set USER Permission
sudo chmod 755 -R /opt/lampp/htdocs
Proper way to install XAMPP in ubuntu is as below.
open your terminal
Official document
COMMANDS
1.) mkdir xampp
2.) cd xampp/
3.) wget https://www.apachefriends.org/xampp-files/5.6.20/xampp-linux-x64-5.6.20-0-installer.run
4.) chmod +x xampp-linux-x64-5.6.20-0-installer.run
5.) sudo ./xampp-linux-x64-5.6.20-0-installer.run
ACCESS phpMyAdmin
6.) sudo vim /opt/lampp/etc/extra/httpd-xampp.conf
AND COMMENT OUT THE FOLLOWING LINE
Require local
EX.
#Require local
Save and quit the file and restart XAMPP service
7.) sudo /opt/lampp/lampp restart
OVER COME THE SECURITY OPTION
8.) sudo /opt/lampp/lampp security
And follow the instruction