Apparently it is not, or at least, it wasn't, once, if you believe this research:
https://bsdimp.blogspot.com/2020/07/when-unix-learned-to-reb...
https://bsdimp.blogspot.com/2020/07/when-unix-learned-to-reb...
Still no confirm or deny on Linux.
I was at +2 and now 0 after this post rose to the top. Am I bitter? No...