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I recently tried to change the default brightness of my ubuntu by echoing values to /sys/class/backlight/acpi_video0/brightness, and installing xbacklight, as suggested by answers to other questions. However, after booting ubuntu after doing the above, the screen just went blank.

After further checking, I found /sys/class/backlight folder is empty, and I have not been able to add a folder even under root permissions.

marked as duplicate by Mitch Mar 13 '15 at 5:26

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Sys is special, you won't be able to create folders there (answers in linked question explain why). Per Fabby's answer to similar question, that would indicate Kernel thinks you have a CRT, therefore you have knobs to adjust brightness and contrast. You may want to search supported hardware to see whether yours is there, or file a bug against kernel.

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