Microsoft worked with Canonical to offer a full Ubuntu-based Bash shell environment that runs atop this subsystem. Technically, this isn't Linux at all. Linux is the underlying operating system kernel, and that isn't available here. Instead, this allows you to run the Bash shell and the exact same binaries you'd normally run on Ubuntu Linux. Free software purists often argue the average Linux operating system should be called "GNU/Linux" because it's really a lot of GNU software running on the Linux kernel. The Bash shell you'll get is really just all those GNU utilities and other software.