具体操作
1、打开源文件
gedit /etc/apt/sources.list
2、添加源
##sohu
deb http://mirrors.sohu.com/ubuntu/ quantal main restricted universe multiverse
deb http://mirrors.sohu.com/ubuntu/ quantal-security main restricted universe multiverse
deb http://mirrors.sohu.com/ubuntu/ quantal-updates main restricted universe multiverse
deb http://mirrors.sohu.com/ubuntu/ quantal-proposed main restricted universe multiverse
deb http://mirrors.sohu.com/ubuntu/ quantal-backports main restricted universe multiverse
deb-src http://mirrors.sohu.com/ubuntu/ quantal main restricted universe multiverse
deb-src http://mirrors.sohu.com/ubuntu/ quantal-security main restricted universe multiverse
deb-src http://mirrors.sohu.com/ubuntu/ quantal-updates main restricted universe multiverse
deb-src http://mirrors.sohu.com/ubuntu/ quantal-proposed main restricted universe multiverse
deb-src http://mirrors.sohu.com/ubuntu/ quantal-backports main restricted universe multiverse
3、更新源
sudo apt-get update
完成之后,再下载一个软件试试。