1. Terminal Solution: Fix Brightness via GRUB & xrandr
📌 Step 1: Edit GRUB configuration
sudo nano /etc/default/grub
📌 Step 2: Find this line:
GRUB_CMDLINE_LINUX_DEFAULT="quiet splash"
Change it to:
GRUB_CMDLINE_LINUX_DEFAULT="quiet splash acpi_backlight=vendor"
📌 Step 3: Update GRUB and reboot
sudo update-grub
sudo reboot
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✅ 2. Software-Based GUI Tool (DEB-based)
🖥️ Option A: Brightness Controller (GUI Tool)
This is a simple GUI-based software. If the system backlight doesn't work, it adjusts brightness using xrandr.
🔧 Install it via terminal:
sudo add-apt-repository ppa:apandada1/brightness-controller
sudo apt update
sudo apt install brightness-controller
🔍 To run:
Go to Applications → Brightness Controller
This tool also supports multiple monitors.
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✅ 3. Temporary Brightness Control using xrandr (Terminal method)
🔍 Step 1: Check your display name
xrandr | grep " connected"
Example output:
eDP-1 connected ...
📉 Step 2: Adjust brightness
xrandr --output eDP-1 --brightness 0.6
(Where 0.6 means 60% brightness — you can use values between 0.1 and 1.0)
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✅ Bonus: Auto-set Brightness at Boot
If you want to apply the brightness automatically at every boot:
1. Create a script:
nano ~/set-brightness.sh
2. Paste this inside:
#!/bin/bash
xrandr --output eDP-1 --brightness 0.6
3. Make it executable:
chmod +x ~/set-brightness.sh
4. Add it to startup (via Startup Applications or .bashrc).
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If you want, I can also provide the .deb installer for Brightness Controller manually.
Could you please tell me:
What is the model of your All-in-One PC?
Confirm your Ubuntu version (e.g., 20.04 or other)?
This will help me tailor the solution precisely.
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Step 1: Check if Brightness Keys Work
Try using Fn + Brightness keys (e.g., F1/F2 or dedicated brightness buttons). If nothing changes, proceed below.
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⚙️ Step 2: Check Current Brightness Control Interface
Run this command in Terminal:
ls /sys/class/backlight/
You may see output like:
acpi_video0
intel_backlight
If this folder is empty, Ubuntu doesn’t detect any backlight interface — that means kernel or driver fix is needed.
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💡 Step 3: Enable Brightness by Editing GRUB
1. Open Terminal:
sudo nano /etc/default/grub
2. Find this line:
GRUB_CMDLINE_LINUX_DEFAULT="quiet splash"
3. Change it to (for Intel/AMD CPUs):
GRUB_CMDLINE_LINUX_DEFAULT="quiet splash acpi_backlight=vendor"
4. Save and exit (Ctrl+O, Enter, Ctrl+X).
5. Then run:
sudo update-grub
sudo reboot
Check brightness again after reboot.
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🧰 Step 4: Install Brightness Controller App
If brightness keys don’t work but system detects backlight, you can try GUI:
sudo apt install brightnessctl
or install this GUI tool:
sudo add-apt-repository ppa:apandada1/brightness-controller
sudo apt update
sudo apt install brightness-controller
Then launch Brightness Controller from the app menu.
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🛠 Step 5: Install Missing Kernel Modules
If your screen driver is missing, you may need to reinstall kernel modules. Run:
sudo apt install --reinstall linux-generic
sudo apt install linux-headers-$(uname -r) build-essential dkms
Then reboot.
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🧪 Optional: Try a Newer Kernel (if issue persists)
Ubuntu 20.04 is older. Your AIO PC may have a newer display device. You can install a newer kernel:
sudo apt install linux-generic-hwe-20.04
Then reboot.
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📌 Final Tip
Let me know your PC model name and graphics card (Intel/AMD/NVIDIA) for more targeted steps. You can get that info by running:
sudo lshw -c video
Or use:
lspci | grep VGA
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Would you like me to check for specific .deb files for kernel or backlight drivers for your PC model?
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