sudo cp /etc/apt/sources.list /etc/apt/sources.list_backup
然后打开源列表，清空内容，将下面源列表粘贴到里面，保存。
sudo gedit /etc/apt/sources.list
更新源
sudo apt-get update
ubuntu 14.04 LTS 阿里云更新源、官方源和第三方更新源列表：
#aliyun
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
#ubuntu
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
#ubuntu other
deb trusty partner
deb trusty main