Public bug reported:
Hello Ubuntu Team,
I am reporting a specific screen brightness issue that triggers only
after system updates (It happened previously on Ubuntu 24, and now again
after a recent update on Ubuntu 26).
Crucial Symptoms:
Slider works but brightness is capped: The brightness UI slider still
works and can be adjusted. However, when the slider is at 100%
(maximum), the actual physical brightness of the screen is only about
50% of what it normally was before the update.
Trigger point during boot: When I power on the laptop, the BIOS/POST
screen is at full, normal brightness. But the exact moment the Ubuntu
loading screen appears (when the kernel/graphics driver loads), the
screen dims significantly, even though the OS slider is set to max.
Failed Workarounds: I have already exhaustively tested all common GRUB
parameters (acpi_backlight=vendor, native, video, none) back when I was
on Ubuntu 24, and absolutely none of them resolved the issue.
This strongly suggests an issue with Kernel Mode Setting (KMS) or the
display driver improperly limiting the maximum backlight value after
recent updates.
Apport hardware and system logs are attached automatically (ubuntu-bug
linux). Please let me know what specific command outputs you need to
trace this regression.
Thank you.
ProblemType: Bug
DistroRelease: Ubuntu 26.04
Package: linux-image-7.0.0-28-generic (not installed)
ProcVersionSignature: Ubuntu 7.0.0-28.28-generic 7.0.12
Uname: Linux 7.0.0-28-generic x86_64
ApportVersion: 2.34.1-0ubuntu0.1
Architecture: amd64
AudioDevicesInUse:
USER PID ACCESS COMMAND
/dev/snd/controlC0: ahmed-elsherbiny 5083 F.... pipewire
ahmed-elsherbiny 5102 F.... wireplumber
/dev/snd/pcmC0D0p: ahmed-elsherbiny 5083 F...m pipewire
/dev/snd/seq: ahmed-elsherbiny 5083 F.... pipewire
CasperMD5CheckResult: unknown
CurrentDesktop: ubuntu:GNOME
Date: Sat Aug 8 05:16:05 2026
MachineType: Dell Inc. Latitude 7430
ProcEnviron:
LANG=en_US.UTF-8
PATH=(custom, no user)
SHELL=/bin/bash
TERM=xterm-256color
XDG_RUNTIME_DIR=<set>
ProcFB: 0 i915drmfb
ProcKernelCmdLine: snapd_recovery_mode=run console=ttyS0,115200n8 console=tty1
panic=-1 quiet splash snapd.xkb="us,pc105,,grp_led:scroll"
SourcePackage: linux
UpgradeStatus: No upgrade log present (probably fresh install)
dmi.bios.date: 05/26/2026
dmi.bios.release: 1.41
dmi.bios.vendor: Dell Inc.
dmi.bios.version: 1.41.0
dmi.board.name: 00N39X
dmi.board.vendor: Dell Inc.
dmi.board.version: A01
dmi.chassis.type: 10
dmi.chassis.vendor: Dell Inc.
dmi.ec.firmware.release: 1.21
dmi.modalias:
dmi:bvnDellInc.:bvr1.41.0:bd05/26/2026:br1.41:efr1.21:svnDellInc.:pnLatitude7430:pvr:rvnDellInc.:rn00N39X:rvrA01:cvnDellInc.:ct10:cvr:sku0B0B:pfaLatitude:
dmi.product.family: Latitude
dmi.product.name: Latitude 7430
dmi.product.sku: 0B0B
dmi.sys.vendor: Dell Inc.
** Affects: linux (Ubuntu)
Importance: Undecided
Status: New
** Tags: amd64 apport-bug resolute wayland-session
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https://bugs.launchpad.net/bugs/2163075
Title:
Max screen brightness is capped at 50% during boot/KMS load despite
slider being at 100% (After updates on Ubuntu 24 & 26)
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