How to enable the root user
OS X Lion (10.7) and later
1.From the Apple menu choose System Preferences.
2.From the View menu choose Users & Groups.
3.Click the lock and authenticate as an administrator account.
4.Click Login Options.
5.Click the "Edit" or "Join" button at the bottom right.
6.Click the "Open Directory Utility" button.
7.Click the lock in the Directory Utility window.
8.Enter an administrator account name and password, then click OK.
9.Choose Enable Root User from the Edit menu.
10.Enter the root password you wish to use in both the Password and Verify fields, then click OK.
OS X, Apple