为什么要更换镜像源啊？下载速度快啊！
Ubuntu镜像源
镜像源的位置在系统中的：
ubuntu@zhangl:~$ vim /etc/apt/sources.list
ubuntu系统（注意系统版本）原镜像内容如下：
deb http://us.archive.ubuntu.com/ubuntu/ trusty main restricted
deb-src http://us.archive.ubuntu.com/ubuntu/ trusty main restricted
deb http://us.archive.ubuntu.com/ubuntu/ trusty-updates main restricted
deb-src http://us.archive.ubuntu.com/ubuntu/ trusty-updates main restricted
deb http://us.archive.ubuntu.com/ubuntu/ trusty universe
deb-src http://us.archive.ubuntu.com/ubuntu/ trusty universe
deb http://us.archive.ubuntu.com/ubuntu/ trusty-updates universe
deb-src http://us.archive.ubuntu.com/ubuntu/ trusty-updates universe
deb http://us.archive.ubuntu.com/ubuntu/ trusty multiverse
deb-src http://us.archive.ubuntu.com/ubuntu/ trusty multiverse
deb http://us.archive.ubuntu.com/ubuntu/ trusty-updates multiverse
deb-src http://us.archive.ubuntu.com/ubuntu/ trusty-updates multiverse
deb http://us.archive.ubuntu.com/ubuntu/ trusty-backports main restricted universe multiverse
deb-src http://us.archive.ubuntu.com/ubuntu/ trusty-backports main restricted universe multiverse
deb http://security.ubuntu.com/ubuntu trusty-security main restricted
deb-src http://security.ubuntu.com/ubuntu trusty-security main restricted
deb http://security.ubuntu.com/ubuntu trusty-security universe
deb-src http://security.ubuntu.com/ubuntu trusty-security universe
deb http://security.ubuntu.com/ubuntu trusty-security multiverse
deb-src http://security.ubuntu.com/ubuntu trusty-security multiverse
deb http://extras.ubuntu.com/ubuntu trusty main
deb-src http://extras.ubuntu.com/ubuntu trusty main
国内163的镜像源内容如下：
deb http://mirrors.163.com/ubuntu/ wily main restricted universe multiverse
deb http://mirrors.163.com/ubuntu/ wily-security main restricted universe multiverse
deb http://mirrors.163.com/ubuntu/ wily-updates main restricted universe multiverse
deb http://mirrors.163.com/ubuntu/ wily-proposed main restricted universe multiverse
deb http://mirrors.163.com/ubuntu/ wily-backports main restricted universe multiverse
deb-src http://mirrors.163.com/ubuntu/ wily main restricted universe multiverse
deb-src http://mirrors.163.com/ubuntu/ wily-security main restricted universe multiverse
deb-src http://mirrors.163.com/ubuntu/ wily-updates main restricted universe multiverse
deb-src http://mirrors.163.com/ubuntu/ wily-proposed main restricted universe multiverse
deb-src http://mirrors.163.com/ubuntu/ wily-backports main restricted universe multiverse
pypi镜像源
镜像源的位置在系统中的：
在安装完pip之后，系统并没有自动生成pip.conf文件，所以要手动创建这个文件。
ubuntu@zhangl:~$ vim .pip/pip.conf
[global]
timeout=600
index-url=http://pypi.123.com/root/pypi/+simple/
timeout ：以免网络慢的情况下安装包下载不完
index-url：要安装的python包存放的链接地址，（一般公司内部会有自己的包库，这里的链接就会指向自己包库的链接地址）
当然，在安装一个包的时候，可以指定包的下载位置如：
pip install flask -i http://pypi.v2ex.com/simple
-i ：指到指定的internet下载包
目前国内的包链接地址如下：
http://pypi.douban.com/ 豆瓣
http://pypi.hustunique.com/ 华中理工大学
http://pypi.sdutlinux.org/ 山东理工大学
http://pypi.mirrors.ustc.edu.cn/ 中国科学技术大学
Ubuntu 15.10更新源已可用，更新到Ubuntu 15.10的方法：http://www.linuxdiyf.com/linux/11955.html
为Linux配置apt-get的更新源：http://www.linuxdiyf.com/linux/12073.html
Ubuntu 15.04更新源：http://www.linuxdiyf.com/linux/11839.html