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I faced this problem when I brought a new HP Laptop , hoping to install Ubuntu(Linux) but when i booted from a Live DVD the brightness was set at max and wouldnt be changed from the function keys or from the brightness settings bar, and it was the same after installation.

Specs- HP Probook 4440s

Intel core i5 3210m Intel HD 4000 graphics 6gb ram Motherboard-HP

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2 Answers 2

up vote 6 down vote accepted

After a lot of searching on the net, I tried the "acpi_backlight=vendor" kernel option, and it worked! , not only for Ubuntu, but for other Linux Os as well, so i am posting a guide.

Test- Restart your system, and when you get to the grub menu, select your distribution (Ubuntu 13.04), dont press enter, but press e (to edit).

This would bring up your menu entry for editing.

Append to the line with starts with linux (and looks like linux /boot/linux3.9. ............ (at the end of this line, leave a space and add) acpi_backlight=vendor

so that it will look like linux /boot/vmlinuz-310-x86_64 root=UUID=3161dd63-38c0-44bc-bc1e-34b692209b0b ro acpi_backlight=vendor

After this press F10 to boot.

Now try changing the brightness. It works for me.

Now we have to make it permanent

To do that we need to edit the Grub configuration file-

In a terminal type

sudo gedit /etc/default/grub

This would open the Grub configuration file. In this file we have to edit the line

GRUB_CMDLINE_LINUX=""

to

GRUB_CMDLINE_LINUX="acpi_backlight=vendor"

After that save the file and run (type in the terminal)

sudo update-grub

to update the Grub configuration file.

Thats It! Now the brigtness settings can be changed any time and will be persistent across reboots (at least for me!)

Thank You!

If anyone has queries please post them here.

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I have a Samsung Series 9 NP900X3C, which has a Intel HD Graphics 4000 chip. When I use the the Fn keys for changing the brightness, it shows me a nice OSD and sets the value in

/sys/class/backlight/samsung/brightness

However, this doesn't do anything to the actual screen. Instead, I have to

echo $number >> /sys/class/backlight/intel_backlight/brightness

This is with the acpi_backlight=vendor option. If I remove it, the OSD turns up, changes the right brightness file, and the keys work! Only the brightness level does not get saved between reboots.

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Perhaps you could manually symlink /sys/class/backlight/samsung/brightness to /sys/class/backlight/intel_backlight/brightness (dont know if it would be persistant across reboots though) –  Aaditya Bagga Dec 20 '13 at 14:40
    
They don't contain the same scale of numbers. Anyway, removing the option makes everything makes it work, albeit the setting vanishes between suspends. –  user207046 Dec 21 '13 at 23:31

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