1. 备份

# 防止换源失败之后无法恢复
mv /etc/yum.repos.d/CentOS-Base.repo /etc/yum.repos.d/CentOS-Base.repo.backup

2. 下载新的 CentOS-Base.repo 到 /etc/yum.repos.d/

CentOS 6

curl -o /etc/yum.repos.d/CentOS-Base.repo https://mirrors.aliyun.com/repo/Centos-6.repo

CentOS 7

wget -O /etc/yum.repos.d/CentOS-Base.repo https://mirrors.aliyun.com/repo/Centos-7.repo
#或者
curl -o /etc/yum.repos.d/CentOS-Base.repo https://mirrors.aliyun.com/repo/Centos-7.repo

CentOS 8

wget -O /etc/yum.repos.d/CentOS-Base.repo https://mirrors.aliyun.com/repo/Centos-8.repo
#或者
curl -o /etc/yum.repos.d/CentOS-Base.repo https://mirrors.aliyun.com/repo/Centos-8.repo

3. 其他

#非阿里云ECS用户会出现 Couldn't resolve host 'mirrors.cloud.aliyuncs.com' 信息，不影响使用。用户也可自行修改相关配置: eg:
sed -i -e '/mirrors.cloud.aliyuncs.com/d' -e '/mirrors.aliyuncs.com/d' /etc/yum.repos.d/CentOS-Base.repo
#之后要生成缓存

4. 运行 yum makecache 生成缓存