Problem:
XAMPP: Another web server is already running

solution:
Step 1 : check the httpd process

ps -eaf | grep httpd
Step 2 : Kill all the process

kill
earlier apahe2 is running on 80 and his pid 564 after kill 564
on port 80 httpd is running and pid is 5873

=================or===========

sudo service apache2 stop