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I tryed ubuntu 14.04 and 15.10, but I can't change the brightness. It is always on maximum.

  • I try changing the xbacklight, max_brightness, íntall driver NVIDIA quadro... – NDLuong Apr 6 '16 at 15:09
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The simplest way is to use a program called xbacklight , open your terminal and type this

sudo apt-get install xbacklight

Brightness range can go upto 100 from 0 . type this xbacklight -set 50 to set brightness to 50 from 100.

you can also increase and decrease the brightness from present value to specified level if you want to increase to 10% from current value of brightness then you can give this

xbacklight -inc 10

and to decrease 10% you can give this

xbacklight -dec 10 
  • I've tried but nothing changed – NDLuong Apr 6 '16 at 14:48
  • What you did exactly ? What's the output ? any error messages ? – storm Apr 6 '16 at 15:08
  • No error messages, but brightness no change ! – NDLuong Apr 7 '16 at 2:39
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You can try to change grub configuration file. Open it

sudo nano /etc/default/grub

and go to the following line:

GRUB_CMDLINE_LINUX_DEFAULT="quiet splash"

Now, next step depend on your computer. Try to change the above line, with one of the following:

GRUB_CMDLINE_LINUX_DEFAULT=”quiet splash acpi_backlight=vendor”

GRUB_CMDLINE_LINUX_DEFAULT=”quiet splash acpi_osi=Linux acpi_backlight=legacy”

GRUB_CMDLINE_LINUX_DEFAULT=”quiet splash acpi_osi=Linux”

GRUB_CMDLINE_LINUX_DEFAULT=”quiet splash acpi_osi=”

Every time that you edit /eft/default/grub file you have to run the following command that will apply changes.

sudo update-grub

To see results you have to reboot your system.

If the previous solution doesn't change your situation, you can try to do 2 things:

  • update your kernel
  • use a workaround

Update your kernel to latest Ubuntu version

sudo apt-get update
sudo apt-get install linux-image-generic

Workaround

Make a script to increment your brightness and one to decrement and bind them to a shortcut. You can try to use mine that I'm using on my PC.

Brighness up:

#! /bin/bash

# get max brightness and actual brighness
MAX=`cat /sys/class/backlight/intel_backlight/max_brightness`
AC_BR=`cat /sys/class/backlight/intel_backlight/brightness`

# grow brightness of 5%
AC_BR=$((MAX / 100 * 5 + AC_BR))

# check if i can set new brightness
if (($AC_BR <= $MAX)); then
  echo $AC_BR > /sys/class/backlight/intel_backlight/brightness
fi

Brightness down:

#! /bin/bash

# get max brightness and actual brighness
MAX=`cat /sys/class/backlight/intel_backlight/max_brightness`
AC_BR=`cat /sys/class/backlight/intel_backlight/brightness`

# decrease brightness of 5%
AC_BR=$((AC_BR - MAX / 100 * 5))

# check if i can set new brightness
if (($AC_BR > 0)); then
  echo $AC_BR > /sys/class/backlight/intel_backlight/brightness
else
  echo 5
fi

Copy the two bash scripts in two different file and give them execution permission:

chmod +x <file_name>

Move two script into your local bin directory to let you access to them everywhere in terminal:

sudo mv <file_brightness_up> <file_brightness_down> /usr/local/bin

Now you are ready to bind the scripts with shortcut. From System Setting select Keyboard and then Shortcuts. Select from the list on the left Custom Shortcuts and press Add shortcut button (+). Insert something as name and <file_brightness_up> file name as command and save. Then double click on right column and press your preferred shortcut.

Do the same for brightness down script.

To be sure that script works you have to change brightness file owner. So open /etc/rc.local file

sudo nano /etc/rc.local

and add the following line before exit 0:

chown <username>:<username> /sys/class/backlight/intel_backlight/brightness 

Where is your user name. Reboot your system to apply changes.

It should work because also your PC have an Intel graphic card. So you should get actual brightness value with:

cat /sys/class/backlight/intel_backlight/brightness

I hope this could help you.

  • In file /sys/class/ have only acpi_video0 and nv_backlight, don't have intel_backlight ! – NDLuong Apr 7 '16 at 2:19

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