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When I need to ask a Linux related question, I normally look at the activity on the related unix.se and sf tags to decide where to post it.
I read in a previous question that cross-posting might be okay if the site is beta (is unix.se still beta?)
The context of the question is important. If you substitute your-tag for rsync in this question and it's answers then you should get a feel for what goes where. There is though considerable overlap.
Unix and Linux was launched from beta some time ago.