Build a Public NTP Server Rumi, March 30, 2020 Install NTPd and Configure NTP server for time adjustment. [root@dlp ~]# yum -y install ntp [root@dlp ~]# vi /etc/ntp.conf # line 18: add the network range you allow to receive requests publicly restrict 0.0.0.0 mask 128.0.0.0 nomodify notrap # change servers for synchronization #server 0.centos.pool.ntp.org iburst #server 1.centos.pool.ntp.org iburst #server 2.centos.pool.ntp.org iburst #server 3.centos.pool.ntp.org iburst server bsti1.time.gov.bd iburst server bsti2.time.gov.bd iburst [root@dlp ~]# systemctl start ntpd [root@dlp ~]# systemctl enable ntpd If Firewalld is running, allow NTP service. NTP uses 123/UDP. [root@dlp ~]# firewall-cmd --add-service=ntp --permanent success [root@dlp ~]# firewall-cmd --reload success Verify it works normally like follows. [root@dlp ~]# ntpq -p remote refid st t when poll reach delay offset jitter ============================================================================== +ntp1.jst.mfeed. 172.29.1.100 2 u 29 64 1 18.826 -0.126 0.000 +ntp2.jst.mfeed. 172.29.2.50 2 u 28 64 1 21.592 0.018 0.000 *ntp3.jst.mfeed. 133.243.236.18 2 u 28 64 1 22.666 -1.033 0.000 Next verify query an NTP server under Windows: C:\> w32tm /stripchart /computer:foo Tracking foo [1.2.3.4]. The current time is 19/07/2012 17:39:48 (local time). 17:39:48 d:-00.0000840s o:-25.3004160s [@ | ] 17:39:50 d:-00.0000680s o:-25.3070080s [@ | ] 17:39:52 d:-00.0000690s o:-25.2987405s [@ | ] 17:39:54 d:-00.0000680s o:-25.3071530s [@ | ] 17:39:56 d:-00.0000690s o:-25.2993985s [@ | ] 17:39:58 d:-00.0000680s o:-25.3070270s [@ | Wireshark shows NTP packets being generated by this. Some versions of w32tm have a /query option C:\>w32tm /stripchart /computer:us.pool.ntp.org /dataonly /samples:5 Tracking us.pool.ntp.org [208.87.221.228:123]. Collecting 5 samples. The current time is 19/07/2012 18:36:32. 18:36:32, +03.3575094s 18:36:34, +03.3573679s 18:36:37, +03.3572986s 18:36:39, +03.3570290s 18:36:41, +03.3565357s You can parallel check the NTP system using windows GUI tool such as Bytefusion’s NTPQuery. or Galleon Src: https://www.server-world.info/en/note?os=CentOS_7&p=ntp&f=1 https://superuser.com/questions/451018/how-can-i-query-an-ntp-server-under-windows/451066 Administrations Configurations (Linux) NTPNTPD