Why are yours changing every day? If they always did that, then yes it would be a stupid idea. But they don't change on their own, or for no reason, so it isn't a stupid idea.

Mine change maybe once every couple of years, if I do a full reinstall without copying over the old host key. And then I know exactly why it changed.

> Why are yours changing every day?

Nobody knows how the hell the host keys are generated in the first place. Don't worry about it.

> And then I know exactly why it changed.

Really? What is a "full" reinstall as opposed to a "non-full" reinstall, and how much exactly reinstall do I need for my host keys to change?

the only time the host keys should change is if you a) delete them (either by wiping the whole machine or just deleting the files), or b) explicitly regenerate them. If they're changing for any other reason you're doing something weird.

I don't think anybody actually generates host keys by hand. It's always some sort of "automation" script in your OS or SSH implementation.

Or they're getting MITM'd repeatedly by multiple different attackers...

Probably not. MITM pretty much never happens in the real world.

A system upgrade reinstalls every package, but does not regenerate host keys (Fedora). A full reinstall is wiping the drive completely, and running the installer from a LiveCD/LiveUSB. Nothing is retained, and new host keys are generated.

If my host keys were changing regularly, I would worry about it. There's no legitimate reason for that to be happening, since I'm not regularly wiping the drive and reinstalling, nor am I regularly manually deleting the host keys (the other way they get regenerated).