To enable auto login in Ubuntu 12.04
1.Open system settings.To open system settings, click the Dash home from unity launcher.And type system settings in the search field. And click system settings.
2.Click User Accounts.
3.Then click Unlock button and type your ubuntu password and hit enter.
4.Set the Automatic Login slider to the ON position by dragging it to the right or click it.
5.Then click lock button and restart.