1、概述
NTP（Network Time Protocol）是用来使计算机时间同步化的一种协议，它可以使计算机对其服务器或时钟源（如石英钟，GPS等等)做同步化，它可以提供高精准度的时间校正（LAN上与标准间差小于1毫秒，WAN上几十毫秒），且可介由加密确认的方式来防止恶毒的协议攻击。（来自 百度百科）
2、集群状况
现在又4台Ubuntu主机，选择其中一台作为提供ntp服务的主机（server01）。
3、安装ntp服务
在提供ntp服务的主机上安装ntpserver:
apt-get install ntp
4、配置ntp服务参数
# /etc/ntp.conf, configuration for ntpd; see ntp.conf(5) for help driftfile /var/lib/ntp/ntp.drift # Enable this if you want statistics to be logged. #statsdir /var/log/ntpstats/ statistics loopstats peerstats clockstats filegen loopstats file loopstats type day enable filegen peerstats file peerstats type day enable filegen clockstats file clockstats type day enable # Specify one or more NTP servers. # Use servers from the NTP Pool Project. Approved by Ubuntu Technical Board # on 2011-02-08 (LP: #104525). See http://www.pool.ntp.org/join.html for # more information. #server 0.ubuntu.pool.ntp.org #server 1.ubuntu.pool.ntp.org #server 2.ubuntu.pool.ntp.org #server 3.ubuntu.pool.ntp.org # Use Ubuntu's ntp server as a fallback. #server ntp.ubuntu.com server 127.127.1.0 minpoll 4 maxpoll 5 fudge 127.127.1.0 stratum 2 # Access control configuration; see /usr/share/doc/ntp-doc/html/accopt.html for # details. The web page <http://support.ntp.org/bin/view/Support/AccessRestrictions> # might also be helpful. # # Note that "restrict" applies to both servers and clients, so a configuration # that might be intended to block requests from certain clients could also end # up blocking replies from your own upstream servers. # By default, exchange time with everybody, but don't allow configuration. restrict -4 default kod notrap nomodify nopeer noquery restrict -6 default kod notrap nomodify nopeer noquery # Local users may interrogate the ntp server more closely. restrict 127.0.0.1 restrict ::1 # Clients from this (example!) subnet have unlimited access, but only if # cryptographically authenticated. #restrict 192.168.123.0 mask 255.255.255.0 notrust ...skipping one line # If you want to provide time to your local subnet, change the next line. # (Again, the address is an example only.) #broadcast 192.168.123.255 # If you want to listen to time broadcasts on your local subnet, de-comment the # next lines. Please do this only if you trust everybody on the network! #disable auth #broadcastclient
5、测试ntp服务
在提供ntp服务的服务器上运行：
ntpdate -q 127.0.0.1
得到结果：
server 127.0.0.1, stratum 3, offset -0.000018, delay 0.02568 2 Sep 16:11:07 ntpdate[5882]: adjust time server 127.0.0.1 offset -0.000018 sec
说明启动正常。
6、其它主机用它来同步时间
在需要同步时间的主机上执行：
ntpdate server01
见结果如下：
2 Sep 15:53:12 ntpdate[8420]: adjust time server 192.168.1.154 offset 0.497131 sec
server01可以是主机名也可以是ip。
7、设置定时同步时间
使用crontab：
crontab -e
设置一小时校准一次：
* */1 * * * /usr/sbin/ntpdate server01