Same as always, apply. Specifically with OS stuff you’ll need to show an aptitude for it, easiest way is if you’re already a college grad and you took an OS design track. If you’re self taught, it’s much harder to prove you have the basics down, so as another person suggested, contribute to OSS projects, which also sounds daunting, but unlike web dev, OS dev is not somewhere where it’s ok to be mediocre.
