准备工作

apt install vim
vim /etc/apt/sources.list

然后注释掉里面的内容，写入下面的内容：

Debian11 bullseye镜像：

deb http://mirrors.163.com/debian/ bullseye main non-free contrib
deb http://mirrors.163.com/debian/ bullseye-updates main non-free contrib
deb http://mirrors.163.com/debian/ bullseye-backports main non-free contrib
deb-src http://mirrors.163.com/debian/ bullseye main non-free contrib
deb-src http://mirrors.163.com/debian/ bullseye-updates main non-free contrib
deb-src http://mirrors.163.com/debian/ bullseye-backports main non-free contrib
#deb http://mirrors.163.com/debian-security/ bullseye/updates main non-free contrib
#deb http://mirrors.ustc.edu.cn/debian-security/ bullseye/updates main non-free contrib
#deb-src http://mirrors.163.com/debian-security/ bullseye/updates main non-free contrib
#deb-src http://mirrors.ustc.edu.cn/debian-security/ bullseye/updates main non-free contrib
deb http://mirrors.ustc.edu.cn/debian-security/ stable-security main non-free contrib
deb-src http://mirrors.ustc.edu.cn/debian-security/ stable-security main non-free contrib