Ubuntu lap screen-brightness-not-working..

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To get working brightness key. try following

execute sudo gedit /etc/default/grub

Change this line

GRUB_CMLINE_LINUX_DEFAULT="

quiet splash"

to something like below

GRUB_CMDLINE_LINUX_DEFAULT="

quiet splash acpi_osi=Linux acpi_backlight=vendor"

Execute sudo update-grub and reboot . See if brightness keys are working.

It is still possible ubuntu won't remember your brightness settings. So you have to change brightness each time.

Please let us know the result as many sony users are facing this problem.

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This is for setting brightness manually after doing the above steps.

Try following for paths shown by ls /sys/class/backlight/*/

brightness and replace accordingly.

example paths will be like

/sys/class/backlight/acpi_

video0/brightness

1. For the above path Get the maximum brightness:

cat /sys/class/backlight/acpi_

video0/max_brightness

Try a lower value to set the brightness, say output is 16 so I will try with half of it

echo 8 | sudo tee /sys/class/backlight/acpi_

video0/brightness

If this works, make this happen in each login automatically by doing the following

sudo gedit /etc/rc.local

Enter this line just before exit 0. It should look like

echo YOUR_VALUE_HERE > /sys/class/backlight/acpi_

video0/brightness exit 0 ==============================
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help link http://askubuntu.com/
questions/162317/screen-brightness-not-working