1.删除原有的yum
rpm -aq|grep yum|xargs rpm -e --nodeps
2.下载yum安装文件 (若没有此包，可以去阿里镜像或网易镜像找到包名一样的下下来即可)
wget http://mirrors.163.com/centos/7/os/x86_64/Packages/yum-3.4.3-150.el7.centos.noarch.rpm
wget http://mirrors.163.com/centos/7/os/x86_64/Packages/yum-metadata-parser-1.1.4-10.el7.x86_64.rpm
wget http://mirrors.163.com/centos/7/os/x86_64/Packages/yum-plugin-fastestmirror-1.1.31-40.el7.noarch.rpm
wget http://mirrors.163.com/centos/7/os/x86_64/Packages/python-iniparse-0.4-9.el7.noarch.rpm
3.进行安装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-3.4.3-150.el7.centos.noarch.rpm rpm yum-plugin-fastestmirror-1.1.31-40.el7.noarch.rpm
注意最后两个包必需同时安装，否则会相互依赖
4.更新repo文件
进入 /etc/yum.repos.d文件夹下，
wget http://mirrors.163.com/.help/CentOS7-Base-163.repo
删除原来的配置文件 rm -rf CentOS-Base.repo
修改新配置文件名 mv CentOS7-Base-163.repo CentOS7-Base.repo
安装结束
