View source for CLI - NTP

__FORCETOC__
=== ntp ===
The Network Time Protocol (NTP) is a networking protocol for clock synchronization between computer systems over packet-switched, variable-latency data networks.<ref>https://en.wikipedia.org/wiki/Network_Time_Protocol</ref> ''Note that the system has already an NTP server that is "ntp.ubuntu.com".''
==== Verifying NTP ====
To verify the NTP servers, enter <code>show ntp server</code> in the user mode. If none of the servers exists, it indicates that there are no NTP servers except for the default.
 LYSH@MyHostName# show ntp servers
To show the status of the Time synchronization, <code>show ntp status</code> in the user mode. It shows the status of, when, and where the time was synchronized.
<pre>
LYSH@MyHostName# show ntp status
● systemd-timesyncd.service - Network Time Synchronization
     Loaded: loaded (/lib/systemd/system/systemd-timesyncd.service; enabled; vendor preset: enabled)
     Active: active (running) since Tue 2021-04-27 13:12:30 KST; 10s ago
       Docs: man:systemd-timesyncd.service(8)
   Main PID: 18992 (systemd-timesyn)
     Status: "Connecting to time server [2001:67c:1560:8003::c8]:123 (ntp.ubuntu.com)."
      Tasks: 2 (limit: 9387)
     Memory: 1.6M
     CGroup: /system.slice/systemd-timesyncd.service
             └─18992 /lib/systemd/systemd-timesyncd
</pre>
You can also verify the Time synchronization by using the <code>show datetime</code> commmand.
<pre>
LYSH@MyHostName# show datetime
               Local time: Tue 2021-04-27 13:32:46 KST
           Universal time: Tue 2021-04-27 04:32:46 UTC
                 RTC time: Tue 2021-04-27 04:32:46
                Time zone: Asia/Seoul (KST, +0900)
System clock synchronized: yes
              NTP service: active
          RTC in local TZ: no
</pre>

==== add / delete ====
You can configure the NTP servers. If you add an NTP server, the system synchronizes the time using added NTP server. If the Time synchronization failed from a server, the system tries to the next server.
<pre>
LYSH@MyHostName# configure
configure# ntp add asia.pool.ntp.org
configure# exit
LYSH@MyHostName# show ntp servers
NTP Servers                   : asia.pool.ntp.org
</pre>

You can see the status of the time synchronization to a time server by the <code>show ntp status</code> command. If the "Status" shows "Idle", it indicates the system couldn't synchronize to one of the NTP servers.
<pre>
LYSH@MyHostName# show ntp status
● systemd-timesyncd.service - Network Time Synchronization
     Loaded: loaded (/lib/systemd/system/systemd-timesyncd.service; enabled; vendor preset: enabled)
     Active: active (running) since Tue 2021-04-27 13:10:36 KST; 12s ago
       Docs: man:systemd-timesyncd.service(8)
   Main PID: 18321 (systemd-timesyn)
     Status: "Initial synchronization to time server 157.119.108.165:123 (asia.pool.ntp.org)."
      Tasks: 2 (limit: 9387)
     Memory: 1.6M
     CGroup: /system.slice/systemd-timesyncd.service
             └─18321 /lib/systemd/systemd-timesyncd
</pre>

To remove one of the NTP servers, enter the <code>ntp delete {ntp-server-name}</code> in the configuration mode.
<pre>
LYSH@MyHostName# configure
configure# ntp delete asia.pool.ntp.org
configure# exit
</pre>

==== enable / disable ====
You can disable the System clock synchronizing using the NTP server.
<pre>
LYSH@MyHostName# configure
configure# ntp disable
Local time: Tue 2021-04-27 10:26:03 KST
           Universal time: Tue 2021-04-27 01:26:03 UTC
                 RTC time: Tue 2021-04-27 01:26:03
                Time zone: Asia/Seoul (KST, +0900)
System clock synchronized: no
              NTP service: inactive
          RTC in local TZ: no
</pre>

You can also enable it. Note that the status of the "System clock synchronized" may show "inactive" for a while after enabling the NTP and the status will be changed to "active" in few seconds.
<pre>
LYSH@MyHostName# configure
configure# ntp enable
  Local time: Tue 2021-04-27 10:26:03 KST
           Universal time: Tue 2021-04-27 01:26:03 UTC
                 RTC time: Tue 2021-04-27 01:26:03
                Time zone: Asia/Seoul (KST, +0900)
  System clock synchronized: active
              NTP service: active
          RTC in local TZ: no
</pre>

=== datetime ===
To show the system time and date, enter the <code>show datetime</code> command.
<pre>
LYSH@MyHostName# show datetime
               Local time: Tue 2021-04-27 13:32:46 KST
           Universal time: Tue 2021-04-27 04:32:46 UTC
                 RTC time: Tue 2021-04-27 04:32:46
                Time zone: Asia/Seoul (KST, +0900)
System clock synchronized: yes
              NTP service: active
          RTC in local TZ: no
</pre>


To change the system time and date, enter the <code>datetime {format}</code>. The format must be 'yyyy-mm-dd hh24:mi:ss'.<br>
Note that if you manually change the system time and date while the NTP is enabled, you encounter the "''Failed to set time: Automatic time synchronization is enabled''" error. Therefore you need to disable the NTP before configuring the system time and date manually.
 LYSH@MyHostName# configure
 configure# datetime 2021-04-27 13:00:00
               Local time: Tue 2021-04-27 13:00:00:49 KST
           Universal time: Tue 2021-04-27 04:00:00 UTC
                 RTC time: Tue 2021-04-27 04:00:00
                Time zone: Asia/Seoul (KST, +0900)
 System clock synchronized: yes
              NTP service: active
          RTC in local TZ: no

=== References ===