Ubuntu20 更新yum 源 （阿里云源）
cd /etc/apt
cp sources.list sources.list.bak.20200622 # 备份源文件，一定要养成这个习惯，即使该配置文件可能不再使用。
> sources.list # 清空原文件内容
vim source.list # 将相关内容拷贝到该文件进行保存
apt-get update # 更新
内容如下：
deb http://mirrors.aliyun.com/ubuntu/ focal main restricted universe multiverse
deb-src http://mirrors.aliyun.com/ubuntu/ focal main restricted universe multiverse
deb http://mirrors.aliyun.com/ubuntu/ focal-security main restricted universe multiverse
deb-src http://mirrors.aliyun.com/ubuntu/ focal-security main restricted universe multiverse
deb http://mirrors.aliyun.com/ubuntu/ focal-updates main restricted universe multiverse
deb-src http://mirrors.aliyun.com/ubuntu/ focal-updates main restricted universe multiverse
deb http://mirrors.aliyun.com/ubuntu/ focal-proposed main restricted universe multiverse
deb-src http://mirrors.aliyun.com/ubuntu/ focal-proposed main restricted universe multiverse
deb http://mirrors.aliyun.com/ubuntu/ focal-backports main restricted universe multiverse
deb-src http://mirrors.aliyun.com/ubuntu/ focal-backports main restricted universe multiverse
其他系统配置阿里云yum源教程地址如下：
https://me.jinchuang.org/archives/37.html
