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How to use your laptop as a second screen in Linux
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extend-screen-vnc.md

Extend your screen using a laptop in Linux

This GitHub Gist presents a detailed guide on how to set up a laptop as a second monitor on a Linux.

alt-text

Prerequisite

  • The machine for which its screen is going to be extended is going to be the host whereas the other machine which will show the extended screen is going to be the client. The host machine must be on Linux. As for the client it does not really matter as long as there is a suitable VNC viewer.

    • In this guide, the host is running on Manjaro 5.7.0.3 and the client is running on Elementary OS Hera 5.1.2

  • The host machine must be running a X Window System. If you are running Wayland this guide will not work beacuse of the way that Wayland is designed.

    • X is pretty network-aware. You can send windows to other computers, you can have multiple screens with remote logins and all sorts of funky things like that. This might seem fairly specialist but it's widely used technology. Wayland appears fairly local and static in comparison. [StackOverflow]

  • This set up will utilize an VNC connection. Therefore both machines must be on the same network or on a network where they can see each-other IP addresses.

    • Optional: For better performance, both machines must be connected by an Ethernet cable. Running this setup on over Wi-Fi will present a lot of latency and stuttering on the client's side

  • This guide assumes that you are already comfortable with working on a console such as editing files or navigating through directories. You will also need to know how to use teletypewriter (tty) consoles to revert possible mistakes while writing your X configuration that might break your X Server.

Setting up the host

Identifying a virtual display

First things first we need to utilize an Virtual display on your host machine. This will be used as a screen to extend the display. However it will not be visible on your host machine. Therefore we will use a VNC connection to mirror this virtual screen onto another display. That's the principle behind this guide.

To check if you already have a Virtual display initialized, type on your terminal xrandr. You will get an output like this:

Screen 0: minimum 8 x 8, current 1920 x 1080, maximum 32767 x 32767
eDP1 connected primary 1920x1080+0+0 (normal left inverted right x axis y axis) 340mm x 190mm
   1920x1080     60.03*+  59.93    47.99  
   1680x1050     59.95    59.88  
   [...]
VIRTUAL1 disconnected (normal left inverted right x axis y axis)

If you see the VIRTUAL1 you can progress on the next step to utilize this virtual screen for VNC connection. If that's not the case, then follow the next section on creating a virtual display.

Creating a virtual display

For creating a virtual display we will edit the Xorg configuration files. In Manjaro 5.7.0.3 the user-configuration files are located at /etc/X11/xorg.conf.d/. Not all Linux distributions (distros) might share the same location for the Xorg configurations and therefore you will have to look it up on your own if the configuration folder is not located on the mentioned location.

You might probably find other configurations in this folder and you might notice that all configurations start with a numbering such as 00-keyboard.conf, 10-optimus-manager.conf and30-touchpad.conf. This numbering displays the priority of the files and how these files will be read from Xorg server when initialized for the first time. Therefore a lower number means a higher priority and that the earlier the configuration will be executed. This is important as the configurations might overwrite each-other if placed inappropriately.

Since my host is an Optimus laptop, I will utilize the Intel drivers before the Optimus manager takes control over the drivers. Therefore, I will create a a new configuration file 01-dummy-monitor.conf and fill the file with this configurations as suggested by this answer from StackOverflow:

Section "Device"
    Identifier      "virtual_device"
    Driver "intel"
    Option "TearLess"   "1"
EndSection

Section "Monitor"
        Identifier      "virtual_monitor"
EndSection

Section "Screen"
        Identifier      "virtual_screen"
        Monitor         "virtual_monitor"
        Device          "virtual_device"
EndSection

Depending on your setup you might want to experiment with the file configuration placement. Nonetheless, this set-up should work on most distros.

Finally reboot your system or restart your display manager via the terminal.

If you are presented with a black screen, follow the troubleshooting section.

To confirm that a virtual screen was created, run xrandr and check that there exits an VIRTUAL1 entry.

Utilizing the virtual screen for VNC connection

This can be done manually or automatically using VirtScreen. However, at the current time of writing this guide, the software is very buggy and might crash time to time. This does not affect the virtual screen configuration but it can be annoying time to time. Therefore, I will discuss the manual way as it's more straightforward and reliable.

Utilize the virtual screen by running the commands from this template on the terminal:

 xrandr --addmode <virtual display> <resolution>
 xrandr --output <virtual display> --mode <resolution>

where <virtual display> is the name of your virtual display (i.e VIRTUAL1) and <resoluion> is the desired resolution for your virtual screen (i.e "1920x1080" with quotations).

