All unix questions are on-topic here, except programming questions (which we redirect to Stack Overflow).
Some unix questions are also on-topic elsewhere (Server Fault, Super User, Ask Ubuntu, Ask Different are the usual suspects). When it comes to questions that are on-topic on multiple sites, the general policy is that they stay where they were asked.
Sometimes a question might be migrated: if it's a far better match for another site and only borderline where it was asked; or if it goes un(satisfactorily)-answered for a while. If the question works where it's posted, it should not be migrated.
Case in point: this question has an accepted answer. It's not a significantly better fit for SF than for U&L. Don't migrate it.