1、 NTP简介
NTP（Network Time Protocol，网络时间协议）是用来使网络中的各个计算机时间同步的一种协议。它的用途是把计算机的时钟同步到世界协调时UTC，其精度在局域网内可达0.1ms，在互联网上绝大多数的地方其精度可以达到1-50ms。
NTP服务器就是利用NTP协议提供时间同步服务的。
2、NTP服务器安装
[root@XXX ~]# rpm -aq ntp
[root@XXX ~]#
[root@XXX ~]# yum -y install ntp
[root@XXX ~]# rpm -aq ntp
ntp-4.2.6p5-10.el6.centos.1.x86_64
3、配置NTP服务（结果如下：）
×××为添加项
绿色为注释项
[root@XXX ~]# cat /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
# 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 注释掉
restrict -6 default kod nomodify notrap nopeer noquery
restrict default nomodify 添加此行
# 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
# 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 》注释掉
#server 3.centos.pool.ntp.org iburst —— |
server ntp1.aliyun.com 添加可用源
server time.nist.gov
#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
[root@XXX ~]#
4、启动NTP服务器
[root@XXX ~]# /etc/init.d/ntpd start
正在启动 ntpd： [确定]
[root@XXX ~]# ntpq -p
remote refid st t when poll reach delay offset jitter
==============================================================================
time5.aliyun.co .INIT. 16 u - 64 0 0.000 0.000 0.000
india.colorado. .NIST. 1 u 2 64 0 0.000 0.000 0.000
[root@XXX ~]# ntpstat
synchronised to NTP server (182.92.12.11) at stratum 3
time correct to within 8024 ms
polling server every 64 s
[root@XXX ~]# ntpdate 10.0.0.86
7 Jun 11:11:07 ntpdate[2286]: the NTP socket is in use, exiting
[root@XXX ~]#
5、客户机时间同步
[root@nfs ~]# date
2016年 06月 07日 星期二 09:11:09 CST
[root@nfs ~]# ntpdate 10.0.0.86
7 Jun 11:16:02 ntpdate[4301]: step time server 10.0.0.86 offset 7477.470757 sec
[root@nfs ~]# date
2016年 06月 07日 星期二 11:16:05 CST
[root@nfs ~]# crontab -e
#时间同步
* * * * * ntpdate 10.0.0.86