Install x11vnc on your system through a package manager

apt install x11vnc #Ubuntu 
pacman -S x11vnc #Arch and Manjaro
zypper in x11vnc #OpenSuse

Then set-up the VNC server. Before running this command read below about <offset>.

 x11vnc -display :0 -clip <resolution>+<offset> -multiptr -forever

There are two ways to specify the -clip parameter. One way does not need to calculate the offset parameter, however the results may be buggy. The other way needs to manually specify the <offset> which is not really that hard. We discuss first the manual way.

Determining the offset

First you need to consider your virtual screen set-up orientation. You can do this either by using the Display Manager graphical-interface in your distro or manually with xrandr (we won't discuss this in this guide). Suppose we have this screen set-up where our primary screen is shown on the left and the virtual screen is shown on the right, so

y
 ^
 | [ Screen ] | [ Screen ]
 | [   1    ] | [   2    ]
 o ------------------------>
							 x

The screens are displayed on an X and Y axis and there will be an explanation to that.

From x11vnc manual we have that-clip WxH+X+Y where WxH determine the <resolution> as width x height and the +X+Y determines the <offset>.

Assume that for Screen 2 we set the resolution 1920x1080 and with the current positioning to the right of Screen 1 we see that Screen 2 is expanding on the X-axis by it's width which is 1920. However it does not affect the height (Y) when compared to Screen 1. Therefore the final offset is going to be +1920+0 and we the final parameter would be:

 x11vnc -display :0 -clip 1920x1080+1920+0 -multiptr -forever

If however you would want to position the screen on top of screen 1, then the command would look like this:

 x11vnc -display :0 -clip 1920x1080+0+1080 -multiptr -forever

as the second screen is expanding on the Y-axis by it's height.

This should give you a clear understanding on how to set the offset even when dealing with custom resolutions which might be greater or smaller than the your current screen resolution.

However, if you would like to use easy way-out without the need of calculating the offset, the command is:

x11vnc -display :0 -clip xinerama1 -multiptr -forever

Keep in mind that you might not work or might output incorrect resolutions and therefore that is the reason why I did not recommend using it as your first option.

If everything went well, your VNC server should now be running and waiting to be initialized by a client.

For more customization read x11vnc manual (or type man x11vnc to read from the terminal) to add more features to your VNC server

Before jumping to the client section, mark down the host IP address and the port that the VNC server is using. The last can be determined by looking at the output of the x11vnc command

[...]
11/07/2020 13:51:03 WARNING: You are running x11vnc WITHOUT a password.  See
11/07/2020 13:51:03 WARNING: the warning message printed above for more info.
11/07/2020 13:51:03 

The VNC desktop is:      djbit-lenotop:1
PORT=5901

******************************************************************************
[...]

Setting up the client

All this needed for a client is a VNC viewer. Simply put your host IP in the VNC viewer and everything should be ready.

For demonstration purposes, I will be using vncviewer in the client machine via the terminal:

vncviewer -shared -ViewOnly -Fullscreen <host ip>

Troubleshooting

I got a black screen after changing the Xorg configuration files

This can be fixed quite easily by going to a tty with the key combination CTRL + ALT + [F1-F10] and reverting your changes on the Xorg file. To determine what caused the Xorg server crash, you can view the logs on /var/log/Xorg.0.log from the tty by doing

cat /var/log/Xorg.0.log

to determine if the crash was caused by a syntax error or incomparability with your system.

After making these changes you can safely restart your PC/Laptop or display manager.

VNC Connection Refused

Check if the client can communicate with the host by doing

ping <host ip>

and check on the host if the VNC port is openend

sudo lsof -i -P | grep -i listen

Terminology

If you are interested to know more about these terms, I will provide some short descriptions and a link to which you can read more. Most of the descriptions are directly from the ArchWiki or from the Wikipedia.

  • Optimus laptop - A laptop that has an intergrated GPU (such as Intel Graphics UHD) and a dedicated GPU (such as an NVIDIA series GPU) and that can switch between them easily (Read More).

  • VNC - Virtual Network Computing is a graphical desktop-sharing system that uses the Remote Frame Buffer protocol to remotely control another computer. (Read More)

  • X Window System - also known as X11 or X, is a windowing system for bitmap displays, common on Unix-like operating systems. (Read More)

  • X.Org Server- is the free and open-source implementation of the display server for the X Window System and it's the most popular display server in the Linux community (Manual) (Read ArchWiki)

  • xrandr - is an official configuration utility to the RandR (Resize and Rotate) [X Window System extension. (Read ArchWiki)

  • Xinerama - is an extension to the X Window System that enables X applications and window managers to use two or more physical displays as one large virtual display. (Read More)

This content is under GNU Free Documentation License 1.3

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