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Fixing Ubuntu 20.04 Brightness Adjust Not Working Issue

Ubuntu 11

If you’re an Ubuntu 20.04 user and you’ve encountered issues with adjusting your screen brightness, you’re not alone. This is a common issue that can be fixed with a few simple steps. In this article, we’ll cover three potential solutions: using xrandr, modifying GRUB settings, and updating the kernel.

Quick Answer

To fix the brightness adjust not working issue in Ubuntu 20.04, you can try using the xrandr command to manually adjust the brightness, modify the GRUB settings to use the vendor-specific driver for the backlight, or update the kernel to resolve any hardware compatibility issues.

Solution 1: Using xrandr

The xrandr command is a primitive command-line tool to interact with the RandR extension of the X Window System. It can resize, rotate, reflect, set the brightness level, and set the orientation of the screen.

To adjust the brightness with xrandr, follow these steps:

  1. Open a terminal. You can do this by pressing Ctrl + Alt + T.
  2. Type the following command: xrandr --output LVDS-1 --brightness 0.95

In this command, --output LVDS-1 specifies the output to adjust. LVDS-1 is typically the default output for the primary monitor. --brightness 0.95 sets the brightness level. This can be any value between 0 (completely dark) and 1 (maximum brightness).

Solution 2: Modifying GRUB settings

The GRUB bootloader can be configured to fix the brightness control issue. Here’s how to do it:

  1. Open a terminal.
  2. Type sudo nano /etc/default/grub to open the GRUB configuration file in a text editor.
  3. Find the line that reads GRUB_CMDLINE_LINUX_DEFAULT="quiet splash".
  4. Change this line to GRUB_CMDLINE_LINUX_DEFAULT="quiet splash acpi_backlight=vendor".
  5. Press Ctrl + X, then Y, then Enter to save and close the file.
  6. Run sudo update-grub to update GRUB with your new settings.

The acpi_backlight=vendor parameter tells the system to use the vendor-specific driver for the backlight.

After modifying the GRUB settings, restart your computer and see if the brightness control is working.

Solution 3: Updating the Kernel

If neither of the above solutions work, you can try updating your kernel. The kernel is the core of the operating system and updating it can often resolve hardware compatibility issues.

To update your kernel, follow the instructions in this post.

After updating your kernel, restart your computer and check if the brightness control is functioning properly.


In this article, we’ve covered three potential solutions for fixing the brightness adjust issue in Ubuntu 20.04. We hope one of these solutions works for you. Remember to always back up your data before making any major changes to your system.

What should I do if the xrandr command doesn’t work for adjusting the brightness?

If the xrandr command doesn’t work for adjusting the brightness, you can try using the xbacklight command instead. Install xbacklight by running sudo apt install xbacklight, and then use the command xbacklight -set [brightness] to adjust the brightness level. Replace [brightness] with a value between 0 and 100.

Will modifying GRUB settings affect other aspects of my system?

Modifying GRUB settings should not affect other aspects of your system. The changes made in the GRUB configuration file are specific to the boot process and should not impact other functionalities. However, it’s always a good practice to create a backup of important files before making any changes to system configurations.

How can I check my current kernel version?

To check your current kernel version, open a terminal and run the command uname -r. This will display the kernel version installed on your Ubuntu 20.04 system.

Is it necessary to update the kernel for fixing the brightness issue?

Updating the kernel is not always necessary for fixing the brightness issue. Solutions 1 and 2 mentioned earlier should be sufficient in most cases. However, if those solutions don’t work, updating the kernel can be a potential solution to resolve hardware compatibility issues.

Can I revert the changes made to the GRUB settings?

Yes, you can revert the changes made to the GRUB settings. Open a terminal and run sudo nano /etc/default/grub to open the GRUB configuration file. Change the line GRUB_CMDLINE_LINUX_DEFAULT="quiet splash acpi_backlight=vendor" back to GRUB_CMDLINE_LINUX_DEFAULT="quiet splash". Save the file, run sudo update-grub, and restart your computer to revert the changes.

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