dev log: building my own distro

Published: 2024-02-26

Another adventure have started: I'm builing my own distro! I'm not sure about the motivations as it started naturally from my fidlings with OSs. Some of the things I remember are:

Turns out there is a cool project called buildroot that makes building a minimal linux system very easy. So I used it to create the linux kernel and userspace programs for a RPi 3B+ I had lying arround.

The result was a system that does the minimum: boots the linux kernel without initrd directly from the RPi bootloader, it then runs a simple shell script as init and drops to a shell.

This system is taking only 22MiB of RAM, which 14 are cache, and 500MiB of disk, which 470MiB are for git binaries. I am very happy. Obviously there are drawbacks: no module hotplugging, this gave me a headache as my keyboard needed a kernel module, it took me a day to figure this out. I tought this was the kernel's job.

So far I'm having a great time learning, turns out there is a lot of details we usually don't need to know. For example, firmware, which for the RPi is a must: in order to load the brcmfmac module its firmware must be present in the correct place. If not whenever you modprobe it you'll get a subtle timeout error.

Luckly buildroot also facilitates this, just select the corresponding option in firmware section. The next steps are now building sbase, ubase and sdhcp. I also included a tiny c compiler so I can compile the rest of the system.

So far this is the init script:


echo "Init started"

export PATH=/usr/bin:/bin:/sbin:/usr/sbin

mount -n -o remount,rw /
mount -t devfs /dev /dev
mount -t proc /proc /proc
mount -t sysfs /sysfs /sys
mount -t tmpfs /tmpfs /run

modprobe hid-apple
modprobe brcmfmac
agetty -n --login-program /bin/dash tty1

shutdown -h

There is too much to do, still. I'll keep you posted.