Ubuntu – I can’t lower the backlight/brightness

16.04amd-graphicsbacklightbrightness

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

Abstract:

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:

     acpi_video0

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)

Conclussion

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!

Best Answer

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.)

Update June 16, 2019

Last month, 2 years after problem was reported, OP discovered LightDM (Ubuntu Unity Desktop Manager) was source of problem. That said, in addition to the list below, there is another grub parameter that can be tried:

video.use_native_backlight=1

See this answer for more.

Original Answer

The ultimate reference seems to be in Arch Linux which is a site I've turned to many times to fix difficult problems.

Kernel Parameters

Looking at your cat /proc/cmdline there are no extra kernel parameters passed. The above link states:

Sometimes, ACPI does not work well due to different motherboard implementations and ACPI quirks. This includes some laptops with dual graphics (e.g. Nvidia/Radeon dedicated GPU with Intel/AMD integrated GPU). On Nvidia Optimus laptops, the kernel parameter nomodeset can interfere with the ability to adjust the backlight. Additionally, ACPI sometimes needs to register its own acpi_video0 backlight even if one already exists (such as intel_backlight), which can be done by adding one of the following kernel parameters:

acpi_backlight=video
acpi_backlight=vendor
acpi_backlight=native

If you find that changing the acpi_video0 backlight does not actually change the brightness, you may need to use acpi_backlight=none.

Try each of the acpi_backlight=xxxx options on your grub kernel paremeters line

When `xbacklight` doesn't work

You've tried xbacklight already and the link above addresses this:

On some systems, the brighness hotkeys on your keyboard correctly modify the values of the acpi interface in /sys/class/backlight/acpi_video0/actual_brightness (As we tried in comments) but the brightness of the screen is not changed. Brigthness applets from desktop environments (ie Ubuntu brightness setting slider bar) may also show changes to no effect.

If you have tested the recommended kernel parameters and only xbacklight works, then you may be facing an incompatibility between your BIOS and kernel driver.

In this case the only solution is to wait for a fix either from the BIOS or GPU driver manufacturer.

A workaround is to use the inotify kernel api to trigger xbacklight each time the value of /sys/class/backlight/acpi_video0/actual_brightness changes.

First install inotify-tools. Then create a script around inotify that will be launched upon each boot or through autostart.

Below is script you need to create called: /usr/local/bin/xbacklightmon

#!/bin/sh

path=/sys/class/backlight/acpi_video0

luminance() {
    read -r level < "$path"/actual_brightness
    factor=$((100 / max))
    printf '%d\n' "$((level * factor))"
}

read -r max < "$path"/max_brightness

xbacklight -set "$(luminance)"

inotifywait -me modify --format '' "$path"/actual_brightness | while read; do
    xbacklight -set "$(luminance)"
done

There is a lot more in the link above but these steps are a good place to start.

Dedicated Forums

For additional support there are dedicated Linux Graphics forums:

Ubuntu – Display brightness cannot be adjusted 18.04

An alternative method is to install a PPA and brightness APP which also adjusts gamma - AWESOME!, and ... for any individual screen TOO!

Here are the 3 simple steps:

$ sudo add-apt-repository ppa:apandada1/brightness-controller
$ sudo apt update
$ sudo apt install brightness-controller

Then find it ...

Brightness Controller

in your App's/Accessories

Always Trying to help, Mark