配置fastDfs时的坑：CentOs7上重启防火墙报
Unit not found
或者
Job for iptables.service failed because the control process exited with error
code. See "systemctl status iptables.service" and "journalctl -xe" for details.
参考博客：
CentOs7与CentOs6的差异问题https://www.cnblogs.com/faunjoe88/p/7003815.html
centos7默认的防火墙是firewalld防火墙，不是使用iptables，所以要先关闭firewalld，再开启iptables
https://blog.csdn.net/sinat_29821865/article/details/80982250
