Problems setting default brightness with /etc/rc.local

[totitoll]

Hey,

I can change my display brightness in the file /sys/class/backlight/intel_backlight/brightness with the command "echo x > /sys/class/backlight/intel_backlight/brightness" were x is a certain brightness level.
I want to use this command to set a default brightness level for every reboot since the actual one is much to bright.

The above command doesnt work right away, as I found out I first have to change the permissions for /sys/class/backlight/intel_backlight/brightness.
I did this with "sudo chmod a+w" (don't know if that's the right way, but it works...?).
But these permissions aren't permanent, when i reboot they're gone, so i tried the following:

I added to /ect/rc.local the two lines (opened with gksudo gedit ...):

chmod a+w /sys/class/backlight/intel_backlight/brightness
echo 134 > /sys/class/backlight/intel_backlight/brightness #(*)

in order to achieve what I described ahead.

But this doesn't work as it sure changes the file permissions (I can use the command "echo x > /sys/.../backlight" afterwards without any "permissions denied"-output),
but the actual command, which i denoted #(*) doesn't get executed, so my display stays bright, if I don't change it "by hand".

For any recommendations thank you very much in advance!

[totitoll]

solved it: I added a "sleep 1" in between the two lines in rc.local, now it works
Can someone explain why this is so?

but there's another problem now:

No matter on which level I set brightness in the above way (=changing the value in the file brightness), if I use then the Fn-Keys to adjust brightness it always jumps again to full brightness (on startup) or the level I just adjusted to with the Fn-keys beforehand. That is annoying. Is there any way to "synchonize" the current Fn-Key brightness level with the one in the file (I have a Sony Vaio z11x9e with Ubuntu 12.04)?

[totitoll]

ok now I should try first and then write, but here is what is found out now:

if i take
/sys/class/backlight/acpi_video1/brightness
instead of
/sys/class/backlight/intel_backlight/brightness
it is indeed syncronized with the Fn-Keys.

Now again there is a but: Now not even the first command is executed on boot
I have:
chmod a+w /sys/class/backlight/acpi_video1/brightness
sleep 1
echo 1 > /sys/class/backlight/acpi_video1/brightness

on the other hand typing "sudo /etc/rc.local start" works...


By the way: there are actually three folders in /sys/class/backlight/ namely acpi_video0, acpi_video1 and intel_backlight. The file ....acpi_video/brightness is the only one of those three which changes it's values if I hit the Fn-Keys. So for what are these other two anyway?

[dcstar]

solved it: I added a "sleep 1" in between the two lines in rc.local, now it works
Can someone explain why this is so?

Because rc.local can be run before the other services (like X) have started. It may only be a fluke that it works due to the randomness of the times each service takes to fire up.

[totitoll]

ah if someone else has the problem:

putting the sleep in front(!) works:

sleep 1
chmod a+w /sys/class/backlight/acpi_video0/brightness
chmod a+w /sys/class/backlight/acpi_video1/brightness
chmod a+w /sys/class/backlight/intel_backlight/brightness
echo 191 >/sys/class/backlight/intel_backlight/brightness
echo 1 >/sys/class/backlight/acpi_video0/brightness
echo 1 >/sys/class/backlight/acpi_video1/brightness

sometimes it's hard to see the obvious...