為了防止意外發生可以先將 /etc/apt/下面的sources.list復制一份並重命名為sources_old.list, 然後將sources.list裡面的內容修改為下面（上面的是中科大的源下面的是阿裡雲的源，可以任選其一）:
debhttp://mirrors.ustc.edu.cn/ubuntu/ trusty main restricted universe multiverse
debhttp://mirrors.ustc.edu.cn/ubuntu/ trusty-security main restricted universe multiverse
debhttp://mirrors.ustc.edu.cn/ubuntu/ trusty-updates main restricted universe multiverse
debhttp://mirrors.ustc.edu.cn/ubuntu/ trusty-proposed main restricted universe multiverse
debhttp://mirrors.ustc.edu.cn/ubuntu/ trusty-backports main restricted universe multiverse
deb-srchttp://mirrors.ustc.edu.cn/ubuntu/ trusty main restricted universe multiverse
deb-srchttp://mirrors.ustc.edu.cn/ubuntu/ trusty-security main restricted universe multiverse
deb-srchttp://mirrors.ustc.edu.cn/ubuntu/ trusty-updates main restricted universe multiverse
deb-srchttp://mirrors.ustc.edu.cn/ubuntu/ trusty-proposed main restricted universe multiverse
deb-srchttp://mirrors.ustc.edu.cn/ubuntu/ trusty-backports main restricted universe multiverse
下面的是阿裡雲的源：
debhttp://mirrors.aliyun.com/ubuntu/ trusty main restricted universe multiverse
debhttp://mirrors.aliyun.com/ubuntu/ trusty-security main restricted universe multiverse
debhttp://mirrors.aliyun.com/ubuntu/ trusty-updates main restricted universe multiverse
debhttp://mirrors.aliyun.com/ubuntu/ trusty-proposed main restricted universe multiverse
debhttp://mirrors.aliyun.com/ubuntu/ trusty-backports main restricted universe multiverse
deb-srchttp://mirrors.aliyun.com/ubuntu/ trusty main restricted universe multiverse
deb-srchttp://mirrors.aliyun.com/ubuntu/ trusty-security main restricted universe multiverse
deb-srchttp://mirrors.aliyun.com/ubuntu/ trusty-updates main restricted universe multiverse
deb-srchttp://mirrors.aliyun.com/ubuntu/ trusty-proposed main restricted universe multiverse
deb-srchttp://mirrors.aliyun.com/ubuntu/ trusty-backports main restricted universe multiverse
修改過後別忘了使用sudo apt-get update更新一下。
如果發生錯誤可以把sources.list刪除,再把sources_old.list名字改為sources.list即可.
注意上面方法只適用於ubuntu14.04系統,其他版本的系統不適合.
