after installing xampp apache does not start code example

Example 1: apache server not starting in xampp ubuntu

sudo /etc/init.d/apache2 stop   
sudo /opt/lampp/lampp start

Example 2: apache2 does not start xampp mac

sudo /Applications/XAMPP/xamppfiles/bin/apachectl start
sudo /Applications/XAMPP/xamppfiles/bin/mysql.server start