测试环境：

NTPserver 192.168.1.252

NTPclient 192.168.1.251

准备工作：

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：

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).

driftfile /var/lib/ntp/drift
restrict default ignore 设置默认策略为拒绝所有访问方式的请求
# 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

# 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
server 1.centos.pool.ntp.org 设置同步服务器
server 2.centos.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

restrict 0.centos.pool.ntp.org nomodify notrap noquery
restrict 1.centos.pool.ntp.org nomodify notrap noquery 允许与上层服务器同步时间
restrict 2.centos.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. 
server 127.127.1.0 # local clock
fudge 127.127.1.0 stratum 10 外界同步源无法联系时，使用本地时间为同步服务

# 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 loops

***************************************************************

三.与上层服务器同步时间：

[root@PXEServer ~]# ntpdate 0.CentOS.pool.ntp.org
8 Nov 11:13:09 ntpdate[4618]: adjust time server 202.112.29.82 offset -0.037618 sec

四.开启NTP服务：

[root@PXEServer ~]# service ntpd start
正在启动 ntpd：[确定]

五.在客户机测试时间同步：

[root@node ~]# ntpdate 192.168.1.252
8 Nov 12:09:36 ntpdate[9118]: adjust time server 192.168.1.252 offset -0.035431 sec

其他：

设置TimeZone：

ln -sf /usr/share/zoneinfo/posix/Asia/Shanghai /etc/localtime

问题1：

[root@PXEServer ~]# 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：

[root@PXEServer ~]# service ntpd stop
关闭 ntpd：[确定]
[root@PXEServer ~]# ntpdate 0.centos.pool.ntp.org
8 Nov 11:13:09 ntpdate[4618]: adjust time server 202.112.29.82 offset -0.037618 sec

[root@PXEServer ~]# service ntpd start
正在启动 ntpd：[确定]