Ubuntu 26.04: Screen brightness resets to 100% on every new session

[devilboy]

I did a clean install of 26.04. I chose no encryption or TPM and Secure Boot is turned off.

devilboy@SATELLITE-L50D-B:~$ lsblk --output=name,fstype,label,mountpoints | grep -v ^loop
NAME FSTYPE LABEL MOUNTPOINTS
sda
├─sda1 vfat /boot/efi
└─sda2 ext4 /
sr0
zram0 swap [SWAP]

[paddylandau]

Thank you. In that case, you can easily test the changes through temporary changes to GRUB.

When you boot your machine, just after your computer’s logo, press Esc. You should be presented with the GRUB menu, probably with a countdown.

When you see the GRUB menu:

• Press the letter E.
• You’ll be shown some code that you might or might not understand.
• Using your cursor keys, move to end of the line that begins with linux /boot/vmlinuz.
• Type a space, and then acpi_backlight=native (or whichever option you’re testing).
• Press F10 to continue booting with this change.

This change is temporary; next time you boot, the change will be thrown away.

This allows you to quickly test each command that has been suggested to you, letting you instantly revert simply by rebooting.

If you find the option that solves the problem, let us know which one it was, and we can talk you through making it permanent (at least until the regression has been fixed).

[devilboy]

Hi everyone, just wanted to share a permanent or temporary solution that finally worked for my screen brightness reset issue on Ubuntu 26.04 (running on an older AMD/Radeon laptop using the radeon_bl0 driver).

Initially, I tried all the standard kernel parameter recommendations like acpi_backlight=vendor, native, and video etc. but none of them worked. I even tried creating a systemd-backlight service override to force the hardware level state at boot, but the GNOME desktop environment kept stomping over it and resetting the screen to 100% anyway.

The Fix: I ended up bypassing the system-level bugs entirely by handling it in user-space. I installed the native GNOME Extension Manager app (sudo apt install gnome-shell-extension-manager) and added the Brightness Restore addon (by AdalbertAlexandru).

Result: It works perfectly inside the user session now! The only minor limitation is that it doesn’t apply to the initial GDM boot login screen (since the user profile hasn’t loaded yet) but the very microsecond I log into the desktop, it safely restores my preferred brightness slider level.

Thank you all individually for replying and helping me here. I hope this issue - if it’s really is an issue and not just happening to me - gets fixed in version 26.04.1.