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Adjust brightness in Linux Mint

I installed Linux Mint Qiana 17.2 on my (very old) Acer Aspire laptop. Was pretty surprised that I was not able to adjust the screen brightness using the laptop buttons.

The hack I got was as follows,
Open terminal (as a superuser)
We now need gksudo to edit the grub file

You can do
gksudo gedit /etc/default/grub
 
In the text file that opens, look for the line which says
GRUB_CMDLINE_LINUX=""

In the empty quotes i.e. the "" insert the words "acpi_backlight=vendor"

The line now looks like this
GRUB_CMDLINE_LINUX="acpi_backlight=vendor"

Remember to save before you close the file
Back again in the terminal session, type sudo update-grub
Reboot

ACPI is Advanced Configuration and Power Interface
It is used when the machine starts to control the amount of power given to each device attached to the computer. When we do acpi_backlight=vendor it tries to load vendor drivers before it tries the default generic driver for screen brightness

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