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I have a couple of old white iMacs, both with Core 2 Duo Intel processors and both running MacOS Lion. I am trying to overwrite the MacOS completely and run Ubuntu native machines.

I have downloaded the latest distribution of Ubuntu for desktop and have created a bootable Ubuntu flash drive using Etcher and a bootable Ubuntu DVD using Disk Utility

When I boot the iMac to Boot Manager by holding down the Option key at the start, neither the flash drive nor the DVD appear on the bootable items list (although the iMac HD and Recovery HD do). I am assuming this is because of their file formats may not be recognisable by MacOS.

Is there a way of preparing the iMac's HD so that either of the flash or DVD bootable system can be recognised and booted from or is there an alternative?

I want to delete the MacOS and boot directly into Ubuntu.

Thanks for any advice.

Andy

I've run into the same problem and found your question. Turns out that the packages from the amd64 ISO images could work in principle but older UEFI Macs fail on the boot loader.

There used to be specifically tuned amd64+mac ISOs for older distribution.

See:
What is different about the Mac ISO image?

What works now is to use i386 images, for example the ones from Ubuntu Mate 18.04.1. Ubuntu Desktop itself unfortunately no longer provides i368.

Triple boot OSX, Ubuntu 18.04, Windows 7 on 2006 iMac 5.1 Core 2 Duo

The core 2 duo is 64 bit, but the EFI is 32 bit. This probably will help on other iMacs and MacBooks as well and some of the points about wifi and display manager are also transferable.

Before you do anything

Read all the instructions. Find your OSX disk, Windows 7 disk and licence. Belarc Advisor will recover key from Windows Registry. If MS download does not like your key use

Heidoc windows images

You can also use softpedia. Burn your ISO to DVD. The Ubuntu site does not have a version that works with older Macs! Don't waste your time, the issue is the old 32 bit EFI. In the end I found

Matt Gadient Ubuntu images for old macs

I downloaded Ubuntu 18.04 Desktop 64 bit Mac and burnt it to disk. Read the page, it is interesting. Perhaps he really is creating a botnet but there are easier ways than this!

Back up your data and learn to love lspci -nn -v .These instructions are not step by step. Others have done that but I do tell you the way so you don’t get lost.

Step 1 – Bootcamp imac Core 2 Duo

Create space for Ubuntu. Decide how much of your disk you want for each OS, but Ubuntu needs to go in the middle! In my case it is 250GB OSX, 500GB Ubuntu, 250GB Windows.

If installed, remove bootcamp. Expand your OSX to be the whole disk.

Re-install bootcamp using your OSX disk, make the Bootcamp partition (250GB) the size you want for Windows and follow Bootcamp instructions. My superdrive is on life support so this the worst part. The Windows 7 install prompted me to call an automated telephone line and provide the product key I had recovered and key in the responses. Torturous but it worked!

Install Bootcamp drivers from OSX disk. Don't let Windows Update touch these drivers, things will break.

Step 2 – Create Ubuntu Partition:

Shrink the OSX partition (250GB in my case) using Disk Utility leaving free space (500GB - MS-dos Fat 32?) for Ubuntu followed by your fresh Windows.

Step 3 – Intall rEFInd:

Without this the iMac will not recognise the DVD. Do not use rEFIt.

Visit Rod Smith's rEFInd pages for instructions and links.

I used Sourceforge rEFInd download and chose refind-bin-0.11.4.zip .

Extract it using finder and then run sudo ./refind-install from a terminal. When you reboot, rEFInd will appear and you will have options for your OSX and Bootcamp.

Step 4 – Install Ubuntu 18.04 on 2006 iMac 5.1

I loaded my Ubuntu disk in my external DVD (my superdrive being superdiva). rEFInd picked up the DVD and allowed me to boot Ubuntu DVD. Use the Ubuntu website for instructions on installing Ubuntu.

Make sure you install in the free partition. Set the install path as “/” and install boot loader (Grub) in the same partition otherwise you will break either rEFInd, OSX or Windows.

You will need to use an ethernet connection. Running Ubuntu Live gave me black windows so just install. I chose to do updates and downloads during install and to pick up proprietary drivers.

Step 5 – Ubuntu and Broadcom WiFi BCM4321

This drove me mad. All of the advice was a waste of time, just trust Ubuntu. In my case I checked Software & Updates app, clicked the Additional Drivers Tab and made sure I was using the proprietary driver Broadcom 802.11 Linux STA bcmwl-kernel-source. Yours may choose something else.

If you have to be clever, check lspci -nn -v in terminal. I saw my kernel driver is wl and my modules are ssb, wl. My controller is BCN4321 [14e4:4328] rev01.

However, I still could not connect to my dual band router but I could tether to my 5G phone. In the end I set my router to have one SSID for 2.4G and a different SSID for 5G. I still cannot connect to 5G on the router but I can connect to 2.4G. Its rock solid. Life has mysteries, embrace them and move on….

Step 6 – Display Manager GDM3 and LightDM on iMac ATI x1600

So, I was ready to hi five the world but my login screen looks like the aliens are sending a message. I guessed that if I hit S for Simon (my account name) and entered my password it might be ok. It was. But this is extra security I don’t need.

Lspci -nn -v showed I had AMD/ATI RV530 x1600 (which I docorrect). I followed a load of dead ends until I discovered gdm3 display manager was my issue. I installed lightdm and made it my default.

Install lightdm instructions

In a terminal do sudo apt-get install lightdm followed by sudo dpkg-reconfigure gdm3 and change to lightdm. Success but my screen saver options are now not working and the lock screen is dull.

The issue with gdm3 is Wayland is the default. So I chose to go back to gdm3 and disable Wayland by editing etc/gdm3/custom.conf

Disable Wayland

So now my Gnome desktop is back and I have working login, lock and screen saver. I feel epic, except when I log out or switch user and the system hangs…forever. So I shutdown and never switch user.

So triple boot with rEFInd present OSX, Ubuntu and Windows7. My iMac lives on.