Ntp
ntpdate -d 似乎成功，但 ntpdate 返回沒有合適的伺服器
我有一個未執行 ntpd 的系統，我正在嘗試使用 ntpdate 更新時鐘。該系統是一個似乎基於 CentOS 6 的設備。
當我執行時
ntpdate 0.pool.ntp.org，我得到：8 Sep 17:52:05 ntpdate[7445]: no server suitable for synchronization found但是，當我這樣做時
ntpdate -d 0.pool.ntp.org，我得到：8 Sep 17:55:14 ntpdate[9499]: ntpdate 4.2.2p1@1.1570-o Fri Nov 18 13:21:21 UTC 2011 (1) Looking for host 0.pool.ntp.org and service ntp host found : 4.53.160.75 transmit(4.53.160.75) receive(4.53.160.75) transmit(4.53.160.75) receive(4.53.160.75) transmit(4.53.160.75) receive(4.53.160.75) transmit(4.53.160.75) receive(4.53.160.75) transmit(4.53.160.75) transmit(64.16.214.60) receive(64.16.214.60) transmit(64.16.214.60) receive(64.16.214.60) transmit(64.16.214.60) receive(64.16.214.60) transmit(64.16.214.60) receive(64.16.214.60) transmit(64.16.214.60) transmit(54.236.224.171) receive(54.236.224.171) transmit(54.236.224.171) receive(54.236.224.171) transmit(54.236.224.171) receive(54.236.224.171) transmit(54.236.224.171) receive(54.236.224.171) transmit(54.236.224.171) transmit(50.22.155.163) receive(50.22.155.163) transmit(50.22.155.163) receive(50.22.155.163) transmit(50.22.155.163) receive(50.22.155.163) transmit(50.22.155.163) receive(50.22.155.163) transmit(50.22.155.163) server 4.53.160.75, port 123 stratum 2, precision -23, leap 00, trust 000 refid [4.53.160.75], delay 0.03160, dispersion 0.00005 transmitted 4, in filter 4 reference time: d7b867d0.f9841075 Mon, Sep 8 2014 17:37:20.974 originate timestamp: d7b86c03.b6a49dae Mon, Sep 8 2014 17:55:15.713 transmit timestamp: d7b86c02.7e12a51e Mon, Sep 8 2014 17:55:14.492 filter delay: 0.03189 0.03188 0.03172 0.03160 0.00000 0.00000 0.00000 0.00000 filter offset: 1.218061 1.217856 1.218023 1.217968 0.000000 0.000000 0.000000 0.000000 delay 0.03160, dispersion 0.00005 offset 1.217968 server 64.16.214.60, port 123 stratum 2, precision -23, leap 00, trust 000 refid [64.16.214.60], delay 0.04886, dispersion 0.00006 transmitted 4, in filter 4 reference time: d7b86425.55948a73 Mon, Sep 8 2014 17:21:41.334 originate timestamp: d7b86c03.f7d91219 Mon, Sep 8 2014 17:55:15.968 transmit timestamp: d7b86c02.bed42c3c Mon, Sep 8 2014 17:55:14.745 filter delay: 0.04919 0.04892 0.04912 0.04886 0.00000 0.00000 0.00000 0.00000 filter offset: 1.210967 1.210879 1.210967 1.210836 0.000000 0.000000 0.000000 0.000000 delay 0.04886, dispersion 0.00006 offset 1.210836 server 54.236.224.171, port 123 stratum 3, precision -20, leap 00, trust 000 refid [54.236.224.171], delay 0.04878, dispersion 0.00011 transmitted 4, in filter 4 reference time: d7b864eb.b06fee7d Mon, Sep 8 2014 17:24:59.689 originate timestamp: d7b86c04.2b9d2547 Mon, Sep 8 2014 17:55:16.170 transmit timestamp: d7b86c02.f1e80bed Mon, Sep 8 2014 17:55:14.944 filter delay: 0.04977 0.04950 0.04878 0.04887 0.00000 0.00000 0.00000 0.00000 filter offset: 1.214091 1.214069 1.213755 1.213750 0.000000 0.000000 0.000000 0.000000 delay 0.04878, dispersion 0.00011 offset 1.213755 server 50.22.155.163, port 123 stratum 2, precision -23, leap 00, trust 000 refid [50.22.155.163], delay 0.07384, dispersion 0.00005 transmitted 4, in filter 4 reference time: d7b869c9.2b3f3d0b Mon, Sep 8 2014 17:45:45.168 originate timestamp: d7b86c04.75472e97 Mon, Sep 8 2014 17:55:16.458 transmit timestamp: d7b86c03.384a83b1 Mon, Sep 8 2014 17:55:15.219 filter delay: 0.07408 0.07414 0.07384 0.07387 0.00000 0.00000 0.00000 0.00000 filter offset: 1.214115 1.214122 1.214012 1.214069 0.000000 0.000000 0.000000 0.000000 delay 0.07384, dispersion 0.00005 offset 1.214012 8 Sep 17:55:15 ntpdate[9499]: step time server 4.53.160.75 offset 1.217968 sec根據我之前的搜尋，這個結果（帶有各種 receive() 行和偏移量）表明它正在與遠端 NTP 伺服器正確通信（沒有被防火牆阻止）。那麼，為什麼我執行它時它不更新我的時鐘？
嘗試將其執行為：
ntpdate -u 0.pool.ntp.org
-u配置為使用非特權埠，當您使用該選項ntpdate時它總是這樣做。-d
-u因此，它適用於-d但不是沒有，我會仔細檢查你的防火牆。從手冊頁：
-u指示 ntpdate 將非特權埠用於傳出數據包。這在阻止傳入流量到特權埠的防火牆後面並且您希望與防火牆之外的主機同步時最有用。請注意，-d 選項始終使用非特權埠。