由于ubuntu 的默认源是国外的，下载软件速度非常慢，并且经常下载失败，下面主要是介绍一种如何添加国内源作为软件下载源的简单方法。
1.软件下载源的配置文件的路径：/etc/apt/sources.list
2.添加下载源地址
（1）打开“Software&Updates”。直接双击“sources.list”文件也可以打开“Software&Updates”。显示对话框如下所示。
（2）点击“Other Software”->“Add...”，打开对话框如下。
（3）将需要添加的下载源地址添加到“APT line”中，点击“Add Source”。
3.更新源列表
sudo apt-get update
sudo apt-get upgrade
附件：从网络中收集的下载源地址：
#tsing hua mirror site
deb http://mirrors.tuna.tsinghua.edu.cn/ubuntu/ xenial main multiverse restricted universe
deb http://mirrors.tuna.tsinghua.edu.cn/ubuntu/ xenial-backports main multiverse restricted universe
deb http://mirrors.tuna.tsinghua.edu.cn/ubuntu/ xenial-proposed main multiverse restricted universe
deb http://mirrors.tuna.tsinghua.edu.cn/ubuntu/ xenial-security main multiverse restricted universe
deb http://mirrors.tuna.tsinghua.edu.cn/ubuntu/ xenial-updates main multiverse restricted universe
deb-src http://mirrors.tuna.tsinghua.edu.cn/ubuntu/ xenial main multiverse restricted universe
deb-src http://mirrors.tuna.tsinghua.edu.cn/ubuntu/ xenial-backports main multiverse restricted universe
deb-src http://mirrors.tuna.tsinghua.edu.cn/ubuntu/ xenial-proposed main multiverse restricted universe
deb-src http://mirrors.tuna.tsinghua.edu.cn/ubuntu/ xenial-security main multiverse restricted universe
deb-src http://mirrors.tuna.tsinghua.edu.cn/ubuntu/ xenial-updates main multiverse restricted universe
#163 mirror site
deb http://mirrors.163.com/debian/ lenny main contrib non-free
deb-src http://mirrors.163.com/debian lenny main contrib non-free
deb http://mirrors.163.com/debian-security/ stable/updates main
deb-src http://mirrors.163.com/debian-security/ stable/updates main
deb http://mirrors.163.com/ubuntu/ trusty main restricted universe multiverse
deb http://mirrors.163.com/ubuntu/ trusty-security main restricted universe multiverse
deb http://mirrors.163.com/ubuntu/ trusty-updates main restricted universe multiverse
deb http://mirrors.163.com/ubuntu/ trusty-proposed main restricted universe multiverse
deb http://mirrors.163.com/ubuntu/ trusty-backports main restricted universe multiverse
deb-src http://mirrors.163.com/ubuntu/ trusty main restricted universe multiverse
deb-src http://mirrors.163.com/ubuntu/ trusty-security main restricted universe multiverse
deb-src http://mirrors.163.com/ubuntu/ trusty-updates main restricted universe multiverse
deb-src http://mirrors.163.com/ubuntu/ trusty-proposed main restricted universe multiverse
deb-src http://mirrors.163.com/ubuntu/ trusty-backports main restricted universe multiverse
#official mirror site
deb http://ftp.debian.org/debian/ lenny main contrib non-free
deb-src http://ftp.debian.org/debian/ lenny main contrib non-free
deb http://ftp.us.debian.org/debian/ lenny main contrib non-free
deb-src http://ftp.us.debian.org/debian/ lenny main contrib non-free
deb http://security.debian.org/ stable/updates main
deb-src http://security.debian.org/ stable/updates main
deb http://volatile.debian.org/debian-volatile stable/volatile main
deb-src http://volatile.debian.org/debian-volatile stable/volatile main
# ustc debian-multimedia
deb http://debian.ustc.edu.cn/debian-multimedia/ stable main
deb-src http://debian.ustc.edu.cn/debian-multimedia/ stable main
# ustc debian-security
deb http://debian.ustc.edu.cn/debian-security/ stable/updates main non-free contrib
deb-src http://debian.ustc.edu.cn/debian-security/ stable/updates main non-free contrib