centos dnf update 和安装 epel-release

来源：https://bobcares.com/blog/error-unknown-repo-epel/

1. 安装 epel 或者

dnf install https://dl.fedoraproject.org/pub/epel/epel-release-latest-8.noarch.rpm

或者

dnf config-manager --set-enabled PowerTools
dnf install epel-release

1. update the software packages

dnf update

1. ensure EPEL repo is enabled

dnf repolist