Sesseion work ofline but not work online

I geting  problem with  session in codeigniter , session work properly at localhost but not work after online

@Mohamma Rafique
We need more information then that...What version of CI are you running? PHP version? When you say not work after online, what do you mean by that? Is CI installed on your local workstation? ISP server? Details, details, details....that is what we need.