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I have installed the xserver-xorg-video-dummy-hwe-18.04 to let I use the VNC without needs to connect HDMI cable to my ubuntu machine.

I followed the Topic here, and successfully able to use VNC connect to Ubuntu machine without plugged-in monitor.

However, there are side effect is that, if I connect the HDMI cable to the ubuntu machine, it will display _ (black screen with cursor blinking at the top) and not show lightdm login screen as expected.

If I remove /etc/X11/xorg.conf from directory, reboot, I can now back using the monitor plugged-in.

Question

Are there possible to able to use video-dummy with/without monitor at the same time? may be like secondary mirroring display mode. How to config /etc/X11/xorg.conf properly?

So that I can use the desktop no matter real monitor has connected to HDMI port or not.

scalopus
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    Hi there, wondering if you were able to solve this problem. Am running into the same problem. – James Wong Dec 08 '20 at 05:01
  • Hi @scalopus, I know it's been a while, but have you found a solution to your issue? If so, I'm now in your situation, i.e. followed the instructions in the topic you mentioned and now I do not have output when a real display is connected. – Thijmen Oct 28 '23 at 11:57

1 Answers1

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Main problem here is that the KMS (Kernel Mode Setting) is on in modern kernels. This needs to be disabled by creating rules to modprobe depending your card:

For ATI graphics:

echo options radeon modeset=0 > /etc/modprobe.d/radeon-kms.conf

For Intel graphics:

echo options i915 modeset=0 > /etc/modprobe.d/i915-kms.conf

For Nvidia i suggest blacklisting nouveau driver and use vesa on xorg.conf

Now if your modeline is setted correctly you should be able to connect your monitor on the fly.

Pasi Suominen
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