How do I change screen brightness from a terminal?

belltown · 05-21-2011, 07:34 PM

I'm running Ubuntu 11.04 with the Gnome Classic (No effects) display manager. My laptop's brightness keys work. However, when I boot or resume from suspend when using the integrated Intel graphics card the display brightness is turned all the way down, and I have to turn up the brightness using the brightness function keys so I that can see the display. I'd like to automate this by putting a terminal command in a script so I can automatically turn up the screen brightness when the system boots.

I've tried the following commands with no success:

Code:

echo 9>/sys/class/backlight/acpi_video0/brightness

What ever I echo in the brightness file has no effect on the screen brightness, and nothing changes in the /sys/class/backlight/acpi_video0/brightness or actual_brightness files. The contents of these files do change, however, if I change the brightness using the keyboard function keys.

Code:

setpci -s 00:02.0 F4.B=10

Some posts have suggested this command might work, but in my case it has no effect. The contents of the F4 register remain at 00, even if I change the screen brightness with the function keys.

Code:

xbacklight -set 90

Using this command I can change the value of xbacklight (i.e. xbacklight -get shows the new value), but the screen brightness does not change. However, if I change the screen brightness using the keyboard function keys then the value of xbacklight -get shows the new value.

Code:

acpi_backlight=vendor

I've tried putting this command on the linux command line when I boot. Even with this parameter I'm still unable to change the screen brightness from the terminal. This parameter also disables the keyboard brightness function keys.

Any suggestions of anything else I could try to change the screen brightness from a terminal?

Snark1994 · 05-22-2011, 03:04 PM

I would look under the Gnome keyboard shortcut configuration, if I remember rightly from when I used Ubuntu you can see what command it runs when you press the brightness keys

and then you should be able to run that from terminal...

roygbiiv · 05-23-2011, 09:35 AM

Quote:

Code:

echo 9>/sys/class/backlight/acpi_video0/brightness

What ever I echo in the brightness file has no effect on the screen brightness, and nothing changes in the /sys/class/backlight/acpi_video0/brightness or actual_brightness files. The contents of these files do change, however, if I change the brightness using the keyboard function keys.

does this work?

Code:

sudo echo 9>/sys/class/backlight/acpi_video0/brightness

remember you can only echo values 0-24 (0 darkest - 24 brightest). i use a bash script that i run with sudo for this purpose. it takes the brightness level as argument:

Code:

#!/bin/bash
# set screen brightness level

if [ "$#" = "0" ]; then
	level= cat /sys/class/backlight/acpi_video0/brightness
	echo -n $level
else
	echo  $1 > /sys/class/backlight/acpi_video0/brightness
fi

belltown · 05-24-2011, 12:07 PM

Quote:

Originally Posted by Snark1994

I would look under the Gnome keyboard shortcut configuration, if I remember rightly from when I used Ubuntu you can see what command it runs when you press the brightness keys

and then you should be able to run that from terminal...

No, there are no keyboard shortcut keys for the brightness controls. I've found some configurable settings under gconf-editor in the Gnome Power Manager, but nothing tells me what Gnome is using to set the brightness.

belltown · 05-24-2011, 12:15 PM

Quote:

Originally Posted by roygbiiv

does this work?

Code:

sudo echo 9>/sys/class/backlight/acpi_video0/brightness

remember you can only echo values 0-24 (0 darkest - 24 brightest). i use a bash script that i run with sudo for this purpose. it takes the brightness level as argument:

Code:

#!/bin/bash
# set screen brightness level

if [ "$#" = "0" ]; then
	level= cat /sys/class/backlight/acpi_video0/brightness
	echo -n $level
else
	echo  $1 > /sys/class/backlight/acpi_video0/brightness
fi

That doesn't work. I can access the acpi brightness file, but any value I try to echo into that file has no effect, e.g:

