Install Linux on a MacBook Air

· originally appeared on robots.thoughtbot.com

I’ve been feeling the pull of desktop Linux for a while now. The last time I tried to use Linux as my daily desktop was almost 10 years ago. It was a pretty big failure.

But after so many years of using, and falling in love with, Linux on the server, I wanted to give it another chance.

So last week I hunkered down and, over the course of a few days, managed to build a functional Linux environment on my laptop. I took rigorous notes as I struggled and encountered breakthroughs, the results of which you’ll find below.

The steps in this guide will take you from a single-boot OS X install on a Macbook Air to a dual-boot system with OS X and NixOS. Many of the steps apply to installing another Linux distribution, too, in particular those dealing with disk encryption (in OS X and Linux) and the requirement for Broadcom drivers.

Other than that, make sure you have any important bits saved somewhere safe, and enjoy the path to Linux below!

Table of Contents

What is NixOS?

There are many, many Linux distributions: distrowatch.com tracks 278 at the moment. Of those 278, you’ve probably heard of some of the major ones: Mint, Ubuntu, Arch, etc. NixOS is not one of the major ones.

So why did I choose it?

I’ve experimented previously with using the Nix package manager, on which NixOS is built, and found it very interesting and powerful.

I really like the idea of having a handful of declarative configuration files from which my entire system can be built. It means I can store it in git and track the history of my configuration, just like with my dotfiles. It also means I can quickly get up to speed on a new machine.

The ability to easily apply– and later rollback– configurations was also appealing, since I knew it would take a lot of experimentation to get the system working like I wanted.

I’d encourage you to read more about NixOS and Nix, especially if you intend to follow the guide below!

Download minimal 64-bit NixOS livecd

The steps below were performed with the minimal installation CD for NixOS version 14.12 found on the NixOS Download page.

(Optional) Disable OS X disk encryption

If you’re not using FileVault for full-disk encryption, you can safely skip this step.

If you use FileVault to encrypt your disk, you will not be able to use Disk Utility to update your disk’s partitions, which will need to be done in a later step.

Open FileVault and disable disk encryption, following the on-screen instructions. After rebooting, re-open FileVault and wait for the disk to be fully decrypted before continuing. This will probably take a while— for me, about 30 minutes.

(Optional) Prepare Broadcom driver

Depending on your particular hardware configuration, it may be necessary to use Broadcom’s unfree drivers. You’ll need to follow the instructions below for any Apple laptop from the last few years.

The steps that follow are almost certainly not the quickest or easiest way to prepare the Broadcom driver for installation. But I had already written most of the steps for a future blog post, so it was something I understood how to do.

Attach your USB device, and configure two partitions in Disk Utility: NIXOS_ISO (600 MB), and DATA (the rest). Each should be formatted as “MS-DOS (FAT)”.

Eject the drive, but keep it plugged in.

Now in the terminal, we’re going to create a VirtualBox VM running the NixOS livecd. If you’re more comfortable with the VirtualBox GUI, you can do all of the following steps there instead.

You should be able to copy and paste the script below, remembering to set nixos_livecd to the path of the downloaded iso.

nixos_livecd=path/to/downloaded/iso

# create vm
VBoxManage createvm \
  --name nixos-livecd \
  --ostype Linux_64 \
  --register

# create a virtual disk
VBoxManage createhd \
  --filename "$HOME/VirtualBox VMs/nixos-livecd/nixos-livecd.vdi" \
  --size 8192

# create virtual disk/cd controller
VBoxManage storagectl nixos-livecd \
  --name IDE \
  --add ide \
  --controller PIIX4 \
  --portcount 2 \
  --hostiocache on \
  --bootable on

# attach disk image to VM
VBoxManage storageattach nixos-livecd \
  --storagectl IDE \
  --type hdd \
  --port 0 \
  --device 0 \
  --medium "$HOME/VirtualBox VMs/nixos-livecd/nixos-livecd.vdi"

# attach livecd
VBoxManage storageattach nixos-livecd \
  --storagectl IDE \
  --type dvddrive \
  --port 1 \
  --device 0 \
  --medium $nixos_livecd

# bump up memory and CPU
VBoxManage modifyvm nixos-livecd --memory 1024 --cpus 2

# enable usb port
VBoxManage modifyvm nixos-livecd --usb on

# start VM
VBoxManage startvm nixos-livecd --type gui

You should now be at a login prompt in a VM window, which you can login to with root and no password.

From the menu bar, select “Devices” and then the name of your USB device to attach it.

Now in the VM window, mount the device:

mount /dev/disk/by-label/DATA /mnt

Now we’ll install the driver:

NIXPKGS_ALLOW_UNFREE=1 nix-env -iA nixos.pkgs.linuxPackages.broadcom_sta

Then we will export the driver and all of its dependencies

# find the installed driver in the nix store
driver=`find /nix/store -maxdepth 1 -name "*broadcom*" ! -name "*.drv"`
# query the driver's dependencies
driver_deps=`nix-store --query --requisites $driver`
# export driver and dependencies to USB drive
nix-store --export $driver_deps > /mnt/broadcom.closure

Finally, unmount the USB drive and shutdown the VM:

# may take a while
umount /mnt
shutdown now

Prepare livecd

Open “Disk Utility” and change the USB partition name to NIXOS_ISO.

