CentOS查看当前系统所用的时区，设置ntpd授时服务之前先调整好时区，例如集群中提供授时服务主机IP为192.168.3.1
[linuxidc@master conf]$ date -R
Mon, 08 Jun 2015 19:24:39 +0800
若不是我们的时区，将时区设置为东8区的时间
cp /usr/share/zoneinfo/Asia/Shanghai /etc/localtime
Mon, 08 Jun 2015 19:24:39 +0800
修改ntpd服务配置文件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
# 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
restrict 192.168.3.0 mask 255.255.255.0 nomodify
restrict 0.0.0.0 mask 0.0.0.0 nomodify notrap noquery notrust
# Use public servers from the pool.ntp.org project.
# Please consider joining the pool ().
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
server 127.127.1.0
#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
重新启动 service ntpd start 服务作为集群中提供授时服务的主机，先利用网络时间更新好授时主机192.168.3.1的时间
ntpdate 0.cn.pool.ntp.org
/sbin/hwclock -w
然后在集群上其他主机上设置crontab服务，同步更新自己时间
crontab -e
10 16 * * * (/usr/sbin/ntpdate 192.168.3.1 && /sbin/hwclock -w) >> /var/log/ntpdate.log
#每天下午16:10同步授时主机上的时间