环境介绍
Node1作为NTP主节点，其他所有节点从node1进行时间同步，
节点 Ip
Node1 192.168.20.101
Node2 192.168.20.102
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所有节点安装ntp包：
yum install ntp - 修改node1主节点的/etc/ntp.conf添加如下内容：
restrict 192.168.20.0 mask 255.255.255.0 nomodify notrap即允许192.168.20.0网段的服务器从该节点同步时间，其中192.168.20.0可以更改为环境的实际ip网段。- 注释掉原有的时间同步源，添加本地时间源，即外部时间服务器不可用时，以本地时间作为时间服务
#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 -
启动ntp服务并设置开机自启动
[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 -
修改其他所有ntp客户端，即node2的/etc/ntp.conf 。删除所有ntp源，并添加node1节点的ntp时间源，其中192.168.20.101为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 192.168.20.1016.启动ntp服务并设置开机自启动
[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，显示如下192.168.20.101为node1节点的ip地址，说明同步成功。
[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- 在node2上查看与node1时间服务器的实际偏差
[root@node2 ~]# ntpdc -c loopinfo offset: 0.000011 s frequency: 0.002 ppm poll adjust: 6 watchdog timer: 270 s