Screen brightness unable to be changed in 20.04, usual solutions don't work
- Editing /etc/default/grub with multiple suggested configurations (with sudo update-grub and reboot after each modification).
- Editing /usr/share/X11/xorg.conf.d/80-backlight.conf and /usr/share/X11/xorg.conf.d/20-intel.conf (with reboots afterwards)
- Editing directly /sys/class/backlight/acpi_video0/brightness and /sys/class/backlight/acpi_video1/brightness (they take values from 1 to 10)
xrandr: Failed to get size of gamma for output default
Screen 0: minimum 1920 x 1080, current 1920 x 1080, maximum 1920 x 1080
default connected primary 1920x1080+0+0 0mm x 0mm
$ xrandr --output default --brightness 0.8
xrandr: Gamma size is 0.
$ ls /sys/class/backlight/
$ cat /usr/share/X11/xorg.conf.d/20-intel.conf
Option "Backlight" "acpi_video1"
$ cat /usr/share/X11/xorg.conf.d/80-backlight.conf
Identifier "Intel Graphics"
Option "AccelMethod" "sna"
Option "Backlight" "acpi_video0"
$ cat /etc/default/grub
# If you change this file, run 'update-grub' afterwards to update
# For full documentation of the options in this file, see:
# info -f grub -n 'Simple configuration'
GRUB_DISTRIBUTOR=`lsb_release -i -s 2> /dev/null || echo Debian`
GRUB_CMDLINE_LINUX_DEFAULT="quiet splash pcie_aspm=force acpi_osi="
##GRUB_CMDLINE_LINUX_DEFAULT="quiet splash acpi_backlight=video1"
# Uncomment to enable BadRAM filtering, modify to suit your needs
# This works with Linux (no patch required) and with any kernel that obtains
# the memory map information from GRUB (GNU Mach, kernel of FreeBSD ...)
# Uncomment to disable graphical terminal (grub-pc only)
# The resolution used on graphical terminal
# note that you can use only modes which your graphic card supports via VBE
# you can see them in real GRUB with the command `vbeinfo'
# Uncomment if you don't want GRUB to pass "root=UUID=xxx" parameter to Linux
# Uncomment to disable generation of recovery mode menu entries
# Uncomment to get a beep at grub start
#GRUB_INIT_TUNE="480 440 1"
$ cat /usr/share/X11/xorg.conf.d/10-nvidia-brightness.conf
VendorName "NVIDIA Corporation"
BoardName "Quadro K1000M"
Option "RegistryDwords" "EnableBrightnessControl=1"
Usage of the laptop keys changes /sys/class/backlight/acpi_video0/brightness, but without apparent further effect.
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