To add a virtual display on Linux Mint 22.3 Cinnamon, use one of these methods, depending on your GPU:

🔹 Method 1: Enable Intel VirtualHeads (Recommended for Intel GPUs)

If you have an Intel GPU, the driver already supports virtual outputs (VIRTUAL1, VIRTUAL2), but they may be disabled by default.

1. Create a config file to enable virtual heads:

   bash

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   sudo nano /usr/share/X11/xorg.conf.d/20-intel.conf

2. Add this content (adjust VirtualHeads count as needed):

   ini

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   Section "Device"
       Identifier  "intelgpu0"
       Driver      "intel"
       Option      "VirtualHeads" "2"
   EndSection

3. Reboot your system:

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   sudo reboot

4. Verify the virtual displays are available:

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   xrandr

   You should see VIRTUAL1 and VIRTUAL2 listed as disconnected.

5. Enable and configure the virtual display (e.g., 1920x1080 to the right of your primary display):

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   xrandr --output VIRTUAL1 --mode 1920x1080 --right-of eDP1

   Replace eDP1 with your primary display name (check with xrandr).

🔹 Method 2: Use xrandr --setmonitor (Works with xrandr ≥1.5)

If you want to split an existing output into virtual monitors (e.g., for screen sharing or multi-region setups):

1. Check your current display name:

   bash

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   xrandr

   Example output: HDMI-A-0 connected primary 1920x1080+0+0

2. Create a virtual monitor (e.g., split HDMI-A-0 into two 1280x1024 regions):

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   xrandr --setmonitor "VIRTUAL-LEFT" 1280/338x1024/270+0+0 HDMI-A-0
   xrandr --setmonitor "VIRTUAL-RIGHT" 1280/338x1024/270+1280+0 none

   • Syntax: --setmonitor "NAME" W/HxH+X+Y OUTPUT
   • none = no physical output (purely virtual).

3. Verify with:

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   xrandr --current

🔹 Method 3: Use a Disconnected Output (Works with Most GPUs)

If your GPU exposes disconnected outputs (e.g., HDMI-2, DP-1, VIRTUAL1):

1. List disconnected outputs:

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   xrandr | grep disconnected

   Example: VIRTUAL1 disconnected (normal left inverted right x axis y axis)

2. Add a custom mode (if needed):

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   xrandr --newmode "1920x1080_60" 173.00 1920 2048 2248 2576 1080 1083 1088 1120 -hsync +vsync
   xrandr --addmode VIRTUAL1 "1920x1080_60"

3. Enable the virtual display:

   bash

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   xrandr --output VIRTUAL1 --mode 1920x1080 --right-of eDP1

🔹 Method 4: Use xserver-xorg-video-dummy (Fallback)

If the above methods fail, install the dummy driver:

1. Install the dummy driver:

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   sudo apt install xserver-xorg-video-dummy

2. Create a config file:

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   sudo nano /usr/share/X11/xorg.conf.d/10-dummy.conf

   Add:

   ini

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   Section "Device"
       Identifier  "DummyDevice"
       Driver      "dummy"
       VideoRam    256000
   EndSection
   
   Section "Screen"
       Identifier  "DummyScreen"
       Device      "DummyDevice"
       Monitor     "DummyMonitor"
       DefaultDepth 24
       SubSection "Display"
           Depth   24
           Modes   "1920x1080"
       EndSubSection
   EndSection

3. Reboot and enable with xrandr:

   bash

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   xrandr --output Dummy-0 --mode 1920x1080 --right-of eDP1

⚠️ Notes

• Intel GPUs: Method 1 (VirtualHeads) is the cleanest and GPU-accelerated.
• NVIDIA/AMD: Use Method 2 (--setmonitor) or Method 3 (disconnected outputs).
• Persistence: Add the xrandr command to Startup Applications or ~/.xprofile to auto-enable on login.
• Cinnamon GUI: Virtual displays may not appear in the GUI settings; use xrandr for configuration.

The error occurs because 1920x1080 is not a predefined mode for VIRTUAL1. You need to create the mode first, then add it to the output.

Solution: Create and Add the Mode

Run these commands in order:

# 1. Create a new mode for 1920x1080 @ 60Hz
xrandr --newmode "1920x1080_60" 173.00 1920 2048 2248 2576 1080 1083 1088 1120 -hsync +vsync

# 2. Add the mode to VIRTUAL1
xrandr --addmode VIRTUAL1 "1920x1080_60"

# 3. Enable VIRTUAL1 with the new mode
xrandr --output VIRTUAL1 --mode "1920x1080_60" --right-of eDP1

Alternative: Use --auto

If you just want to enable VIRTUAL1 with a default mode (no need to specify resolution):

xrandr --output VIRTUAL1 --auto --right-of eDP1

Verify

Check if it worked:

xrandr

You should see VIRTUAL1 connected 1920x1080+2256+0 (or similar).

🔹 Persist Across Reboots

Add the commands to Startup Applications or ~/.xprofile:

echo 'xrandr --newmode "1920x1080_60" 173.00 1920 2048 2248 2576 1080 1083 1088 1120 -hsync +vsync && xrandr --addmode VIRTUAL1 "1920x1080_60" && xrandr --output VIRTUAL1 --mode "1920x1080_60" --right-of eDP1' >> ~/.xprofile