1、查找安装的yum，进行移除
rpm -qa | grep yum
rpm -e --nodeps xxxxxx
2、下载安装包
http://mirrors.163.com/centos/7.9.2009/os/x86_64/Packages/python-iniparse-0.4-9.el7.noarch.rpm
http://mirrors.163.com/centos/7.9.2009/os/x86_64/Packages/yum-metadata-parser-1.1.4-10.el7.x86_64.rpm
http://mirrors.163.com/centos/7.9.2009/os/x86_64/Packages/yum-3.4.3-168.el7.centos.noarch.rpm
http://mirrors.163.com/centos/7.9.2009/os/x86_64/Packages/yum-plugin-fastestmirror-1.1.31-54.el7_8.noarch.rpm
3、按顺序安装
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-3.4.3-168.el7.centos.noarch.rpm yum-plugin-fastestmirror-1.1.31-54.el7_8.noarch.rpm
4、替换源
cd /etc/yum.repos.d
mv redhat.repo redhat.repo-backup
下载一份源文件进行修改，移至目录下 /etc/yum.repos.d/CentOS7-Base-163.repo
http://mirrors.163.com/.help/CentOS7-Base-163.repo
替换 $releasever 为版本号 7.9.2009 ，替换好的：
# CentOS-Base.repo # # The mirror system uses the connecting IP address of the client and the # update status of each mirror to pick mirrors that are updated to and # geographically close to the client. You should use this for CentOS updates # unless you are manually picking other mirrors. # # If the mirrorlist= does not work for you, as a fall back you can try the # remarked out baseurl= line instead. # # [base] name=CentOS-7.9.2009 - Base - 163.com #mirrorlist=http://mirrorlist.centos.org/?release=7.9.2009&arch=$basearch&repo=os baseurl=http://mirrors.163.com/centos/7.9.2009/os/$basearch/ gpgcheck=1 gpgkey=http://mirrors.163.com/centos/RPM-GPG-KEY-CentOS-7 #released updates [updates] name=CentOS-7.9.2009 - Updates - 163.com #mirrorlist=http://mirrorlist.centos.org/?release=7.9.2009&arch=$basearch&repo=updates baseurl=http://mirrors.163.com/centos/7.9.2009/updates/$basearch/ gpgcheck=1 gpgkey=http://mirrors.163.com/centos/RPM-GPG-KEY-CentOS-7 #additional packages that may be useful [extras] name=CentOS-7.9.2009 - Extras - 163.com #mirrorlist=http://mirrorlist.centos.org/?release=7.9.2009&arch=$basearch&repo=extras baseurl=http://mirrors.163.com/centos/7.9.2009/extras/$basearch/ gpgcheck=1 gpgkey=http://mirrors.163.com/centos/RPM-GPG-KEY-CentOS-7 #additional packages that extend functionality of existing packages [centosplus] name=CentOS-7.9.2009 - Plus - 163.com baseurl=http://mirrors.163.com/centos/7.9.2009/centosplus/$basearch/ gpgcheck=1 enabled=0 gpgkey=http://mirrors.163.com/centos/RPM-GPG-KEY-CentOS-7
5 、清理、刷新缓存
yum clean all
yum makecache