Unix & Linux Stack Exchange is a question and answer site for users of Linux, FreeBSD and other Un*x-like operating systems. Join them; it only takes a minute:

Sign up
Here's how it works:
  1. Anybody can ask a question
  2. Anybody can answer
  3. The best answers are voted up and rise to the top

I'm trying to use Linux on a Toshiba P855 laptop. And I have one big problem: the screen brightness can't be changed, and stays at maximum.

Tried different distros, also tried many boot options in the /etc/default/grub file, but no success. Currently I'm with Kubuntu 12.04, and the function keys for brightness don't work (they never did on any distro), so I'm able to use only the slider for the brightness. But even then - nothing really changes.

All is working on Windows. What's wrong here?

EDIT: Additional information

Well, in /sys/class/backlight I have a symlink:

toshiba -> ../../devices/LNXSYSTM: 00/TOS1900:00/backlight/toshiba/

and in that toshiba folder I have:

  • actual_brightness

  • bl_power

  • brightness

device -> ../../../TOS1900:00/

  • max_brightness

  • power (folder)

  • subsystem -> ...

  • type

  • uevent

and in /proc/acpi/ I have:

  • ac_adapter (folder)

  • battery (folder)

  • button (folder)

  • event

  • toshiba (folder)

  • wakeup

share|improve this question
Do you have some brightness-control-files in /sys/class/backlight/ or in /proc/acpi/? – dchirikov Feb 12 '13 at 20:33
Probably, you want this for eye problems? I managed to change the brightness on my Debian, but I have forgotten how (but it was the hardware keys) - anyway, I stopped all that and now exclusive use a projector (no TV, no devices) and my desktop looks like this - that's Emacs, but the shell looks the same (I use the Linux VTs/ttys/"console") - i.e., fullscreen (no swapping back and forth between windows, BLACK background, and LARGE font). Your problems may be less severe, but if they get worse, remember those things - they work. – Emanuel Berg Feb 13 '13 at 1:25
Looks like there's simply no kernel / driver support for the specific model / chipset the P855 has. – domsom Feb 13 '13 at 10:05

You could try using xbacklight. It uses the XRandR interface to set the backlight (Works on my ThinkPad running FC17)

share|improve this answer

Try the following command in your terminal

sudo setpci -s 00:02.0 F4.B=XX

replacing XX with a hex number 00 is darkest (this will black out your screen so don't advise going for that) and FF is the brightest.

If this works I would suggest putting it in a script.

share|improve this answer

Last month the NVidia video driver updated itself, and now I'm able to change the brightness ;) :) ... it's version 319.32 now. (Changing is not from the Fn keys - they still don't work - but from the slider in the "Battery monitor" popup ... but it's OK for me ;) ...)

share|improve this answer

Your Answer


By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.