yum 誤刪 ，所以重裝，我的系統是centos7.2。
以下文章實測有效：
https://www.cnblogs.com/xdjun/p/11770418.html
http://mirrors.163.com/centos/7/os/x86_64/Packages/python-devel-2.7.5-86.el7.x86_64.rpm
http://mirrors.163.com/centos/7/os/x86_64/Packages/yum-plugin-fastestmirror-1.1.31-52.el7.noarch.rpm
http://mirrors.163.com/centos/7/os/x86_64/Packages/yum-plugin-protectbase-1.1.31-52.el7.noarch.rpm
http://mirrors.163.com/centos/7/os/x86_64/Packages/yum-plugin-aliases-1.1.31-52.el7.noarch.rpm
http://mirrors.163.com/centos/7/os/x86_64/Packages/yum-metadata-parser-1.1.4-10.el7.x86_64.rpm
http://mirrors.163.com/centos/7/os/x86_64/Packages/yum-3.4.3-163.el7.centos.noarch.rpm
http://mirrors.163.com/centos/7/os/x86_64/Packages/yum-utils-1.1.31-52.el7.noarch.rpm
http://mirrors.163.com/centos/7/os/x86_64/Packages/rpm-python-4.11.3-40.el7.x86_64.rpm
http://mirrors.163.com/centos/7/os/x86_64/Packages/python-chardet-2.2.1-3.el7.noarch.rpm
http://mirrors.163.com/centos/7/os/x86_64/Packages/python-kitchen-1.1.1-5.el7.noarch.rpm
http://mirrors.163.com/centos/7/os/x86_64/Packages/python-setuptools-0.9.8-7.el7.noarch.rpm
http://mirrors.163.com/centos/7/os/x86_64/Packages/python-urlgrabber-3.10-9.el7.noarch.rpm
http://mirrors.163.com/centos/7/os/x86_64/Packages/python-pycurl-7.19.0-19.el7.x86_64.rpm
http://mirrors.163.com/centos/7/os/x86_64/Packages/python-iniparse-0.4-9.el7.noarch.rpm
http://mirrors.163.com/centos/7/os/x86_64/Packages/python-2.7.5-86.el7.x86_64.rpm
http://mirrors.163.com/centos/7/os/x86_64/Packages/python-backports-ssl_match_hostname-3.5.0.1-1.el7.noarch.rpm
http://mirrors.163.com/centos/7/os/x86_64/Packages/python-backports-1.0-8.el7.x86_64.rpm
http://mirrors.163.com/centos/7/os/x86_64/Packages/python-ipaddress-1.0.16-2.el7.noarch.rpm
http://mirrors.163.com/centos/7/os/x86_64/Packages/python-libs-2.7.5-86.el7.x86_64.rpm
http://mirrors.163.com/centos/7/os/x86_64/Packages/libxml2-python-2.9.1-6.el7_2.3.x86_64.rpm
http://mirrors.163.com/centos/7/os/x86_64/Packages/lvm2-python-libs-2.02.185-2.el7.x86_64.rpm
下載執行：
#rpm -Uvh --replacepkgs lvm2-python-libs*.rpm --nodeps --force
#rpm -Uvh --replacepkgs libxml2-python*.rpm --nodeps --force
#rpm -Uvh --replacepkgs python*.rpm --nodeps --force
#rpm -Uvh --replacepkgs rpm-python*.rpm yum*.rpm --nodeps --forc
情況2：安裝成功後，遇到
https://blog.csdn.net/qq_39720249/article/details/84104646
yum repolist 爲0， cd /etc/yum.repos.d/ 顯示文件夾下爲空，沒有CentOS-Base.repo文件
情況3： https://blog.csdn.net/u010454030/article/details/78807281
執行wget -O /etc/yum.repos.d/CentOS-Base.repo http://mirrors.aliyun.com/repo/Centos-7.repo 下載文件
執行 yum clean all
yum makecache