[Unix] Abbreviation for ‘Read The Fucking Manual’.
1. Used by gurus to brush off questions they consider trivial or annoying. Compare Don't do that then!.
2. Used when reporting a problem to indicate that you aren't just asking out of randomness. “No, I can't figure out how to interface Unix to my toaster, and yes, I have RTFM.” Unlike sense 1, this use is considered polite. See also FM, RTFAQ, RTFB, RTFS, STFW, RTM, all of which mutated from RTFM, and compare UTSL.