解除原有源
rpm -aq|grep yum|xargs rpm -e --nodeps
rpm -aq|grep python-iniparse|xargs rpm -e --nodeps

rpm -qa | grep yum
检验是否删除干净
下载四个包：
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包

wget -c http://centos.ustc.edu.cn/centos/7/os/x86_64/Packages/yum-3.4.3-150.el7.centos.noarch.rpm

rpm -ivh *.rpm
注意可能需要根据提示多删除或添加一些包
rpm -qa | grep yum
检验yum是否安装成功

替换文件内容，注意repo网址需可达
vim /etc/yum.repos.d/CentOS-Base.repo

[base]
name=CentOS-$releasever - Base - 163.com
#mirrorlist=http://mirrorlist.centos.org/?release=$releasever&arch=$basearch&repo=os
baseurl=http://mirrors.163.com/centos/7.1.1503/os/$basearch/
gpgcheck=1
gpgkey=http://mirrors.163.com/centos/RPM-GPG-KEY-CentOS-7

#released updates
[updates]
name=CentOS-$releasever - Updates - 163.com
#mirrorlist=http://mirrorlist.centos.org/?release=$releasever&arch=$basearch&repo=updates
baseurl=http://mirrors.163.com/centos/7.1.1503/updates/$basearch/
gpgcheck=1
gpgkey=http://mirrors.163.com/centos/RPM-GPG-KEY-CentOS-7

#additional packages that may be useful
[extras]
name=CentOS-$releasever - Extras - 163.com
#mirrorlist=http://mirrorlist.centos.org/?release=$releasever&arch=$basearch&repo=extras
baseurl=http://mirrors.163.com/centos/7.1.1503/extras/$basearch/
gpgcheck=1
gpgkey=http://mirrors.163.com/centos/RPM-GPG-KEY-CentOS-7

#additional packages that extendfunctionality of existing packages
[centosplus]
name=CentOS-$releasever - Plus - 163.com
baseurl=http://mirrors.163.com/centos/7.1.1503/centosplus/$basearch/
gpgcheck=1
enabled=0
gpgkey=http://mirrors.163.com/centos/RPM-GPG-KEY-CentOS-7

yum clean all

yum makecache