Beyond that, Mac OS X and Ubuntu are cousins, Mac OS X being based off of FreeBSD/BSD, and Ubuntu being Linux based, which are two separate branches off of UNIX.

Does Mac use Linux?

Mac OS X is based on BSD. BSD is similar to Linux but it is not Linux. However a big number of commands is identical. That means that while many aspects will be similar to linux, not EVERYTHING is the same.

Do I need Ubuntu for Mac?

There are plenty of reasons for having Ubuntu run on a Mac, including the ability to broaden your technology chops, learn about a different OS, and run one or more OS-specific apps. You may be a Linux developer and realize that the Mac is the best platform to use, or you may simply want to try out Ubuntu.