Debian 系统镜像下载地址：
http://mirrors.163.com/debian-cd/
备份
cp /etc/apt/sources.list /etc/apt/sources.list.bak
更换
vim /etc/apt/sources.list
输入以下内容：
注意权限问题，否则可能编辑不了此文件。
deb http://mirrors.aliyun.com/debian/ buster main non-free contrib
deb-src http://mirrors.aliyun.com/debian/ buster main non-free contrib
deb http://mirrors.aliyun.com/debian-security buster/updates main
deb-src http://mirrors.aliyun.com/debian-security buster/updates main
deb http://mirrors.aliyun.com/debian/ buster-updates main non-free contrib
deb-src http://mirrors.aliyun.com/debian/ buster-updates main non-free contrib
deb http://mirrors.aliyun.com/debian/ buster-backports main non-free contrib
deb-src http://mirrors.aliyun.com/debian/ buster-backports main non-free contrib
更新
apt-get update