Can't adjust the screen brightness using keyboard shortcut (fn+f2/f3). Running Xubuntu 13.04 w/ xfce4-power-manager on a Toshiba L840 laptop.
Tried editing the grub file w/
GRUB_CMDLINE_LINUX_DEFAULT="quiet splash acpi_backlight=vendor" -> no luck
Removed power-manager from autostart and included 'xfce4-power-manager --no-daemon' to auto start -> no luck
Only thing works is
echo 1 | sudo tee /sys/class/backlight/acpi_video0/brightness - > (brightness 1 to 7) from searching
very inconvenient way of doing it.
It would be great if someone could tell me how to rectify this problem or direct me to a source of information.

  • Take a look at this Post, see if it helps.
    – Mitch
    Jul 22, 2013 at 22:06

1 Answer 1


Did you tried this way:

step 1: terminal sudo gedit /etc/default/grub

step 2: modify your file at line GRUB_CMDLINE_LINUX="" like that: GRUB_CMDLINE_LINUX="acpi_osi=\"Windows 2012\""

step 3: terminal sudo update-grub

step 4: reboot

Worked for me on Asus X501A running Ubuntu 13.04 (same problem with fn keys)

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