[64 bit] lenovo G580 brightness control not working in ubuntu 12.04

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http://ubuntuforums.org – I recently purchased a lenovo G580 laptop. It does not have a separate graphics card. I also installed ubuntu and windows 7 64 bit . Lenovo provided a driver cd for windows 7. I installed all the drivers. The lenovo FN+up and down brightness control works fine in windows 7. But it does not work in Ubuntu. When I press the key combination, the brightness control appears and it shows the brightness is decreasing or increasing, but actually nothing happens. As i am new to linux, I did some search in the forums and found out two solution. 1. changing the etc/default/grub file to modify the ent (Hardware)