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How to check if external monitor is turned on and connected

rated 0 times [ 4] [ 0] / answers: 1 / hits: 2088 / 1 Year ago, mon, april 24, 2023, 12:48:24

I'm looking for a scripted way to check if the external monitor is on and connected.

My Ubuntu laptop often fails to turn on the external monitor after sleep or a blank screen. I've long since solved the problem using xset dpms force on; xset dpms force off;.

This solution is less than perfect because the monitor goes through a cycle of black screen / blue screen, and the xset operation must be executed while the monitor is in the black screen state. I often repeat the command multiple times until it works.

If I could check if the monitor is properly connected I could better automate the script that re-engages the monitor using xset dpms force on|off.

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atelti

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4 Years ago

answered 1 Year ago tonhorn · Accepted Answer

You could filter (grep, awk, sed, etc.) the output of several commands that provide info on screens/monitors.
If you only need to know if the external monitor is connected, more than one of them are possibly enough.
I am listing below a few examples of what I see. I don't have an external monitor to test, but I guess you can work out the details.

xrandr.

Screen 0: minimum 320 x 200, current 1344 x 744, maximum 8192 x 8192

LVDS connected primary 1344x744+0+0 (normal left inverted right x axis y axis) 344mm x 193mm

   1344x744_60.00  59.90*+

   ...

HDMI-0 disconnected (normal left inverted right x axis y axis)

VGA-0 disconnected (normal left inverted right x axis y axis)

xdpyinfo

...

default screen number:    0

number of screens:    1



screen #0:

  ... (a lot of useful information)

inxi -aG

As per man page, it can give info on the real monitor/s (e.g., "the real monitor size, not the Xorg full Screen diagonal size, which can be quite different"), although I am not seeing that.

hwinfo | grep -i -B 3 -A 3 monitor

 ...

 37: None 00.0: 10002 LCD Monitor

   [Created at monitor.125]

   Unique ID: rdCR.0BRfQK9ozR8

   Parent ID: vSkL.mJc3+3Ia6n4

   Hardware Class: monitor

   Model: "AUO LCD Monitor"

   Vendor: AUO "AUO"

   Device: eisa 0x20ec

   Resolution: 1366x768@60Hz

 ...