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Thread: VNC doesn't work with display switched off

  1. #1
    Join Date
    Nov 2018

    Question VNC doesn't work with display switched off

    I have my Ubuntu 19.10 HTPC plugged-in to a HDMI switch, which then routes to my monitor. Most of the time that HDMI switch is set to my Nvidia ShieldTV streaming device and the TV is off.

    When I VNC into my HTPC I am usually unable to do anything on the screen. Mouse and keyboard inputs through VNC are completely ignored. Nothing software fixes this including systemctl restart gdm. Looking through syslog, I found a "monitor is undefined" error.

    Oct 21 15:37:30 myhost gnome-shell[1119]: JS ERROR: Extension TypeError: monitor is undefined#012checkIfFocusedMonitor@/home/myuser/.local/share/gnome-shell/extensions/<@resource:///org/gnome/shell/ui/extensionSystem.js:482:13#012collectFromDatadirs@resource:///org/gnome/shell/misc/fileUtils.js:27:17#012_loadExtensions@resource:///org/gnome/shell/ui/extensionSystem.js:457:9#012_enableAllExtensions@resource:///org/gnome/shell/ui/extensionSystem.js:491:13#012_sessionUpdated@resource:///org/gnome/shell/ui/extensionSystem.js:522:13#012init@resource:///org/gnome/shell/ui/extensionSystem.js:32:9#012_initializeUI@resource:///org/gnome/shell/ui/main.js:245:5#012start@resource:///org/gnome/shell/ui/main.js:141:5#012@<main>:1:31
    Sure enough, when I turned the TV on everything immediately starts to work. From my research, I found this question below which addresses running Ubuntu headless.

    How to use Ubuntu 18.04 on VNC without display attached?

    However I am not running headless, I have a monitor attached, it's just turned off. Any way to make this work at the X/Gnome level?
    Additionally I tried disabling all Gnome extensions entirely in the tweak tool and the problem still happened. So this is not an extension problem.

  2. #2
    Join Date
    Oct 2011

    Re: VNC doesn't work with display switched off

    I leave my HTPC hooked up to my TV and don't have this problem. I suspect the switch is the issue, not the fact that the monitor is turned off. At an electrical level a display connected via HDMI is still detectable even if the display is off. If the connection is not made because the cable is unplugged or the switch effectively makes the cable unplugged then you are effectively headless and all those suggestion solutions apply: dummy resistor display connected, software dummy display, etc. Could you hook the computer to another input on the monitor instead of the switch? even if you used a DVI adapter for example?


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