CentOS 7 搭建ntp时钟服务器的步骤详解

# cat /etc/redhat-release 
CentOS Linux release 7.0.1406 (Core)

# yum install ntp ntpdate -y

server time.windows.com
server s2m.time.edu.cn
server 0.asia.pool.ntp.org
server 1.asia.pool.ntp.org
server 2.asia.pool.ntp.org
server 3.asia.pool.ntp.org
server 127.127.1.0 iburst  local clock 当外部时间不可用时，使用本地时间。
restrict 192.168.137.1 mask 255.255.255.0 nomodify  允许更新的IP地址段

systemctl start ntpd
systemctl enable ntpd.service 设置开机启动服务

# ntpq -p

  remote   refid  st t when poll reach delay offset jitter
==============================================================================
 211.138.200.209 .INIT.   16 u - 64 0 0.000 0.000 0.000
 ns.pku.edu.cn .INIT.   16 u - 64 0 0.000 0.000 0.000
 211.138.200.208 .INIT.   16 u - 64 0 0.000 0.000 0.000
 nipper.paina.jp .INIT.   16 u - 64 0 0.000 0.000 0.000
 send.mx.cdnetwo .INIT.   16 u - 64 0 0.000 0.000 0.000
*LOCAL(0)  .LOCL.   5 l 52 64 1 0.000 0.000 0.000

# date -R
Fri, 15 Jul 2016 15:28:34 +0800

# date 
Fri Jul 15 15:31:22 CST 2016
# ntpdate 192.168.137.3
15 Jul 15:33:04 ntpdate[63912]: step time server 192.168.137.3 offset -4.492463 sec

crontab -e
00 01 * * * root /usr/sbin/ntpdate 192.168.137.3; /sbin/hwclock -w