Can I fine-tune my screen brightness keys? (Ubuntu Studio, Thinkpad T420s)

I am in a similar situation as question Can I fine-tune my screen brightness? . For me, Thinkpad T420s and Ubuntu Studio 11.10. The brightness keys work fine but the increments are too large. I have the /sys/class/backlight/acpi_video0 and I can see the value of actual_brightness changing as I use the brightness keys - it changes between values 0,3,6,9,12,15.

None of the listed answers for fine control works here, as follows:

• As the root user I can echo integers to brightness in the above folder. As an ordinary user I cannot.
• I do not have /usr/sbin/gnome-power-backlight-helper (because I'm using xfce perhaps?), and not sure what package it's from or if installing such a package would make sense since it's not what's currently managing the backlight.

EDIT: In an answer below, I describe a command-line way to do it. However, I'd like the brightness keys on my keyboard to do smaller steps. I don't know what component handles those keys (I'm in Xfce BTW). Which component is handling it, and how can I configure it to use finer steps please?

Solution 1:

Found a commandline way to do it:

pkexec /usr/lib/gnome-settings-daemon/gsd-backlight-helper --set-brightness 8

(It seems the -backlight-helper was moved from gnome-power-manager to gnome-settings-daemon, hence this change of address.) Still need to know how to hook this to the keyboard keys.

Solution 2:

You need root to write system hardware configurations.

gnome-power-backlight-helper is probably a simple program with root uid set so it can modify system files. You can achieve a similar effect by writing a shell script and add it to the rules in sudoers. See man sudoers for details.