My Ubuntu laptop’s screen brightness resets everytime after reboot. I have found a way to make the brightness adjustment ‘stay permantly’:
1) Adjust the brightness to the level that I like, then run ‘cat /sys/class/backlight/acpi_video0/brightness ‘. The command will return the brightness level in a integer value. Mine is 12.
2) Add the line ‘echo 12 > /sys/class/backlight/acpi_video0/brightness‘ into the /etc/rc.local file.