首先备份本地的源

cp /etc/apt/sources.list /etc/apt/sources.list.bak

编辑源文件

vim /etc/apt/sources.list

删除原有内容，添加下面内容

deb  trusty main restricted universe multiverse 
deb  trusty-security main restricted universe multiverse 
deb  trusty-updates main restricted universe multiverse 
deb  trusty-proposed main restricted universe multiverse 
deb  trusty-backports main restricted universe multiverse 
deb-src  trusty main restricted universe multiverse 
deb-src  trusty-security main restricted universe multiverse 
deb-src  trusty-updates main restricted universe multiverse 
deb-src  trusty-proposed main restricted universe multiverse 
deb-src  trusty-backports main restricted universe multiverse

更新源

apt-get update