This follow-up shows a lot of maturity. Both sides are obviously at fault here, although you instigated it.
I suspect you could still get the internship if you send an apology like "Sorry for my previous emails they were out of line. You're essentially correct and here's an updated resume to reflect that."
I don't see how the candidate instigated anything. The recruiter was either being deliberately obtuse or does not understand the role he/she is recruiting for. At almost any tech company, when a hiring manager asks for Unix/Linux experience for an internship role, there is a 99.9% chance that the hiring manager is looking for general experience on unix-like operating systems. I would bet my life on it. If Solaris/HP-UX/etc. experience was really specifically needed, it would have been spelled out as such.
I'm imagining a recruiter saying "We're looking for someone with graphics programming experience. Your resume says 'OpenGL and DirectX experience.' If you do not have graphics programming experience, I can try to find another role for you." As a candidate, I would think I was interacting with an idiot.
I don't think I'll be able to convince you otherwise, but this would read to most people as two assholes arguing with each other. Also OPs explanation of why UNIX == POSIX was pretty confusing, and I had to look up more information.
Plus, recruiters are incredibly busy this time of year. I don't blame him for choosing not to engage with candidates who reply with a wall of text when given a simple request.
Would be interesting to conduct a survey among your friends. Seems a lot of commenters here read it as the recruiter being overly strict, and Stanley trying to accommodate him/her while sticking to his integrity.
Thank you - I actually did send an apology email, but since I'm pretty sure I'm not quite qualified for the position, I didn't bother pursuing it any further than that.
Are you insisting that you're not qualified for the position on the basis of that Linux / Unix distinction alone ?
If so, that's really really sad. Even more so if you thought "Unix-like" genuinely disqualifies you because it's not strictly "Unix" !
You need to be more confident about your skills. Most interns don't know how POSIX relates to UNIX and Linux like you do, if they are even familiar with the word !
Look, I'm a former Facebook production engineer. I won't exactly reveal a secret by saying that FB is wholly Linux based. It's not a bank with legacy commercial Unix systems, and you were of course right about the 1970s engineers comment.
Positions requiring expertise with a specific brand of Unix are less and less common, and these would always mention the flavor they're after anyway (mostly Solaris, possibly some AIX/HP-UX).
One more general piece of advice : let others decide that you're not qualified for, don't self-censor before you even get a chance to fight.
Pure Unix is not even thought to CS students anymore. Looking for Unix experience for internships is utterly pointless. The Recruiter should have been happy that there was Linux experience, because even that is not a given.
You had nothing to apologize for. There are tons of recruiters in this industry who do not know what they are recruiting for and are dumbly trying to match text. I've had a recruiter tell me that they are looking for experience programming "graphics drivers", and would I kindly update my resume to say that instead of "display drivers". If a company uses recruiters this clueless, you dodged a bullet.
As general career advice going forward, I recommend letting the employers filter you out instead of disqualifying yourself based on technical skills. They're good enough at it themselves, and job listings are oftentimes half-truths at best.
If you know enough Linux to do anything useful with Arch, and you're as CS student at CMU, you're almost certainly qualified for a PE internship there.
I suspect you could still get the internship if you send an apology like "Sorry for my previous emails they were out of line. You're essentially correct and here's an updated resume to reflect that."