问题现象：ntp进程运行一段时间后自动退出

排查过程：

查看/var/log/message ntp异常信息如下

Feb 20 22:54:41 xnu_1 ntpd[2187]: 0.0.0.0 0617 07 panic_stop -28777 s; set clock manually within 1000 s.

Feb 20 22:54:57 xnu_1 ntpd_intres[2193]: parent died before we finished, exiting

查看官方文档，有如下说明：

-g

Normally, ntpd exits with a message to the system log if the offset exceeds the panic threshold, which is 1000 s by default. This option allows the time to be set to any value without restriction; however, this can happen only once. If the threshold is exceeded after that, ntpd will exit with a message to the system log. Th