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i have repeatedly found it very difficult on desktops. echo 40 > /sys/class/backlight/ doesn't work as there are no backlight files. in laptop too sometimes there are not there but fn key works! so i from where does the fn key change backlight when no backlight found? i want to follow the same method my laptop is using and able to change brightness without the backlight file. so for desktop it should be possible via an alternate method?

i installed xbacklight but it doesn't work as there are no backlight files. i usually use desktop where i never ever found backlight files despite installing 6 distros. this is the o/p of xrandr -q | grep " connected"

VGA-1 connected 1600x900+0+0 (normal left inverted right x axis y axis) 443mm x 250mm and this is o/p of xrandr --output LVDS1 --brightness 0.5

warning: output LVDS1 not found; ignoring xrandr: Need crtc to set gamma on. so how to use xrand wihtout any errors

and sudo setpci -s 00:02.0 F4.B=80 setpci: Warning: No devices selected for "F4.B=80".

and http://pastebin.com/gBSBsZ1w is o/p of lspci i also did sudo setpci -s 01:00.0 F4.B=20 without any error since that is the VGA from lspci cmd. but nothing happened

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  • You are trying to echo into a folder. In /sys/class/backlight/ there should be another directory , for example mine is acpi_video0, where you have brightness and max_brightness file. Jan 25, 2016 at 15:40
  • Try this: askubuntu.com/questions/273045/…
    – Genokan
    Jan 25, 2016 at 15:57

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In my case, I installed my nvidia video card driver and I changed the brightness from the driver's settings. Maybe you should install your video card's driver and then look there.

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  • wait a sec, do u have brightness file on your desktop?? not laptop-which always has it and is no problemo
    – doeydha
    Jan 28, 2016 at 16:24
  • This is where I change the brightness: imgur.com/84S31uX
    – Vio
    Feb 2, 2016 at 10:25

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