首先备份默认源：
sudo cp /etc/apt/sources.list /etc/apt/sources.list.old
清空默认源：
sudo cat /dev/null > /etc/apt/sources.list
添加源：
sudo vim /etc/apt/sources.list
推荐源：
#网易的源（163源，无论是不是教育网，速度都很快）
deb http://mirrors.163.com/ubuntu/ raring main universe restricted multiverse
deb-src http://mirrors.163.com/ubuntu/ raring main universe restricted multiverse
deb http://mirrors.163.com/ubuntu/ raring-security universe main multiverse restricted
deb-src http://mirrors.163.com/ubuntu/ raring-security universe main multiverse restricted
deb http://mirrors.163.com/ubuntu/ raring-updates universe main multiverse restricted
deb http://mirrors.163.com/ubuntu/ raring-proposed universe main multiverse restricted
deb-src http://mirrors.163.com/ubuntu/ raring-proposed universe main multiverse restricted
deb http://mirrors.163.com/ubuntu/ raring-backports universe main multiverse restricted
deb-src http://mirrors.163.com/ubuntu/ raring-backports universe main multiverse restricted
deb-src http://mirrors.163.com/ubuntu/ raring-updates universe main multiverse restricted
#搜狐的源（sohu 源今天还没有更新，不过应该快了）
deb http://mirrors.sohu.com/ubuntu/ raring main restricted
deb-src http://mirrors.sohu.com/ubuntu/ raring main restricted
deb http://mirrors.sohu.com/ubuntu/ raring-updates main restricted
deb-src http://mirrors.sohu.com/ubuntu/ raring-updates main restricted
deb http://mirrors.sohu.com/ubuntu/ raring universe
deb-src http://mirrors.sohu.com/ubuntu/ raring universe
deb http://mirrors.sohu.com/ubuntu/ raring-updates universe
deb-src http://mirrors.sohu.com/ubuntu/ raring-updates universe
deb http://mirrors.sohu.com/ubuntu/ raring multiverse
deb-src http://mirrors.sohu.com/ubuntu/ raring multiverse
deb http://mirrors.sohu.com/ubuntu/ raring-updates multiverse
deb-src http://mirrors.sohu.com/ubuntu/ raring-updates multiverse
deb http://mirrors.sohu.com/ubuntu/ raring-backports main restricted universe multiverse
deb-src http://mirrors.sohu.com/ubuntu/ raring-backports main restricted universe multiverse
deb http://mirrors.sohu.com/ubuntu/ raring-security main restricted
deb-src http://mirrors.sohu.com/ubuntu/ raring-security main restricted
deb http://mirrors.sohu.com/ubuntu/ raring-security universe
deb-src http://mirrors.sohu.com/ubuntu/ raring-security universe
deb http://mirrors.sohu.com/ubuntu/ raring-security multiverse
deb-src http://mirrors.sohu.com/ubuntu/ raring-security multiverse
deb http://extras.ubuntu.com/ubuntu raring main
deb-src http://extras.ubuntu.com/ubuntu raring main
#台湾源（台湾的ubuntu 更新源还是很给力的）
deb http://tw.archive.ubuntu.com/ubuntu/ raring main universe restricted multiverse
deb-src http://tw.archive.ubuntu.com/ubuntu/ raring main universe restricted multiverse
deb http://tw.archive.ubuntu.com/ubuntu/ raring-security universe main multiverse restricted
deb-src http://tw.archive.ubuntu.com/ubuntu/ raring-security universe main multiverse restricted
deb http://tw.archive.ubuntu.com/ubuntu/ raring-updates universe main multiverse restricted
deb-src http://tw.archive.ubuntu.com/ubuntu/ raring-updates universe main multiverse restricted
#骨头源，骨头源是bones7456架设的一个Ubuntu源 ，提供ubuntu,deepin
deb http://ubuntu.srt.cn/ubuntu/ raring main universe restricted multiverse
deb-src http://ubuntu.srt.cn/ubuntu/ raring main universe restricted multiverse
deb http://ubuntu.srt.cn/ubuntu/ raring-security universe main multiverse restricted
deb-src http://ubuntu.srt.cn/ubuntu/ raring-security universe main multiverse restricted
deb http://ubuntu.srt.cn/ubuntu/ raring-updates universe main multiverse restricted
deb http://ubuntu.srt.cn/ubuntu/ raring-proposed universe main multiverse restricted
deb-src http://ubuntu.srt.cn/ubuntu/ raring-proposed universe main multiverse restricted
deb http://ubuntu.srt.cn/ubuntu/ raring-backports universe main multiverse restricted
deb-src http://ubuntu.srt.cn/ubuntu/ raring-backports universe main multiverse restricted
deb-src http://ubuntu.srt.cn/ubuntu/ raring-updates universe main multiverse restricted
#ubuntu.cn99.com源（推荐）:
deb http://ubuntu.cn99.com/ubuntu/ raring main restricted universe multiverse
deb http://ubuntu.cn99.com/ubuntu/ raring-updates main restricted universe multiverse
deb http://ubuntu.cn99.com/ubuntu/ raring-security main restricted universe multiverse
deb http://ubuntu.cn99.com/ubuntu/ raring-backports main restricted universe multiverse
