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!
Re: Cannot change backlight brightness Ubuntu 14.04
Try getting into BIOS and change the "Load Legacy Option Rom" to "Enabled".
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.
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
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
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"
Re: Cannot change backlight brightness Ubuntu 14.04
I have tried to do that (and run update-grub) but unfortunately it does not help :(
Re: Cannot change backlight brightness Ubuntu 14.04
Quote:
Originally Posted by
cyrus_the_virus
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:
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
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
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