debian 9（代号为 stretch）的
镜像源
已经从jessie更新到了stretch。为了确保安全，首先需要备份原有配置，然后再配置新的镜像源。以下是修改debian 9镜像源的步骤：
1、备份原有镜像源配置文件：执行命令
2、打开sources.list文件，注释掉原有的CD源代码，并将镜像源地址更新为163镜像源。具体代码如下：
配置完成后，输入命令
来更新系统镜像源配置文件。
cp /etc/apt/sources.list /etc/apt/sources.list.bakdeb http://mirrors.163.com/debian/ stretch main non-free contrib
deb http://mirrors.163.com/debian/ stretch-updates main non-free contrib
deb http://mirrors.163.com/debian/ stretch-backports main non-free contrib
deb-src http://mirrors.163.com/debian/ stretch main non-free contrib
deb-src http://mirrors.163.com/debian/ stretch-updates main non-free contrib
deb-src http://mirrors.163.com/debian/ stretch-backports main non-free contrib
deb http://mirrors.163.com/debian-security/ stretch/updates main non-free contrib
deb-src http://mirrors.163.com/debian-security/ stretch/updates main non-free contribapt update