This question already has an answer here:
If you have a question which is applicable to two or more different communities but you don't get an answer in the first community you post it to, is it acceptable to ask it in one or more others? If so, how long would people suggest waiting? 24 hours or so seems fair except in urgent situations...?
An example would be the following:
Which has yet to receive an answer on the Linux Stack Exchange, so I'm wondering if it would be acceptable to repost in Super User...?