Yes it's come to this for us, too. We had 3/3 interviews this week clearly and mechanically reading definitions at us instead of discussing tradeoffs. We're a full remote company but we're considering onsite interviews now.

Consider pair work (a generalization of pair programming):

Spin up a VM for you and the candidate to SSH into. Start a shared screen/tmux session. Work on some sysadmin task(s) together. Switch between driving/typing and navigating/directing at regular intervals (15 minutes is typical, though a 30 minute interview would require a <10 minute interval).

You'll have to come up with a task (or set of tasks) that deals with the skills you need. The task(s) would ideally be very difficult for an LLM or search engine to provide a complete answer for; but they shouldn't be gotchas, since that might be false negatives.

Test your task(s) with other people in your company first, so you'll be comfortable when doing it with a candidate.

I can't say that this will 100% prevent cheating. But, you will surely learn a lot about the candidate's habits, in terms of reasoning and communication. If the candidate pastes commands, then that's a possible indication of LLM-usage; if the candidate doesn't use tab-completion, then they might be typing text in from somewhere else (e.g. an LLM, a guide).

I enjoy using the command-line, so I suspect I would enjoy this sort of interview.

At any rate, I hope you find a good candidate.

never ever waste interview time asking candidates questions that can be looked up in a book.

seriously, interview 101, your poor interview skills are the problem if you are worried about ‘cheating’.

Absolutely. We give a system design problem in a blank shared document. as a conversation starter.

Even open questions like "how did you select that technology component over this other one, and what are the tradeoffs?" We're getting long-winded, overly formal, mechanical definitions instead of an honest conversation.