Enable-WindowsOptionalFeature : Feature name Microsoft-Windows-Subsystem-Linux is unknown.

Enable-WindowsOptionalFeature : Feature name Microsoft-Windows-Subsystem-Linux is unknown.
You got this error while trying to enable "Microsoft-Windows-Subsystem-Linux" feature to get the bash on ubuntu on Windows 10 through PowerShell command.
This simply indicates your system has not met the proper criteria to upgrade to get the Windows 10, with OS build at least 14316.

If you think you have the pre-requisite to get the developer mode Windows 10, please check below pre-requisites:

Prerequisites

1. Windows 10 Anniversary Update - build 14316
2.  Available as of 8/2/2016
3. x64-based processor
4. Your PC must have an AMD/Intel x64 compatible CPU
5. You must be a member of the (free) Windows Insider Program (Preferably Fast-Ring)
6. Your PC must be running a 64-bit version of Windows 10 Anniversary Update build 14316 or later

You can verify the below requisites through below steps.

1. To Check the Windows build version press Windows + R & then type winver.
2. To check the processor Go to this path through Windows Explorer:                                    Control Panel\System and Security\System
3. To be a member of the Windows Insider program, you need to apply it through below steps.

• Open Settings(Type settings in Cortana Search box) -> Update and Security -> For developers
• Select the Developer Mode radio button.
• Reboot Your system.

• Enable the Windows Subsystem for Linux feature (GUI)

1. Hit start and search for "Turn Windows features on or off" (type 'turn')
2. Select Windows Subsystem for Linux (beta)
3. Click Ok.