AH00558: apache2: Could not reliably determine the server's fully qualified domain name, using 127.0.1.1. Set the 'ServerName' directive globally to suppress this message code example
Example: httpd: Could not reliably determine the server's fully qualified domain name, using 192.168.123.156. Set the 'ServerName' directive globally to suppress this message
If you go to:
/etc/apache2/apache2.conf
and insert:
ServerName localhost
and then restart apache by typing into the terminal:
sudo systemctl reload apache2