[CentOS] Linux newbie asks about sonypi on laptop

Okay.  I've been able to set my laptop's screen brighter by working with 
the program spicctrl and the sonypi device.

But everytime I boot, I login under my username then have to do the 
following every time...
First I go into the bash terminal, then su because I can't do this under 
my login name

mknod /dev/sonypi c 10 250  #because sonypi is not listed in /dev - it 
disappears everytime I shut down

then I type

chmod o+w sonypi #because I want to be able under my login name, not 
root, to set the brightness

then i exit su

and type spicctrl --setbrightness=150

and it works...

My questions are:

Why do I have to recreate the device every time?  Shouldn't it be there 
every time?

Your comments would be greatly appreciated.

Ralph Loizzo