Redhat 的更新包只对注册的用户生效，所以我们自己手动更改成CentOS 的更新包，CentOS几乎和redhat是一样的.
1、首先查看redhat 7.0系统本身所安装的那些yum 软件包：
[[email protected] ~]# rpm -qa | grep yum
yum-utils-1.1.31-24.el7.noarch
yum-langpacks-0.4.2-3.el7.noarch
yum-metadata-parser-1.1.4-10.el7.x86_64
yum-rhn-plugin-2.0.1-4.el7.noarch
yum-3.4.3-118.el7.noarch
2、删除这些软件包；
[[email protected] ~]# rpm -e yum-3.4.3-118.el7.noarch --nodeps
[[email protected] ~]# rpm -e yum-utils-1.1.31-24.el7.noarch --nodeps
[[email protected] ~]# rpm -e yum-rhn-plugin-2.0.1-4.el7.noarch --nodeps
[[email protected] ~]# rpm -e yum-metadata-parser-1.1.4-10.el7.x86_64 --nodeps
[[email protected] ~]# rpm -e yum-langpacks-0.4.2-3.el7.noarch --nodeps
[[email protected] ~]# rpm -e PackageKit-yum-0.8.9-11.el7.x86_64 --nodeps
3、本机电脑得能上网（废话，不上网怎么用）
4、自己选择一个合适的镜像网站，找到自己系统所对应的文件包版本更新：
https://www.centos.org/download/mirrors/
我用的aws 美国 NJ州所以选择了http://centos.mirror.constant.com/
5、找到自己所需要的版本下载：
wget http://centos.mirror.constant.com/7/os/x86_64/Packages/yum-3.4.3-132.el7.centos.0.1.noarch.rpm
wget http://centos.mirror.constant.com/7/os/x86_64/Packages/yum-metadata-parser-1.1.4-10.el7.x86_64.rpm
wget http://centos.mirror.constant.com/7/os/x86_64/Packages/yum-utils-1.1.31-34.el7.noarch.rpm
wget http://centos.mirror.constant.com/7/os/x86_64/Packages/yum-updateonboot-1.1.31-34.el7.noarch.rpm
wget http://centos.mirror.constant.com/7/os/x86_64/Packages/yum-plugin-fastestmirror-1.1.31-34.el7.noarch.rpm
6、安装软件包，注意依赖关系：
rpm -ivh yum-3.4.3-132.el7.centos.0.1.noarch.rpm yum-plugin-fastestmirror-1.1.31-34.el7.noarch.rpm yum-metadata-parser-1.1.4-10.el7.x86_64.rpm
rpm -ivh yum-utils-1.1.31-34.el7.noarch.rpm
rpm -ivh yum-updateonboot-1.1.31-34.el7.noarch.rpm
7、新建repo 配置文件；
vi /etc/yum.repos.d/CentOS-Base.repo
内容如下：
根据自己的镜像替换掉网址http://centos.mirror.constant.com/为自己的镜像网址
# 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-$releasever - Base
mirrorlist=http://mirrorlist.centos.org/?release=$releasever&arch=$basearch&repo=os
#baseurl=http://mirror.centos.org/centos/$releasever/os/$basearch/
baseurl=http://centos.mirror.constant.com/7/os/$basearch/
gpgcheck=1
gpgkey=file:///etc/pki/rpm-gpg/RPM-GPG-KEY-CentOS-7
#released updates
[updates]
name=CentOS-$releasever - Updates
mirrorlist=http://mirrorlist.centos.org/?release=$releasever&arch=$basearch&repo=updates
#baseurl=http://mirror.centos.org/centos/$releasever/updates/$basearch/
baseurl=http://centos.mirror.constant.com/7/updates/$basearch/
gpgcheck=1
gpgkey=file:///etc/pki/rpm-gpg/RPM-GPG-KEY-CentOS-7
#additional packages that may be useful
[extras]
name=CentOS-$releasever - Extras
mirrorlist=http://mirrorlist.centos.org/?release=$releasever&arch=$basearch&repo=extras
#baseurl=http://mirror.centos.org/centos/$releasever/extras/$basearch/
baseurl=http://centos.mirror.constant.com/7/extras/$basearch/
gpgcheck=1
gpgkey=file:///etc/pki/rpm-gpg/RPM-GPG-KEY-CentOS-7
#additional packages that extend functionality of existing packages
[centosplus]
name=CentOS-$releasever - Plus
mirrorlist=http://mirrorlist.centos.org/?release=$releasever&arch=$basearch&repo=centosplus
#baseurl=http://mirror.centos.org/centos/$releasever/centosplus/$basearch/
baseurl=http://centos.mirror.constant.com/7/centosplus/$basearch/
gpgcheck=1
enabled=0
gpgkey=file:///etc/pki/rpm-gpg/RPM-GPG-KEY-CentOS-7
8、导入RPM-GPG-KEY-CentOS-7
cd /etc/pki/rpm-gpg/
wget http://centos.mirror.constant.com/RPM-GPG-KEY-CentOS-7
9、清理原先缓存，创建新缓存
yum clean all
yum makecache
10、安装试试
yum -y install zlib zlib-devel openssl openssl-devel pcre pcre-devel gd gd-devel
后记，注意：
1，莫忘记导入key
2，删除或禁用原先的repo文件
3，--nodeps
4，镜像网址切换
5，Centos和Redhat版本