codeigniter code not working in ubantu operting system

I was working on a windows system till few days ago. I made a website in code-igniter framework .few days back I shifted from windows to Ubuntu . now my default controller is loading but as I access any other functions in any controller it shows requested URL was not found on this server. the project which was running on windows system is down in Ubuntu. Have no idea what to look for as I am new to Ubuntu.