Mount the downloaded livecd, and then copy its contents onto the USB device.

cp -R /Volumes/NIXOS_ISO\ 1/* /Volumes/NIXOS_ISO

Eject the ISO and the USB device.

Prepare partition

Open Disk Utility, click on “Macintosh HD”, add new partition, choose size (e.g., half), choose format as free space, apply.

Boot into livecd

Now reboot the machine, with the USB device inserted, and hold down the Option key.

You should be presented with three choices: “Machintosh HD”, “Recovery”, and “EFI Boot”. Select EFI Boot.

(Optional) Install Broadcom driver

Skip this if you didn’t follow the steps in “Prepare Broadcom driver”.

First, mount the USB device’s DATA partition and import the Broadcom driver and dependencies.

mount /dev/disk/by-label/DATA /mnt
nix-store --import < /mnt/broadcom.closure
umount /mnt

Now install the driver:

NIXPKGS_ALLOW_UNFREE=1 nix-env -iA nixos.pkgs.linuxPackages.broadcom_sta

Finally, load the driver:

modprobe b43
insmod $(find .nix-profile/lib/ -name wl.ko)

Create disk partitions

We will be creating two new partitions in the free space we made in the previous step. The first will be 512MB, and be used as our Linux boot partition. The second will use the remaining free space and be used for our Linux swap and root partitions.

$ gdisk /dev/sda
n       # new partition
<enter> # default partition #
<enter> # default start location
+512M   # size 512MB
ef00    # type boot

n       # new partition
<enter> # default partition #
<enter> # default start location
<enter> # size remaining space
<enter> # type default

w       # write partitions
y       # confirm

Make note of the partition numbers assigned to the partitions. You can always find them again by running fdisk -l and reading the device name of the last two entries, whose types should be “EFI Boot” and “Linux Filesystem”.

Configure disk encryption

On OS X, the standard for disk encryption is FileVault. On Linux, it’s LUKS.

We’ll be using a strategy called LVM On LUKS, where the partition we created above is an encrypted LUKS partition, on top of which we’ll layer root and swap partitions with LVM.

root_partition=/dev/sda$PARTITION_NUMBER # e.g., /dev/sda5

cryptsetup luksFormat $root_partition
cryptsetup open --type luks $root_partition enc-pv
pvcreate /dev/mapper/enc-pv
vgcreate vg /dev/mapper/enc-pv
lvcreate -L 10G -n swap vg
lvcreate -l 100%VG -n root vg

Format partitions

boot_partition=/dev/sda$PARTITION_NUMBER # e.g., /dev/sda4

mkfs.ext2 -L boot $boot_partition
mkfs.ext4 -j -L root /dev/vg/root
mkswap -L swap /dev/vg/swap

And then mount them:

mount /dev/vg/root /mnt
mkdir /mnt/boot
mount $boot_partition /mnt/boot
swapon /dev/vg/swap

You can recover back to this step, by booting into the livecd and running:

cryptsetup open --type luks $root_partition
lvchange -ay

Connect to wireless network

You will need a network connection to complete your NixOS installation. The following commands will update your wireless configuration to recognize your local wireless network.

wpa_passphrase "Network SSID" "passphrase" | grep -v "#psk" >> /etc/wpa_supplicant.conf
systemctl restart wpa_supplicant

Within a few seconds, you should be connected and a command like ping -c 1 google.com should be successful.

Configure and install system

Start by generating a template configuration:

nixos-generate-config --root /mnt

This will produce two files:

If you followed this guide’s Broadcom instructions above, you’ll need to apply an edit to hardware-configuration.nix. Find the line which starts with boot.extraModulePackages and enable the Broadcom kernel module by removing the surrounding quotes:

boot.extraModulePackages = [ config.boot.kernelPackages.broadcom_sta ];

Now we will need to edit configuration.nix to contain the minimum requirements:

# enable support for broadcom_sta
nixpkgs.config.allowUnfree = true;

# load fbcon early in boot process
boot.initrd.kernelModules = [ "fbcon" ];

# register our root luks device
boot.initrd.luks.devices = [
  { name = "rootfs";
    device = "/dev/sda5";
    preLVM = true; }
];

Also, you should ensure that the grub device is correct. For me, this was:

boot.loader.grub.device = "/dev/sda";

Now copy your wireless configuration:

cp /etc/wpa_supplicant.conf /mnt/etc

And then install!

nixos-install

If everything goes well, reboot to boot into your new NixOS system!

OS X final steps

When you updated the partition table with gdisk, the recovery disk partition lost some metadata, and shows up as “EFI Disk” instead of “Recovery”. If you go into Disk Utility, and hit “Repair” on “Macintosh HD”, that will fix this.

Also, don’t forget to re-enable FileVault if you turned it off earlier!

Where to go from here

At this point, you should be able to dual-boot into a functional, if not particularly useful, NixOS system.

Now starts the fun part, which I’m still going through myself, of exploring Nix, NixOS, and Linux to build your new environment. I can recommend some resources to help you on your way:

References and credits