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>> It suggests because a Linux distribution and a rump kernel can both be made small enough to fit in RAM, they are therefore similar. That does not sound right.

It's a good question. Given a unikernel and an extremely trim Linux kernel plus application code only, what's the practical difference? Does it matter at any real level if there's 4.5 megabytes of Linux kernel in there?

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Huge difference. It's not the kernel size, it's the interface (ABI).

In a unikernel, the kernel is part of the application (like a library). Instead of a complex/slow transition from user space to kernel space, you just call a function.

A unikernel will also know exactly what your application needs (i.e. if you only use UDP, it doesn't bother including TCP.) It's possible to strip down the Linux kernel, but it requires a LOT of work (basically, remove something, then test that your application still works.)

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