Ubuntu: I can't lower the backlight/brightness


Why I can't control the brightness/backlight level?

At the first:

Notebook Positivo BGH - C500 Series.   Processor: AMD C60 series (dual core 800 mhz-1ghz)  GPU: Radeon HD 6290 (worked with fglrx/Catalyst)  

Hello everybody, this is my first post in 8-years-use of Ubuntu/Kubuntu, I've never had problems with any version, but when I've upgraded from Willy to Xenial I haven't take care in the latest version that the AMD/ATI property drivers (fglrx) have been discontinued or unsupported by the developers, and they advice against not upgrade for AMD users. The Fn keys dosen't work!

However, after upgrade, when I was configuring, I want install drivers from console:

sudo apt-get install fglrx fglrx-updates   "fglrx" and "fglrx-updates" has no candidates  

In the version Willy (and previous versions), I can't control or lower the brightness/backlight util the property drivers have been instaled.

In Ubuntu 16.04, the drivers are:

xserver-xorg-video-amdgpu  xserver-xorg-video-radeon  

And These are open drivers, but this is not the trouble really.

I've tried the following procedures:

I tried to put various links, but the newbies can't post more 2 links


1. Can't change backlight level by installing driver.

    sudo apt-get install xserver-org-video-amdgpu      sudo apt-get install xserver-org-video-radeon  

##2. It persist high shine, despite modifing /sys/class/backlight, and the promp shows me (radeon_bl0 is present):

    lspci | grep ati      00:01.0 VGA compatible controller: Advanced Micro Devices, Inc. [AMD/ATI] Wrestler [Radeon HD 6290]      ls /sys/class/backlight      radeon_bl0  

Inside the folder, brightness, max_brightness, actual_brightness, bl_power and others are present

    echo > 10 /sys/class/backlight/radeon_bl0/brightness   

There is no effect

    echo > 100 /sys/class/backlight/radeon_bl0/max_brightness      permission denied      chmod 0777 /sys/class/backlight/radeon_bl0/max_brightness      nano /sys/class/backlight/radeon_bl0/max_brighness      modifing 255 to 100      Ctrl+O > I/O Error       chmod 0777 /sys/class/backlight      The same result >  I/O Error   

And find another way:

    ls -alh /sys/class/backlight      lrwxrwxrwx  1 root root 0 abr 23 12:23 radeon_bl0 -> ../../devices/pci0000:00/0000:00:01.0/drm/card0/card0-LVDS-1/radeon_bl0  

And trying the same, and no effect.

3. Modifing the grub:

    GRUB_CMDLINE_LINUX="acpi_osi=Linux" | No effect      GRUB_CMDLINE_LINUX="acpi_backlight=none" | No effect      GRUB_CMDLINE_LINUX="acpi_backlight=vendor" | No effect      GRUB_CMDLINE_LINUX="acpi_backlight=video" | No effect      GRUB_CMDLINE_LINUX="acpi_backlight0" | No effect      GRUB_CMDLINE_LINUX="acpi_backlight=radeon_bl0" | No effect  

Rebooting and edit grub (with the same sentences) before start Ubuntu, strangely It don't start. Starting in "recovery mode", /sys/class/backlight, shows me:


But the SDDM dosen't start.

4. Adding the X11 configuration.

      cd /usr/share/X11/xorg.conf.d        dir > 10-amdgpu.conf is present        nano 10-amdgpu.conf | shows me                   Section "OutputClass"                   Identifier "AMDgpu"                   MatchDriver "amdgpu"                   Driver "amdgpu"                 EndSection  I added                  Section "Device"                  Identifier "card0" | put also "AMDgpu"                  Driver "amdgpu"                   Option "Backlight" "radeon_bl0"                  BusID "PCI:00:01:01"               End Section  

But it dosen't work, due option "Backlight" is for intel driver. I revised man of amdgpu and not figure this option. In several times, neither starts SDDM.

