安装几个月后的红帽8在使用yum安装服务时，提示This system is not registered to Red Hat Subscription Management. You can use subscription-manager to register.

查了以下说是使用redhat的yum源是需要注册付费的。

所以此时我们需要更换yum源，把redhat自带的源更换成国内的镜像源，类似阿里源、清华源、网易源等

（此处我们使用阿里源进行替换）

一、首先查询并删除redhat自带的yum源

rpm -qa|grep yum##查看红帽自带的yum源
[root@localhost yum.repos.d]# rpm -qa|grep yum
yum-4.0.9.2-5.el8.noarch
[root@localhost yum.repos.d]# rpm -qa|grep yum|xargs rpm -e --nodeps##使用命令直接删除

二、找到阿里镜像源网站并下载对应的rpm包，并安装。

1、wget  https://mirrors.aliyun.com/centos/8/BaseOS/x86_64/os/Packages/yum-4.7.0-4.el8.noarch.rpm
wget  https://mirrors.aliyun.com/centos/8/BaseOS/x86_64/os/Packages/yum-utils-4.0.21-3.el8.noarch.rpm
2、rpm -ivh yum-utils-4.0.21-3.el8.noarch.rpm yum-4.7.0-4.el8.noarch.rpm##一起安装
[root@localhost yum.repos.d]# rpm -ivh yum-4.7.0-4.el8.noarch.rpm yum-utils-4.0.21-3.el8.noarch.rpm 
Verifying...                          ################################# [100%]
Preparing...                          ################################# [100%]
Updating / installing...
   1:yum-utils-4.0.21-3.el8           ################################# [ 50%]
   2:yum-4.7.0-4.el8                  ################################# [100%]

ps：若遇见执行rpm -ivh提示error: Failed dependencies时，需要在rpm -ivh 包名 --nodeps --force（不检查，强制安装）

三、在阿里源中下载对应的repo包，并替换repo文件中相应字段，最后完成换源

1、wget -P /etc/yum.repos.d/ https://mirrors.aliyun.com/repo/Centos-8.repo ##使用wget将repo包下载到对应目录中
2、替换文件中的$releasever为版本号7，修改刚下载的文件。因为我的版本是8，如果你的版本不是8，那就替换成你的版本号。
vim /etc/yum.repos.d/CentOS-Base.repo
在vim中敲击 ：输入：
:%s/$releasever/8/ge
3、yum clean all && yum makecache ##清除yum缓存，然后新建缓存
4、[root@localhost tmp]# yum info -y nfs-utils.x86_64 
Updating Subscription Management repositories.
Unable to read consumer identity
This system is not registered to Red Hat Subscription Management. You can use subscription-manager to register.##还是会提醒需要付费，但是已经能够正常使用yum源了
Last metadata expiration check: 0:44:31 ago on Fri 13 Oct 2023 04:44:01 PM CST. 
Installed Packages
Name         : nfs-utils
Epoch        : 1
Version      : 2.3.3
Release      : 14.el8
Arch         : x86_64
Size         : 1.4 M
Source       : nfs-utils-2.3.3-14.el8.src.rpm
Repo         : @System
From repo    : anaconda
Summary      : NFS utilities and supporting clients and daemons for the kernel NFS server
URL          : http://linux-nfs.org/
License      : MIT and GPLv2 and GPLv2+ and BSD
Description  : The nfs-utils package provides a daemon for the kernel NFS server and
             : related tools, which provides a much higher level of performance than the
             : traditional Linux NFS server used by most users.
             : 
             : This package also contains the showmount program.  Showmount queries the
             : mount daemon on a remote host for information about the NFS (Network File
             : System) server on the remote host.  For example, showmount can display the
             : clients which are mounted on that host.
             : 
             : This package also contains the mount.nfs and umount.nfs program.