Notes about open source software, computers, other stuff.

Fixing backlight control with Ubuntu on my ThinkPad T440s

Some time ago I bought a ThinkPad T440s for work. It’s an amazing machine! Before that I used a ThinkPad X121, which served me very well on my daily commute. This machine was getting a bit old, and given that my new job (more about which in a later post) also requires me to have a better machine with more screen real estate, it was high time to upgrade.

Ubuntu (13.10 and 14.04) runs well on the T440s, only two things didn’t work as expected:

  • The WWAN interface (mobile internet, from Ericsson) seems to connect when I select it in the network manager, but the adaptor seems to disappear almost immediately after that. A few seconds it appears again. [edit 20140514]I just found out that it’s working, probably this was fixed in Ubuntu 14.04[/edit]
  • The screen’s backlight brightness can be reduced/increase using the Fn-F5 and Fn-F6 keys, but only in a weird way: several key presses are needed for one unit of decrease/increase.

This last bug can be fixed by booting with the following kernel argument:


Simply add this to the GRUB_CMDLINE_LINUX_DEFAULT line in /etc/default/grub:

  GRUB_CMDLINE_LINUX_DEFAULT="acpi_backlight=vendor quiet splash"

and run sudo update-grub. Reboot and you will be able to change the backlight brightness in finer steps.

I found this solution somewhere on the internet a few weeks ago, wrote it down, but can’t remember anymore what the original URL was. My apologies.


  1. Luigi

    Hi do you know if upgrading my T440s from 12.04 to 14.04 will generate any errors? I am afraid to upgrade to the new Ubuntu version.. any suggestions?
    Thanks in advance!

    • LCK

      I upgraded the laptop from 13.10 to 14.04 without problems, no idea if it works as smooth when upgrading from 12.04. However, I have upgraded several servers from 12.04 to 14.04 without problems.

  2. Benjamin


    today i got my new t440s backlight is working fine, but i can’t get the keyboard light working. Any sugesstions ?



    • LCK

      That’s strange! It works out of the box for me (use fn-space to cycle through the three brightness levels). I assume you are running Ubuntu 14.04 as well?

  3. Dionysos

    Hi maybe someone from here could help me. This question is on as well ():
    I’ve purchased a Lenovo ThinkPad S540. It had Windows 8.1 preloaded, but when I booted Ubuntu 14.04 from an USB-stick everything worked just fine. So I erased the entire hard drive, deleted all partitions on it, and installed Ubuntu 14.04. Now ThinkPad extras like the trackpoint and keyboard background-lighting (fn + space) and the fn-key keylight don’t work any more. I’ve tried everything I found online, even stuff that was made for other ThinkPad models (I couldn’t find that much for the S540). Does anyone have a (dummy) solution for this?

  4. NeeL

    Hi, I’ve had the same problem with Fn F5 and F6 for the brightness on my S440. I used ‘sudo watch -n0.1 -d cat /sys/class/backlight/acpi_video/actual_brightness’ to read the value for the brightness. I figured the buttons increased and decreased the value with 6. Moving the bar in ‘System Settings/Brightness & Lock’ with the arrow keys, I noticed they had an increasement of 1. The value has a max of 100. I noticed the screen brightness only changed if the value was a multiple of 5. By pressing Fn+F5 and the left arrow, I managed to actually go to 0, with still the full brightness on the screen, by skipping all the multiples of 5.

    Hope it helps to understand the problem.

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