Ubuntu 16.04 - problems with keyboard backlight

Soooo I posted this one askubuntu, thinking someone has already solved this, but atlas, no one has responded.

Background: Dell Precision M4500. Known working backlit keyboard. When booting after grub keyboard goes dark. Only fix is boot into Windows 7, re-enable keyboard backlight (through Dell keyboard control panel settings, backlight and intensity is ultimately controlled by Bios/firmware). Problem did not exist in Windows 10 (no driver support but fn-key still functioned), Gnome Ubuntu (14.04.4 & 15.10), Debian Testing (rolling, used Gnome), Linux Mint 17.3 (Ubuntu 14.04 based).

Things tried:
- xset led x(x=1-32: all numbers tested individually)
- echo 10 | tee sudo /sys/class/LEDs/dell::kbd<something>/brightness (this file is tied to the Dell smbios API that has kernel hooks in it)
- yell at it
- shake it (I have dual ssds, only risk is the hinges for the display)
- bust out some google-foo and get my *** handed to me....

So, help me Obi-won Kenobi, you're my only hope!

I don't have the same model but when I had similar problems with my Asus G73 laptop there were a couple of things that helped identify the problem.

When I dropped to the console (ctrl + alt + f3 for example) the backlight keyboard started to work. This told me that the UI was getting in the way. On another model (I can't remember which) I had to make a modification to grub.

For yours I suspect that its going to be some grub option that gets set at boot time. Off the top of my head I am thinking it may be the acpi_backlight option you may want to investigate. You can also try turning of ACPI in grub altogether

Further to this have you tried looking into /sys/class/backlight instead of LED which you poked at?

Yeah backlight has display/NVIDIA files in it. I know for sure I have used console (not terminal) multiple times, and the backlight was still off. In dmesg there were some acpi errors (unknown device) and when booting back into Windows the keyboard stayed off until I went into the "Dell keyboard backlight" and clicked the enable check box. So on boot, after grub, Ubuntu 16.04 is forcing the keyboard backlight off, and I do not know where to force it back on. The dev for the kernel module and associated /sys/class config files just says write a value to the file to alter it. Both echo with a sudo tee, running echo as SU, and sudo/SU nano and save does not make the keyboard hold the value.

Edit: just to verify, clean install of 14.04.4 has no issue with backlight. I will reinstall 16.04 and try the acpi enabled in grub.

Interesting note, reinstalling Ubuntu 16.04: decided to boot into the live distro, and sure as **** the keyboard is glowing brightly. We will see if it holds over installation.

Well, marking this as solved... Reinstall did the trick. Musta been a borked config file or something. Guess that's what I get for a fresh download on release day