Installing Gentoo with LiveCD

Table of Contents

• Introduction
• Prerequisites
• Installation
  • Step 1: Set up the Asahi U-Boot Environment
  • Step 2: Acquire the Gentoo Asahi LiveCD image
  • Step 3: Boot into the LiveCD
  • Step 4: Install Asahi support files
  • Step 5: Have fun!
• Maintenance
  • Updating U-Boot and m1n1
  • Upgrading the kernel
  • Syncing the Asahi overlay

Introduction

Installing Gentoo on Apple Silicon is not that different to doing so on a bog-standard amd64 machine. We have a LiveCD image that is almost identical to the standard Gentoo arm64 one, customised only to enable it to boot on Apple Silicon devices.

The only major deviation from the Handbook is using chadmed's asahi-gentoosupport package to automate the installation of the kernel, GRUB, overlay, m1n1, and U-Boot. You are of course welcome to attempt installing these manually, however it will take you longer than bootstrapping the rest of the system combined.

This guide will assume that you are familiar withe the Asahi Linux installer and will not walk you through using it.

If you've never used a Portage overlay before, take a few minutes to read the final section on maintaining the system. Failure to do so properly may result in you missing critical system updates or leaving your machine in an unbootable state.

Important prerequisite information

• Please do not use genkernel to build your initramfs. The only supported initramfs generator is dracut. The asahi-configs package installed later will supply the necessary configuration files to make dracut work seamlessly.

• U-Boot's USB stack is not fantastic, to say the least. You may find that various USB sticks or keyboards do not work reliably with it. Unfortunately, there is nothing we can do about this at the moment and you will just have to try different USB devices until you find one that works.

Step 1: Set up the Asahi U-Boot Environment

Use the Asahi Installer to set up the minimal m1n1 + U-boot UEFI environment. Ensure that you tell the installer to leave the amount of free space you want for your Gentoo system. It may be easier to simply use the Fedora Asahi Remix Minimal installation option. We won't be using it, but it will guarantee that space is reserved for your root filesystem.

It is assumed going forward that you have fully "completed" the Asahi installation.

Step 2: Acquire the Gentoo Asahi LiveCD image

We build lightly customised Gentoo LiveCDs which allow booting on Apple Silicon machines. Grab the latest one from https://chadmed.au/pub/gentoo/install-arm64-asahi-latest.iso.

The LiveCDs are built using the standard Gentoo release engineering tooling. The Catalyst specfiles can be found at https://github.com/chadmed/gentoo-asahi-releng.

Flash this on to a USB stick using your favourite method. As always, plain old dd works best.

Step 3: Boot into the LiveCD

Boot the machine with the USB stick you flashed plugged in. U-Boot will enumerate your USB devices, then give you 2 seconds to interrupt its automatic boot sequence. If you opted for the m1n1 + U-Boot installation option, you should be safe to just let it continue booting. It will automatically boot from your USB stick.

If you installed one of the complete operating system images, you will need to interrupt the boot process and force U-Boot to boot from the USB. Once you have interrupted U-Boot's automatic boot sequence, run this series of commands:

setenv boot_targets "usb"
setenv bootmeths "efi"
boot

If your U-Boot plays nicely with your USB stick, this will boot you into the LiveCD's GRUB. From here, you can simply follow the Gentoo Handbook for amd64, stopping only when it is time to install a kernel.

NOTE: When partitioning your machine, it is absolutely vital that you do not alter any partitions other than the space reserved for your rootfs. This includes the EFI System Partition set up by the Asahi Installer. You are free to partition the rootfs space in any manner you wish, but do not modify any other structure on the disk. You will most likely require a DFU restore of your Mac if you do.

Step 4: Install Asahi support files

Merge Git by running emerge -av dev-vcs/git, then clone chadmed/asahi-gentoosupport from GitHub. Run ./install.sh and follow the prompts. This will

• Install the Asahi Overlay, which provides the kernel, boot tooling and (possibly) patched packages
• Install the sys-apps/asahi-meta package, which will pull in all the Asahi-specific goodies necessary for booting, including a dist-kernel.
• Install and update GRUB.

This allows you to skip setting up GRUB, the kernel, and the boot tooling yourself which can be a bit of a hassle on these machines and may leave you with an unbootable Linux setup.

Step 5: Have fun!

Finish off the rest of your usual Gentoo install procedure, reboot, and have fun! It's a good idea to customise the kernel as you see fit since the running config will be based on Arch/Asahi Linux. Remember to save the running kernel and initramfs as a fallback so you can easily boot it from GRUB should anything go wrong.

Maintenance

Getting and applying system updates is a little more involved than a totally vanilla Gentoo installation. You need to keep the Asahi overlay synced and make sure that system firmware is updated correctly.

Updating U-Boot and m1n1

When you update the U-Boot or m1n1 packages, Portage will only install the resultant binaries to /usr/lib/asahi-boot/. This is both a security and a reliability measure. m1n1 ships with a script, update-m1n1, which must be run as root every time you update the kernel, U-Boot, or m1n1 itself. This script is responsible for collecting the m1n1, U-Boot and Devicetree blobs, packaging them up into a single binary object, and installing it on the EFI System Partition. For more information on how this works and why it must work this way, consult Open OS ecosystem on Apple Silicon Macs

Upgrading the kernel

When you are running through a kernel upgrade, it is extremely important that you update the Stage 2 m1n1 payload at the same time. m1n1 Stage 2 contains the Devicetree blobs required for the kernel to find the hardware, probe it properly, and boot the system. Devicetrees are not stable, and a kernel upgrade with new DTs may result in an unbootable system, loss of function, or missing out on a newly enabled feature. To make sure this does not occur, it is imperative that you run

root# update-m1n1

after every kernel upgrade.

Note for developers and advanced users: You may also wish to install multiple kernels, and make use of eselect kernel to swap the symlink to /usr/src/linux. This is supported, however you must run eselect kernel set and update-m1n1 before every reboot into different kernel. This is to ensure that you are always booting with the correct DTBs.

Syncing the Asahi overlay

In order to receive Asahi-specific updates, you must ensure that the Asahi overlay remains synchronised. Portage will do this for you if you use emerge --sync, but not if you use emerge-webrsync. To synchronise the overlay manually, run

root# emaint -r asahi sync

before trying to update. No other steps are necessary to make sure that packages are updated, just update your system like you normally would at this point.