Add Fake Display when No Monitor is Plugged In

Question

I have an Ubuntu 14.04 server that has no external monitor connected. I use NoMachine to remote control the machine. When I do so, the Unity/Gnome interface doesn't see any monitors connected, so I can only use 800x600 when connecting with NoMachine. If I plug in a monitor, I can set the resolution to whatever size the NoMachine window is on the remote computer.

Is there a way to create a "fake" monitor device on Ubuntu so I can set a desktop resolution in Unity/Gnome?

score 100 · Accepted Answer · edited May 11 '23 at 07:20

Found a way to do it without requiring a dummy plug: Ubuntu Headless VNC VESA 800x600 Resolution Fix ~ Andy Hawkins @ June 12, 2011

Basically install a dummy driver:

sudo apt-get install xserver-xorg-video-dummy

Then write it in the /usr/share/X11/xorg.conf.d/xorg.conf (or possibly /etc/X11/xorg.conf) file (create one, if it does not exist):

Section "Device"
    Identifier  "Configured Video Device"
    Driver      "dummy"
    # Default is 4MiB, this sets it to 16MiB
    VideoRam    16384
EndSection
Section "Monitor"
    Identifier  "Configured Monitor"
    HorizSync 31.5-48.5
    VertRefresh 50-70
EndSection
Section "Screen"
    Identifier  "Default Screen"
    Monitor     "Configured Monitor"
    Device      "Configured Video Device"
    DefaultDepth 24
    SubSection "Display"
    Depth 24
    Modes "1024x800"
    EndSubSection
EndSection

Then restart your X session by logging out.

score 27 · Answer 2 · answered Dec 27 '15 at 02:58

Specify the resolution on a Ubuntu 14.04 desktop without a monitor connected:

From the xrandr man page:

--fb widthxheight
   Reconfigures the screen to the specified size. All configured 
   monitors must fit within this size. When this option is not 
   provided, xrandr computes the smallest screen size that will 
   hold the set of configured outputs; this option provides a 
   way to override that behaviour.

Therefore use the command after connecting:

xrandr --fb 1280x1024

Rufus · Answer 3 · 2023-07-10T10:28:31.260

25

Consider Xvfb which is probably least likely to mess up the display when you actually plug in a real monitor.

The following commands will start lightdm on a fake display with ID 1 and resolution 1024x76

export DISPLAY=:1
Xvfb :1 -screen 0 1024x768x16 &
sleep 1
#exec gnome-session & use gnome-session instead of lightdm
exec lightdm-session &

Probably relevant

edited Jul 10 '23 at 10:28

answered Jan 22 '19 at 09:26

Rufus

943

user.dz · Answer 4 · 2021-02-21T12:35:04.067

Hardware Solution

This is a hardware solution/workaround which may work for some graphics hardware/driver. Also could be better, if you need to plug physical monitor frequently, so you don't have to restart X Server like with dummy/vesa/fb driver (static configuration).

Either you buy a Dummy VGA (or DVI analog) plug or some calling it Dummy Dongle.
Or just build it, use 3 resistors of around 75 Ohm (a standard) at the VGA output: 1→6, 2→7, 3→8.

+/- 10 Ohm may work without any problem. Some cards work with just one resistor. (Like my Intel, 2→7 or 3→8, will detected as a monitor). By the way, this is standard impedance which implemented in the VGA monitors.

Reference: How to create dummy plugs for your graphics cards.

Users who are curious to read more about monitor & its resolution detection, I would recommend reading about VESA DDC & EDID too.

score 6 · Answer 5 · answered Oct 28 '19 at 11:51

For me no one of the above solution works. To add a new device/screen VIRTUAL1, what has worked for me is :

Install the packet xserver-xorg-video-dummy
Update xorg.conf

All details are here : Add Fake Display when No Monitor is Plugged In

Info : for me, it works in editing /etc/X11/xorg.conf instead of /usr/share/X11/xorg.conf.d/xorg.conf

score 5 · Answer 6 · edited Jul 02 '23 at 08:13

I'm on Ubuntu 18.04, this is how I solved it:

I've created the virtual display using the answer to this question: https://unix.stackexchange.com/questions/378373/add-virtual-output-to-xorg

Create a 20-intel.conf file:

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

Add the following configuration information into the file:
Section "Device"
    Identifier "intelgpu0"
    Driver "intel"
    Option "VirtualHeads" "2"
EndSection
This tells the Intel GPU to create 2 virtual displays. You can change the number of VirtualHeads to your needs.

