Force legacy boot on old iMac to address Radeon driver issues

[shutterfreak]

I'm desperately trying to get my old iMac 2008 boot Linux Mint 21.3 MATE in legacy mode, but so far to no avail.

The USB thumb drive with the ISO installer invariably boots in UEFI mode, even when I select legacy mode from the GRUB menu.

I tried the default installation, which results in a GPT partition scheme and UEFI boot.

I tried transforming the GPT partition scheme to MBR with GPT fdisk, but I still boot in UEFI mode.

I tried creating my own partition scheme as MBR without EFI partition but then GRUB won't install as it requires EFI. This makes my system unbootable, or in the best case I get into the GRUB shell.

What steps are needed for installing and running Linux Mint MATE as single OS in legacy mode on an iMac 2008?

[Reddog1]

Macs don't have a bios -- they are strictly uefi, and the only way to enter the uefi is if you are doing it from macOS/OSX. There is no 'legacy' bios mode. And, since 2007 or so, all macs have been 64 bit, even if the efi is listed as 32-bit. Any 64-bit system can boot on them without reverting to the 32-bit uefi. I don't understand how you would actually address the Radeon issue, because the problem is with the modern kernel radeon drivers.

The Radeon drivers on old macs are a real problem, and require that the usb be booted in 'compatibility mode'. The problem really comes after install, and it is an UBUNTU problem. Because you need to run your old mac with the 'nomodeset' kernel parameter, you need to be able to edit your grub boot options in order to get to a desktop to do so (there is another way, but you really don't want to go there). With an apple system, the keyboard will NOT work to bring up the grub menu because the keyboard isn't initialized until later in the boot process and you will be stuck with a black screen and no way to get out of it (the system will recognize the old Radeon and install the 'new' Radeon drivers, which do not work with the old gpu, which equals 'black screen').

I recommend that you use LMDE6, which is the Debian version of Mint, and avoid the ubuntu developer's decision to hide grub if linux is the only OS installed. Debian shows grub unless the user edits grub to hide it. Once you are shown the grub options, the 'e' key (for edit) will allow you to add the 'nomodeset' to the line that begins with 'linux' and you can boot to a desktop. Once there, you can add nomodeset to the /etc/default/grub and get a working desktop and subsequent boots.

[shutterfreak]

Macs don't have a bios -- they are strictly uefi, and the only way to enter the uefi is if you are doing it from macOS/OSX. There is no 'legacy' bios mode. And, since 2007 or so, all macs have been 64 bit, even if the efi is listed as 32-bit. Any 64-bit system can boot on them without reverting to the 32-bit uefi. I don't understand how you would actually address the Radeon issue, because the problem is with the modern kernel radeon drivers.

So far I only found bits of information scattered across different threads. It appears that the wakeup after suspend problem with the custom AMD RV610/M74 [Mobility Radeon HD 2400 XT] hardware and driver combination on e.g. the iMac 2008 was resolved for the happy few who managed to boot their iMac in non-UEFI mode. This mode is apparently supported for Boot Camp (MS Windows on Apple hardware) to work.

The Radeon drivers on old macs are a real problem, and require that the usb be booted in 'compatibility mode'. The problem really comes after install, and it is an UBUNTU problem. Because you need to run your old mac with the 'nomodeset' kernel parameter, you need to be able to edit your grub boot options in order to get to a desktop to do so (there is another way, but you really don't want to go there).

I have no Idea how the thumb drive with Linux Mint MATE installer can be booted in 'legacy' or 'compatibility' mode. What I see, is a Grub menu with 2 entries for launching Linux Mint installer: "plain" and "(compatibility)". Either launches in UEFI mode (the folder /sys/firmware/efi exists and is nonempty).

The "plain" entry runs fine out of the box but the "compatibity" entry requires me to actually remove the nomodeset boot parameter in order to get a GUI.

With an apple system, the keyboard will NOT work to bring up the grub menu because the keyboard isn't initialized until later in the boot process and you will be stuck with a black screen and no way to get out of it (the system will recognize the old Radeon and install the 'new' Radeon drivers, which do not work with the old gpu, which equals 'black screen').

Now this is interesting.

I recommend that you use LMDE6, which is the Debian version of Mint, and avoid the ubuntu developer's decision to hide grub if linux is the only OS installed. Debian shows grub unless the user edits grub to hide it. Once you are shown the grub options, the 'e' key (for edit) will allow you to add the 'nomodeset' to the line that begins with 'linux' and you can boot to a desktop. Once there, you can add nomodeset to the /etc/default/grub and get a working desktop and subsequent boots.

I gave LMDE6 a try and apparently it correctly handles our antiquated extended aluminum "Macintosh" keyboard whereas MATE swapped the "@" key and the "<" key. The Wireless chipset worked out of the box (no need for installing extra Broadcom drivers as was the case when installing MATE). I also got the builtin Apple iSight camera working.

The computer boots in EFI mode so I still have the pink screen noise after waking up from suspending the computer, which I expected since it appears that it can only be circumvented if the computer manages to boot in compatibility mode (which so far it never did).