Code:

root@john-laptop:/home/john# sudo su
root@john-laptop:/home/john# cat /sys/class/backlight/acpi_video0/brightness
10
root@john-laptop:/home/john# echo 5> /sys/class/backlight/acpi_video0/brightness 

root@john-laptop:/home/john# cat /sys/class/backlight/acpi_video0/brightness
10

Evgenii Frolov · 03-20-2013, 12:10 AM

Quote:

Originally Posted by belltown

That doesn't work. I can access the acpi brightness file, but any value I try to echo into that file has no effect, e.g:

Code:

root@john-laptop:/home/john# sudo su
root@john-laptop:/home/john# cat /sys/class/backlight/acpi_video0/brightness
10
root@john-laptop:/home/john# echo 5> /sys/class/backlight/acpi_video0/brightness 

root@john-laptop:/home/john# cat /sys/class/backlight/acpi_video0/brightness
10

This worked for me!!! Add quotes around a number!!!

Code:

sudo echo "9">/sys/class/backlight/acpi_video0/brightness

Quote:

Originally Posted by roygbiiv

does this work?

Code:

sudo echo 9>/sys/class/backlight/acpi_video0/brightness

remember you can only echo values 0-24 (0 darkest - 24 brightest). i use a bash script that i run with sudo for this purpose. it takes the brightness level as argument:

For me it is 0-20 range!

tcuc · 09-17-2014, 03:50 AM

this worked great:

Code:

echo "24">/sys/class/backlight/acpi_video0/brightness

but how can i do this as a regular user?
I want to bind this to a hotkey in openbox but i cant exactly do stuff as root there.

Evgenii Frolov · 09-17-2014, 04:28 AM

Quote:

Originally Posted by tcuc

but how can i do this as a regular user?
I want to bind this to a hotkey in openbox but i cant exactly do stuff as root there.

You should use "xbacklight" package then. If you have it installed then first of all see

Code:

man xbacklight

. There you can find, e.g.

Code:

xbacklight -inc 20

It increases brightness on 20%. It is the best way.
xbacklight man page on-line.

tcuc · 09-17-2014, 06:43 AM

that was perfect! thanks allot!

Evgenii Frolov · 09-17-2014, 08:01 AM

Quote:

Originally Posted by tcuc

that was perfect! thanks allot!

You are wellcome! Have a nice linux time and smooth workflow with it (=

feeling · 01-06-2015, 04:24 AM

Hi, I'm new at linux and got a similiar problem:

Hotkeys won't work.
(sudo) echo xx>/sys... gives bash: /sys/class/backlight/acpi_video0/brightness: Permission denied
(sudo) echo "xx">/sys... gives the same
btw: brightness has -rw-r--r--

then I installed xbacklight
but no matter what I wrote in commandline (xbacklight -get, xbacklight -set 10, xbacklight -inc 20, ...) nothing happens nor output.
Can someone help me?

I'm working on a Thinkpad Edge something with Linux Mint 17 and cinnamon

Please feel free to correct my english so that I can improve it.

Head_on_a_Stick · 01-06-2015, 01:53 PM

Code:

sudo tee /sys/class/backlight/acpi_video0/brightness <<< "value"

EDIT: Your English is very good, but it should be:
"and I have a similar problem"
"nothing happens and there is no output"

feeling · 01-06-2015, 03:13 PM

Your code gives just out 1 or 5 or 10 or whatever I wrote for value. But the actual brightness doesn't change.
Do you have more suggestions, maybe?

Thanks anyway

Head_on_a_Stick · 01-06-2015, 03:20 PM

What is the output of:

Code:

ls /sys/class/backlight

If there are other backlight folders, try modifying the "brightness" file in there instead.

Which kernel version and graphics card are you using?

feeling · 01-06-2015, 06:34 PM

great, the command aplied on ...radeon_bl0/brightness works.
thanks for that hind.

Quote:

Originally Posted by Head_on_a_Stick

Which kernel version and graphics card are you using?

3.13.0-24-generic and [AMD/ATI] Kabini [Radeon HD 8240]
But I think that doesn't matter anymore.

Thanks for your help. Good night