1.下载三个rpm离线包
ntpdate-4.2.6p5-29.el7.centos.2.x86_64
ntp-4.2.6p5-29.el7.centos.2.x86_64
autogen-libopts-5.18-5.el7.x86_64
地址：
http://mirror.centos.org/centos/7/os/x86_64/Packages/ntpdate-4.2.6p5-29.el7.centos.2.x86_64.rpm
http://mirror.centos.org/centos/7/os/x86_64/Packages/ntp-4.2.6p5-29.el7.centos.2.x86_64.rpm
http://mirror.centos.org/centos/7/os/x86_64/Packages/autogen-libopts-5.18-5.el7.x86_64.rpm
2.上传至centos安装
ntp -ivh ntpdate-4.2.6p5-29.el7.centos.2.x86_64.rpm
ntp -ivh ntp-4.2.6p5-29.el7.centos.2.x86_64
ntp -ivh autogen-libopts-5.18-5.el7.x86_64.rpm
3.查看安转版本 rpm -q ntp
4. 启用ntp服务 systemctl enable ntpd
5.开始ntp服务 systemctl start ntpd
查看状态 systemctl status ntpd
6. 编辑master的机器的文件/etc/ntp.conf
restrict 192.168.3.0 mask 255.255.255.0 nomodify notrap
这里的意思代表，192.168.3的网段的机器都参与ntp的时间同步
# 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).
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.
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.
restrict 127.0.0.1
restrict ::1
# Hosts on local network are less restricted.
restrict 192.168.111.0 mask 255.255.255.0 nomodify notrap
# Use public servers from the pool.ntp.org project.
# Please consider joining the pool (http://www.pool.ntp.org/join.html).
server ntp1.aliyun.com
server ntp2.aliyun.com
server ntp3.aliyun.com
server 127.0.0.1
fudge 127.0.0.1 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
server ntp1.aliyun.com
server ntp2.aliyun.com
server ntp3.aliyun.com
///当以上三个时间服务器不可用时，就是以本机时间作为集群机器的统一时间。
server 127.0.0.1
fudge 127.0.0.1 stratum 10
6.更新时间 ntpdate -u ntp2.aliyun.com
7.配置客户机 /etc/ntp.conf
server 192.168.111.128
同步时间命令 ntpdate -u 192.168.111.128 需要关闭防火墙
