On Ubuntu 12.04 LTS on a Dell Vostro 2420 laptop, each time I start Ubuntu, the screen brightness is set to the maximum level, which gives a high glare. (I have recently installed Ubuntu on the laptop, but did not change any default settings related to brightness, IIRC.) I am currently lowering the brightness manually each time after starting, using the System Settings icon on the left of the screen. Looking for a permanent way to set it to a lower value.

3 Answers 3


After you set the brightness to your desired level open up a terminal and check what the brightness is set to by using

cat /sys/class/backlight/acpi_video0/brightness

Then you can take that value and

sudo gedit /etc/rc.local

Right above exit 0 add

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

and then save the file. This will permanently set the brightness to your value as rc.local is executed at each reboot.

Note: This only works if you have a file named brightness in /sys/class/backlight/acpi_video0/

  • Thanks, have made that change. Not rebooted to test it yet. Will do so shortly and then reply here whether it worked. Pretty sure it will, since I saw the value in the file change even when I changed the brightness via System Settings. Commented Jul 31, 2013 at 17:11
  • I rebooted, and the changes have taken effect. Thanks! Commented Jul 31, 2013 at 18:13
  • @TooBrightScreen Glad it worked, please feel free to mark it as answered so others could easily find the solution.
    – bigbash
    Commented Jul 31, 2013 at 18:16
  • How to mark it as answered? I looked in most places in this screen, also hovered mouse over most of the icons, but don't see any way to mark it as answered. Do I need to be above some value for reputation to mark it? Commented Jul 31, 2013 at 18:32
  • @TooBrightScreen What should I do when someone answers my question?
    – bigbash
    Commented Jul 31, 2013 at 18:36

Install backlight on your system.

Place the command xbacklight -set value in your startup.

It will automatically do the job for you. Hope this helps!

  • You mean install xbacklight? Commented Jun 24, 2017 at 23:57

@bigbash after setting the brightness to a desired set value i am typing this command, /sys/class/backlight/acpi_video0/brightness, did the way u have suggested but it is not working.One more thing what ever value i set for brightness from settings after putting the above command always i am getting the same value i.e 15.

  • That means you have more than one display output. Or at least, you did plug at least one before. Try looking at /sys/class/backlight/acpi_video1/brightness. I hope this helps. Commented Nov 5, 2014 at 16:11

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