View Full Version : [ubuntu] 8.10 - brightness user controls not working, but works via /sys

December 2nd, 2008, 10:32 PM
Since I upgraded to 8.10 from 8.04, LCD brightness control via the applet and the specific keys on the laptop are no longer working. However, I can change the brightness via /sys/devices/virtual/backlight/acpi_video0/brightness. By default the value is 7, which matches what's specified by "max_brightness" in the same directory, and changing the value of the file from 7 to something lower, appropriately lowers the brightness proportionally to the value.

Now, I've checked /etc/hal/fdi/policy/backlight.fdi and it's appropriately pointing to the right /sys directory mentioned above. In addition, I've run "acpi_listen" and confirmed that the keys are generating the values defined in /etc/acpi/events/video_brightness[up|down], so acpi_fakekey is being called with the correct values. so I'm at loss as to what could be causing the applet and the keys not to work.

Short of hacking /etc/acpi/video_brightness[up|down] to add some code to go and mess with /sys/devices/virtual/backlight/acpi_video0/brightness directly (which is what gnome and hal should be taking care of), I'm not sure what I can do.

December 2nd, 2008, 11:41 PM
Have you tried right clicking on the top panel and adding the Brightness Applet to the panel and using it to adjust the screens brightness? That's how I control mine.

Guess that's the applet you said you tried already.

December 3rd, 2008, 09:19 AM
That was indeed the applet I was referring to.

I've tried running Fedora 10 on this laptop, and the brightness control works flawlessly!

So clearly an Ubuntu 8.10 specific issue. It's always great when you "upgrade" to find yourself having a downgraded feature set when it comes to your day to day use of the system.

December 4th, 2008, 09:25 PM
I have the same issue, except that /sys/devices/virtual/backlight/acpi_video0/max_power states 7 and actual_brightness bl_power and brightness have 0 in them. I work for a month on this new notebook now and i have to say my vision detiriorated sevierly during that time, since brightness is stuck at 100% and have no other computer to work on. Is there a way to comunicate with bios or the vga directly, since the keys for the display are working even in the bios screen.
I didn't understand how to change it via /sys/devices/virtual/backlight/acpi_video0/ or anything around there :/