Debian 11 改用阿里云源

从 Debian 官网下载 Debian 11 的网络安装盘后，软件源列表里随便选了一个，进入界面后运行 apt update 发现速度比较慢而且会出错，还是换成习惯用的阿里云Debian 11的源好用。

修改/etc/apt/sources.list,加入下面的行：

deb https://mirrors.aliyun.com/debian/ bullseye main non-free contrib
deb-src https://mirrors.aliyun.com/debian/ bullseye main non-free contrib
deb https://mirrors.aliyun.com/debian-security/ bullseye-security main
deb-src https://mirrors.aliyun.com/debian-security/ bullseye-security main
deb https://mirrors.aliyun.com/debian/ bullseye-updates main non-free contrib
deb-src https://mirrors.aliyun.com/debian/ bullseye-updates main non-free contrib
deb https://mirrors.aliyun.com/debian/ bullseye-backports main non-free contrib
deb-src https://mirrors.aliyun.com/debian/ bullseye-backports main non-free contrib

并把原来定义的源用#号注释掉，保存。

接下来运行 apt update 可能会报错： 

Could not handshake: Error in the certificate verification.

这是因为安全证书认证失败了，没法更新系统。这时候可以先把源网址的协议从https改成http，暂时不使用安全链接。然后安装ca-certificates

apt install ca-certificates

待ca-certificates安装完成后，再把源网址改回https，这样就可以正常使用 Debian 11 的阿里云源进行更新和升级了。