在使用redhat7的yum命令安裝軟件時，發現總是提示This system is not registered to Red Hat Subscription Management. You can use subscription-manager to register. 或如下錯誤信息：This system is not registered with RHN. RHN support will be disabled.原來RHEL7的yum服務是付費的，因爲沒有付費，所以無法使用yum安裝軟件，只能替換爲CentOs的yum工具，下面是具體操作步驟。
-- 查看yum
rpm -qa |grep yum
--卸載yum
rpm -qa | grep yum | xargs rpm -e --nodeps
--拷貝centos系統yum工具安裝程序到linux指定目錄下
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
安裝程序見附件
--安裝yum包
rpm -ivh yum-*
--導入key(記不清需要不需要了)
rpm --import public.gpg.key
sudo rpm --import /etc/pki/rpm-gpg/RPM-GPG-KEY*
--在阿里雲開源軟件鏡像站點下載資源文件，目標地址是/etc/yum.repos.d/CentOS-Base.repo（覆蓋寫）
wget -O /etc/yum.repos.d/CentOS-Base.repo http://mirrors.aliyun.com/repo/Centos-7.repo
--替換CentOS-Base.repo文件$releasever變量爲相關linux版本，這裏替換爲“7”就可以了，具體操作：
vi /etc/yum.repos.d/CentOS-Base.repo
:%s/$releasever/7/ge
:wq
使用yum下載安裝軟件就ok了，如下提示已經開始從阿里雲鏡像服務器下載軟件了。
# yum install -y telnet
已加載插件：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"
正在嘗試其它鏡像。
(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
正在解決依賴關係
--> 正在檢查事務
---> 軟件包 telnet.x86_64.1.0.17-59.el7 將被 安裝
--> 解決依賴關係完成
依賴關係解決
===============================================================================================================================================================================================
Package 架構 版本 源 大小
===============================================================================================================================================================================================
正在安裝:
telnet x86_64 1:0.17-59.el7 base 63 k
事務概要
===============================================================================================================================================================================================
安裝 1 軟件包
總下載量：63 k
安裝大小：113 k