How to make Brightness Keys work on LXDE.

[kagashe]

I am using Ubuntu 14.04.2 on Lenovo G50-45 and the Brightness Fn keys (they are at no 11 and 12) work well on it.

Due to 2 GB RAM (only 1716 left after video) I have added LXDE Desktop.
The Brightness is too much and I have set it in /etc/rc.local by adding the following line before exit 0

echo 75 > /sys/class/backlight/radeon_bl0/brightness

But I would like to adjust it through Fn 11 Fn 12 keys as I do on Unity Desktop.

I know that I need to add the keybindings on ~/.config/openbox/lxde-rc.xml to make the Fn keys work but need the exact syntax to be added.

Kamalakar

[vasa1]

..
I know that I need to add the keybindings on ~/.config/openbox/lxde-rc.xml to make the Fn keys work but need the exact syntax to be added.

Kamalakar
See if this offers any hints:
<!-- Keybindings for Multimedia Keys and LCD Backlight -->
<keybind key="C-F7"> # turn off screen immediately
<action name="Execute"><command>sleep 2;xset dpms force off</command></action>
</keybind>
<keybind key="C-F10"> # decrease screen brightness
<action name="Execute"><command>xbacklight -dec 10</command></action>
</keybind>
<keybind key="C-F11"> # increase screen brightness
<action name="Execute"><command>xbacklight -inc 10</command></action>
</keybind>

[kagashe]

See if this offers any hints:
<!-- Keybindings for Multimedia Keys and LCD Backlight -->
<keybind key="C-F7"> # turn off screen immediately
<action name="Execute"><command>sleep 2;xset dpms force off</command></action>
</keybind>
<keybind key="C-F10"> # decrease screen brightness
<action name="Execute"><command>xbacklight -dec 10</command></action>
</keybind>
<keybind key="C-F11"> # increase screen brightness
<action name="Execute"><command>xbacklight -inc 10</command></action>
</keybind>

The following command does not work in the Terminal:

S xbacklight -dec 10
Therefore this is not going to work.
I think Unity Desktop is doing it differently.

Kamalakar

[kagashe]

I have done some googling.

xbacklight does not work for radeon driver.

only solution is to echo the required value to /sys/class/backlight/radeon_bl0/brightness file as root user (even sudo does not work).

I wonder what command the Fn key is using. Is there any way to know on Ubuntu Unity Desktop?

Kamalakar

[kagashe]

I wonder what command the Fn key is using. Is there any way to know on Ubuntu Unity Desktop?

Kamalakar
I got the command from auth.log after pressing the keys:

pkexec[8165]: user: Executing command [USER=root] [TTY=unknown] [CWD=/home/vidya] [COMMAND=/usr/lib/unity-settings-daemon/usd-backlight-helper --set-brightness 28]
It is executed as root.

Kamalakar

[kagashe]

Finally I could solve the problem as follows:

Since the command to be executed required root privileges I created two bash shell files on my desktop:

File ~/home/Desktop/Brightness1

#! /bin/bash

# script to set the initial brightness on login

[ "$UID" -eq 0 ] || exec gksu bash "$0" "$@"
/usr/lib/unity-settings-daemon/usd-backlight-helper --set-brightness 12

File ~/home/Desktop/Brightness2

#! /bin/bash

# script to set the initial brightness on login

[ "$UID" -eq 0 ] || exec gksu bash "$0" "$@"
/usr/lib/unity-settings-daemon/usd-backlight-helper --set-brightness 24

I made the files executable and tested them. The script asked for sudo password and set the required brightness.

Then I inserted following Keycodes in ~/.config/openbox/rc.xml

<!-- Keybindings for LCD Backlight -->
<keybind key="XF86MonBrightnessDown"> # decrease screen brightness
<action name="Execute"><command>/home/user/Desktop/Brightness1</command></action>
</keybind>
<keybind key="XF86MonBrightnessUp"> # increase screen brightness
<action name="Execute"><command>/home/user/Desktop/Brightness2</command></action>
</keybind>

and it works by pressing Fn+F11 and Fn+F12 i.e. it asks for sudo password and sets the required brightness.

However writing the command

gksu /usr/lib/unity-settings-daemon/usd-backlight-helper --set-brightness 12
directly in ~/.config/openbox/rc.xml does not work.

Marking the thread as solved, I hope it is useful.

Kamalakar