Complete newbie here. I have installed Ubuntu and love it, but the screen brighness is far too low. I cannot use the computer in the daytime. I have insalled Ubuntu single boot in an intel iMac with rEFInd.
Forgive me if I give too litle information; happy to post outputs of any commands.
Some facts so far:
The slider on “brightness and lock” has no effect at all.
I have tried installing xbacklight and the -in and -dec commands do nothing.
I changed the grub file to say:
GRUB_CMDLINE_LINUX_DEFAULT="quiet splash acpi_backlight=none acpu_osi= " GRUB_CMDLINE_LINUX="acpi_osi=Linux acpi_backlight=vendor"
I also tried "native" and "video" in this last line. No change.
Then I tried this solution: link
sudo apt install sysfsutils
“ls /sys/class/backlight/” returns "acpi_video0"
I don’t have a folder called /sys/class/brightness.
$ lspci -nnk | grep "VGA" -A2 gives:
01:00.0 VGA compatible controller : Advanced Micro Devices, Inc. [AMD/ATI] Whistler [Radeon HD 6630M/6650M/6750M/7670M/7690M] [1002:6741]
Then I tried for i in /sys/class/backlight/*; do echo $i; cat $i/brightness; cat $i/actual_brightness; cat $i/max_brightness; done
15 15 15
I installed “indicator brightness, which shows values from 1 -15 but has no effect.
I think that what is happening is that the acpi_video0 control is given to a root or BIOS device (maybe EFI partition?)and stuck at 15, which I cannot change.
Any suggestions on what I should do to be able to use Ubuntu is daylight conditions? Much appreciated.
UPDATE: I tried to edit /usr/share/X11/xorg.conf.d/10-radeon.conf the orginal reads:
Section "OutputClass" Identifier "Radeon" MatchDriver "radeon" Driver "radeon" EndSection
I changed it to read:
Section "Device" Identifier "card0" Driver "Radeon" Option "Backlight" "radeon_backlight" BusID "PCI:0:2:0" EndSection
But that dodn't work: the reboot hung on "start user manager for UID 121". So I have edited the file back to the orginal from the live USB.
Any help would be much appreciated!