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--- wiki:centos_ntp_server [2019/10/04 13:51] – walkeradmin
+++ wiki:centos_ntp_server [2023/03/09 22:35] (current) – external edit 127.0.0.1
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 In this example, I have three CentOS systems, and the first will be the NTP server, with the second two being NTP clients. I did this for a <color #00a2e8>Split ABR Encoding</color> system, so I did not have to rely on any external NTP servers.
+\\
+\\
+If you have installed the OS from a MediKind .ISO (as opposed to using the CentOS minimal .ISO) then you will have to do the following:
+<file>
+. Create the CentOS-Base.repo in /etc/yum.repos.d
+. Ensure you have access to the internet
+. Ensure DNS is running (or you won't connect to any repos)
+You will still have to perform steps 2 and 3 if you used the CentOS Minimal install.
+</file>
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+If the OS was installed using a MediKind .iso, you may have to remove ChronyD:
+    systemctl stop chronyd
+    systemctl disable chronyd
+Now install NTP:
+    yum install ntp
+The NTP settings will have to be modified, you will need to edit the following file.
+    vim /etc/ntp.conf
+Find the list of public servers:
+<file>
+# Use public servers from the pool.ntp.org project.
+# Please consider joining the pool (http://www.pool.ntp.org/join.html).
+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
+</file>
+\\
+When the OS was installed, if hte correct regional settings were selected, this ntp list will be fine. You can find local servers to you using the url https://www.ntppool.org/en/use.html.
+\\
+\\
+You can restrict the range of IPs that can ask for NTP services by using the following:
+<file>
+# Hosts on local network are less restricted.
+restrict 10.43.30.0 mask 255.255.255.0 nomodify notrap
+This will restrict NTP services to IP Addresses in the 10.43.30.x range
+</file>
+Ensure that CentOS is using the correct timezone:
+<file>
+cd /etc
+rm localtime
+ls /usr/share/zoneinfo/
+ln -s /usr/share/zoneinfo/[expected_time_zone] localtime (I normally use GMT or UTC)
+</file>
+Finally start and enable NTP services.
+\\
+<file>
+systemctl start ntpd
+systemctl enable ntpd
+</file>
+At this point, the server should have the correct time (if using UTC, depending on the time of year it could look 1 hour off). If the time is way out, ensure you have internet access, that the firewall is not blocking NTP and that your timezone is correct.
+\\
+\\
+==== NTP Clients ====
+----
+If the OS was installed using a MediKind .iso, you may have to remove ChronyD:
+    systemctl stop chronyd
+    systemctl disable chronyd
+Now install NTP:
+    yum install ntp
+The NTP settings will have to be modified, you will need to edit the following file.
+    vim /etc/ntp.conf
+Find the list of public servers:
+<file>
+# Use public servers from the pool.ntp.org project.
+# Please consider joining the pool (http://www.pool.ntp.org/join.html).
+server 10.43.30.11 iburst
+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
+</file>
+In the server list, we have added the following line, as the first server in the list:
+\\
+    server 10.43.30.11 iburst - This is the IP Address of the NTP server we previously configured.
+\\
+When the OS was installed, if the correct regional settings were selected, this NTP list will be fine. You can find local servers to you using the url https://www.ntppool.org/en/use.html.
+\\
+\\
+Ensure that CentOS is using the correct timezone:
+<file>
+cd /etc
+rm localtime
+ls /usr/share/zoneinfo/
+ln -s /usr/share/zoneinfo/[expected_time_zone] localtime (I normally use GMT or UTC)
+</file>
+Finally start and enable NTP services.
+\\
+<file>
+systemctl start ntpd
+systemctl enable ntpd
+</file>
+Use the command line 'date' to check the time and date of each server, and check they are the same. Synchronization normally only takes up to 10 seconds.
+\\
+<file>
+# date
+Fri Oct  4 13:45:46 UTC 2019
+</file>
+\\
+\\