Bash script redirect-brightness
Your problem is function keys to increase/decrease brightness are updating /sys/class/backlight/acpi_video0/brightness instead of /sys/class/backlight/nv_backlight/brightness
The original request was to intercept the function keys and use them to control the nv_backlight driver. The problem with this is:
- Tricky
udev scripts
- No pop-up notification slider displaying brightness without complicated Python scripting.
The solution is to use inotify to monitor changes to acpi_video0. Then calculate the brightness percentage and apply that same percentage to nv_backlight.
In the bash script below you need to set:
WatchDriver="/sys/class/backlight/acpi_video0/brightness"
PatchDriver="/sys/class/backlight/nv_backlight/brightness"
Place the script in /usr/local/bin and make it executable using:
chmod a+x /usr/local/bin/redirect-brightness
First run the script from the command line using
redirect-brightness -l
If there is a problem check the log file using:
cat /tmp/redirect-brightness.log
If all works well add redirect-brightness to your startup applications.
redirect-brightness bash script
#!/bin/bash
# NAME: redirect-brightness
# PATH: /usr/local/bin
# DESC: Redirect to correct driver when Ubuntu is adjusting the wrong
# /sys/class/DRIVER_NAME/brightness
# DATE: June 13, 2018. Modified June 14, 2018.
# NOTE: Written for Ubuntu question:
# https://askubuntu.com/q/1045624/307523
WatchDriver="/sys/class/backlight/intel_backlight"
PatchDriver="/sys/class/backlight/intel_backlight"
# Must be running as sudo
if [[ $(id -u) != 0 ]]; then
echo >&2 "Root access required. Use: 'sudo redirect-brightness'"
exit 1
fi
# inotifywait required
type inotifywait >/dev/null 2>&1 || \
{ echo >&2 "'inotifywait' required but it's not installed. Aborting."; \
echo >&2 "Use 'sudo apt install inotify-tools' to install it.'"; \
exit 1; }
# Was right watch driver directory name setup correctly?
if [[ ! -d $WatchDriver ]]; then
echo >&2 "Watch directory: '$WatchDriver'"; \
echo >&2 "does not exist. Did you spell it correctly? Aborting.'"; \
exit 1;
fi
# Was right patch driver directory name setup correctly?
if [[ ! -d $PatchDriver ]]; then
echo >&2 "Redirect to directory: '$PatchDriver'"; \
echo >&2 "does not exist. Did you spell it correctly? Aborting.'"; \
exit 1;
fi
# Get maximum brightness values
WatchMax=$(cat $WatchDriver/max_brightness)
PatchMax=$(cat $PatchDriver/max_brightness)
# PARM: 1="-l" or "--log-file" then write each step to log file.
fLogFile=false
if [[ $1 == "-l" ]] || [[ $1 == "--log-file" ]]; then
fLogFile=true
LogFile=/tmp/redirect-brightness.log
echo redirect-brightness LOG FILE > $LogFile
echo WatchMax: $WatchMax PatchMax: $PatchMax >> $LogFile
fi
SetBrightness () {
# Calculate watch current percentage
WatchAct=$(cat $WatchDriver/actual_brightness)
WatchPer=$(( WatchAct * 100 / WatchMax ))
[[ $fLogFile == true ]] && echo WatchAct: $WatchAct WatchPer: $WatchPer >> $LogFile
# Reverse engineer patch brightness to set
PatchAct=$(( PatchMax * WatchPer / 100 ))
echo $PatchAct | sudo tee $PatchDriver/brightness
[[ $fLogFile == true ]] && echo PatchAct: $PatchAct >> $LogFile
}
# When machine boots, set brightness to last saved value
SetBrightness
# Wait forever for user to press Fn keys adjusting brightness up/down.
while (true); do
inotifywait --event modify $WatchDriver/actual_brightness
[[ $fLogFile == true ]] && \
echo "Processing modify event in $WatchDriver/actual_brightness" >> $LogFile
SetBrightness
done
Original Answer June 11, 2018.
Work In Progress Answer
There are many nVidia users with similar problems in Ubuntu 18.04:
Before writing a script
I can write a script to mimic changes to /acpi_video and populate /nv_backlight but before I do try this:
- Edit
/etc/default/grub.
- Find
quiet splash
- Add behind splash:
acpi_backlight=vendor
- Save the file
- Run
sudo update-grub
According to this answer it should work for you: Xubuntu 18.04: make Fn brightness keys work with /sys/class/backlight/nv_backlight/
Wayland
Brightness doesn't work under Wayland. Make sure you aren't using it. See: The brightness of laptop screen cannot be adjusted with either the buttons or the slider. Edit
acpi_backlight=vendorin the answer below? Did it work?acpi_backlisht=vendor, theacpi_video0option goes away and a new optionsonycomes in and the hotkeys reflect changes insony/brightness, with no actual display brightness change. Thenv_backlightoption remains though and the manual changes to it still give me the actual change in brightness.acpi_video0and pump the equivalent percentage into nVidieo backlight.