1. cd /etc/apt
2. vim sources.list
3.
deb https://mirrors.tuna.tsinghua.edu.cn/ubuntu/ eoan main restricted universe multiverse
deb https://mirrors.tuna.tsinghua.edu.cn/ubuntu/ eoan-security main restricted universe multiverse
deb https://mirrors.tuna.tsinghua.edu.cn/ubuntu/ eoan-updates main restricted universe multiverse
deb https://mirrors.tuna.tsinghua.edu.cn/ubuntu/ eoan-proposed main restricted universe multiverse
deb https://mirrors.tuna.tsinghua.edu.cn/ubuntu/ eoan-backports main restricted universe multiverse
deb-src https://mirrors.tuna.tsinghua.edu.cn/ubuntu/ eoan main restricted universe multiverse
deb-src https://mirrors.tuna.tsinghua.edu.cn/ubuntu/ eoan-security main restricted universe multiverse
deb-src https://mirrors.tuna.tsinghua.edu.cn/ubuntu/ eoan-updates main restricted universe multiverse
deb-src https://mirrors.tuna.tsinghua.edu.cn/ubuntu/ eoan-proposed main restricted universe multiverse
deb-src https://mirrors.tuna.tsinghua.edu.cn/ubuntu/ eoan-backports main restricted universe multiverse
4. apt-get update
5. apt-get upgrade