# Screen brightness not changing on Acer 5742 notebook

Screen brightness is not changing on my ACER 5742 notebook. I have Ubuntu 10.10 installed inside Windows 7 OS. Hotkeys are used for changing brightness. Though, a bar displaying brightness level appears on screen but there is no actual change in brightness of screen.

This worked for me. Run:

gksu gedit /etc/default/grub


Change the line:

GRUB_CMDLINE_LINUX=""


GRUB_CMDLINE_LINUX="acpi_osi=Linux"


Then run sudo update-grub and reboot. Credit to this guy.

Modifying both these lines in /etc/default/grub worked for my 4810T:

GRUB_CMDLINE_LINUX_DEFAULT="quiet splash acpi_backlight=vendor"
GRUB_CMDLINE_LINUX="acpi_osi=Linux"


I had the same problem with my Acer 5749. The bar displaying the brightness would show that the brightness was moving up and down, but the actual brightness wasn't changing.

In /etc/default/grub, I tried just:

GRUB_CMDLINE_LINUX="acpi_osi=Linux"


But it didn't work. Then I tried:

GRUB_CMDLINE_LINUX_DEFAULT="quiet splash acpi_backlight=vendor"
GRUB_CMDLINE_LINUX="acpi_osi=Linux"


and that did work.

In both cases I edited the lines in /etc/default/grub then ran sudo update-grub and rebooted.

### Another way, by editing just one line:

Finally I tried just:

GRUB_CMDLINE_LINUX_DEFAULT="quiet splash acpi_backlight=vendor"


and that worked too. I put the other line back to how it was originally and the brightness control still works after running sudo update-grub and rebooting again:

GRUB_CMDLINE_LINUX=""

• I'm glad I posted this because the hard drive failed and was replaced. Now I need to fix the brightness problem again. I'll try just editing the GRUB_CMDLINE_LINUX_DEFAULT line in /etc/default/grub and running 'sudo update-grub'. – Chris Moore Jul 24 '12 at 23:49
• That worked. . . – Chris Moore Jul 25 '12 at 0:58