The latest stable edition of MongoDB is version 2.6.4, but the version available in the repositories of Linux distributions, including Fedora and Debian/Ubuntu, is version 2.4.6. There are functions available on version 2.6.4 that are not supported in version 2.4.6, so if you are taking any of the online classes provided by MongoDB, Inc, you should be running version 2.6.4.