Setup FQDN for Ubuntu 18.04 LTS
The Fully Qualified Domain Name (FQDN) of the system is the name that the resolver returns for the host name. You can check the FQDN using commend: hostname –fqdn or hostname -f. The domain name using: dnsdomainname command.
Example:
127.0.1.1 abc.example.com abc
Where is abc – hostname, example.com – domain name.