# yum install ntp wget http://mirrors.163.com/centos/5/os/i386/CentOS/ntp-4.2.2p1-15.el5.centos.i386.rpm rpm -ivh ntp-4.2.2p1-15.el5.centos.i386.rpm
2. 立即更新时间
sudo /sbin/ntpdate time.nist.gov
3. 每天定时更新时间
sudo vi /etc/crontab 0 * * * * /sbin/ntpdate time.nist.gov