我的系统误删了yum和python后导致yum包管理器不能使用，在网上找了好多教程，因为Centos 7已经不维护了，好多rpm包都是404页面，找了好久才找到下面可以下载所有rpm包的网站，如果有其它问题缺rpm包的也可以去https://vault.centos.org/7.9.2009/os/x86_64去找，不过自己修改一下系统版本就好了
1. 删除现有Python
rpm -qa|grep python|xargs rpm -ev --allmatches --nodeps ## 强制删除已安装程序及其关联
whereis python |xargs rm -frv ## 删除所有残余文件 ## xargs，允许你对输出执行其他命令
whereis python ## 验证删除
2. 删除现有Yum
rpm -qa|grep yum|xargs rpm -ev --allmatches --nodeps ## 强制删除已安装程序及其关联
whereis yum |xargs rm -frv ## 删除所有残余文件 ## xargs，允许你对输出执行其他命令
whereis yum ## 验证删除
3. 检查系统版本
cat /etc/redhat-release ## 检查系统版本
4. 下载对应版本的20个RPM包
注：我这里的版本是7.9.2009，将下面所有7.9.2009改成自己系统版本
wget https://vault.centos.org/7.9.2009/os/x86_64/Packages/python-backports-ssl_match_hostname-3.5.0.1-1.el7.noarch.rpm
wget https://vault.centos.org/7.9.2009/os/x86_64/Packages/python-2.7.5-89.el7.x86_64.rpm
wget https://vault.centos.org/7.9.2009/os/x86_64/Packages/python-ipaddress-1.0.16-2.el7.noarch.rpm
wget https://vault.centos.org/7.9.2009/os/x86_64/Packages/yum-metadata-parser-1.1.4-10.el7.x86_64.rpm
wget https://vault.centos.org/7.9.2009/os/x86_64/Packages/python-chardet-2.2.1-3.el7.noarch.rpm
wget https://vault.centos.org/7.9.2009/os/x86_64/Packages/python-libs-2.7.5-89.el7.x86_64.rpm
wget https://vault.centos.org/7.9.2009/os/x86_64/Packages/rpm-python-4.11.3-45.el7.x86_64.rpm
wget https://vault.centos.org/7.9.2009/os/x86_64/Packages/yum-plugin-protectbase-1.1.31-54.el7_8.noarch.rpm
wget https://vault.centos.org/7.9.2009/os/x86_64/Packages/yum-3.4.3-168.el7.centos.noarch.rpm
wget https://vault.centos.org/7.9.2009/os/x86_64/Packages/libxml2-python-2.9.1-6.el7.5.x86_64.rpm
wget https://vault.centos.org/7.9.2009/os/x86_64/Packages/yum-plugin-fastestmirror-1.1.31-54.el7_8.noarch.rpm
wget https://vault.centos.org/7.9.2009/os/x86_64/Packages/python-pycurl-7.19.0-19.el7.x86_64.rpm
wget https://vault.centos.org/7.9.2009/os/x86_64/Packages/yum-plugin-aliases-1.1.31-54.el7_8.noarch.rpm
wget https://vault.centos.org/7.9.2009/os/x86_64/Packages/lvm2-python-libs-2.02.187-6.el7.x86_64.rpm
wget https://vault.centos.org/7.9.2009/os/x86_64/Packages/yum-utils-1.1.31-54.el7_8.noarch.rpm
wget https://vault.centos.org/7.9.2009/os/x86_64/Packages/python-setuptools-0.9.8-7.el7.noarch.rpm
wget https://vault.centos.org/7.9.2009/os/x86_64/Packages/python-urlgrabber-3.10-10.el7.noarch.rpm
wget https://vault.centos.org/7.9.2009/os/x86_64/Packages/python-iniparse-0.4-9.el7.noarch.rpm
wget https://vault.centos.org/7.9.2009/os/x86_64/Packages/python-backports-1.0-8.el7.x86_64.rpm
wget https://vault.centos.org/7.9.2009/os/x86_64/Packages/python-kitchen-1.1.1-5.el7.noarch.rpm
5. 安装
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 --force
6. 检查
yum --version
python --version