在使用redhat7的yum命令安装软件时，发现总是提示This system is not registered to Red Hat Subscription Management. You can use subscription-manager to register. 或如下错误信息：This system is not registered with RHN. RHN support will be disabled.原来RHEL7的yum服务是付费的，因为没有付费，所以无法使用yum安装软件，只能替换为CentOs的yum工具，下面是具体操作步骤。
-- 查看yum
rpm -qa |grep yum
--卸载yum
rpm -qa | grep yum | xargs rpm -e --nodeps
--拷贝centos系统yum工具安装程序到linux指定目录下
yum-3.4.3-132.el7.centos.0.1.noarch.rpm
yum-plugin-fastestmirror-1.1.31-34.el7.noarch.rpm
yum-updateonboot-1.1.31-34.el7.noarch.rpm
yum-utils-1.1.31-34.el7.noarch.rpm
yum-metadata-parser-1.1.4-10.el7.x86_64.rpm
安装程序见附件
--安装yum包
rpm -ivh yum-*
--导入key(记不清需要不需要了)
rpm --import public.gpg.key
sudo rpm --import /etc/pki/rpm-gpg/RPM-GPG-KEY*
--在阿里云开源软件镜像站点下载资源文件，目标地址是/etc/yum.repos.d/CentOS-Base.repo（覆盖写）
wget -O /etc/yum.repos.d/CentOS-Base.repo http://mirrors.aliyun.com/repo/Centos-7.repo
--替换CentOS-Base.repo文件$releasever变量为相关linux版本，这里替换为“7”就可以了，具体操作：
vi /etc/yum.repos.d/CentOS-Base.repo
:%s/$releasever/7/ge
:wq
使用yum下载安装软件就ok了，如下提示已经开始从阿里云镜像服务器下载软件了。
# yum install -y telnet
已加载插件：fastestmirror, product-id, subscription-manager
This system is not registered to Red Hat Subscription Management. You can use subscription-manager to register.
base | 3.6 kB 00:00:00
extras | 3.4 kB 00:00:00
updates | 3.4 kB 00:00:00
(1/4): base/x86_64/group_gz | 155 kB 00:00:00
(2/4): extras/x86_64/primary_db | 101 kB 00:00:00
(3/4): updates/x86_64/primary_db | 3.1 MB 00:00:02
base/x86_64/primary_db FAILED
http://mirrors.aliyuncs.com/centos/7/os/x86_64/repodata/c6411f1cc8a000ed2b651b49134631d279abba1ec1f78e5dcca79a52d8c1eada-primary.sqlite.bz2: [Errno 14] curl#7 - "Failed connect to mirrors.aliyuncs.com:80; Connection refused"
正在尝试其它镜像。
(4/4): base/x86_64/primary_db | 5.3 MB 00:00:03
Determining fastest mirrors
* base: mirrors.aliyun.com
* extras: mirrors.aliyun.com
* updates: mirrors.aliyun.com
正在解决依赖关系
--> 正在检查事务
---> 软件包 telnet.x86_64.1.0.17-59.el7 将被 安装
--> 解决依赖关系完成
依赖关系解决
===============================================================================================================================================================================================
Package 架构 版本 源 大小
===============================================================================================================================================================================================
正在安装:
telnet x86_64 1:0.17-59.el7 base 63 k
事务概要
===============================================================================================================================================================================================
安装 1 软件包
总下载量：63 k
安装大小：113 k