Ask HN: What certifications/courses do you think are worth it?

I've been looking into what certifications and courses I might be able to do to enhance my career and thought some people here would have some experience or advice.

Personally I'd be interested in doing more Linux kernel development and have been looking into whether it's worth paying for a course or just trying to dive in.

If you have done any course/certification what was your experience? did it help your career noticeably? It could be anything doesn't have to be programming related.