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I have Ubuntu 14.04 32 bit machine on my lenovo g580. Default brightness keys are not working and can't decrease brightness in settings also. The brightness has been fixed at maximum. I followed few similar questions and modified grub document in /etc/default/grub, but I'm not being able to save this file after modification. Even though I have logged in as admin.It shows "You do not have the necessary permission to save the file", when I tried "save as" in the same location with the same name. What should I do to decrease brightness? Please help.

kevy
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Subrahmanya Sriram
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    How did you try editing `/etc/default/grub`? – kevy Mar 13 '15 at 14:43
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    possible duplicate of [How do I get permissions to edit system configuration files?](http://askubuntu.com/questions/92379/how-do-i-get-permissions-to-edit-system-configuration-files) – David Foerster Mar 13 '15 at 15:29

2 Answers2

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Add a simple line : quiet splash acpi_backlight=vendor to grub

  1. gksudo gedit /etc/default/grub

  2. Replace GRUB_CMDLINE_LINUX_DEFAULT="quiet splash"
    with GRUB_CMDLINE_LINUX_DEFAULT="quiet splash nomodeset acpi_backlight=vendor"

  3. sudo update-grub && sudo reboot

It worked on:

  • Ubuntu 12.04 LTS (Asus U31SD-XH51 )
  • Ubuntu 14.04 LTS (Dell 14z)
  • Ubuntu 14.04 LTS (Lenovo g500, remove nomodeset and it will work fine)

You could try adding a line to /etc/rc.local that will set the desired brightness level. To edit the file, run gksudo gedit /etc/rc.local and add following line: 

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

Substitute the X by the desired brightness level.

karel
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kevy
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  • I did all the things you specified. But still not working. Downloaded an app called "Brightness Controller". Even that is not working. And i don't have rc.local in the above given location. I found that in /etc/rc2.d/S99rc.local . But not getting where should I add the code that you have given. And thanks for helping. – Subrahmanya Sriram Mar 14 '15 at 14:59
  • Have you tried `sudo apt-get update; sudo apt-get upgrade`? – kevy Mar 14 '15 at 15:59
  • Yeah I had.. Now I'm using Windows 7, thinking of switching back to Ubuntu.. – Subrahmanya Sriram May 11 '15 at 13:12
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Try this:

  • Open the Terminal app (Ctrl+Alt+T)
  • Type gksudo gedit
  • Type your password when asked for it (it will not show nothing, even asterisks) and press Enter
  • Text editor will open up
  • Then select Open and open the file to edit
  • Edit the file
  • Save the file
David Foerster
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0x2b3bfa0
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