NTP服务端：
1. 安装NTP服务
rpm -qa|grep ntp #查看是否安装ntp，以下为已安装
yum -y install ntp ntpdate #安装命令
2. 查找当前地区最适合的时间服务器
http://www.pool.ntp.org/zone/asia
注：本章使用aliyun时间服务器
ntp1.aliyun.com
ntp2.aliyun.com
ntp3.aliyun.com
ntp4.aliyun.com
3.验证ntp服务是否开启
yum install -y nmap
nmap -sU ntp1.aliyun.com -p 123
4. 编辑/etc/ntp.conf
#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 ntp1.aliyun.com iburst
#server ntp2.aliyun.com iburst
#server ntp3.aliyun.com iburst
#server ntp4.aliyun.com iburst
server 127.127.1.0 iburst #作为服务端配置这条即可
5. 启动ntp服务
systemctl start ntpd.service
systemctl enable ntpd.service
6.配置服务器时间
date #系统时间
date -s "2019-12-06 09:59:00"
hwclock #硬件时间
hwclock --set --date "2019-12-06 09:59:30"
NTP客户端：
1. 安装ntp服务
rpm -qa|grep ntp
yum -y install ntp ntpdate
2. 设置ntp.conf
# Hosts on local network are less restricted.
#restrict 192.168.1.0 mask 255.255.255.0 nomodify notrap
restrict 192.168.0.60 nomodify notrap noquery
# Use public servers from the pool.ntp.org project.
# Please consider joining the pool (http://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
server 192.168.0.60
3.同步ntp服务时间
ntpdate -u 192.168.0.60
ntpdate参数介绍：
-q Query only - don’t set the clock.
-s Divert logging output from the standard output (default) to the system syslog facility. This is
designed primarily for convenience of cron scripts.
-u Direct ntpdate to use an unprivileged port for outgoing packets. This is most useful when behind a
firewall that blocks incoming traffic to privileged ports, and you want to synchronize with hosts
beyond the firewall. Note that the -d option always uses unprivileged ports.
4. 创建同步时间定时任务
crontab -e
0 * * * * /usr/sbin/ntpdate -u 192.168.0.60 #每小时同步
crontab -l
5.验证时间服务
ntpq -p
6.centos6/7开启ntp服务
centos6：
service ntpd start
chkconfig ntpd on
centos7：
systemctl start ntpd.service
systemctl enable ntpd.service