Then I made a shell script (don't forget to set executable) and put that in Startup Applications:

#! /bin/bash
/usr/bin/xrandr -d :0 --output VIRTUAL1 --primary --auto
/usr/bin/xrandr --newmode "1600x900_60.00" 118.25 1600 1696 1856 2112 900$
/usr/bin/xrandr --addmode VIRTUAL1 "1600x900_60.00"
/usr/bin/xrandr

That way, VIRTUAL1 is set as output and connected. At boot, a new mode (found using "cvt 1600 900") is being created and appointed to VIRTUAL1.

Only issue with this is: dock is missing at reboot... Haven't solved that yet.

score 1 · Answer 7 · edited Jun 01 '23 at 11:00

This works as an additional monitor/display once there is an existing one

# I think I may have spoken too soon. I was able to create a "virtual" display by adding a new mode to one of the disconnected displays listed in xrandr using
xrandr --addmode VIRTUAL1 1024x768
I then simply enabled the display like you would normally:
xrandr --output VIRTUAL1 --mode 1024x768 --left-of HDMI3
Furthermore, combined with x11vnc -clip, I am able to use this to convert my android tablet to a second monitor.  The perfomrance is pretty crappy at the moment, unfortunately, but that's whole other area to be explored.

https://bbs.archlinux.org/viewtopic.php?pid=1410831#p1410831

score 1 · Answer 8 · answered May 11 '21 at 09:06

John Chapman's answer didn't work for me. I can suggest this link for a fixed dummy display with 1024x768 24bit. I can successfully connect to my pc without any display attached. My system is Ubuntu 16.04. You should install VESA video driver.

sudo apt-get install xserver-xorg-video-vesa

Code is in your /usr/share/X11/xorg.conf.d/xorg.conf file or /etc/X11/xorg.conf file

Section "Device"
Identifier    "Configured Video Device"
Driver        "vesa"
EndSection
Section "Monitor"
    Identifier    "Configured Monitor"
    HorizSync 42.0 - 52.0 
    VertRefresh 55.0 - 65.0 
    Modeline "1024x768" 60.80  1024 1056 1128 1272   768  768  770  796
    Modeline "800x600" 38.21 800 832 976 1008 600 612 618 631
    Modeline "640x480" 24.11 640 672 760 792 480 490 495 50
EndSection
Section "Screen"
    Identifier    "Default Screen"
    Monitor        "Configured Monitor"
    Device        "Configured Video Device"
    DefaultDepth    24
    Subsection "Display"
        Depth       24
        Modes       "1024x768" "800x600" "640x480"
       EndSubsection
EndSection

score 0 · Answer 9 · answered Apr 06 '21 at 13:58

Got it working

Just install the dummy driver

sudo apt-get install xserver-xorg-video-dummy

dont edit the xorg.conf file I however just created an empty file here

/usr/share/X11/xorg.conf.d/xorg.conf

now when you have a monitor hooked in it will work as earlier but if you boot it without a monitor that should work too and you should be able to ssh into your machine.

hope it works for you too.

tested on ubuntu 19.04 and intel nuc.

Add Fake Display when No Monitor is Plugged In

9 Answers9

Hardware Solution

I then simply enabled the display like you would normally:

Furthermore, combined with x11vnc -clip, I am able to use this to convert my android tablet to a second monitor. The perfomrance is pretty crappy at the moment, unfortunately, but that's whole other area to be explored.

Linked

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