vi /etc/apt/sources.list
deb http://mirrors.ustc.edu.cn/debian/ bullseye main non-free contrib
deb-src http://mirrors.ustc.edu.cn/debian/ bullseye main non-free contrib
deb http://mirrors.ustc.edu.cn/debian-security/ bullseye-security main
deb-src http://mirrors.ustc.edu.cn/debian-security/ bullseye-security main
deb http://mirrors.ustc.edu.cn/debian/ bullseye-updates main non-free contrib
deb-src http://mirrors.ustc.edu.cn/debian/ bullseye-updates main non-free contrib
deb http://mirrors.ustc.edu.cn/debian/ bullseye-backports main non-free contrib
deb-src http://mirrors.ustc.edu.cn/debian/ bullseye-backports main non-free contrib
apt-get clean #删除所有已下载的包文件
apt-get update #取回更新的软件包列表信息
apt-get upgrade #进行一次升级
