[Unix] Abbreviation for ‘Read The Fucking Binary’. Used when neither documentation nor source for the problem at hand exists, and the only thing to do is use some debugger or monitor and directly analyze the assembler or even the machine code. “No source for the buggy port driver? Aaargh! I hate proprietary operating systems. Time to RTFB.”
Of the various RTF? forms, ‘RTFB’ is the least pejorative against anyone asking a question for which RTFB is the answer; the anger here is directed at the absence of both source and adequate documentation.