this is the first occurrence where su was required for me.
I read an article about changing the value in /sys/devices/virtual/backlight/acpi_video0/brightness to alter my laptop's screen brightness.
I first noticed that when I would
$ sudo echo 10 > brightness I would get permission denied.
I switched to root using su and
# echo 10 > brightness changed my brightness almost instantly.
The last weird thing to me happened when I tried
# echo 20 > brightness (maxbrightness file holds the value 15) and I got a write error
Could someone explain this difference between sudo and su to me? Understanding the write error would be an added bonus. Any help, pointers, and/or links would be much appreciated.