踩坑說明：
yum install安裝rpm包時經常報錯：Failed connect to mirrors.cloud.aliyuncs.com:80; Connection refused
避坑指南：
究其原因，是由於非阿里雲ECS用戶無法解析主機“mirrors.cloud.aliyuncs.com”
只需將CentOS-Base里包含aliyuncs.com的行刪除即可。
脫坑方案：
1. 備份CentOS-Base
[root@centos7 ~]# cp /etc/yum.repos.d/CentOS-Base.repo{,.bak}
2. 下載CentOS-Base
[root@centos7 ~]# wget -O /etc/yum.repos.d/CentOS-Base.repo https://mirrors.aliyun.com/repo/Centos-7.repo
或
[root@centos7 ~]# curl -o /etc/yum.repos.d/CentOS-Base.repo https://mirrors.aliyun.com/repo/Centos-7.repo
3. 編輯CentOS-Base
[root@centos7 ~]# sed -i -e '/mirrors.cloud.aliyuncs.com/d' -e '/mirrors.aliyuncs.com/d' /etc/yum.repos.d/CentOS-Base.repo