[CENTOS] A memorandum with NTP (chrony) set

A memorandum with NTP (chrony) set

When I was operating with the default settings of the server, I noticed that the time synchronization was out of sync, so the procedure for setting NTP is shown below.

environment

$ cat /etc/redhat-release 
CentOS Linux release 8.1.1911 (Core) 

Setup steps

$ cp -pi /etc/chrony.conf{,.org}
$ vi /etc/chrony.conf
$ diff chrony.conf chrony.conf.org 
3,5c3
< #pool 2.centos.pool.ntp.org iburst
< pool ntp.nict.jp iburst
< pool ntp.jst.mfeed.ad.jp iburst
---
> pool 2.centos.pool.ntp.org iburst
$ systemctl restart chronyd.service
$ systemctl enable chronyd.service 
Created symlink /etc/systemd/system/multi-user.target.wants/chronyd.service → /usr/lib/systemd/system/chronyd.service. 

Note

Who is "2.centos.pool.ntp.org"? ??

I looked it up, but I didn't understand ...

Whois information was not returned.

$ whois 2.centos.pool.ntp.org
NOT FOUND
>>> Last update of WHOIS database: 2020-09-14T04:47:48Z <<<

Access to Public Interest Registry WHOIS information is provided to assist persons in determining the contents of a domain name registration record in the Public Interest Registry registry database. The data in this record is provided by Public Interest Registry for informational purposes only, and Public Interest Registry does not guarantee its accuracy. This service is intended only for query-based access. You agree that you will use this data only for lawful purposes and that, under no circumstances will you use this data to (a) allow, enable, or otherwise support the transmission by e-mail, telephone, or facsimile of mass unsolicited, commercial advertising or solicitations to entities other than the data recipient's own existing customers; or (b) enable high volume, automated, electronic processes that send queries or data to the systems of Registry Operator, a Registrar, or Afilias except as reasonably necessary to register domain names or modify existing registrations. All rights reserved. Public Interest Registry reserves the right to modify these terms at any time. By submitting this query, you agree to abide by this policy.

The Registrar of Record identified in this output may have an RDDS service that can be queried for additional information on how to contact the Registrant, Admin, or Tech contact of the queried domain name.

Since nslookup is also answered by the cache DNS server, not the authoritative server, the location cannot be specified ...

$ nslookup 2.centos.pool.ntp.org
Server:         118.27.60.132
Address:        118.27.60.132#53

Non-authoritative answer:
Name:   2.centos.pool.ntp.org
Address: 79.143.250.119
Name:   2.centos.pool.ntp.org
Address: 193.25.222.240
Name:   2.centos.pool.ntp.org
Address: 64.225.34.103
Name:   2.centos.pool.ntp.org
Address: 66.85.78.80
Name:   2.centos.pool.ntp.org
Address: 2606:4700:f1::123
Name:   2.centos.pool.ntp.org
Address: 2400:8500:1801:418:a118:27:37:521
Name:   2.centos.pool.ntp.org
Address: 2001:470:fc6f::123
Name:   2.centos.pool.ntp.org
Address: 2606:4700:f1::1