# cat /etc/redhat-release
源配置目录
cd /etc/yum.repos.d
vi CentOS-AppStream.repo baseurl=https://mirrors.aliyun.com/centos/$releasever/AppStream/$basearch/os/
vi CentOS-Base.repo baseurl=https://mirrors.aliyun.com/centos/$releasever/BaseOS/$basearch/os/
vi CentOS-Extras.repo baseurl=https://mirrors.aliyun.com/centos/$releasever/extras/$basearch/os/
# dnf -y install epel-release
# dnf clean all
# dnf makecache
# dnf repolist