How to interview a programmer?

Hey. It is interesting to know your opinion or advice. On such a simple question, as an IT manager / personnel manager, hire a competent php \ ruby ​​\ c ++ \ etc programmer without knowing the subject at a sufficient level. What to ask questions, what to pay attention to first of all, we consider the purely professional side. It is clear that you need to watch resumes, watch experience, participate in specialized forums. Please do not send “to agencies”.

Have you encountered such a problem as you solved?