Page 1 of 2 12 LastLast
Results 1 to 10 of 15

Thread: Cannot change backlight brightness Ubuntu 14.04

  1. #1
    Join Date
    Dec 2007
    Beans
    78

    Cannot change backlight brightness Ubuntu 14.04

    This morning I found that I cannot change the brightness of my Dell XPs 13 laptop's display anymore. I tried the following to change the brightness

    - Use keyboard brightness keys
    - Run the commands shown below
    - Boot with kernel option acpi_backlight=vendor. This resulted in a dell_something folder being present in the /sys/class/backlight folder. Changing the brightness file in that folder does not help.
    - Add 'intel_backlight' to xorg.conf
    - Set "load legacy option ROM" BIOS option to enabled and "secure boot" to disabled
    - Boot with kernel option i915.disable-pch_pwm=0
    - Boot from a fresh Ubuntu 12.04 USB stick installation. I can still not control the brightness. Maybe this a hardware problem?

    Any ideas why this broke suddendly? I've upgraded from 12.04 to 14.04 in April and till yesterday the brightness keys were working fine.

    Code:
    echo 100 > /sys/class/backlight/intel_backlight/brightness
    echo 100 > /sys/class/backlight/acpi_video0/brightness
    Thanks!
    Last edited by cyrus_the_virus; June 5th, 2014 at 01:08 PM.

  2. #2
    Join Date
    May 2011
    Beans
    165

    Re: Cannot change backlight brightness Ubuntu 14.04

    Try getting into BIOS and change the "Load Legacy Option Rom" to "Enabled".

  3. #3
    Join Date
    Dec 2007
    Beans
    78

    Re: Cannot change backlight brightness Ubuntu 14.04

    Thanks for your help. I've tried this but unfortunately it does not work for me. I did some more research and found this related bug report. It seems that this is a very common problem.

  4. #4
    Join Date
    May 2014
    Beans
    619

    Re: Cannot change backlight brightness Ubuntu 14.04

    Cyrus, does the osd for brightness appear on your display when you try the brightness hotkeys? Do you get any resonse from terminal command
    Code:
    acpi_listen

  5. #5
    Join Date
    Dec 2007
    Beans
    78

    Re: Cannot change backlight brightness Ubuntu 14.04

    Hi Jeremy,

    Yes, the OSD brightness appears when I use the hotkeys. The acpi_listen command shows the following:
    Code:
    $ acpi_listen
    video/brightnessup BRTUP 00000086 00000000
     PNP0C14:00 000000d0 00000000
    video/brightnessup BRTUP 00000086 00000000
     PNP0C14:00 000000d0 00000000
    video/brightnessdown BRTDN 00000087 00000000
     PNP0C14:00 000000d0 00000000
    video/brightnessdown BRTDN 00000087 00000000
     PNP0C14:00 000000d0 00000000
    video/brightnessdown BRTDN 00000087 00000000
     PNP0C14:00 000000d0 00000000

  6. #6
    Join Date
    May 2014
    Beans
    619

    Re: Cannot change backlight brightness Ubuntu 14.04

    Code:
    video.use_native_backlight=1
    in grub without anything other than quiet splash

    Your line in /etc/default/grub should be
    Code:
    GRUB_CMDLINE_LINUX_DEFAULT="quiet splash video.use_native_backlight=1"
    Last edited by jeremy31; June 6th, 2014 at 11:27 AM.

  7. #7
    Join Date
    Dec 2007
    Beans
    78

    Re: Cannot change backlight brightness Ubuntu 14.04

    I have tried to do that (and run update-grub) but unfortunately it does not help

  8. #8
    Join Date
    May 2014
    Beans
    619

    Re: Cannot change backlight brightness Ubuntu 14.04

    Quote Originally Posted by cyrus_the_virus View Post
    I have tried to do that (and run update-grub) but unfortunately it does not help
    I am just wondering what is going on
    Code:
    cat /proc/cmdline
    Code:
    ls /sys/class/backlight
    Code:
    cat /var/log/Xorg.0.log | grep backlight
    And what exactly did you do to add intel_backlight to xorg.conf? Where is the file at and what is it named and what does it contain?

    Have you run Toz's handy script
    Code:
    for interface in /sys/class/backlight/*; do echo $interface; cat $interface/actual_brightness; cat $interface/max_brightness; done

  9. #9
    Join Date
    Dec 2007
    Beans
    78

    Re: Cannot change backlight brightness Ubuntu 14.04

    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:

    Code:
    $ 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
    Code:
    $ ls /sys/class/backlight
    intel_backlight
    Code:
    $ 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')
    Code:
    $ 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

  10. #10
    Join Date
    Dec 2007
    Beans
    78

    Re: Cannot change backlight brightness Ubuntu 14.04

    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:

    Code:
    $ 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
    Code:
    $ ls /sys/class/backlight
    intel_backlight
    Code:
    $ 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')
    Code:
    $ 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

Page 1 of 2 12 LastLast

Tags for this Thread

Bookmarks

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •