更换清华源

1. 换源
   直接输入以下即可

echo "deb https://mirror.tuna.tsinghua.edu.cn/ubuntu-ports/ focal main restricted universe multiverse
deb https://mirror.tuna.tsinghua.edu.cn/ubuntu-ports/ focal-updates main restricted universe multiversedeb https://mirror.tuna.tsinghua.edu.cn/ubuntu-ports/ focal-backports main restricted universe multiversedeb https://mirror.tuna.tsinghua.edu.cn/ubuntu-ports/ focal-security main restricted universe multiversedeb https://mirror.tuna.tsinghua.edu.cn/ubuntu-ports/ focal-proposed main restricted universe multiverse">/etc/apt/sources.list&&apt update

2.测试

# 安装个软件试试
apt install vim