安装方式：
yum install ntp -y
文件位置： /etc/ntp.conf
restrict ntp服务的防火墙
server ntp服务需要同步时间的上层ntp服务器
错误排查：
[root@localhost ~]# ntpdate -d 192.168.100.100
10 Apr 23:03:12 ntpdate[1155]: ntpdate 4.2.6p5@1.2349-o Fri Apr 13 12:52:28 UTC 2018 (1)
Looking for host 192.168.100.100 and service ntp
host found : 192.168.100.100
transmit(192.168.100.100)
transmit(192.168.100.100)
transmit(192.168.100.100)
transmit(192.168.100.100)
transmit(192.168.100.100)
192.168.100.100: Server dropped: no data
server 192.168.100.100, port 123
stratum 0, precision 0, leap 00, trust 000
refid [192.168.100.100], delay 0.00000, dispersion 64.00000
transmitted 4, in filter 4
reference time: 00000000.00000000 Mon, Jan 1 1900 8:05:43.000
originate timestamp: 00000000.00000000 Mon, Jan 1 1900 8:05:43.000
transmit timestamp: e0588436.d5e0ea36 Wed, Apr 10 2019 23:03:18.835
filter delay: 0.00000 0.00000 0.00000 0.00000
0.00000 0.00000 0.00000 0.00000
filter offset: 0.000000 0.000000 0.000000 0.000000
0.000000 0.000000 0.000000 0.000000
delay 0.00000, dispersion 64.00000
offset 0.000000
10 Apr 23:03:20 ntpdate[1155]: no server suitable for synchronization found
出现no date，说明是防火墙或者firewall或者restrict 做了限制
[root@localhost ~]# ntpdate -d 192.168.100.100
11 Apr 06:46:45 ntpdate[1217]: ntpdate 4.2.6p5@1.2349-o Fri Apr 13 12:52:28 UTC 2018 (1)
Looking for host 192.168.100.100 and service ntp
host found : 192.168.100.100
transmit(192.168.100.100)
receive(192.168.100.100)
transmit(192.168.100.100)
receive(192.168.100.100)
transmit(192.168.100.100)
receive(192.168.100.100)
transmit(192.168.100.100)
receive(192.168.100.100)
192.168.100.100: Server dropped: strata too high
server 192.168.100.100, port 123
stratum 16, precision -24, leap 11, trust 000
refid [192.168.100.100], delay 0.02606, dispersion 0.00003
transmitted 4, in filter 4
reference time: 00000000.00000000 Mon, Jan 1 1900 8:05:43.000
originate timestamp: e058807e.05119c87 Wed, Apr 10 2019 22:47:26.019
transmit timestamp: e058f0db.acb31585 Thu, Apr 11 2019 6:46:51.674
filter delay: 0.02606 0.02643 0.02658 0.02640
0.00000 0.00000 0.00000 0.00000
filter offset: -28765.6 -28765.6 -28765.6 -28765.6
0.000000 0.000000 0.000000 0.000000
delay 0.02606, dispersion 0.00003
offset -28765.655310
11 Apr 06:46:51 ntpdate[1217]: no server suitable for synchronization found
出现 strata too high ，则可能是ntp服务版本高于4.2导致
ntpq -c version 可以查看ntp服务版本
解决办法：在/etc/ntp.conf加入
server 127.127.1.0 fudge
127.127.1.0 stratum 8
原文：https://www.cnblogs.com/l610479744/p/10686920.html