使用yum报错：this system is not registered to red hat subscription management；原因：没在红帽订阅

两种解决方案：1、购买正版；2、更换成centos的yum包。

很显然，我拿来玩的，肯定选第二种，下面地址是centos7的yum包

https://mirrors.aliyun.com/centos/7/os/x86_64/Packages/yum-3.4.3-168.el7.centos.noarch.rpm
https://mirrors.aliyun.com/centos/7/os/x86_64/Packages/yum-metadata-parser-1.1.4-10.el7.x86_64.rpm
https://mirrors.aliyun.com/centos/7/os/x86_64/Packages/yum-plugin-fastestmirror-1.1.31-54.el7_8.noarch.rpm

步骤：

1、卸载红帽自带的yum

rpm -e --nodeps yum

2、下载相关yum包，即上面三个

wget https://mirrors.aliyun.com/centos/7/os/x86_64/Packages/yum-3.4.3-168.el7.centos.noarch.rpm
wget https://mirrors.aliyun.com/centos/7/os/x86_64/Packages/yum-metadata-parser-1.1.4-10.el7.x86_64.rpm
wget https://mirrors.aliyun.com/centos/7/os/x86_64/Packages/yum-plugin-fastestmirror-1.1.31-54.el7_8.noarch.rpm

这时出现了一个问题，最小化安装系统没有自带wget工具，报错-bash: wget: command not found；网上查询教程大多让使用sudo yum install wget来安装wget，哈哈哈哈，我就是来解决yum用不了的，给我来这一手；这时我们要想到另一个Linux重要的下载命令curl，下载命令如下

curl -O https://mirrors.aliyun.com/centos/7/os/x86_64/Packages/yum-3.4.3-168.el7.centos.noarch.rpm
curl -O https://mirrors.aliyun.com/centos/7/os/x86_64/Packages/yum-metadata-parser-1.1.4-10.el7.x86_64.rpm
curl -O https://mirrors.aliyun.com/centos/7/os/x86_64/Packages/yum-plugin-fastestmirror-1.1.31-54.el7_8.noarch.rpm

直接安装会报错提示缺少依赖包，可以直接尝试安装；随着版本更新，依赖包也会变化；这里根据提示更新或安装依赖包，下面是我本次需要的：

下载依赖包
curl -O https://mirrors.aliyun.com/centos/7/os/x86_64/Packages/rpm-4.11.3-45.el7.x86_64.rpm
curl -O https://mirrors.aliyun.com/centos/7/os/x86_64/Packages/python-urlgrabber-3.10-10.el7.noarch.rpm
安装更新rpm
rpm -Uvh rpm-4.11.3-32.el7.x86_64.rpm --nodeps
下面这个是缺少的另一个依赖包，直接更新试了好几次，不行，选择卸载重装
查询现有版本：rpm -q python-urlgrabber
python-urlgrabber-3.10-4.el7.noarch
卸载
rpm -e python-urlgrabber-3.10-4.el7.noarch
安装新版本
rpm -ivh python-urlgrabber-3.10-10.el7.noarch.rpm

3、安装

rpm -ivh yum-metadata-parser-1.1.4-10.el7.x86_64.rpm
rpm -ivh yum-3.4.3-168.el7.centos.noarch.rpm yum-plugin-fastestmirror-1.1.31-54.el7_8.noarch.rpm