New work

https://github.com/NixOS/mobile-nixos supports sc7180 now. If it doesn't work, contribute to it, it's a much better framework than this. Maybe you'll even get the LTE working.

Preparing the installation

You must first set your Chromebook to developer mode. Then you can boot from an external storage device. You can thus prepare an external storage device with something like the approach noted below so that you can install onto the internal eMMC.

Set-up

Use gptfdisk as normal, have 1 partition with type ChromeOS kernel (7F00) that is at least 320 MiB in size. Unfortunately the initrd is quite big right now, mostly due to a lack of optimization on my side. Then, make your other partitions as usual. I personally recommend a single partition for root using LUKS and F2FS:

cryptsetup luksFormat /dev/mmcblk1p2 --type luks2
cryptsetup luksOpen /dev/mmcblk1p2 cryptroot
mkfs.f2fs /dev/mapper/cryptroot -O extra_attr,compression,inode_checksum,sb_checksum

You must now make two NixOS configurations: One just for booting, and one for your system. Respectively, one that imports boot-kpart.nix, and one that imports lazor.nix.

When you build the boot configuration, you will get a system, which you won't actually use. You instead use just the kpart file from it, and do sudo cp ./result/kpart /dev/mmcblk1p1. When your laptop boots, it will first boot this "system", that just kexecs directly into the real system before leaving the initrd. The reason it's done this way, is that rebuilding the kpart is quite expensive and annoying to do every time you want to rebuild your system.

The other configuration will be your main configuration, and should be configured in the standard way. To install this onto your root filesystem, simply do nix-build --store /mnt, then nix-env -p /nix/var/nix/profiles/system --set ./result. The initrd in the first partition will on boot kexec the system you have in /nix/var/nix/profiles/system.

Tips

Building a NixOS configuration

nix-build '<nixpkgs/nixos>' --argstr configuration /my/config.nix

Image for booting from SD card or USB

nix-build -A image

Sound

Use Pipewire, it works much better than PulseAudio in general.

Root filesystem

Make "/" a tmpfs. This is a good practice in general.

Known issues

• Hardware decode through mpv --hwdec=v4l2m2m_copy doesn't work great, especially seeking.
• No way to choose profile to boot (but should be easy to implement honestly)