Ubuntu – Brightness setting is reset to maximum at login

1) Edit etc/rc.local and add the below line

echo 4 > /sys/class/backlight/acpi_video0/brightness

Where 4 is the 50 % of brightness. 8 is the maximum

2) reboot

If brightness still goes back to max go to step 3

3) In terminal run the following:

sudo -i
mv /etc/init.d/rc.local /root/
update-rc.d rc.local remove
mv /root/rc.local /etc/init.d/
update-rc.d rc.local defaults

If above 3 steps failed to resolve

Then add sleep 10 to rc.local

Example

sleep 10 
echo 5 > /sys/class/backlight/acpi_video0/brightness
exit 0

You can have root run the brightness commands upon reboot, by adding those commands to /etc/rc.local (gksudo gedit /etc/rc.local), so that it looks like:

#!/bin/sh -e
#
# rc.local
#
# This script is executed at the end of each multiuser runlevel.
# Make sure that the script will "exit 0" on success or any other
# value on error.
#
# In order to enable or disable this script just change the execution
# bits.
#
# By default this script does nothing.

echo 130 >> /sys/class/leds/smc::kbd_backlight/brightness
echo 42311 > /sys/class/backlight/gmux_backlight/brightness

exit 0

See also Brightness is reset to Maximum on every Restart