1、先备份
sudo cp /etc/apt/sources.list /etc/apt/sources.list.backup （备份下当前的源列表，有备无患嘛.）
2、修改更新源
sudo gedit /etc/apt/sources.list （打开源列表文件）
3、修改
deb http://mirrors.sohu.com/ubuntu/ karmic main restricted
deb-src http://mirrors.sohu.com/ubuntu/ karmic main restricted
deb http://mirrors.sohu.com/ubuntu/ karmic-updates main restricted
deb-src http://mirrors.sohu.com/ubuntu/ karmic-updates main restricted
deb http://mirrors.sohu.com/ubuntu/ karmic universe
deb-src http://mirrors.sohu.com/ubuntu/ karmic universe
deb http://mirrors.sohu.com/ubuntu/ karmic-updates universe
deb-src http://mirrors.sohu.com/ubuntu/ karmic-updates universe
deb http://mirrors.sohu.com/ubuntu/ karmic multiverse
deb-src http://mirrors.sohu.com/ubuntu/ karmic multiverse
deb http://mirrors.sohu.com/ubuntu/ karmic-updates multiverse
deb-src http://mirrors.sohu.com/ubuntu/ karmic-updates multiverse