I can partially reproduce this bug on Dell Latitude E6420. Namely in 16.04 (4.4 kernel) backlight was always on after (re)boot and screenlock, however waking up (opening laptop) does not switch backlight on. Moreover I could control the backlight (i.e. switch it off), contrary to some reports above.
After downgrade to 14.04.4 (4.2 kernel; downgraded for plethora of more serious issues) this still occurs at least after boot and screenlock (I'm still copying my backup to hdd so I don't want to test waking up). I can still control it and switch it off (with Fn+rightarrow on my model). Last kernel this worked for me properly was 3.19 (14.04.3 with vivid kernel I believe). -- You received this bug notification because you are a member of Kernel Packages, which is subscribed to linux in Ubuntu. https://bugs.launchpad.net/bugs/1510344 Title: Keyboard Backlight Turns on at boot Status in Dell Sputnik: Confirmed Status in One Hundred Papercuts: Confirmed Status in Linux: New Status in linux package in Ubuntu: Confirmed Bug description: System: Dell XPS 13 9343 Action: Boot computer Expected Behavior: Keyboard backlight would be off when computer is booted Actual Behavior: Keyboard backlight is on at boot This did not happen with Ubuntu 15.04 There are new files in Ubuntu 15.10 - /sys/class/leds/dell::kbd_backlight$ cat stop_timeout 60s cat start_triggers +keyboard +touchpad cat trigger [none] AC-online BAT0-charging-or-full BAT0-charging BAT0-full BAT0-charging-blink-full-solid usb-gadget usb-host cpu0 cpu1 cpu2 cpu3 mmc0 rfkill0 cat brightness 2 --- Unsure if these files are important, but included in the report ProblemType: Bug DistroRelease: Ubuntu 15.10 Package: linux-image-4.1.0-2-generic 4.1.0-2.2 ProcVersionSignature: Ubuntu 4.1.0-2.2-generic 4.1.3 Uname: Linux 4.1.0-2-generic x86_64 ApportVersion: 2.18-0ubuntu5 Architecture: amd64 AudioDevicesInUse: USER PID ACCESS COMMAND /dev/snd/controlC1: ubuntu 2488 F.... pulseaudio /dev/snd/controlC0: ubuntu 2488 F.... pulseaudio CasperVersion: 1.362 CurrentDesktop: Unity Date: Tue Oct 27 01:29:47 2015 IwConfig: enx00249b0981e3 no wireless extensions. lo no wireless extensions. LiveMediaBuild: Ubuntu 15.10 "Wily Werewolf" - Alpha amd64 (20150730) MachineType: Dell Inc. XPS 13 9343 ProcEnviron: TERM=xterm-256color PATH=(custom, no user) XDG_RUNTIME_DIR=<set> LANG=en_US.UTF-8 SHELL=/bin/bash ProcFB: 0 inteldrmfb ProcKernelCmdLine: BOOT_IMAGE=/casper/vmlinuz.efi file=/cdrom/preseed/username.seed boot=casper quiet splash --- cdrom-detect/try-usb=true noprompt RelatedPackageVersions: linux-restricted-modules-4.1.0-2-generic N/A linux-backports-modules-4.1.0-2-generic N/A linux-firmware 1.145 RfKill: 0: hci0: Bluetooth Soft blocked: no Hard blocked: no SourcePackage: linux UdevLog: Error: [Errno 2] No such file or directory: '/var/log/udev' UpgradeStatus: No upgrade log present (probably fresh install) dmi.bios.date: 07/14/2015 dmi.bios.vendor: Dell Inc. dmi.bios.version: A05 dmi.board.name: 0TM99H dmi.board.vendor: Dell Inc. dmi.board.version: A00 dmi.chassis.type: 9 dmi.chassis.vendor: Dell Inc. dmi.modalias: dmi:bvnDellInc.:bvrA05:bd07/14/2015:svnDellInc.:pnXPS139343:pvr:rvnDellInc.:rn0TM99H:rvrA00:cvnDellInc.:ct9:cvr: dmi.product.name: XPS 13 9343 dmi.sys.vendor: Dell Inc. To manage notifications about this bug go to: https://bugs.launchpad.net/dell-sputnik/+bug/1510344/+subscriptions -- Mailing list: https://launchpad.net/~kernel-packages Post to : kernel-packages@lists.launchpad.net Unsubscribe : https://launchpad.net/~kernel-packages More help : https://help.launchpad.net/ListHelp