RedHat8.1-RHEL8.1修改yum/dnf源，目标alliyun的yum

// root下执行以下命令

mv /etc/yum.repos.d/CentOS-Base.repo /etc/yum.repos.d/CentOS-Base.repo.backup
wget -O /etc/yum.repos.d/CentOS-Base.repo https://mirrors.aliyun.com/repo/Centos-8.repo
vim /etc/yum.repos.d/CentOS-Base.repo 
:%s/$releasever/8/g
:wq
mv  /etc/yum.repos.d/redhat.repo /etc/yum.repos.d/redhat.repo.bak
yum clean all
yum makecache

mv /etc/yum.repos.d/epel.repo /etc/yum.repos.d/epel.repo.backup
mv /etc/yum.repos.d/epel-testing.repo /etc/yum.repos.d/epel-testing.repo.backup
yum install -y https://mirrors.aliyun.com/epel/epel-release-latest-8.noarch.rpm
sed -i 's|^#baseurl=https://download.fedoraproject.org/pub|baseurl=https://mirrors.aliyun.com|' /etc/yum.repos.d/epel*
sed -i 's|^metalink|#metalink|' /etc/yum.repos.d/epel*