Brightness and nomodeset persistence with UBUNTU on iMac


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Hello Community,
my name is Martin and I am from Austria. I have been a Linux user for a number of years now, in addition, we also have an iMac from mid 2010 here. As the iMac is starting to show its age, no more OS updates available for this model, programs becoming out of date, I decided a few days ago to try and dual boot Linux UBUNTU 20.04 on the imac.

Here the basic specs:
iMac mid 2010
12Gb Ram
3Ghz i3
UBUNTU 20.04 with Kernel 5.4
Boot Manager used is rEFInd
Graphics Radeon HD4670

UBUNTU is running very well on the iMac, I am writing this now from the Linux installation, there are just 2 nagging issues I would appreciate your support with:

1. Brightness. It is not possible at all to adjust the screen brightness. Looking into /sys/class/brightness the only entry is acpi_video0 . I have spent days looking through the forums trying to find a solution for this but to no avail.

2. If I simply select linux as the boot option from the boot manager, linux will boot but the screen quickly turns black. I can get around this each time by pressing f2 in the boot manager with the linux option selected. In the command line show I insert "nomodeset" withoout the inverted commas. Linux then boots normally. My question here is, how do I make this nomodeset option permanent so I dont need to enter it each time. I have tried putting it in the Grub config file and updating grub, but I assume that the rEFInd makes grub redundant so the command is not being read.

Many thanks in advance for your support.

Last edited:


New Member
i managed to solve point 2. rEFInd provides a script for setting up a refind_linux_conf file in the /boot directory. This script must be run in linux, not in the mac installation.

copy the script mkrlconf to the linux partition, say on the desktop
from linux open terminal and cd to desktop
make the file executable with chmod +x mkrlconf
execute script with sude ./mkrlconf

that should be it.

Now just need to get the screen brightness sorted out. Any ideas?


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