1.输入该命令按回车键：dnf -y install epel-release
2.输入该命令按回车键：dnf -y update
3.输入该命令按回车键：dnf -y install rpmconf yum-utils
4.输入该命令按回车键：rpmconf -a，若出现提示输入Y按回车键
5.输入该命令按回车键：dnf -y remove rpmconf yum-utils epel-release
6.输入该命令按回车键：rpm -e --nodeps `rpm -qa|grep centos`
7.输入该命令按回车键：rpm -ivh --nodeps --force https://mirrors.aliyun.com/centos-stream/9-stream/BaseOS/x86_64/os/Packages/centos-stream-release-9.0-12.el9.noarch.rpm，
8.输入该命令按回车键：rpm -ivh --nodeps --force https://mirrors.aliyun.com/centos-stream/9-stream/BaseOS/x86_64/os/Packages/centos-gpg-keys-9.0-12.el9.noarch.rpm
9.输入该命令按回车键：rpm -ivh --nodeps --force https://mirrors.aliyun.com/centos-stream/9-stream/BaseOS/x86_64/os/Packages/centos-stream-repos-9.0-12.el9.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：dnf -y --releasever=9 --allowerasing --setopt=deltarpm=false distro-sync
12.输入该命令按回车键：rpm --rebuilddb
13.输入该命令按回车键：rpm -e --nodeps `rpm -qa|grep -i kernel`
14.输入该命令按回车键：dnf -y install kernel
15.输入该命令按回车键：dnf -y install kernel-core
16.输入该命令按回车键：dnf -y install shim
17.输入该命令按回车键：dnf group install minimal-environment -y
18.输入该命令按回车键：dnf -y install epel-release
19.输入该命令按回车键：dnf -y install rpmconf yum-utils
20.输入该命令按回车键：dnf -y update
21.输入该命令按回车键：rpmconf -a，若出现提示输入Y按回车键
22.输入该命令按回车键：grub2-mkconfig -o /boot/grub2/grub.cfg
23.输入该命令按回车键：grub2-install /dev/sda
24.输入该命令按回车键：echo "PermitRootLogin yes" >> /etc/ssh/sshd_config
25.输入该命令按回车键重启后再操作连接：reboot
26.输入该命令按回车键查看版本：cat /etc/redhat-release
