0. 使用的tuna更新源，可能需要先安装https支持
apt install apt-transport-https ca-certificates
1. 备份/etc/apt/sources.list
mv /etc/apt/sources.list /etc/apt/sources.list.bak
2. 修改使用 TUNA 的软件源镜像
vi /etc/apt/sources.list
替换为以下内容
# 默认注释了源码镜像以提高 apt update 速度，如有需要可自行取消注释
deb https://mirrors.tuna.tsinghua.edu.cn/debian/ buster main contrib non-free
# deb-src https://mirrors.tuna.tsinghua.edu.cn/debian/ buster main contrib non-free
deb https://mirrors.tuna.tsinghua.edu.cn/debian/ buster-updates main contrib non-free
# deb-src https://mirrors.tuna.tsinghua.edu.cn/debian/ buster-updates main contrib non-free
deb https://mirrors.tuna.tsinghua.edu.cn/debian/ buster-backports main contrib non-free
# deb-src https://mirrors.tuna.tsinghua.edu.cn/debian/ buster-backports main contrib non-free
deb https://mirrors.tuna.tsinghua.edu.cn/debian-security buster/updates main contrib non-free
# deb-src https://mirrors.tuna.tsinghua.edu.cn/debian-security buster/updates main contrib non-free
3. 检查更新
apt update
4. 更新（已经部署好的环境慎用！）
apt upgrade
* 有些场景下可能需要恢复默认
# /etc/apt/sources.list
# deb cdrom:[Debian GNU/Linux 10.4.0 _Buster_ - Official amd64 DVD Binary-1 20200509-10:26]/ buster contrib main
deb cdrom:[Debian GNU/Linux 10.4.0 _Buster_ - Official amd64 DVD Binary-1 20200509-10:26]/ buster contrib main
deb http://security.debian.org/debian-security buster/updates main contrib
deb-src http://security.debian.org/debian-security buster/updates main contrib
# buster-updates, previously known as 'volatile'
# A network mirror was not selected during install. The following entries
# are provided as examples, but you should amend them as appropriate
# for your mirror of choice.
#
# deb http://deb.debian.org/debian/ buster-updates main contrib
# deb-src http://deb.debian.org/debian/ buster-updates main contrib
参考：
https://mirror.tuna.tsinghua.edu.cn/help/debian/
https://wiki.debian.org/SourcesList