$ cp /etc/apt/source.list /etc/apt/source.list.bak
$ vim /etc/apt/source.list
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.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