mismatch”的报错，具体如下：
root@localhost:~# apt-get update
......
......
W: Failed to fetch http://us.archive.ubuntu.com/ubuntu/dists/precise/main/source/Sources Hash Sum mismatch
W: Failed to fetch http://us.archive.ubuntu.com/ubuntu/dists/precise/restricted/source/Sources Hash Sum mismatch
W: Failed to fetch http://us.archive.ubuntu.com/ubuntu/dists/precise/universe/source/Sources Hash Sum mismatch
W: Failed to fetch http://us.archive.ubuntu.com/ubuntu/dists/precise/multiverse/source/Sources Hash Sum mismatch
W: Failed to fetch http://us.archive.ubuntu.com/ubuntu/dists/precise/main/binary-amd64/Packages Hash Sum mismatch
W: Failed to fetch http://us.archive.ubuntu.com/ubuntu/dists/precise/restricted/binary-amd64/Packages Hash Sum mismatch
W: Failed to fetch http://us.archive.ubuntu.com/ubuntu/dists/precise/universe/binary-amd64/Packages Hash Sum mismatch
W: Failed to fetch http://us.archive.ubuntu.com/ubuntu/dists/precise/multiverse/binary-amd64/Packages Hash Sum mismatch
W: Failed to fetch http://us.archive.ubuntu.com/ubuntu/dists/precise/main/binary-i386/Packages Hash Sum mismatch
W: Failed to fetch http://us.archive.ubuntu.com/ubuntu/dists/precise/restricted/binary-i386/Packages Hash Sum mismatch
W: Failed to fetch http://us.archive.ubuntu.com/ubuntu/dists/precise/universe/binary-i386/Packages Hash Sum mismatch
W: Failed to fetch http://us.archive.ubuntu.com/ubuntu/dists/precise/multiverse/binary-i386/Packages Hash Sum mismatch
E: Some index files failed to download. They have been ignored, or old ones used instead.
产生原因：
所使用的网络供应商，有些会设置一些透明缓存，以增加网络内部速度，减少出口的流量，所获取的某些文件不是源服务器上的真正文件，是从缓存中获取的，当缓存中获取的一些校验信息跟源中不一致的时候，自然提示校验失败，无法继续更新。
解决办法：
1）删掉/var/lib/apt/lists 这个目录下的东西
sudo rm -fR /var/lib/apt/lists/*
2）新建相应文件夹
sudo mkdir /var/lib/apt/lists/partial
3）重新update
sudo apt-get update
