一台centos最小化安装的机器，yum -y install ntpdate安装ntpdate同步时间。执行ntpdate time.nist.gov，无法与服务器同步时间，并出现以下错误：ntpdate[1897]: no server suitable for synchronization found

执行：ntpdate -d time.nist.gov命令调试的时候，打印结果如下：

ntpdate[1976]: ntpdate 4.2.6p5@1.2349-o Mon Feb  6 07:22:46 UTC 2017 (1)

Looking for host time.nist.gov and service ntphost found : nist1-lnk.binary.nettransmit(216.229.0.179)transmit(216.229.0.179)transmit(216.229.0.179)transmit(216.229.0.179)transmit(216.229.0.179)

216.229.0.179: Server dropped: no data

意思是客户端发往服务器的transmit包无响应，windows环境下ping time.nist.gov可以正常解析服务器的ip，而contos客户端ping time.nist.gov则不能正常解析域名的ip。 试用命令ntpdate -d 216.229.0.179调试，打印结果如下：                                                                                                    ntpdate[1977]: ntpdate 4.2.6p5@1.2349-o Mon Feb  6 07:22:46 UTC 2017 (1)

Looking for host 216.229.0.179 and service ntphost found : nist1-lnk.binary.nettransmit(216.229.0.179)receive(216.229.0.179)transmit(216.229.0.179)receive(216.229.0.179)transmit(216.229.0.179)receive(216.229.0.179)transmit(216.229.0.179)transmit(216.229.0.179)server 216.229.0.179, port 123stratum 1, precision -29, leap 00, trust 000refid [ACTS], delay 0.25931, dispersion 8.00000transmitted 4, in filter 4reference time:    dc5d5e5a.4c1e35c6  Sun, Feb 26 2017 22:02:02.297originate timestamp: dc5d5e8b.668a82f6  Sun, Feb 26 2017 22:02:51.400transmit timestamp:  dc57bb36.5fc3fc0b  Wed, Feb 22 2017 15:24:38.374filter delay:  0.30286  0.26347  0.25931  0.00000          0.00000  0.00000  0.00000  0.00000 filter offset: 369493.1 369493.1 369493.1 0.000000         0.000000 0.000000 0.000000 0.000000delay 0.25931, dispersion 8.00000offset 369493.143347

说明使用IP方式，可以同步服务器的时间。执行命令：

ntpdate 216.229.0.179

26 Feb 22:03:13 ntpdate[1978]: step time server 216.229.0.179 offset 369493.008399 sec 解决问题