How to change brightness on linux desktop through the command line?

Question

I have a Debian Linux desktop. I want to change the screen's brightness without pressing the brightness button of my monitor. How can I do this? is this possible in command line or is there an application to be installed?

Answer 1

Look under /sys/class/backlight for the appropriate files to frob.

echo -n 6 > /sys/class/backlight/acpi_video0/brightness

Answer 2

You could give this solution a try:

echo -n 100 > /proc/acpi/video/VGA/LCD/brightness

Also, in the comments, there are some hints what to do alternatively if it doesn't work (f.e. using GLX0 instead of VGA.

EDIT: As this doesn't seem to help, another user in the comments suggests to install xbacklight and calling xbacklight -set 100.

EDIT2: And another one says if you don't have a video folder, try sudo modprobe video.

Answer 3

If you don't have hardware support for changing the brightness of your monitor you could use the command xrandr together with its option flags --output and --brightness, as can be seen in my answer to a similar question on askubuntu.com

Answer 4

You need to control the monitor over DDC. See http://ddccontrol.sourceforge.net/ for one program that lets you do this.

Answer 5

$ sudo apt-get install xbacklight

How to set brightness to 50%

$ xbacklight -set 50

How to increase brightness 10%

$ xbacklight -inc 10

How to decrease brightness 10%

$ xbacklight -dec 10

More info here

Answer 6

After searching around, I think I found a pretty good way to get this done on most laptops. The first command gets the name of your screen, something like LVDS1. If this does not work, try getting the name of your screen with xrandr --current. There are probably more elegant ways to do this, the sed command removes everything after the first space, the head and tail commands simply remove everything except the second line of the output. The second line uses the screen name to change the brightness to 1.0. This can be set to almost anything, including 0.0 for a black screen or 50.0 for a completely white screen, but I think 1.0 is the desired value here.

screenName=$(xrandr --current | sed s/\ .*// | head -n2 | tail -n1);
xrandr --output $screenName --brightness 1.0

The command below sets the brightness to the maximum allowed brightness, as I noticed that just setting it to '100' does not simply work, at least not on all systems.

sudo sh -c 'echo -n $(cat /sys/class/backlight/acpi_video0/max_brightness) > /sys/class/backlight/acpi_video0/brightness'

This worked on multiple laptops running Ubuntu 12.04.