准备工作：
server ip:10.1.1.119
client ip :10.1.1.56
关闭selinux：
vi /etc/selinux/config
SELINUX=disabled
关闭iptables：
service iptables stop
chkconfig iptables off
一.安装NTP软件包：
yum -y install ntp /*yum安装NTP服务*/
chkconfig --add ntpd /*添加NTP*/
chkconfig ntpd on /*开机自启动NTP*/
二.修改NTP配置文件：
vim /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).
driftfile /var/lib/ntp/drift
#设置默认策略为拒绝所有访问方式的请求
restrict default ignore
# Permit time synchronization with our time source, but do not
# permit the source to query or modify the service on this system.
restrict default kod nomodify notrap nopeer noquery
restrict -6 default kod 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 -6 ::1
# Hosts on local network are less restricted.
#restrict 192.168.1.0 mask 255.255.255.0 nomodify notrap
#允许局域网内机器同步时间(这里有待test能不能测试多个网段同步时间)
restrict 10.1.1.0 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 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
#设置同步服务器加prefer表示优先
server 0.cn.pool.ntp.org prefer
server 1.s2m.time.edu.cn
server 2.1.cn.pool.ntp.org
#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
#允许与上层服务器同步时间
restrict 0.cn.pool.ntp.org nomodify notrap noquery
restrict 1.s2m.time.edu.cn nomodify notrap noquery
restrict 2.1.cn.pool.ntp.org nomodify notrap noquery
# Undisciplined Local Clock. This is a fake driver intended for backup
# # and when no outside source of synchronized time is available.
#外界同步源无法联系时，使用本地时间为同步服务
server 127.127.1.0 # local clock
fudge 127.127.1.0 stratum 0
# 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
注意：这里要注意机器的所在时区
/usr/share/zoneinfo/Asia/ #下保存着系统各个时区信息
/etc/localtime 保存当前系统时区及时间信息
修改时区前显示：
[[email protected] ~]# date
Mon Jul 27 21:41:14 PDT 2015
示例修改时区
[[email protected] ~]# cp /usr/share/zoneinfo/Asia/Shanghai /etc/localtime
cp: overwrite `/etc/localtime‘? y
修改时区以后显示：
[[email protected] ~]# date
Tue Jul 28 12:43:00 CST 2015
PDT 是Pacific Daylight Time的简称,意思是太平洋夏令时
UTC 世界协调时间UTC
格林威治标准时间GMT
CST可以同时表示美国，澳大利亚，中国，古巴四个国家的标准时间
三.与上层服务器同步时间：
[[email protected] ~]# ntpdate cn.pool.ntp.org
启动NTP服务
[[email protected] ~]# service ntpd start
正在启动 ntpd： [确定]
[[email protected] ~]# date
2015年 07月 28日 星期二 12:19:55 CST
五.在客户机测试时间同步：
[[email protected] ~]# ntpdate 10.1.1.119
28 Jul 12:43:40 ntpdate[1551]: adjust time server 10.1.1.119 offset 0.057411 sec
问题1：
[[email protected] ~]# ntpdate 0.centos.pool.ntp.org
8 Nov 11:12:34 ntpdate[4606]: the NTP socket is in use, exiting
原因：该机已经运行NTP服务。
解决：
[[email protected] ~]# service ntpd stop
关闭 ntpd：[确定]
[[email protected] ~]# ntpdate 0.centos.pool.ntp.org
8 Nov 11:13:09 ntpdate[4618]: adjust time server 202.112.29.82 offset -0.037618 sec
[[email protected] ~]# service ntpd start
正在启动 ntpd：[确定]