For inspiration see:
- Github rowanphipps/macOS_rEFInd_guide
- EFI-Booting Ubuntu on a Mac
- How to Install and Set up Ubuntu 20.04 on an Old MacBook Pro
Here is what I did:
- Download ubuntu-22.04 and writing it onto a USB-stick
- restart the iMac, when the Apple chime sounds press the Option-Key
- select the Orange EFI icon
- select try/install ubuntu from the Grub menu
- After some time I got the Ubuntu welcome chime, so the iMac had booted into ubuntu-22.04, BUT the screen was just black all the time.
The iMac I wanted to install Ubuntu on has had its graphics card down-graded to 4850, I do not know if this was the reason that it didn’t work, I am sure apple has never sold a configuration this, so I understand if the Ubuntu people hadn’t testet it.
On next boot: press e (for edit) on the Grub Menu selection screen, replaced quiet splash with nomodeset and F10 will boot into Ubuntu. This time the iMac booted as expected. And Ubuntu can be installed onto a free partition.
chroot into the just installed Ubuntu
To make apt and other commands work on the newly installed Ubuntu-partition while still booted on the USB-stick, you need to have access to parts of the current root-filesystem, here how:
# root-disk-partion mounted on /target
cd /target
for i in dev dev/pts proc sys run;do mount -o bind /$i $i;done
chroot .
# set cmdline for linux
sed -i /etc/default/grub \
-e 's/^GRUB_TIMEOUT_STYLE=.*$/GRUB_TIMEOUT_STYLE=menu/' \
-e 's/^GRUB_TIMEOUT=.*/GRUB_TIMEOUT=3/' \
-e 's/^GRUB_CMDLINE_LINUX_DEFAULT=.*$/GRUB_CMDLINE_LINUX_DEFAULT="nomodeset"/' \
-e 's/^GRUB_TERMINAL=.*/GRUB_TERMINAL=console/'
#
apt update apt install refind
# use efibootmgr to set bootorder, I have refind firstonce you are done you can reboot your iMac
