I can't lower the backlight/brightness
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.)
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Matias González
Updated on September 18, 2022Comments
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Matias González over 1 year
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!
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hackerb9 over 4 yearsHmm... I'm getting down votes on this, but it is not clear that my answer was incorrect or unhelpful for this specific question. Before down voting, please leave a comment here so I can understand and improve my answer. Thanks!
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rjt about 3 yearsYou are correct. The posting has
echo > 100 /sys/class/backlight/radeon_bl0/max_brightness
which is definitely not going to work. Might not be the actual answer, but gets the op on a better path.