1 备份原来的sources.list

sudo su
cp -rf /etc/apt/sources.list /etc/apt/sources.list.bak

2 编辑sources.list

rm /etc/apt/sources.list
vi /etc/apt/sources.list

3 从以下源中选择一种

#阿里云源
deb http://mirrors.aliyun.com/ubuntu/ eoan main restricted universe multiverse
deb-src http://mirrors.aliyun.com/ubuntu/ eoan main restricted universe multiverse
deb http://mirrors.aliyun.com/ubuntu/ eoan-security main restricted universe multiverse
deb-src http://mirrors.aliyun.com/ubuntu/ eoan-security main restricted universe multiverse
deb http://mirrors.aliyun.com/ubuntu/ eoan-updates main restricted universe multiverse
deb-src http://mirrors.aliyun.com/ubuntu/ eoan-updates main restricted universe multiverse
deb http://mirrors.aliyun.com/ubuntu/ eoan-backports main restricted universe multiverse
deb-src http://mirrors.aliyun.com/ubuntu/ eoan-backports main restricted universe multiverse
deb http://mirrors.aliyun.com/ubuntu/ eoan-proposed main restricted universe multiverse
deb-src http://mirrors.aliyun.com/ubuntu/ eoan-proposed main restricted universe multiverse

#中科大源
deb https://mirrors.ustc.edu.cn/ubuntu/ eoan main restricted universe multiverse
deb-src https://mirrors.ustc.edu.cn/ubuntu/ eoan main restricted universe multiverse
deb https://mirrors.ustc.edu.cn/ubuntu/ eoan-updates main restricted universe multiverse
deb-src https://mirrors.ustc.edu.cn/ubuntu/ eoan-updates main restricted universe multiverse
deb https://mirrors.ustc.edu.cn/ubuntu/ eoan-backports main restricted universe multiverse
deb-src https://mirrors.ustc.edu.cn/ubuntu/ eoan-backports main restricted universe multiverse
deb https://mirrors.ustc.edu.cn/ubuntu/ eoan-security main restricted universe multiverse
deb-src https://mirrors.ustc.edu.cn/ubuntu/ eoan-security main restricted universe multiverse
deb https://mirrors.ustc.edu.cn/ubuntu/ eoan-proposed main restricted universe multiverse
deb-src https://mirrors.ustc.edu.cn/ubuntu/ eoan-proposed main restricted universe multiverse

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

#清华源
deb https://mirrors.tuna.tsinghua.edu.cn/ubuntu/ eoan main restricted universe multiverse
deb-src https://mirrors.tuna.tsinghua.edu.cn/ubuntu/ eoan main restricted universe multiverse
deb https://mirrors.tuna.tsinghua.edu.cn/ubuntu/ eoan-updates main restricted universe multiverse
deb-src https://mirrors.tuna.tsinghua.edu.cn/ubuntu/ eoan-updates 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-backports main restricted universe multiverse
deb https://mirrors.tuna.tsinghua.edu.cn/ubuntu/ eoan-security main restricted universe multiverse
deb-src https://mirrors.tuna.tsinghua.edu.cn/ubuntu/ eoan-security main restricted universe multiverse
deb https://mirrors.tuna.tsinghua.edu.cn/ubuntu/ eoan-proposed main restricted universe multiverse
deb-src https://mirrors.tuna.tsinghua.edu.cn/ubuntu/ eoan-proposed main restricted universe multiverse

4 更新源

sudo apt-get update