Hacker News Reader

Comment by lasiotus | Hacker News Reader

Unikernels are on the smaller side of the spectrum; Linux on the larger side, with a lot of room in the middle...

For that matter, the actual Linux kernel need not be large at all. It's really the user space stuff that takes up the bulk of what people think of as the largess of Linux.

Still, there's a whole pile of stuff there that many applications don't need. If you truly can run the entire of the OCaml runtime and standard libraries etc without it, and you're happy writing your apps in OCaml... MirageOS has always felt winning-ish to me as a general idea.

And to TFA's point, now with LLMs the relative exotic nature of OCaml as a platform need not be a huge hindrance. I like the language, but have only dipped my toes in. Definitely tempting to try writing apps on it w/ MirageOS now. Though I doubt I'd convince anybody to pay me to do that...

I was involved a bit in Unikernel Linux (https://github.com/unikernelLinux/) which is basically a Linux kernel where you can run a single application linked with the kernel. It can run baremetal or as a guest under KVM. It's both the best and worst of all worlds.

A lot of comments here about observability. Well UKL solves this nicely because you can run regular userspace processes in the unikernel, thus you can (optionally of course) run a shell, perf, and anything else you need to observe what the machine is doing.

I don't agree that "the actual Linux kernel need not be large at all", and I think that's because my idea of "large at all" is very different from yours. You're comparing to what you know is possible, and I'm comparing to what I know is possible.

Linux is about 40 million lines of code, and even if you disable almost everything optional, it's hard to get a usefully bootable Linux below about a megabyte.

The seL4 kernel is about 9000 lines of code, a code base that's 4000 times smaller, and I think it compiles to about 80KiB, about 12× smaller than Linux.

I elicited a small unikernel web server from Claude the week before last, and, not counting lwIP, it's 385 lines of code. The built unikernel image, which does include lwIP, is 58K, about 17× smaller than Linux.

The KokalOS kernel I've been working on over the last week, originally by refactoring the unikernel web server, is currently about 900 lines of code (65536× smaller than Linux) and compiles to just under 10KiB (128× smaller than Linux), but it's currently just running a CLI and a web server with a single Ethernet card. I anticipate that in a finished state it will probably be close to the size of seL4.

Part of the problem with being old like I've become... and having used Linux since 1991 on a 486 is that in my mind Linux can still be thing I installed off a few 1.44MB 3.5" floppies and ran -- complete with emacs and XFree86 -- in under 8MB of RAM.

Sel4 is cool stuff.

I think it's still possible to make a Linux boot/root floppy, but it's a lot more difficult than it used to be, and it can be hard to find the 1.44MB 3.5" floppy drive in the junk closet. I don't think you were ever getting GNU Emacs on there, though — maybe JOVE.

Reply on news.ycombinator.com