Oracle XE - Ubuntu - Solution to 'cannot access'

I received some queries lately from various users regarding unable to open page http://localhost:8081/apex or

The linux environment reported was Ubuntu and here is how to solve this error:

Open command prompt and execute the following command:

sudo /etc/init.d/oracle-xe force-reload 

This command will reload the database and settings. (If you are using SQL Plus session connection with database be sure to save all your data as the above command will restart the database.)