Why does cephadm keep saying Host is down

Solution 1:

Yes, one of the cephadm requirements is listed as Systemd. Unfortunately, WSL doesn't support Systemd. It uses its own init process as PID 1 instead, since it needs to initialize things differently due to the interop between Windows and WSL (networking, drive mounts, etc.).

While you can find methods of installing/enabling systemd on WSL, they are typically fairly buggy (by their admission -- I haven't tried it myself). Here's one I've been meaning to try, though. (Side Note -- Yes, it's on Stack Overflow, and really off-topic there, but it is too old to migrate. Thank you for moving yours over here instead.) I do now know if this would be enough to satisfy cephadm's requirements or not.

Also, while cephadm appears to be a fairly new convenience tool (and the recommended way to install now), you may be better off considering one of the alternative installation methods under WSL. I also ran across this guide.