剛安裝了ubuntu之后的主要安裝命令無非就是apt-get install了，然而很多都在這里就夭折了。
使用apt-get install ***需要先執行apt-get update 加載文件包
而有些ubuntu 的 apt-get update 並沒有想象的一樣好使，竟然一直報錯 E:Some index files failed to download. They have been ignored, or old ones used instead
主要是有些源並不存在才會導致報錯，所以只要更換update源即可
解決方案
1. vi etc/apt/sources.list
2. 將里面的內容替換成下面這些(artful可以更換，主要看http://mirrors.163.com/ubuntu/dists/下面有哪些可用的前綴自行更換)
deb http://mirrors.163.com/ubuntu/ artful main restricted universe multiverse deb http://mirrors.163.com/ubuntu/ artful-security main restricted universe multiverse deb http://mirrors.163.com/ubuntu/ artful-updates main restricted universe multiverse deb http://mirrors.163.com/ubuntu/ artful-proposed main restricted universe multiverse deb http://mirrors.163.com/ubuntu/ artful-backports main restricted universe multiverse deb-src http://mirrors.163.com/ubuntu/ artful main restricted universe multiverse deb-src http://mirrors.163.com/ubuntu/ artful-security main restricted universe multiverse deb-src http://mirrors.163.com/ubuntu/ artful-updates main restricted universe multiverse deb-src http://mirrors.163.com/ubuntu/ artful-proposed main restricted universe multiverse deb-src http://mirrors.163.com/ubuntu/ artful-backports main restricted universe multiverse