I am an experienced Unix developer but new to Linux. I am researching doing a project using Linux. I need hard determinism and am looking at how RT-Linux, LynxOS and others play together. There is a lot of "noise" out there. Is there anyone here that can offer some real guidance rather than marketing hype? ;(

You need "hard determinism"? Are you doing a philosophical project or are you using this term in a different way?

Sorry, I assumed I'd get replies from experienced real-time developers:

1) Determinism - the kernel has predictable and repeatable. It provides for some "deadline" (+/- any jitter). The worst case perfromance is known.
2) Hard Determinism - it MUST meet the deadline 100% of the time - or something blows up!
3) Soft Determinism - it "usually" meets the deadline. When using a "soft" deterministic kernel, what "usually" means needs to be quantified.

If you're looking for experienced developers, real-time or otherwise, you're definitely in the wrong forum.

And by the way, applying the term "hard determinism" to kernels is a very new application of the phrase. Any casual student of philosophy or theology would understand it in a very different sense.