On Knsole(GUI) I executed

xrandr --output HDMI1 --brightness 976

then the screen turned to almost a white board. I can't use GUI any more. Press ctrl+alt+F2, got a tty. I want to reset brightness, but execute xrandr got

can't not open display

Can I change brightness from tty?

  • 1
    Have you actually tried setting the display variable? e.g. DISPLAY=:0 xrandr --output HDMI1 --brightness 1.0 Dec 31 '17 at 1:41
  • Tried, but got can't open display :0
    – Aladin Lee
    Dec 31 '17 at 2:20
  • Well the primary X server display may be something other than :0 - check with ps -ef | grep '[X]org' for example Dec 31 '17 at 2:32
  • Confirmed, it's :0 loginctl show-session c1 | grep Display Display=:0
    – Aladin Lee
    Dec 31 '17 at 2:49
  • 2
    So the issue was that you were logging into the tty as a different user from that owning the display? Dec 31 '17 at 3:28


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

That will set brightness to 40%. You may need to change the directory to match your video card. Note also that you'll have to be in the video group.

xbacklight can be also helpful, e.g.

xbacklight -d :0 -dec 30

should decrease brightness by 30%.

Be aware that these two are hardware modification (people usually prefer that to manipulate screen brightness), and your initial command xrandr --brightnes uses software to manipulate gamma. The screen may or may not look exactly the same after applying these different techniques.

  • Awesome use of /sys. Although I'm pretty sure @steeldriver's command should also work.
    – jdwolf
    Dec 31 '17 at 1:46
  • I reboot and solved problem. I tried xbacklight -d :0 -dec 30 in GUI, no error but nothing happened. Only xrandr --output HDMI1 --brightness .8 change brightness as expected.
    – Aladin Lee
    Dec 31 '17 at 2:33
  • @AladinLee How about xbacklight -d :0 -set 10?
    – jimmij
    Dec 31 '17 at 2:37
  • Also no effect. And also change /sys/class/backlight/intel_backlight/brightness no effect.
    – Aladin Lee
    Dec 31 '17 at 2:42

The command you are using:

xrandr --output HDMI1 --brightness 976

is telling xrandr to set the brightness 976 times higher than normal.

  • 1.0 sets to normal brightness
  • 1.1 sets 10% above normal brightness but it's not recommended to go over 1.0 as colours wash out.
  • 0.75 or .75 sets to 75% of normal brightness
  • 0.66 sets to 2/3 normal brightness, etc.

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