步骤 1：备份原有源配置（重要！）

sudo mkdir /etc/yum.repos.d/backup
sudo mv /etc/yum.repos.d/CentOS-* /etc/yum.repos.d/backup/

步骤 2：下载阿里云源配置

sudo curl -o /etc/yum.repos.d/CentOS-Base.repo https://mirrors.aliyun.com/repo/Centos-7.repo

步骤 3：更新额外仓库配置

sudo curl -o /etc/yum.repos.d/epel.repo https://mirrors.aliyun.com/repo/epel-7.repo

步骤 4：清除缓存并生成新缓存

sudo yum clean all
sudo rm -rf /var/cache/yum
sudo yum makecache

步骤 5：测试源可用性

sudo yum repolist
# 应看到类似输出：
# repo id             repo name                      status
# base/7/x86_64       CentOS-7 - Base - mirrors.aliyun.com  10,072
# updates/7/x86_64    CentOS-7 - Updates - mirrors.aliyun.com 3,098
# extras/7/x86_64     CentOS-7 - Extras - mirrors.aliyun.com  484
# epel/x86_64         Extra Packages for Enterprise Linux 7 - mirrors.aliyun.com 13,759