首先確保能ping通公網（已聯網）
一.查詢已安裝的yum
1.#rpm -qa | grep yum
二.使用root權限卸載已安裝的yum
1.#rpm -qa | grep yum | xargs rpm -e --nodeps
三.下載並安裝阿里的yum源rpm包
1.# 創建安放rpm包的文件夾(創建目錄位置隨意)
cd /etc/yum.repos.d/
mkdir yum-rpm && cd yum-rpm
2.# 下載rpm包
#wget https://mirrors.aliyun.com/centos/7/os/x86_64/Packages/yum-3.4.3-161.el7.centos.noarch.rpm
#wget https://mirrors.aliyun.com/centos/7/os/x86_64/Packages/yum-langpacks-0.4.2-7.el7.noarch.rpm
#wget https://mirrors.aliyun.com/centos/7/os/x86_64/Packages/yum-rhn-plugin-2.0.1-10.el7.noarch.rpm
#wget https://mirrors.aliyun.com/centos/7/os/x86_64/Packages/yum-utils-1.1.31-50.el7.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 https://mirrors.aliyun.com/centos/7/os/x86_64/Packages/python-iniparse-0.4-9.el7.noarch.rpm
#wget https://mirrors.aliyun.com/centos/7/os/x86_64/Packages/python-urlgrabber-3.10-9.el7.noarch.rpm
#wget https://mirrors.aliyun.com/centos/7/os/x86_64/Packages/rpm-4.11.3-35.el7.x86_64.rpm
#wget https://mirrors.aliyun.com/centos/7/os/x86_64/Packages/yum-plugin-fastestmirror-1.1.31-50.el7.noarch.rpm
以上命令，最好一條條復制下載，如無法下載安裝，
根據rpm包主要關鍵字到阿里雲CentOS-yum源庫地址庫中搜索
獲取最新rpm包的地址后，使用wget進行下載安裝即可。
四、安裝rpm包
1.#cd /etc/yum.repos.d/yum-rpm
2.#rpm -ivh *.rpm --force --nodeps
加上--force參數強制安裝，解決安裝過程中的的依賴問題
五、下載阿里鏡像到/etc/yum.repos.d/目錄下
#wget -O /etc/yum.repos.d/CentOS-Base.repo http://mirrors.aliyun.com/repo/Centos-7.repo
六、修改Centos-7.repo文件將所有$releasever替換為7
#vim /etc/yum.repos.d/CentOS-Base.repo
:%s/$releasever/7/g
七、運行以下命令
#yum clean all
#yum makecache
#yum update