I've found 'list 10 two-letter linux commands and their use'
They don't actually have to think of 10, but their answer can show what they've actually had to do on a *nix system. Its also lets you prod them with questions like 'how might I get disk usage' or if they mention dd, ask them how they use it, what its good for etc.
To be honest, a reason I like it is that if they free-think and say 'what about sed, oh of course thats three characters', shows what they know. Also whether shell-built ins count too.
They don't actually have to think of 10, but their answer can show what they've actually had to do on a *nix system. Its also lets you prod them with questions like 'how might I get disk usage' or if they mention dd, ask them how they use it, what its good for etc.