https://blog.wongcw.com/2018/11/04/centos-7-%e9%85%8d%e7%bd%aersynclsyncd%e5%ae%9e%e7%8e%b0%e6%b5%b7%e9%87%8f%e6%96%87%e4%bb%b6%e5%ae%9e%e6%97%b6%e5%90%8c%e6%ad%a5/