1. 备份源文件
sudo cp /etc/apt/sources.list /etc/apt/sources.list.backup
2. 编辑/etc/apt/sources.list文件
网易163源
# 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 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-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-backports main restricted universe multiverse
# 预发布软件源，不建议启用
# deb http://mirrors.163.com/ubuntu/ focal-proposed main restricted universe multiverse
# deb-src http://mirrors.163.com/ubuntu/ focal-proposed main restricted universe multiverse
3. 执行更新命令
sudo apt-get update
sudo apt-get upgrade
