Multiple operating systems on a MacBook Pro 28 Dec 2020

Booting from multiple operating systems on a mac can be a bit of a pain. This is a quick guide to be able to boot into OSX/Linux/Windows 10:

Resize disk via Disk Utility: go to Partition and resize the partition where OSX is. Optional step: create partitions for Linux, Windows, and maybe an extra one to easily transfer files between OSes.

Note: Disk Utility will convert the partitioning scheme from GPT to Hybrid MBR. Windows 10 install won’t be happy with this (see #2 and #3).

Temporarily disable System Integrity Protection (SIP): reboot holding Cmd+R, open a terminal, and type csrutil disable. This is necessary for the next step, otherwise the changes will keep being reverted.

Install gdisk and convert the partitioning scheme from Hybrid MBR back to GPT:

brew install gdisk
sudo gdisk /dev/disk0

# type the following inside gdisk. in case the menu changes, type `?` before
# each of them to double check they actually point to the correct menu entry
x   # extra functionality (experts only)
n   # create a new protective MBR
w   # write table to disk and exit

Install Windows 10 and/or your linux distro of choice. Depending on your distro, installing linux last will include Windows in the Grub configuration automatically. This may be useful if you intend to use Grub as the boot loader.

While Grub may pick up the Windows configuration, in order to boot into OSX, you’ll have to hold the option key while rebooting. If you don’t like this behavior, after installing your linux distro, install rEFInd (e.g. sudo apt install refind). rEFInd will scan all drives for any bootable info (e.g. EFI partitions, linux kernels, bootable USB sticks, etc) and allow you to choose one at runtime.