First you have to Enable the developer option on your android device.To do so Go to Settings » About phone » Tap seven times on Build number.Now return back to Settings main menu and now you can see Developer options from there.
Now open Developer options
Look for Root access setting, and set it Apps and ADB or Apps only orADB only, as per your need.
Done!!!!! Now your Device which is running android Marshmallow via CM 13 has full root access.
To verify the root status install Root Checker.
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