[Ubuntu] apt-get update 更新時失敗

今天做了幫 ubuntu 12.04.4 那台虛擬機做更新時，竟然吐出下列的失敗訊息

Ign http://ppa.launchpad.net trusty/main Translation-en                    
Get:2 http://free.nchc.org.tw trusty/universe i386 Packages [5886 kB]      
Fetched 11.8 MB in 18s (651 kB/s)                                          
W: Failed to fetch bzip2:/var/lib/apt/lists/partial/free.nchc.org.tw_ubuntu_dists_trusty_universe_binary-amd64_Packages  Hash Sum mismatch
W: Failed to fetch bzip2:/var/lib/apt/lists/partial/free.nchc.org.tw_ubuntu_dists_trusty_universe_binary-i386_Packages  Hash Sum mismatch
E: Some index files failed to download. They have been ignored, or old ones used instead.

很顯然的，裡頭有個關鍵「Hash Sum mismatch」、「 Failed to fetch 」，興沖沖進去「/var/lib/apt/lists/partial/」裡頭把它刪掉，嘿！沒用！，又把「/var/lib/apt/lists/」全部刪掉，還是沒用！

後來，把 source.list 的站台從「free.nchc.org.tw」改成「tw.archive.ubuntu.com」，再更新，哇！正常了！