When we received message XAMPP: Another web server is already running. it means the port we use for apache have been used by another application. I have changed the port using /opt/lampp/etc/httpd.conf to another port but still got the message.
This message came out because I use Nginx for front-end of the server and using port 80.
Then I edit /opt/lampp/xampp search for startApache then search for 80. Change the port to your need.
The problem resolved.
