由于在安装Redhat7 想安装gcc 使用yum install gcc 报错：
This system is not registered to Red Hat Subscription Management. You can use subscription-manager to register.
大概意思是让先注册一下，这是redhat 自带的yum需要注册。
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第一步：先卸载原来的yum
[root@localhost ~]# rpm -qa |grep yum （查看原来是否安装）
[root@localhost ~]# rpm -qa|grep yum|xargs rpm -e –-nodeps （直接卸载）
第二步：下载替换包
新建目录 mkdir /home/yum (上传到这里yum下面)
执行： rpm -ivh *.rpm 一次性安装依赖包。
[root@localhost yum]# rpm -ivh *.rpm
第三步 ： 新建配置文件 1.repo
（home/yum/1.repo）
vim 1.repo
第四步： 把下面的配置文件复制到 1.repo 里边
#CentOS-Base.repo
#
# The mirror system uses the connecting IP address of the client and the
# update status of each mirror to pick mirrors that are updated to and
# geographically close to the client. ?You should use this for CentOS updates
# unless you are manually picking other mirrors.
# If the mirrorlist= does not work for you, as a fall back you can try the
# remarked out baseurl= line instead.
[base]
name=CentOS-$7 - Base - 163.com
#mirrorlist=http://mirrorlist.centos.org/?release=$7&arch=$basearch&repo=os
baseurl=http://mirrors.163.com/centos/7/os/$basearch/
gpgcheck=1
gpgkey=http://mirrors.163.com/centos/RPM-GPG-KEY-CentOS-7
#released updates
[updates]
name=CentOS-$7 - Updates - 163.com
#mirrorlist=http://mirrorlist.centos.org/?release=$7&arch=$basearch&repo=updates
baseurl=http://mirrors.163.com/centos/7/updates/$basearch/
gpgcheck=1
gpgkey=http://mirrors.163.com/centos/RPM-GPG-KEY-CentOS-7
#additional packages that may be useful
[extras]
name=CentOS-$7 - Extras - 163.com
#mirrorlist=http://mirrorlist.centos.org/?release=$7&arch=$basearch&repo=extras
baseurl=http://mirrors.163.com/centos/7/extras/$basearch/
gpgcheck=1
gpgkey=http://mirrors.163.com/centos/RPM-GPG-KEY-CentOS-7
#additional packages that extend functionality of existing packages
[centosplus]
name=CentOS-$7 - Plus - 163.com
baseurl=http://mirrors.163.com/centos/7/centosplus/$basearch/
gpgcheck=1
enabled=0
gpgkey=http://mirrors.163.com/centos/RPM-GPG-KEY-CentOS-7
第五步：清楚缓存
[root@localhost yum.repos.d]# yum cear all
[root@localhost yum.repos.d]# yum makecache
既yum配置完成。