How to dual boot Ubuntu and macOS without rEFInd?

I'm trying to install Ubuntu on my MacBook Air 2019 with Catalina 10.15.6. However, my MacBook has the secure boot feature which doesn't allow rEFInd to work at all and I'm not feeling comfortable to disable secure boot.

Is there any way to dual boot without rEFInd?

Solution 1:

If you employ all the security offered by the T2 chip, then you can not boot Ubuntu. Also, you can not boot the Ubuntu Live USB flash drive to install Ubuntu. So with secure boot enabled, you can not install Ubuntu.

If you lower the security, then you can install and boot with or without using rEFInd. Installing Ubuntu to the internal drive of the newest Macs may not yet be possible.

With rEFInd, the following happens:

1. The firmware boots rEFInd.
2. The user chooses Ubuntu from the rEFInd menu.
3. rEFInd instructs the firmware to boot Grub.
4. The firmware boots GRUB from the EFI partition.
5. Grub boots Ubuntu from a linux formatted partition.

Without rEFInd, the following happens:

1. The user holds down the option key at startup until the firmware boots to the Mac Startup Manager.
2. The user chooses Ubuntu from the Startup Manager. (By default, the label is EFI Boot.)
3. The shim boot loader is booted from the EFI partition by the firmware.
4. The shim boot loader boots Grub from the EFI partition. Ubuntu is also made the default operating system to boot.
5. Grub boots Ubuntu from a linux formatted partition.

There is also option with rEFInd to do a Grubless boot of Ubuntu. In this case, the following happens.

1. The firmware boots rEFInd.
2. A driver is installed by rEFInd that allows the firmware (and thus rEFInd) to read linux formatted partitions.
3. The user chooses Ubuntu from the rEFInd menu.
4. rEFInd instructs the firmware to boot Ubuntu from a linux formatted partition.
5. The firmware boots Ubuntu.

There are other scenarios for booting Ubuntu. The three given are fairly common.

Solution 2:

I recall being able to install Linux with Boot Camp but that was some time ago, my recollection may be incorrect and Boot Camp support from Apple has been fading in recent years. Support for Boot Camp will end with the end of Intel based Macs, meaning not much effort has been put into keeping it updated, and there's nothing I've seen to suggest an equivalent technology for future ARM based systems.

Is there a reason to dual boot as opposed to using a virtual machine? I gave up on dual booting a very long time ago. In that time computers got cheap enough, and reliable enough, that I can afford keeping an old computer (or seven) around for running whatever OS I want and avoid the need to reboot. There's also been considerable advancements in virtual machine software. I now routinely run one or two virtual machines on my newer computers. This let's me flip between Linux, macOS, and Windows with a key macro instead of having to reboot or go to another computer. This ability to run multiple operating systems also comes with the speed, low cost, and durability of modern computers.

The problem with the T2 chip and running Linux has little to do with rEFInd. The problem is that with the T2 chip enabled only signed operating systems will boot. I don't know if Apple bars Linux from being signed, nobody bothered to go through the process of signing the OS/kernel/whatever, or why the two don't meet.

Until there's a Linux OS that's "blessed" by Apple there's a choice you will have to make. You can boot Linux with the T2 chip at lowered security settings. You can run Linux in a virtual machine. You can not run Linux on this computer. If there's another choice then I'm not aware of it.