Ubuntu 20.04: "No input signal" in large blue box upper right hand corner

jawolf · 02-15-2023, 05:24 PM

I'm using Ubuntu 20.04 LTS. Suddenly I have a large blue box in the upper right hand corner of the screen with the words "No input signal". It is a major nuisance since it blocks things I need. I tried rebooting, powering down, using alsamixer, and the thing is still there. Suggestions?

michaelk · 02-15-2023, 07:08 PM

My first random thought is a monitor message and not associated with the operating system. If it was pop up message it should of disappeared or you should be able to click it to make it go away. Normally I would expect the no input signal message to go away but that usually is when the monitor automatically goes to sleep. Have you cycled power on the monitor?

mrmazda · 02-16-2023, 04:20 AM

Try the following in an X terminal:

Code:

# sudo xrandr --listactivemonitors
 0: +HDMI-1 1920/518x1200/324+0+0  HDMI-1

The last part is the name you need to apply to the second command, so HDMI-1 is just an example that may or may not match your output name(s).

Code:

# sudo xrandr --output HDMI-1 --auto

If this wasn't helpful, try simply:

Code:

# xrandr

Output head will resemble:

Code:

Screen 0: minimum 320 x 200, current 1920 x 1200, maximum 16384 x 16384
VGA-1 disconnected primary (normal left inverted right x axis y axis)
HDMI-1 connected 1920x1200+0+0 (normal left inverted right x axis y axis) 518mm x 324mm
   1920x1200     59.95*+
   1600x1200     60.00
   1680x1050     59.88
   1280x1024     75.02    60.02

If the mode at the start of the line that also has *+ on it has more than one mode listed, such as does the last above line, try plugging that second (or third, or fourth) number as the last element of another xrandr command, e.g.

Code:

sudo xrandr --rate 60.02

If either of these causes worse trouble, key in Ctrl-Alt-F3, which should present a login prompt. From there, key in whatever 20.04 is using to return to X, probably one of Alt-F1, Alt-f7, Alt-F8 or Alt-F2. On return to X it should restore the configuration you started with.