1.输入该命令按回车键：yum -y install epel-release
2.输入该命令按回车键：yum -y install rpmconf yum-utils
3.输入该命令按回车键：rpmconf -a，出现提示输入Y按回车键
4.输入该命令按回车键：yum -y install dnf
5.输入该命令按回车键：dnf -y remove yum yum-metadata-parser
6.输入该命令按回车键：rm -rf /etc/yum
7.输入该命令按回车键：dnf -y upgrade
8.输入该命令按回车键：dnf -y install https://mirrors.aliyun.com/centos/8/BaseOS/x86_64/os/Packages/{centos-linux-repos-8-3.el8.noarch.rpm,centos-linux-release-8.5-1.2111.el8.noarch.rpm,centos-gpg-keys-8-3.el8.noarch.rpm}
9.输入该命令按回车键dnf -y upgrade https://mirrors.bfsu.edu.cn/epel/epel-release-latest-8.noarch.rpm
10.输入该命令按回车键：dnf clean all
11.输入该命令按回车键：rpm -e `rpm -q kernel`
12.输入该命令按回车键：rpm -e --nodeps sysvinit-tools
13.输入该命令按回车键：dnf -y --releasever=8 --allowerasing --setopt=deltarpm=false distro-sync
14.输入该命令按回车键查看版本：cat /etc/redhat-release
