[root@master ~]# yum -y install ntp

[root@master ~]# systemctl start ntpd

[root@master ~]# systemctl enable ntpd

[root@master ~]# vi /etc/ntp.conf

# For more information about this file, see the man pages
# ntp.conf(5), ntp_acc(5), ntp_auth(5), ntp_clock(5), ntp_misc(5), ntp_mon(5).
#記錄system clock的誤差值開機時不會丟失
driftfile /var/lib/ntp/drift

# Permit time synchronization with our time source, but do not
# permit the source to query or modify the service on this system.
#默認拒絕所有來源的任何訪問
restrict default nomodify notrap nopeer noquery

# Permit all access over the loopback interface.  This could
# be tightened as well, but to do so would effect some of
# the administrative functions.
#允許本機地址一切操作
restrict 127.0.0.1
restrict ::1

# Hosts on local network are less restricted.
#restrict 192.168.1.0 mask 255.255.255.0 nomodify notrap
#restrict 對ntp做權限控制 ignore：忽略所有類型的NTP連接請求 nomodify：限制客戶端不能使用命令ntpc和ntpq來修改服務器端的時間
#noquery：不提供NTP網絡校時服務 notrap：不接受遠程登錄請求 notrust：不接受沒有經過認證的客戶端的請求

#允許局域網66網段內所有client連接到這台服務器同步時間.但是拒絕讓他們修改服務器上的時間和遠程登錄
restrict 192.168.66.0 mask 255.255.255.0 nomodify notrap
# Use public servers from the pool.ntp.org project.
# Please consider joining the pool (//www.pool.ntp.org/join.html).
#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

#指定ntp服務器的地址
#將當前主機作為時間服務器
server 127.127.1.0
#時間服務器層級0-15 0表示頂級 10通常用於給局域網主機提供時間服務
fudge 127.127.1.0 stratum 10

#broadcast 192.168.1.255 autokey        # broadcast server
#broadcastclient                        # broadcast client
#broadcast 224.0.1.1 autokey            # multicast server
#multicastclient 224.0.1.1              # multicast client
#manycastserver 239.255.254.254         # manycast server
#manycastclient 239.255.254.254 autokey # manycast client

# Enable public key cryptography.
#crypto

includefile /etc/ntp/crypto/pw

# Key file containing the keys and key identifiers used when operating
# with symmetric key cryptography.
keys /etc/ntp/keys

# Specify the key identifiers which are trusted.
#trustedkey 4 8 42

# Specify the key identifier to use with the ntpdc utility.
#requestkey 8

# Specify the key identifier to use with the ntpq utility.
#controlkey 8

# Enable writing of statistics records.
#statistics clockstats cryptostats loopstats peerstats

# Disable the monitoring facility to prevent amplification attacks using ntpdc
# monlist command when default restrict does not include the noquery flag. See
# CVE-2013-5211 for more details.
# Note: Monitoring will not be disabled with the limited restriction flag.
disable monitor

[root@master ~]# systemctl restart ntpd

[root@master ~]# ntpstat
synchronised to local net (127.127.1.0) at stratum 11
   time correct to within 7948 ms
   polling server every 64 s
[root@master ~]# 

[root@node1 ~]# vi /etc/ntp.conf

# Use public servers from the pool.ntp.org project.
# Please consider joining the pool (//www.pool.ntp.org/join.html).
#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
#client端僅僅加入server端IP

server master

[root@node1 ~]# systemctl restart ntpd

[root@node1 ~]# ntpq -p
     remote           refid      st t when poll reach   delay   offset  jitter
==============================================================================
*master          LOCAL(0)        11 u   43   64   37    0.223  -134.33  92.058
[root@node1 ~]#