# apache2ctl -t
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
Syntax OK

/etc/apache2/apache2.conf

ServerName 127.0.0.1

#/etc/init.d/apache2 restart
[ ok ] Restarting apache2 (via systemctl): apache2.service.

# apache2ctl -t
Syntax OK