Comment by tombert | Hacker News Reader

Comment by tombert | Hacker News Reader

I love blog posts like this. You're not wrong in saying that the kernel is sort of this magical block box to most engineers (including me). I know how to use systemd and I know how to use bash and I know a few other things, but the kernel has always been "the kernel", and it's something I've never really tried to mess with. But you're right: ulimately the kernel is just a program. Yes, it's a big and important program that works at a lower level than I typically work at, but it's probably not something that is impossible for me to learn some basic stuff around.

I have had a bit of a dream of building a full desktop operating system around seL4 [1], with all drivers in user space and the guts fully verified in Isabelle, but learning about this level of code kind of feels like drinking from a firehose. I would like to port over something like xserver and XFCE and go from there, but I've never made a proper attempt because of how overwhelming it feels.

[1] I know about sculpt and Genode, and while those are interesting, not quite what I want.

You can actually disable most features of the Linux kernel, including multi-user support (everything will run as root). The end result is a stripped down kernel fit for only running your single desired application.

    gmake tinyconfig all

The result of that probably won't boot your friendly neighbourhood desktop distro.

> But you're right: ulimately the kernel is just a program.

Play a bit with user mode linux [1] the kernel becomes literally a linux program, that I believe you can even debug with gdb (hazy memory as I tried uml last time maybe a decade ago)

In theory you can also attach gdb to qemu running linux, but that's more complicated.

[1] https://en.wikipedia.org/wiki/User-mode_Linux

And User Mode Linux was the basic technology for dirt cheap (not so) virtual machines at some VPS providers 15yrs ago. This had some disadvantages, for instance you could not load custom kernel modules in the VM (such as for VPN), actually you could not modify the kernel at all.

Another major disadvantage, at least back then, was that it did not support SMP at all

Try working on NetBSD or OpenBSD. You can learn kernel hacking by literally reading the man pages. Changing, rebuilding,and booting your own custom kernel is tremendously exciting.

It reminds me of when people speak of money as a product. Sure, maybe you are right, but I think more of it as something in relation to products/programs than as a product/program itself.

The fact that it's also a product/program is some brainfucky exercise that might either be an interesting hobby thought experiment OR it might be a very relevant nuance that will be useful to the top 0.1% of professionals who need a 99.9% accuracy, like the difference between classical and relativistic mechanics.

I mean, sure you are right that kernels are programs and that money is a product, and that gravity is not a force. But I am a mere mortal and I will stick to my incorrect and incomplete mental model at a small expense of accuracy to the great advantage of being comprehensible.

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