1. 所有節點安裝ntp包：

   yum install ntp

2. 修改node1主節點的/etc/ntp.conf添加如下內容：

restrict 192.168.20.0 mask 255.255.255.0 nomodify notrap

即允許192.168.20.0網段的服務器從該節點同步時間，其中192.168.20.0可以更改為環境的實際ip網段。
3.註釋掉原有的時間同步源，添加本地時間源，即外部時間服務器不可用時，以本地時間作為時間服務

#server 0.centos.pool.ntp.org iburst
#server 1.centos.pool.ntp.org iburst
#server 2.centos.pool.ntp.org iburst
#server 3.centos.pool.ntp.org iburst
server  127.127.1.0     # local clock
fudge   127.127.1.0 stratum 10

4.啟動ntp服務並設置開機自啟動

[root@node1 ~]# systemctl start ntpd
[root@node1 ~]# systemctl enable ntpd
Created symlink from /etc/systemd/system/multi-user.target.wants/ntpd.service to /usr/lib/systemd/system/ntpd.service.
[root@node1 ~]# systemctl status ntpd
● ntpd.service - Network Time Service
   Loaded: loaded (/usr/lib/systemd/system/ntpd.service; enabled; vendor preset: disabled)
   Active: active (running) since Wed 2018-10-17 22:39:05 CST; 17s ago
 Main PID: 2529 (ntpd)
   CGroup: /system.slice/ntpd.service
           └─2529 /usr/sbin/ntpd -u ntp:ntp -g
Oct 17 22:39:05 node1 ntpd[2529]: Listen normally on 6 lo ::1 UDP 123
Oct 17 22:39:05 node1 systemd[1]: Started Network Time Service.
Oct 17 22:39:05 node1 ntpd[2529]: Listen normally on 7 eno50332184 fe80::20c:29ff:fe93:4ece UDP 123
Oct 17 22:39:05 node1 ntpd[2529]: Listen normally on 8 eno16777736 fe80::20c:29ff:fe93:4eba UDP 123
Oct 17 22:39:05 node1 ntpd[2529]: Listen normally on 9 eno33554960 fe80::20c:29ff:fe93:4ec4 UDP 123
Oct 17 22:39:05 node1 ntpd[2529]: Listening on routing socket on fd #26 for interface updates
Oct 17 22:39:05 node1 ntpd[2529]: 0.0.0.0 c016 06 restart
Oct 17 22:39:05 node1 ntpd[2529]: 0.0.0.0 c012 02 freq_set kernel 0.000 PPM
Oct 17 22:39:05 node1 ntpd[2529]: 0.0.0.0 c011 01 freq_not_set
Oct 17 22:39:06 node1 ntpd[2529]: 0.0.0.0 c514 04 freq_mode
 

5.修改其他所有ntp客戶端，即node2的/etc/ntp.conf 。刪除所有ntp源，並添加node1節點的ntp時間源，其中192.168.20.101為node1的ip，可用node1域名代替。

#server 0.centos.pool.ntp.org iburst
#server 1.centos.pool.ntp.org iburst
#server 2.centos.pool.ntp.org iburst
#server 3.centos.pool.ntp.org iburst
server 192.168.20.101

6.啟動ntp服務並設置開機自啟動

[root@node2 ~]# systemctl start ntpd 
[root@node2 ~]# systemctl enable ntpd 
Created symlink from /etc/systemd/system/multi-user.target.wants/ntpd.serviceto /usr/lib/systemd/system/ntpd.service.
 

7.查看是否同步成功，顯示如下192.168.20.101為node1節點的ip地址，說明同步成功。

[root@node2 ~]# ntpq -p
     remote           refid      st t when poll reach   delay   offset  jitter
==============================================================================
*192.168.20.101  LOCAL(0)        11 u   49   64  377    0.293    0.011   0.253

8.在node2上查看與node1時間服務器的實際偏差

[root@node2 ~]# ntpdc -c loopinfo
offset:               0.000011 s
frequency:            0.002 ppm
poll adjust:          6
watchdog timer:       270 s

內網配置NTP時鐘同步