Unable to login to Ubuntu host with monitor off

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  • #33419
    Avatarkleinfelter
    Participant

    My NoMachine is not updating the virtual display unless the physical monitor is powered on and connected. How can I get NoMachine to update my client-side display when the host’s physical monitor is powered off?

    It *is* processing keyboard and mouse events. It is just not updating the display. I know this because I can login blind, and when I power on the physical monitor, I see the logged in desktop.

    After I’m logged in, I get similar behavior.  e.g. If I turn off the physical monitor, blindly move the client’s or the physical mouse, and power the monitor on, I find the mouse pointer where I blindly moved it.

    Connecting to NoMachine 7.4.1_1 on Ubuntu 20.04.2 LTS server from NoMachine 7.0.211 on MacOS 10.13.6. I’m running GDM3 (default) display manager and GNOME 3.36 (default) desktop environment on my Ubuntu. The host hardware is an HP EliteDesk 800 G2.

    How can I get NoMachine to update my client-side display when the host’s physical monitor is powered off?

    #33449
    AvatarBritgirl
    Keymaster

    Can you try the tips for headless servers here?

    How to solve black screen and other possible problems on headless machines
    https://knowledgebase.nomachine.com/AR03P00973

     

    #33458
    Avatarkleinfelter
    Participant

    Thank you for the suggestion.

    • The fake-monitor dongle won’t work for me. The server is attached to a KVM switch, which simply disconnects the not-selected machine.  Shopping for a pricey KVM switch that emulates a connected monitor interface to the disconnected machine would be a theoretical alternative. Can anyone recommend an affordable 3-4 port HDMI KVM that does this?
    • If I sudo systemctl stop gdm && sudo /etc/NX/nxserver --restart && sudo systemctl stop gdm would it have the effect of running both a NoMachine X server *and* GDM?
    • Is there a way to just tell NoMachine to always launch its X server in addition to the one for the physical monitor?  I don’t need to ‘share’ the physical session — I just need to connect remotely to *an* X session.
    #33459
    Avatarkleinfelter
    Participant

    Ha! I think I found a hardware solution.  Looks like I need an HDMI EDID Emulator with pass-through.

    If it works as described, the computer will “see” a connected monitor, whether the monitor is on/off or connected/disconnected.

    #33485
    AvatarCarin
    Participant

    Hi kleinfelter,

    We are glad you found a valid hardware solution.

    Is there a way to just tell NoMachine to always launch its X server in addition to the one for the physical monitor?  I don’t need to ‘share’ the physical session — I just need to connect remotely to *an* X session.

    Actually, with a NoMachine Workstation license, you could enjoy the virtual desktop sessions, effortlessly.

    A possible way to prevent the physical display from turning off when the monitor is disconnected would be to create a custom EDID file and reconfigure Xorg to use it.

    #33516
    Avatarkleinfelter
    Participant

    In case someone else comes along after me with a similar problem: Confirmed:

    • If NoMachine connects to the physical console X session on a Linux box
    • and your monitor is turned off, unplugged, or the Linux box is the inactive monitor on a KVM or HDMI switch
    • and it shows a black screen and/or ignores your keyboard/mouse
    • and your monitor is connected via HDMI (or if, like me, your computer has DisplayPort and you use a DP to HDMI cable)

    placing one Hdmi Edid Emulator on the monitor end of your cable will make your computer “think” the monitor is turned on and connected.

    i.e. one Hdmi Edid Emulator on the monitor end of your cable will fix the issue where NoMachine doesn’t work well without a connected monitor. It will work with or without a monitor.

    #33526
    AvatarCarin
    Participant

    Hi kleinfelter,

    We are glad your solution works. Thank you again for sharing it.

    i.e. one Hdmi Edid Emulator on the monitor end of your cable will fix the issue where NoMachine doesn’t work well without a connected monitor. It will work with or without a monitor.

    Just adding a small note here, the problem is not that NoMachine doesn’t work well with headless machines, it’s rather related with the machine video out, that has limited functionality when running headless.

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