試過阿里雲源，效果不好gcc安裝失敗，安裝其他包時會出現包損壞的error，

更換網易163源後沒問題

內容引自：https://www.cnblogs.com/zqifa/p/12910989.html

第一步：備份原始檔：
sudo cp /etc/apt/sources.list /etc/apt/sources.list.backup

第二步：編輯/etc/apt/sources.list檔案

在檔案最前面新增以下條目(操作前請做好相應備份)：
vi /etc/apt/sources.list

網易163源

deb http://mirrors.163.com/ubuntu/ focal main restricted universe multiverse
deb http://mirrors.163.com/ubuntu/ focal-security main restricted universe multiverse
deb http://mirrors.163.com/ubuntu/ focal-updates main restricted universe multiverse
deb http://mirrors.163.com/ubuntu/ focal-proposed main restricted universe multiverse
deb http://mirrors.163.com/ubuntu/ focal-backports main restricted universe multiverse
deb-src http://mirrors.163.com/ubuntu/ focal main restricted universe multiverse
deb-src http://mirrors.163.com/ubuntu/ focal-security main restricted universe multiverse
deb-src http://mirrors.163.com/ubuntu/ focal-updates main restricted universe multiverse
deb-src http://mirrors.163.com/ubuntu/ focal-proposed main restricted universe multiverse
deb-src http://mirrors.163.com/ubuntu/ focal-backports main restricted universe multiverse

第三步：執行更新命令：

sudo apt-get update
sudo apt-get upgrade