how to map ip address to domain name in ubuntu

ubuntu@nonames:/etc$  hostname --fqdn
nonames.com
ubuntu@nonames:/etc$

Setting your hostname:

• You’ll want to edit /etc/hostname with your new hostname.
• Then, run sudo hostname $(cat /etc/hostname).

Setting your domain:

• Then, in /etc/resolvconf/resolv.conf.d/head, you’ll add then line domain your.domain.name (not your FQDN, just the domainname).
• Then, run sudo resolvconf -u to update your /etc/resolv.conf (alternatively, just reproduce the previous change into your /etc/resolv.conf).

Both:

Finally, update your /etc/hosts file. There should be at least one line starting with one of your IP (loopback or not), your FQDN and your hostname. grepping out ipv6 addresses, your hosts file could look like this:

127.0.0.1 localhost
1.2.3.4 service.domain.com service

ubuntu@nonames:/etc$ hostnamectl
   Static hostname: nonames.com
         Icon name: computer-vm
           Chassis: vm
        Machine ID: 0edddc7ee9394aec8b44c30670b611c5
           Boot ID: 4bdaebcdf36a487792fc02abf1a6b958
    Virtualization: xen
  Operating System: Ubuntu 18.04.3 LTS
            Kernel: Linux 4.15.0-1060-aws
      Architecture: x86-64