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.

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  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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