備份源文件

sudo cp /etc/apt/sources.list /etc/apt/sources.list.bak

更改為清華大學源

用編輯器打開 /etc/apt/sources.list
參考 ：http://www.3fwork.com/kaifa215/019781MYM000613/

sudo vi /etc/apt/sources.list

替換成以下內容

默認註釋了源碼鏡像以提高 apt update 速度，如有需要可自行取消註釋

deb https://mirrors.tuna.tsinghua.edu.cn/ubuntu/ focal main restricted universe multiverse

deb-src https://mirrors.tuna.tsinghua.edu.cn/ubuntu/ focal main restricted universe multiverse

deb https://mirrors.tuna.tsinghua.edu.cn/ubuntu/ focal-updates main restricted universe multiverse

deb-src https://mirrors.tuna.tsinghua.edu.cn/ubuntu/ focal-updates main restricted universe multiverse

deb https://mirrors.tuna.tsinghua.edu.cn/ubuntu/ focal-backports main restricted universe multiverse

deb-src https://mirrors.tuna.tsinghua.edu.cn/ubuntu/ focal-backports main restricted universe multiverse

deb https://mirrors.tuna.tsinghua.edu.cn/ubuntu/ focal-security main restricted universe multiverse

deb-src https://mirrors.tuna.tsinghua.edu.cn/ubuntu/ focal-security main restricted universe multiverse

預發佈軟件源，不建議啓用

deb https://mirrors.tuna.tsinghua.edu.cn/ubuntu/ focal-proposed main restricted universe multiverse

deb-src https://mirrors.tuna.tsinghua.edu.cn/ubuntu/ focal-proposed main restricted universe multiverse

還可以通過sed 命令直接源地址改為 mirrors.tuna.tsinghua.edu.cn

sudo sed -i "s@http://.archive.ubuntu.com@https://mirrors.tuna.tsinghua.edu.cn@g" /etc/apt/sources.list
sudo sed -i "s@http://.security.ubuntu.com@https://mirrors.tuna.tsinghua.edu.cn@g" /etc/apt/sources.list