Dual Boot Ubuntu Alongside macOS

1. Overview

Apple Macs aren’t primarily intended for use by other operating systems; it’s not their cup of tea. Indeed, the newer Apple silicon-based Macs dropped support for Boot Camp and third-party EFI boot managers.

However, there are still many working Intel-based Macs hanging around that Apple no longer supports. Unfortunately, using outdated macOS on these devices is a security risk.

In this article, we’ll discuss how to address this by installing Ubuntu alongside macOS on Intel-based Macs. First, we’ll see how Apple boots an operating system on a Mac. Then, we cover the installation and dual-booting process for Ubuntu.

2. Introduction

In this section, we cover the Apple boot process and the need for additional bootloaders that enable using other operating systems on Intel-based Macs.

2.1. Prerequisites

Before installing Ubuntu on a Mac, we should know that dual-booting is only supported on Intel-based Macs. In addition, we also need to have a working macOS installed on the Mac.

We’ll also need a bootable Ubuntu flash drive for the installation. We can create one using balenaEtcher.

2.2. The Apple Boot Process

The sole purpose of the Apple Boot Manager is to present a list of bootable devices. By default, the boot manager will boot macOS on the primary EFI partition, without any prompts. Therefore, we’ll need to explicitly invoke the boot manager by holding down the Option (⌥) key as soon as we power on the machine.

The Apple Boot Manager searches for bootable devices connected to the Mac. However, it’s primitive and doesn’t know how to load a kernel into the system memory. Therefore, we need a bootloader for that purpose. Once we select a bootable device, the boot manager will run the appropriate bootloader.

For instance, if we choose Ubuntu, it will launch the GRUB bootloader, which loads the Linux kernel, as depicted:

Essentially, the boot manager gives control to GRUB after we select Ubuntu from the boot menu.

Furthermore, the Apple Boot Manager is very limited in terms of features. However, there are open-source boot managers like rEFInd, which includes many features and can be customized.

With that background in mind, let’s jump into dual-booting Ubuntu alongside macOS.

3. Dual Booting Ubuntu 18+ and macOS

Installing the modern versions of Ubuntu on a Mac is as easy as installing it on a PC or a ThinkPad.

3.1. Step 1: Disable FileVault

Make sure that the FileVault is turned off. Otherwise, it will prevent us from creating new partitions. We can turn it off in Settings → Privacy & Security.

3.2. Step 2: Create the Partition

We’ll need to create a separate partition for Ubuntu using the Disk Utility, which comes with macOS. In Disk Utility, we create a FAT32 (MS-DOS) partition and resize it as needed.

3.3. Step 3: Boot Into the Ubuntu Installer

Now, we restart the machine and boot from the Ubuntu flash drive by holding down the “⌥” key and selecting the Ubuntu installer from the list. It will load the GRUB menu, where we choose the appropriate entry.

3.4. Step 4: Install Ubuntu

We’ll install Ubuntu on the newly created partition. Optionally, if needed, we can format it as EXT3 or EXT4. However, we don’t need to make any changes to the EFI or recovery partitions. The installer will take care of putting the appropriate EFI files on the EFI partition.

3.5. Step 5: Restart

Once installed, we can restart the machine and boot from the Ubuntu partition by holding down the “⌥” key.

4. Older Versions of Ubuntu

If we install Ubuntu 17 or an earlier version on a Mac, the installer will put the EFI file inside /EFI/EFI/ubuntu directory. So, we won’t be able to boot to Ubuntu. Fortunately, we can resolve this using a few extra steps.

4.1. Step 1: Installation

Install Ubuntu as we did in the previous section. Then, restart the machine and boot to macOS.

4.2. Step 2: Create EFI Directories

In macOS, open up Terminal and mount the EFI partition. Usually, it’s the first partition on the disk:

$ sudo diskutil mount disk0s1

However, if you’re not sure, we can check it using list:

$ diskutil list

We create the EFI/Boot directory on the EFI partition:

$ mkdir -p /Volumes/EFI/EFI/Boot

4.3. Step 3: Copy the EFI File

Finally, we’ll copy the grubx64.efi to the previously created directory:

$ cp /EFI/EFI/ubuntu/grubx64.efi /EFI/EFI/Boot/grubx64.efi

That’s it. GRUB 2 will now load when we select Ubuntu from the list.

4.4. Step 4: Unmount the ESP Partition

Though optional, we can unmount the partition to be on the safe side:

$ sudo diskutil umount /Volumes/EFI

5. Optional: Adding Ubuntu Bootloader Icon

We can change the icon for Ubuntu in the boot manager by creating or downloading a ready-made *.icns and copying it to /EFI:

$ cp ubuntu.icns /Volumes/EFI/.VolumeIcon.icns

We can use mac-icns, which is a free icon pack.

6. Conclusion

In this article, we learned how to install Ubuntu along with macOS on Intel-based Macs. First, we got familiar with how the Apple boot process works. Then, we took a step-by-step approach to dual-booting Ubuntu alongside macOS on the same disk.