deb http://ubuntu.cn99.com/ubuntu-cn/ raring main restricted universe multiverse
#教育网源
#电子科技大学
deb http://ubuntu.uestc.edu.cn/ubuntu/ raring main restricted universe multiverse
deb http://ubuntu.uestc.edu.cn/ubuntu/ raring-backports main restricted universe multiverse
deb http://ubuntu.uestc.edu.cn/ubuntu/ raring-proposed main restricted universe multiverse
deb http://ubuntu.uestc.edu.cn/ubuntu/ raring-security main restricted universe multiverse
deb http://ubuntu.uestc.edu.cn/ubuntu/ raring-updates main restricted universe multiverse
deb-src http://ubuntu.uestc.edu.cn/ubuntu/ raring main restricted universe multiverse
deb-src http://ubuntu.uestc.edu.cn/ubuntu/ raring-backports main restricted universe multiverse
deb-src http://ubuntu.uestc.edu.cn/ubuntu/ raring-proposed main restricted universe multiverse
deb-src http://ubuntu.uestc.edu.cn/ubuntu/ raring-security main restricted universe multiverse
deb-src http://ubuntu.uestc.edu.cn/ubuntu/ raring-updates main restricted universe multiverse
#中国科技大学
deb http://debian.ustc.edu.cn/ubuntu/ raring main restricted universe multiverse
deb http://debian.ustc.edu.cn/ubuntu/ raring-backports restricted universe multiverse
deb http://debian.ustc.edu.cn/ubuntu/ raring-proposed main restricted universe multiverse
deb http://debian.ustc.edu.cn/ubuntu/ raring-security main restricted universe multiverse
deb http://debian.ustc.edu.cn/ubuntu/ raring-updates main restricted universe multiverse
deb-src http://debian.ustc.edu.cn/ubuntu/ raring main restricted universe multiverse
deb-src http://debian.ustc.edu.cn/ubuntu/ raring-backports main restricted universe multiverse
deb-src http://debian.ustc.edu.cn/ubuntu/ raring-proposed main restricted universe multiverse
deb-src http://debian.ustc.edu.cn/ubuntu/ raring-security main restricted universe multiverse
deb-src http://debian.ustc.edu.cn/ubuntu/ raring-updates main restricted universe multiverse
#北京理工大学
deb http://mirror.bjtu.edu.cn/ubuntu/ raring main multiverse restricted universe
deb http://mirror.bjtu.edu.cn/ubuntu/ raring-backports main multiverse restricted universe
deb http://mirror.bjtu.edu.cn/ubuntu/ raring-proposed main multiverse restricted universe
deb http://mirror.bjtu.edu.cn/ubuntu/ raring-security main multiverse restricted universe
deb http://mirror.bjtu.edu.cn/ubuntu/ raring-updates main multiverse restricted universe
deb-src http://mirror.bjtu.edu.cn/ubuntu/ raring main multiverse restricted universe
deb-src http://mirror.bjtu.edu.cn/ubuntu/ raring-backports main multiverse restricted universe
deb-src http://mirror.bjtu.edu.cn/ubuntu/ raring-proposed main multiverse restricted universe
deb-src http://mirror.bjtu.edu.cn/ubuntu/ raring-security main multiverse restricted universe
deb-src http://mirror.bjtu.edu.cn/ubuntu/ raring-updates main multiverse restricted universe
#兰州大学
deb ftp://mirror.lzu.edu.cn/ubuntu/ raring main multiverse restricted universe
deb ftp://mirror.lzu.edu.cn/ubuntu/ raring-backports main multiverse restricted universe
deb ftp://mirror.lzu.edu.cn/ubuntu/ raring-proposed main multiverse restricted universe
deb ftp://mirror.lzu.edu.cn/ubuntu/ raring-security main multiverse restricted universe
deb ftp://mirror.lzu.edu.cn/ubuntu/ raring-updates main multiverse restricted universe
deb ftp://mirror.lzu.edu.cn/ubuntu-cn/ raring main multiverse restricted universe
#上海交通大学（上海交大源，教育网的速度不用说了）
deb http://ftp.sjtu.edu.cn/ubuntu/ raring main multiverse restricted universe
deb http://ftp.sjtu.edu.cn/ubuntu/ raring-backports main multiverse restricted universe
deb http://ftp.sjtu.edu.cn/ubuntu/ raring-proposed main multiverse restricted universe
deb http://ftp.sjtu.edu.cn/ubuntu/ raring-security main multiverse restricted universe
deb http://ftp.sjtu.edu.cn/ubuntu/ raring-updates main multiverse restricted universe
deb http://ftp.sjtu.edu.cn/ubuntu-cn/ raring main multiverse restricted universe
deb-src http://ftp.sjtu.edu.cn/ubuntu/ raring main multiverse restricted universe
deb-src http://ftp.sjtu.edu.cn/ubuntu/ raring-backports main multiverse restricted universe
deb-src http://ftp.sjtu.edu.cn/ubuntu/ raring-proposed main multiverse restricted universe
deb-src http://ftp.sjtu.edu.cn/ubuntu/ raring-security main multiverse restricted universe
deb-src http://ftp.sjtu.edu.cn/ubuntu/ raring-updates main multiverse restricted universe
最后更新一下：sudo apt-get update