Summary
The root user in Mac OS X is disabled by default. Follow the steps in this article to enable and use it, if needed.
Important: If you are not familiar with the meaning of “root user,” read this entire article to learn important precautionary information before using the root user. You must have an administrator account and password to complete the steps below.
Note: If you are using Mac OS X Server, root is already enabled by default. Advice contained in this article to disable root access when used infrequently does not apply to Mac OS X Server. It should remain enabled. For more information on related behavior, see this article.
via Enabling and using the “root” user in Mac OS X.
