Ubuntu – I cannot change the screen brightness

12.10backlightbrightnesshp

here's my problem:

Ever since I installed Ubuntu 12.10 on my computer I haven't been able to change the screen brightness, it was always set to the maximum. I did take a look at this post:

Decrease Backlight Below Minimum

And it helped me resolved the issue with the unbearable brightness, however one problem persists: I cannot change it through "Brightness & Lock" or the function buttons (F2 and F3), when I press the buttons, the animation shows up but nothing happens.
I tried the following:

http://www.refreshit.info/2012/08/solved-brightness-increase-and-decrease.html

It did nothing…

If it helps:

I have an HP-dv6 6185la, it has an ATI Radeon 6770M HD card and an Intel HD Integrated Graphics Card

It only detects the "Intel® Sandybridge Mobile"

Thanks in advance.

Best Answer

What worked for me was to change the /etc/default/grub file as follows:

Open a terminal (Ctrl + Alt + T) and type sudo gedit /etc/default/grub
Find the line: GRUB_CMDLINE_LINUX_DEFAULT="quiet splash" and modify it to one of the following:

GRUB_CMDLINE_LINUX_DEFAULT="quiet splash acpi_backlight=vendor"

or

GRUB_CMDLINE_LINUX_DEFAULT="quiet splash acpi_osi=Linux acpi_backlight=vendor" (try this if the first one doesn't work)
Save and close gedit.
Then type sudo update-grub
Reboot your pc.

EDIT

As from Ubuntu 13.10, this did not solve the problem for me on a Toshiba laptop. I needed one extra step for the problem to be solved.

I had to create an xorg.conf file in /etc/X11/ with the following contents:

Section "Device"
       Identifier      "Configured Video Device"
       Driver          "intel"
       Option          "Backlight"       "intel_backlight"
EndSection
#
Section "Monitor"
       Identifier      "Configured Monitor"
EndSection
#
Section "Screen"
       Identifier      "Default Screen"
       Monitor         "Configured Monitor"
       Device          "Configured Video Device"
EndSection

WARNING!! Getting the file wrong or if this configuration is not compatible with your hardware, might end up with an unbootable system! It happened to me.

In that case, you'll have to delete (or rename) the file, but to do so requires either booting from a liveUSB or liveDVD (the simplest way) or booting in recovery mode, making the Ubuntu partition rewritable and then delete the offending xorg.conf file.

EDIT2

Starting with kernel 4.4, the toshiba backlight device is blacklisted and doesn't appear any longer thus rendering these workarounds redundant.

Related Solutions

Ubuntu – Brightness control on Samsung Ativ Book 6

I managed to solve this by doing a fresh 14.04 install, the screen brightness commands now works right after the install without any trick needed. I reinstalled after upgrading to 14.10 bricked my graphic interface.

Ubuntu – I can’t lower the backlight/brightness

There's something very odd about the syntax you're using to write to the files in /sys/class/backlight/. Please try this, instead:

echo 128 | sudo tee /sys/class/backlight/radeon_bl0/brightness

By the way, you were not able to modify "max_brightness" because that file is just there to let you know the maximum brightness you can use. You need to change the file named "brightness".

About your shell syntax: The shell redirection operator > only works if you're already running a shell as root (for example, using sudo -s), but I should let you know that doing so is generally considered a bad idea. Logging in to a root shell gives you great power; and with great power comes great whopping mistakes. It's easy to forget you're running as root and then accidentally mess up your whole system. That's why I recommend sudo, as in the example above. Sudo is a reminder to be careful: anything after the word sudo is normally off-limits and potentially dangerous.

However, if you are curious, it is possible to use the > file redirection operator the way you were asking, but you'd need to change the arguments around. The part that comes after the > is the filename to write to, the part before it is the command whose output you want to redirect. So, for example,

$ sudo -s
# cd /sys/class/backlight/*/
# echo 128
128
# echo 100 > brightness
# cat brightness
100
# echo 200 > brightness
# cat max_brightness
255
# cat max_brightness > brightness
# cat brightness
255
# exit
$

(You'll notice your prompt changes to a hash mark when you're running a root shell. That's a subtle warning sign. Typing exit will get you back to the safety of your normal user account.)