Yes, that is definitely one of the gaps I had, thank you (also the other replies to my comment -- upvoted all of you). I'm generally on a Mac (which runs docker

Yes, that is definitely one of the gaps I had, thank you (also the other replies to my comment -- upvoted all of you). I'm generally on a Mac (which runs docker in a linux VM -- the reason why is much clearer now) and so my exposure to linux is mostly in the context of ssh-ing into a server. I think the fact that OS X is linux-like without actually being a linux distro also subtly led me astray, as I've been thinking of different distros in the same way I think of OS X as different from Windows, and not really thinking about the "userland" vs "kernel" distinction.