RedHat7.2修改yum源

 1.删除自带的yum： rpm -aq | grep yum | xargs rpm -e --nodeps

 2.下载CentOS的yum安装文件：

　　wget http://mirrors.163.com/centos/7.2.1511/os/x86_64/Packages/yum-3.4.3-132.el7.centos.0.1.noarch.rpm

　　wget http://mirrors.163.com/centos/7.2.1511/os/x86_64/Packages/python-iniparse-0.4-9.el7.noarch.rpm

　　wget http://mirrors.163.com/centos/7.2.1511/os/x86_64/Packages/yum-metadata-parser-1.1.4-10.el7.x86_64.rpm

　　wget http://mirrors.163.com/centos/7.2.1511/os/x86_64/Packages/yum-plugin-fastestmirror-1.1.31-34.el7.noarch.rpm

 3.安装yum：

　　rpm -ivh python-iniparse-0.4-9.el7.noarch.rpm

　　rpm -ivh yum-metadata-parser-1.1.4-10.el7.x86_64.rpm

　　rpm -ivh yum-3.4.3-132.el7.centos.0.1.noarch.rpm

　　rpm -ivh yum-plugin-fastestmirror-1.1.31-34.el7.noarch.rpm

 4.更新repo文件：从http://mirrors.163.com/.help/centos.html下载对应版本的repo文件，将$releasever替换为对应版本号，并将gpgkey后面的值替换为http://mirrors.163.com/centos/7.2.1511/os/x86_64/RPM-GPG-KEY-CentOS-7

 5.清除所有缓存：yum clean all

 6.测试：yum update

 7.安装epel源：yum install epel-release