[ubuntu] Problems setting default brightness with /etc/rc.local

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http://ubuntuforums.org – Hey, I can change my display brightness in the file /sys/class/backlight/intel_backlight/brightness with the command "echo x > /sys/class/backlight/intel_backlight/brightness" were x is a certain brightness level. I want to use this command to set a default brightness level for every reboot since the actual one is much to bright. The above command doesnt work right away, as I found out I first have to change the permissions for /sys/class/backlight/intel_backlight/brightness. I did this with "sudo chmod a+w" (don't know if that's the right way, but it works...?). But (Hardware)