更換軟件源：https://www.cnblogs.com/flyinggod/p/7979108.html
1. 備份
sudo cp /etc/apt/sources.list /etc/apt/sources.list.bak
2.修改
sudo vim /etc/apt/sources.list
將source.list文件內容替換成下面的（網易163的 軟件源）
deb http://mirrors.163.com/ubuntu/ trusty main restricted universe multiverse
deb http://mirrors.163.com/ubuntu/ trusty-security main restricted universe multiverse
deb http://mirrors.163.com/ubuntu/ trusty-updates main restricted universe multiverse
deb http://mirrors.163.com/ubuntu/ trusty-proposed main restricted universe multiverse
deb http://mirrors.163.com/ubuntu/ trusty-backports main restricted universe multiverse
deb-src http://mirrors.163.com/ubuntu/ trusty main restricted universe multiverse
deb-src http://mirrors.163.com/ubuntu/ trusty-security main restricted universe multiverse
deb-src http://mirrors.163.com/ubuntu/ trusty-updates main restricted universe multiverse
deb-src http://mirrors.163.com/ubuntu/ trusty-proposed main restricted universe multiverse
deb-src http://mirrors.163.com/ubuntu/ trusty-backports main restricted universe multiverse
3. 更新
sudo apt-get update
4.重新的下載安裝。