5. Using the command setpci:

     setpci -s 00:01.0 F4.B=7F | Not work       setpci -s 00:01.0 F4.B=FF | Not work       setpci -s 00:01.0 F4.B=50 | Not work       setpci -s 00:01.0 F4.B=80 | Not work  

This video card not support by the setpci

6. Installing xbacklight

     sudo apt-get install xbacklight       xbacklight -s 80 | there is no effect        No outputs have backlight property        xbacklight -d LVDS -s 80       RANDR Query Version returned error -1  

It dosen't work, I've searched, and xbacklight is deprecated for xf86-video-ati for control of backlight, I've installed script "light" (lightscript) but It dosen't work too.

7. Making udev rule:

          nano /etc/udev/rules.d/81-backlight.rules              # Set backlight level to 8           SUBSYSTEM=="backlight", ACTION=="add", KERNEL=="acpi_video0", ATTR{brightness}="8"            Save & Exit and there is no effect after boot  

8. Using systemd-backlight service.

           I don't understeand how this works, but I've got this from the prompt:              systemctl list-units | grep -i backl               systemd-backlight@backlight:radeon_bl0.service     loaded active exited    Load/Save Screen Backlight Brightness of backlight:radeon_bl0               system-systemd\x2dbacklight.slice       loaded active active    system-systemd\x2dbacklight.slice  

The systemd-backlight service is loaded for /sys/class/backlight ! But It dosen't work, the backlight don't change.

9. Using xrandr

       Finally I put in the console:  xrandr --output LVDS-1 --brightness 0.6 | 0.4 | 0.3  Previously identified output   

This "worked" for me, but when I restart the values of xrandr going to default, by more than I put xrandr --output LVDS1 --brightness 0.5 at start session. (On Kde by the System Settings>Start and Shutdown)


In all cases, the brightness/backlight ever is high, it dosen't matter I do, the Fn Keys don't work, and the Kde Indicator for brightness goes to 0 and the LCD looks the Christmas tree because it's turn up/down infinitely.

Anyone have more ideas?

Sorry for my bad english!


There's something very odd about the syntax you're using to write to the files in /sys/class/backlight/. Please try this, instead:

echo 128 | sudo tee /sys/class/backlight/radeon_bl0/brightness  

By the way, you were not able to modify "max_brightness" because that file is just there to let you know the maximum brightness you can use. You need to change the file named "brightness".

About your shell syntax: The shell redirection operator > only works if you're already running a shell as root (for example, using sudo -s), but I should let you know that doing so is generally considered a bad idea. Logging in to a root shell gives you great power; and with great power comes great whopping mistakes. It's easy to forget you're running as root and then accidentally mess up your whole system. That's why I recommend sudo, as in the example above. Sudo is a reminder to be careful: anything after the word sudo is normally off-limits and potentially dangerous.

However, if you are curious, it is possible to use the > file redirection operator the way you were asking, but you'd need to change the arguments around. The part that comes after the > is the filename to write to, the part before it is the command whose output you want to redirect. So, for example,

$ sudo -s  # cd /sys/class/backlight/*/  # echo 128  128  # echo 100 > brightness  # cat brightness  100  # echo 200 > brightness  # cat max_brightness  255  # cat max_brightness > brightness  # cat brightness  255  # exit  $   

(You'll notice your prompt changes to a hash mark when you're running a root shell. That's a subtle warning sign. Typing exit will get you back to the safety of your normal user account.)


there is no standard brightness level resolution in universal implementation. For example one of my linux boxes is a Toshiba Satellite L510 and has an 8 bit resolution. i.e. my /sys/class/backlight/acpi_video0/brightnesswill only accept values in [0,7]. I also have seen one other system has a resolution of 23 bits. i.e. [0-22].

To know the range of brightness values, read your /sys/class/backlight/radeon_bl0/max_brightness file. Also the value of the max_brightness file is most likely set by your system's firmware and you can not write to it. But the /sys/class/backlight/radeon_bl0/brightness file can be written to as long as the value being written is between 0 and the result of

cat /sys/class/backlight/radeon_bl0/max_brightness

also suspending your system and waking it up usually fixes some problems with regard to ACPI and UEFI - by extension functions keys. to suspend your system use the following command.

sudo pm-suspend

then wake your system by pressing the power button and check is the function keys are working.

Note:If u also have question or solution just comment us below or mail us on toontricks1994@gmail.com
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