Ubuntu and Levono: Brightness is reset to maximum on every restart

I'm using Ubuntu 14.04 and my labtop is Lenovo ThinkPad. The brightness is reset to maximum every time I reboot my machine. I have fixed the problem by:

1. Adjust the brightness to the level you want (by pressing the brightness key, Fn and F5/F6 in my case).

2. Note the output value of the following command.

cat /sys/class/backlight/intel_backlight/actual_brightness

In my case, it's 1700. It's the current level of brightness. If you want to know the maximum value, you can adjust the brightness to maximum and then run the command.

3. Add the following line to the file /etc/rc.local

echo 1700 > /sys/class/backlight/intel_backlight/brightness

So the content of my file would be:

GNU nano 2.2.6                                  File: /etc/rc.local                                                                            

#!/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.

chmod 666 /sys/class/backlight/intel_backlight/brightness
echo 1600 > /sys/class/backlight/intel_backlight/brightness

exit 0

I also added the command to modify the permission of the file to be writable by all users. I experienced the problem that even though I already modified the file's permission to be writable by all users, it was reset back to not writable even if for root user after reboot.

4. Add acpi_osi=Linux acpi_backlight=vendor to the value of the GRUB_CMDLINE_LINUX_DEFAULT variable inside /etc/default/grub file. Below is the file's content snippet after I've updated.

# If you change this file, run 'update-grub' afterwards to update
# /boot/grub/grub.cfg.
# For full documentation of the options in this file, see:
#   info -f grub -n 'Simple configuration'

GRUB_DEFAULT=0
#GRUB_HIDDEN_TIMEOUT=0
GRUB_HIDDEN_TIMEOUT_QUIET=true
GRUB_TIMEOUT=10
GRUB_DISTRIBUTOR=`lsb_release -i -s 2> /dev/null || echo Debian`
GRUB_CMDLINE_LINUX_DEFAULT="quiet splash acpi_osi=Linux acpi_backlight=vendor"
...

5. Run the following command:

sudo update-grub
Generating grub configuration file ...
Found linux image: /boot/vmlinuz-3.13.0-24-generic
Found initrd image: /boot/initrd.img-3.13.0-24-generic
Found memtest86+ image: /memtest86+.elf
Found memtest86+ image: /memtest86+.bin
Found Windows 8 (loader) on /dev/sda1
done

Please note that step 1, 2 and 3 keep the screen brightness level remain the same after reboot but it will be reset to maximum if the machine is suspended or the screen is lock. Step 4 and 5 will fix this.



Reference
http://askubuntu.com/questions/151651/brightness-is-reset-to-maximum-on-every-restart
http://askubuntu.com/questions/138386/the-brightness-gets-reset-after-unlocking