AH00558: Could not reliably determine the server's fully qualified domain name fix error

 REFERENCES: 

https://www.digitalocean.com/community/tutorials/apache-configuration-error-ah00558-could-not-reliably-determine-the-server-s-fully-qualified-domain-name

Run the following to check Apache’s status using systemctl:

        1) sudo systemctl status apache2.service -l --no-pager

Run the following to check Apache’s status using journalctl to get more info:

        2)sudo journalctl -u apache2.service --since today --no-pager

Troubleshooting using apachectl

        3)sudo apachectl configtest

Setting a global server name directive 

        4)sudo nano /etc/apache2/apache2.conf

Add below line to the end of above file

            ServerName 127.0.0.1

        5)sudo apachectl configtest

it will show result ok

         6) sudo systemctl reload apache2.service