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I've tried following the Ubuntu hotkeys/media keys troubleshooting guide and /usr/share/doc/udev/README.keymap.txt.gz to make the Fn keys work. After copying the map file and modifying /lib/udev/rules.d/95-keymap.rules I get the correct key names from sudo /lib/udev/keymap -i input/event4, but none of them do anything at all.

How do I make sure that at least wlan and kbdillumup/kbdillumdown work?

$ /lib/udev/findkeyboards
AT keyboard: input/event4
$ cat /sys/class/dmi/id/sys_vendor
$ cat /sys/class/dmi/id/product_name

samsung-90x3a map file:

0xCE prog1 # Fn+F1 Unknown
0x8D prog3 # Fn+F6 Economy mode
0x97 kbdillumdown # Fn+F7 Keyboard background light down
0x96 kbdillumup # Fn+F8 Keyboard background light up
0xD5 wlan # Fn+F12 Wifi on/off

$ udevadm info --export-db

Update: The information below will be from Arch Linux since I no longer have Ubuntu.

xdotool key XF86KbdBrightnessUp prints nothing, but returns with exit code 0. I'm not sure if that means anything.

acpi_listen prints nothing when pressing Fn+F7/Fn+F8.

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You can test whether your kernel is supporting these functions on your laptop with xdotool. Try xdotool key XF86KbdBrightnessUp and see if you get the expected results. – drs Apr 23 '13 at 17:39
what acpi-listen give you when you type Fn+f7 ? – Kiwy Nov 29 '13 at 10:22
@chirp - did you try the jablonskis tutorial‌​. Did that not solve the issue for you? – slm Nov 30 '13 at 2:38
here is how you associate a keypress to a command with KDE: linuxintro.org/wiki/Configure_your_multimedia_keys – Thorsten Staerk Dec 18 '13 at 15:39
I am guessing you are UEFI booting? – jasonwryan Feb 11 '14 at 22:44

Quite often, to get the backlight adjustment to work, you need to edit your GRUB configuration to contain the following:

GRUB_CMDLINE_LINUX_DEFAULT="splash acpi_backlight=vendor"

That worked for enabling backlight controls on most of my laptops.

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