Toshiba L755D-S5218 Extremely Dim Lighting while using LiveCD Distros

Sum1 · 07-19-2014, 07:01 PM

I'm completely satisfied with the notebook.
CPU: AMD A-Series A6-3420M
GPU: AMD Radeon HD 6520G

I have a Windows 7 hard drive and a Red Hat 6.5 hard drive.
Both OS's provide accurate screen/pixel/video performance, etc.

The problem: I sometimes need to use LiveCD distros on the fly for work purposes (LPS, Tails, SystemRescueCD) and the screen is so so so dim that I need to find a dark room with all the blinds closed to see what's on the screen.

I've tried using the (FN) function key and F7 to increase screen brightness but it doesn't change anything.

I'm aware of the backlighting problems with Toshiba gear some years ago; but, obviously my hardware runs fine in a typical hard drive installation.

Anyone have a similar problem and solved it?

Thank you for your help.
Your guidance greatly appreciated.

Sum1 · 07-20-2014, 07:10 PM

So googling I find a possible shell command to change the screen brightness but I run into the read-only Live CD problem.

Code:

echo -n 8 > /sys/class/backlight/acpi_video0/brightness

The "8" is a max figure out of a possible 0 - 8 setting.
The current setting in the brightness file is "4".
When I issue the command above while running Linux Portable Security LiveCD, the result is:

Code:

bash: can't create /sys/class/backlight/acpi_video0/brightness: Permission denied

So then I try - chmod 0644 /sys/class/backlight/acpi_video0/brightness:

Code:

chmod: brightness: Operation not permitted

So then I try to su to root but I don't have the root password.
The operation is also not permitted when I try to create a password for root.

I suppose the next step is to try a LiveCD that will allow me to act as root user.

Sum1 · 07-20-2014, 07:35 PM

Next up: Systemrescuecd

I go to the "brightness" file and open it up with text editor nano.
I insert the number "8" and when I try to save it, I receive "Invalid Argument."
Then tried numbers "6" and "7" and received the same, "Invalid Argument."

Went back to shell and tried the command echo -n 8 > /foo/foo/foo/brightness and also receive "Invalid Argument."

No solution so far.

syg00 · 07-20-2014, 08:12 PM

Are you doing the echo into the /proc "file" as root/sudo ?

/proc is a psuedo fiesystem, "files" (which aren't really files at all) are created in kernelspace. The code that creates the "file" decides what you can do to it - concepts like chmod are (generally) irrelevant. All you can generally do (at most) is read and maybe write - if allowed.

Sum1 · 07-20-2014, 09:28 PM

Quote:

Originally Posted by syg00

Are you doing the echo into the /proc "file" as root/sudo ?

Hi Syg00,
Thanks for responding.
I believe I'm doing the echo into the root filesystem of the LiveCD.
I cd to /.
ls -alh to view the entire filesystem tree.
I see the /sys directory and then get to the "brightness" file by navigating through the sub-directories of /sys.

syg00 · 07-20-2014, 09:33 PM

What I meant was you have to have root user priviledges. Try it as

Code:

sudo echo -n 8 > /sys/class/backlight/acpi_video0/brightness

Most liveCDs have sudo, and don't require any password to use it.

Sum1 · 07-20-2014, 10:01 PM

Ok, now I understand.

Started up SystemRescueCD.
The bash shell states: root@sysresccd

When I enter the echo -n 8 command the result is: echo: write error: invalid argument

syg00 · 07-20-2014, 10:22 PM

May not have acpi- try the liveCD that you could read the file on.

Sum1 · 07-21-2014, 06:57 AM

Update:

The max_brightness file is set to "7".
Tried echo -n 7 > brightness and received no errors but nothing changed as to the screen brightness.
So tried echo -n 7 > actual_brightness and receive and Input/Output error.

Shell activity from SystemrescueCD:

Code:

root@sysresccd /sys/class/backlight/acpi_video0 % ls -alh
total 0
drwxr-xr-x 3 root root    0 Jul 21 07:40 .
drwxr-xr-x 3 root root    0 Jul 21 07:40 ..
-r--r--r-- 1 root root 4.0K Jul 21 07:44 actual_brightness
-rw-r--r-- 1 root root 4.0K Jul 21 07:44 bl_power
-rw-r--r-- 1 root root 4.0K Jul 21 07:44 brightness
lrwxrwxrwx 1 root root    0 Jul 21 07:44 device -> ../../../0000:00:01.0
-r--r--r-- 1 root root 4.0K Jul 21 07:44 max_brightness
drwxr-xr-x 2 root root    0 Jul 21 07:44 power
lrwxrwxrwx 1 root root    0 Jul 21 07:44 subsystem -> ../../../../../class/backlight
-r--r--r-- 1 root root 4.0K Jul 21 07:44 type
-rw-r--r-- 1 root root 4.0K Jul 21 07:40 uevent
root@sysresccd /sys/class/backlight/acpi_video0 % echo -n 7 > brightness
root@sysresccd /sys/class/backlight/acpi_video0 % 
root@sysresccd /sys/class/backlight/acpi_video0 % 
root@sysresccd /sys/class/backlight/acpi_video0 % chmod 0644 actual_brightness
root@sysresccd /sys/class/backlight/acpi_video0 % echo -n 7 > actual_brightness
echo: write error: Input/output error
root@sysresccd /sys/class/backlight/acpi_video0 %

Still dim.

Sum1 · 07-21-2014, 01:15 PM

I remain unable to solve this issue.

I am going to try an alternative.
I purchased the following: SanDisk 32GB Extreme SD SDHC Card UHS-I Class 10 45MB/s 300X with USB 3.0 Reader

I'll use an install-to-hard-drive option for either LPS, Tails, or SystemRescueCD, and try booting the OS from the SDHC flash memory.