Change boot order on a Mid 2010 Mac Pro, without MacOS

Question

I have a mid 2010 Mac Pro.

I don't have MacOS installed on it.

Instead I have two separate Debian installs (I've recently upgraded the hard drive to an SSD, but still want to keep the previous hard drive installed)

Currently, the boot order is set so that the hard drive boots before the SSD. I can over ride this on a per boot basis by holding down option (or alt) and selecting the other hard drive.

Unfortunately, I don't know how to permanently change the boot order without a MacOS install.

I have tried:

• Configuring EFI using efibootmgr, which gives the error: EFI variables are not supported on this system.
• Removing the boot flag from the hard drive with fdisk/gparted, which does not stop the Mac from booting into the other disk.

Answer 1

It turns out you can permanently change the startup disk from the startup manager, by holding ctrl while making a selection.

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