Basically in almost all linux machines we will be having root access for login.but in ubuntu by default that option was not enabled.If u want to have root login in ubuntu then u have to do some changes in ur Ubuntu machines
Steps to follow

1.First enter into ubuntu as your user login.
2.Then open the terminal and type the command sudo -s,it will ask for root access and type the password.
3.Then type passwd root it will ask for new password
4.Open terminal and go to the path /etc/gdm/
5.Open gdm.conf
6.search for AllowRoot=false
7.and then change AllowRoot=true
8.now restart ur machine
9.now u can enjoy with root access

Alternatively, you can:

open the System -> Administration menu
open Login Window
select the Security tab
check the allow local system administrator login box
close window
restart Ubuntu

However, it is strongly recommended that you not run as root, as that is one of the most vital layers to Linux security with any distro.