1.安装软件包：
Yum install ntp
Ntp的配置文件是/etc/ntp.conf，工作目录是/etc/ntp/,接着编辑/etc/ntp.conf文件。
2.服务端配置：
IP:192.168.1.110
编辑/etc/ntp.conf文件：
[root@rhel5 ~]# cat /etc/ntp.conf
# 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
# Hosts on local network are less restricted.
restrict 192.168.1.0 mask 255.255.255.0 nomodify notrap(允许内网通讯)
restrict 0.0.0.0 mask 0.0.0.0 nomodify notrap noquery notrust(禁止其他ip来更新时间)
# Use public servers from the pool.ntp.org project.
# Please consider joining the pool (
http://www.pool.ntp.org/join.html).
server 0.pool.ntp.org(redhat默认情况下是server 0.redhat.pool.ntp.org)
server 1.pool.ntp.org(redhat默认情况下是server 1.redhat.pool.ntp.org)
server 2.pool.ntp.org(redhat默认情况下是server 2.redhat.pool.ntp.org)
#broadcast 192.168.1.255 key 42 # broadcast server
#broadcastclient # broadcast client
#broadcast 224.0.1.1 key 42 # multicast server
#multicastclient 224.0.1.1 # multicast client
#manycastserver 239.255.254.254 # manycast server
#manycastclient 239.255.254.254 key 42 # manycast client
# 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
fudge 127.127.1.0 stratum 10
# Drift file. Put this in a directory which the daemon can write to.
# No symbolic links allowed, either, since the daemon updates the file
# by creating a temporary in the same directory and then rename()'ing
# it to the file.
driftfile /var/lib/ntp/drift (driftfile 选项，则指定了用来保存系统时钟频率偏差的文件， ntpd程序使用它来自动地补偿时钟的自然漂移， 从而使时钟即使在切断了外来时源的情况下，仍能保持相当的准确度)
# 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
Logfile /var/log/ntp.log(定义日志信息)
# Specify the key identifier to use with the ntpq utility.
#controlkey 8
restrict 0. pool.ntp.org mask 255.255.255.255 nomodify notrap noquery
restrict 1. pool.ntp.org mask 255.255.255.255 nomodify notrap noquery
restrict 1. pool.ntp.org mask 255.255.255.255 nomodify notrap noquery
如果restric 后面不带参数，表示可以允许全部权限.以上三个影响/etc/ntp/ step-tickers这个文件，它会随着/etc/ntp.conf文件的变化而变化。
/etc/sysconfig/clock是用来设置时区的文件，例如：
[root@rhel5 ntp]# cat /etc/sysconfig/clock
# The ZONE parameter is only evaluated by system-config-date.
# The timezone of the system is defined by the contents of /etc/localtime.
ZONE="Asia/Chongqing"
UTC=true
ARC=false
/usr/share/zoneinfo这个目录里规定了各主要时区的时间设定文件，例如重庆：/usr/share/zoneinfo/Asia/Chongqing
如果想把同步好的时间写入BIOS里，就要设置/etc/sysconfig/ntp文件，将其中的SYNC_HWCLOCK=no更改为SYNC_HWCLOCK=yes。
启动ntp服务：
[root@rhel5 ntp]# service ntpd restart
Shutting down ntpd: [ OK ]
ntpd: Synchronizing with time server: [ OK ]
Starting ntpd: [ OK ]
[root@rhel5 ntp]#chkconfig ntpd on
3.客户端的设置：
可以通过使用system-config-time来设置，将其中的时间服务器更改为192.168.1.110即可，或者使用ntpdate -u 192.168.1.110来和时间服务器同步。切记更改完以后要重新启动NTP服务，使其生效。或者使用crontab -e来编辑：
*/5 * * * * /usr/sbin/ntpdate -u 192.168.1.110 表示每五分钟同步一次。重启crond服务即可。
可以使用ntpq –p查看同步状态。
