REDHAT7 重启服务器后，NTP不能正常进行时间同步

Question

系统是Redhat7
服务器可以使用NTP同步时间
[root@localhost Desktop]# ntpstat
synchronised to NTP server (172.16.30.254) at stratum 11
time correct to within 7938 ms
polling server every 64 s

已经设定了NTP服务开机启动
[root@localhost Desktop]# systemctl is-enabled ntpd.service
enabled

但是每次重启后，都会显示NTP同步失败，要restart ntpd.service才能生效
[root@localhost Desktop]# ntpstat
unsynchronised
polling server every 64 s

请问还应该设置什么呢？ 另外使用 timedatectl status查看时，NTP enabled总是no，为什么呢？
[root@localhost Desktop]# timedatectl status
Local time: Wed 2015-07-15 04:37:40 CST
Universal time: Tue 2015-07-14 20:37:40 UTC
RTC time: Sat 2015-07-18 15:04:55
Timezone: Asia/Shanghai (CST, +0800)
NTP enabled: no
NTP synchronized: yes
RTC in local TZ: no
DST active: n/a

谢谢！

Answer 1

http://wenku.baidu.com/link?url=Ff2KliHZWtJO9gCeo0K8W_Gh4wrQ-ArwAc-eh9HEt-TC9f76upGhrR7J6iLNT4_9d4A6ICSdquYaFbaBZaznUwsNLvDAr_dLc3WpjFIcflK