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Can't change brightness on Acer 4810t (8.04)

Link to this post 28 Aug 09

Hi

8.04 all working nice and stable on my new Acer 4810t dual core, but still with some outstanding issues.

I haven't found a way to get the brightness to change at all, am wondering if anyone can help.

Looking around the brightness control could be here:

/proc/acpi/video/VGA/LCD/brightness

and if I try

cat /proc/acpi/video/VGA/LCD/brightness

I get something like

~$ cat /proc/acpi/video/VGA/LCD/brightness
levels: 100 80 30 40 50 60 70 80 90 100
current: 70

which I've just noticed is controlled by the hotkeys. Unfortunately it has no effect on the brightness. Using the echo command has no effect on it.

There is also

/sys/class/backlight/acer_acpi/brightness

and if I try

cat /sys/class/backlight/acer_acpi/brightness

I get

9

but echo changes nothing.

There is also

/proc/acpi/acer/brightness

and if I try

cat /proc/acpi/acer/brightness

I get

8

but the echo command makes no difference.

Any ideas where I'm going wrong?

Jim

Link to this post 28 Aug 09

How are you attempting to manuall input values into the driver files? ie... echo "7">/sys/class/backlight/acer_acpi/brightness?

I am not the most experieinced with laptops and the brightness functionality, but I will push and learn to try to help you resolve this issue.

Link to this post 28 Aug 09

Thanks for getting back to me

I try this

sudo echo 7 /sys/class/backlight/acer_acpi/brightness

which, after giving the password, gives me

7 /sys/class/backlight/acer_acpi/brightness

But then, if I check with

cat /sys/class/backlight/acer_acpi/brightness

the answer still comes back as

9

Link to this post 28 Aug 09

The issue you are having with the echo command is because you are using it incorrectly.

The echo command is used to output a string to your terminal, when you enter sudo echo 7 /sys/class/backlight/acer_acpi/brightness is returns everything after the word echo because that is what you are telling it to do.

What wou want to try is sudo echo 7>/sys/class/backlight/acer_acpi/brightness

the 7 is the string that you want to display,
> is telling echo to ouput the display into a file (replacing the file, >> is used to append to a file)
/sys/class/backlight/acer_acpi/brightness is the file which will have it's contents replaced by the ouput of the echo command.

If this works, then we can dive a little deeper and figure out why the buttons are not modifying the values in the perspective files.

Link to this post 28 Aug 09

Hi

Not very good with the Command Line, me.

I thought that you'd solved it, but I'm afraid it made no difference. I've tried with the different 'brightness' files that I have found and simply get 'Permission Denied' even when I try it as root. Here's a copy:


~$ cat /proc/acpi/video/VGA/LCD/brightness
levels: 100 80 30 40 50 60 70 80 90 100
current: 100
~$ echo 40>/proc/acpi/video/VGA/LCD/brightness
bash: /proc/acpi/video/VGA/LCD/brightness: Permission denied
~$ sudo echo 40>/proc/acpi/video/VGA/LCD/brightness
bash: /proc/acpi/video/VGA/LCD/brightness: Permission denied

However, I can use the function keys on the keyboard to change this value (above), though it has no effect on the actual screen brightness.

~$ cat /sys/class/backlight/acer_acpi/brightness
9
~$ echo 4>/sys/class/backlight/acer_acpi/brightness
bash: /sys/class/backlight/acer_acpi/brightness: Permission denied
~$ sudo echo 4>/sys/class/backlight/acer_acpi/brightness
bash: /sys/class/backlight/acer_acpi/brightness: Permission denied

And finally...

~$ cat /proc/acpi/acer/brightness
6
~$ echo 2>/proc/acpi/acer/brightness
bash: /proc/acpi/acer/brightness: Permission denied
~$ sudo echo 2>/proc/acpi/acer/brightness
bash: /proc/acpi/acer/brightness: Permission denied

:(

Jim

Link to this post 29 Aug 09

Your reponse indicates that those are output files, other files are being used to direct the input to the kernel. Later this evening I will research further to see if I can locate them.

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