centos7 ntp时间同步
yum install ntp -y
#启动
systemctl start ntpd.service
#加入开机自启动
systemctl enable ntpd.service
centos6 ntp时间同步
/etc/init.d/ntpd start
#加入开机自启动
vim /etc/rc.local
/etc/init.d/ntpd start