Cannot change backlight brightness Ubuntu 14.04

[jeremy31]

I used this/ article that suggests making a change in xorg.conf. I removed this later because it does solve my problem. I think it just tells to which file the brightness value should be echoed, but since echoing a value manually does not work this solution does not work either.

Here is the output of the commands that you gave me:

$ cat /proc/cmdline
BOOT_IMAGE=/boot/vmlinuz-3.13.0-29-generic root=UUID=4e04ddb0-3020-4b02-827f-635306f670db ro quiet splash video.use_native_backlight=1 vt.handoff=7

$ ls /sys/class/backlight
intel_backlight

$ cat /var/log/Xorg.0.log | grep backlight
[    11.054] Kernel command line: BOOT_IMAGE=/boot/vmlinuz-3.13.0-29-generic root=UUID=4e04ddb0-3020-4b02-827f-635306f670db ro quiet splash video.use_native_backlight=1 vt.handoff=7
[    11.101] (--) intel(0): found backlight control interface intel_backlight (type 'raw')

$ for interface in /sys/class/backlight/*; do echo $interface; cat $interface/actual_brightness; cat $interface/max_brightness; done
/sys/class/backlight/intel_backlight
4882
4882

Note that this was done with video.use_native_backlight=1

Have you tried to set the brightness using

echo 3500 | sudo tee /sys/class/backlight/intel_backlight/brightness

with and without video.use_native_backlight?

It sounds like using the 3.14.5 kernel fixes a backlight bug on the XPS13 per a bug report https://bugs.freedesktop.org/show_bug.cgi?id=76276

[cyrus_the_virus]

Hi, sorry for my late reply.

Today I wanted to look into your latest comments and I found out that the display is completely broken now. There is no backlight at all black even during the initial boot up. So, I think it is safe to assume that this is a hardware problem. I will contact Dell support to send it back for repair.

[jeremy31]

That isn't good, hopefully Dell will have it fixed and back to you soon

[cyrus_the_virus]

I hope so too. Thanks again for your help with troubleshooting the problem

[firewireo]

Hi there!

I don't know whether you solved this problem alread or not but I just upgraded from 12.04 to 14.04 on an Asus N56VZ laptop and I'm having the same problem: my Fn+F5 or Fn+F6 keys are not adjusting the brightness, so I googled and googled and found the suggestions of adding /usr/share/X11/xorg.conf.d/20-intel.conf file. and the suggestion to add some lines in your grub after "quiet splash"....
I did all that and non worked!! then I noticed that my graphics isn't showing Inte in "settings>details>graphics" it was showing Gallium!!... anyways... I decided to start over and delete the files that I added in /usr/share/X11/xorg.conf.d/20-intel.conf as well as delete the line after "quiet splash" in grub, and whilst i was at it, I also deleted "nomodeset" line from the grub. I don't even know why it's there to begin with, it shouldn't be there! and by the way I was updating grub and restaring all the time, nothing worked, then I finally started in recovert mode and chose "failsafe graphic" and switched to "...generic..." , restarted one more time and VOILA Function key works!, I went to settings>details and graphics say Intel Ivy bridge!!!
I have no idea what the hell was that all about but it's working now!
One more thing that I noticed before running in recovery mode: everytime I ran "ls /sys/class/backlight" it showed asus-nb-wmi
but after recovery when I booted in normal and ran "ls /sys/class/backlight" it showed "intel_backlight"

Sorry for rather long reply, I'm hoping my experience can benefit the developer and give them a clue as to what was causing the bug.

Best of luck