Where is ros2doctor?

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I am going through the tutorials on dashing distro. Up to this point (mostly) ok, but this is baffling. I am at the "Getting started with ros2doctor", but "doctor" or "wtf" do not exist as a ros2 command. It is not included in the command list from "ros2 -h" either (and neither is in the example output in earlier tutorial!). So why should it even be available? (ubuntu 18, binary version). Thanks!