How to set up a Linux box with a persistent session and VNC access

This is how I managed to set up a headless Linux server with VNC access. Instructions are adapted from these instructions on Steam, x11vnc man page, Arch wiki page for x11vnc and various tutorials/blog posts online

You will get a single always-on local desktop session to which you can login via VNC. No multiple sessions or users!

Prerequisites:

• A linux system with a working graphical environment on X11
  • install the system with a monitor, keyboard and mouse plugged in. You'll need a way to generate the edid.txt file and /etc/X11/xorg.conf. I had an NVIDIA card so I used nvidia-settings to do that. On AMD/Intel graphics you should be able to use sudo Xorg -configure (https://www.cyberciti.biz/tips/create-a-xorgconf-file.html), but I haven't tried this. You can also use the edid.txt provided in the Steam instructions link above, there are options for 1920x1080 and a 1440x900 monitors. Copy and paste the EDID informations to e.g. /etc/X11/edid.txt.
• x11vnc installed
• You can unplug the monitor and peripherals after you have generated the xorg.conf and edid.txt
• an SSH server running is a good idea so you have some other way of accessing the headless box
• I've tried this with Xfce, MATE, LXQt and GNOME, so I assume most DEs will work, but the experience is better on a lighter DE with few or no animations
• I've tested on Fedora, CentOS, Ubuntu and Ubuntu MATE, and the above instructions (Steam) are for Arch Linux, so most distros will probably work. There might be slight differences you'll have to figure out yourself

Acquiring xorg.conf and edid.txt on NVIDIA

• Install the NVIDIA proprietary drivers, log in to an Xorg session of your chosen desktop environment. Open a terminal and run sudo nvidia-settings (sudo is required so you can generate /etc/X11/xorg.conf

• Generate /etc/X11/xorg.conf:

  • from "X Server Display Configuration, click "Save to X configuration file" and set the path /etc/X11/xorg.conf

• Generate /etc/X11/edid.txt: (or use the provided one, you can also save this anywhere you like)

  • From the list of ports, choose the one your monitor is connected to (for me it was DVI-I-1) and click "Acquire EDID", then select EDID File Format as ASCII. Save the file somewhere, I used /etc/X11/edid.txt

• Edit /etc/X11/xorg.conf and in the <Device> section add the lines:

  Option "ConnectedMonitor" "<display>"
  Option "CustomEDID" "<display>:<path>/edid.txt"
  

  Replace <display> and <path> with yours, for me it was Option "ConnectedMonitor" "DVI-I-1" and Option "CustomEDID" "DVI-I-1:/etc/X11/edid.txt"

• Save the file

• Edit (create) /etc/X11/Xwrapper.config:

  • add the line allowed_users=anybody
  • this will allow the X session to be started anywhere, It seems this is necessary to start X without an attached display. You can try without it too.

• You can disconnect the monitor at this stage if you want, but for troubleshooting it's better to keep it connected

Make GDM use Xorg instead of Wayland:

• edit /etc/gdm/custom.conf and uncomment the line WaylandEnable = false

Set up automatic login:

• For GDM: (Ubuntu) Arch wiki

  • Under the [Daemon] section in /etc/gdm/custom.conf, add

  AutomaticLogin=username
  AutomaticLoginEnable=True
  

  • replace username with your username
  • you can also do this from the GUI if you still have the monitor attached
  • edit /var/lib/AccountsService/users/<username> and make sure the XSession=<your preferred DE> is correct. The possible sessions are in /usr/share/xsessions, use one of those without the .desktop extension. This should be correct if you have only one DE installed.

• For SDDM: Arch wiki

  • create the file /etc/sddm/sddm.conf.d/autologin.conf with the following content:

  [Autologin]
  User=<username>
  Session=<session>.desktop
  

  • replace <username> and <session> with your values

• For other DMs you can find instructions online

Test that everything is working so far

• Reboot and see that you get logged in correctly to an Xorg session with the display still connected. If you already disconnected the monitor, SSH in and check that your user is logged in on tty :0

Set up x11vnc

• install x11vnc if you haven't already

• Generate a password for the VNC session:

  • run x11vnc -storepasswd as your regular user
  • Please note that VNC is by default unencrypted! If you use this over the internet, I suggest using a VPN connection or tunneling over SSH
  • You can also set up the VNC to be encrypted, but I used a VPN (Wireguard)

• Make sure at least port 5900 is open in your firewall. The server might be using other ports too, and the clients can autodetect the port, so it's a good idea to open ports 5900-5903.

• Test:

  • run x11vnc -usepw
  • connect from another machine using VNC client software of your choosing
  • there are other options for the VNC server, such as -noxdamage, but I haven't got so far as to try any of them out. You could probably improve performance a lot by experimenting with different options. The output of the above command gives good hints. Note that when you disconnect the VNC client, with the above command the VNC server terminates, and to connect again, it must be started again. We'll set up automatic starting next

• Once you have tested that the server and connecting to it works, create an autostart desktop file ~/.config/autostart/x11vnc.desktop:

  [Desktop Entry]
  Name=x11vnc
  Comment=VNC server
  Exec=/usr/bin/x11vnc -usepw -loop -forever
  Type=Application
  NoDisplay=true
  X-GNOME-Autostart-enabled=true
  

  • note the -forever and -loop options, -forever makes the server not quit when the client connection is closed, and -loop makes the server try restarting even if the X server is terminated/restarted. Add any other useful options you want.

• Reboot

• Test that the connection is working

• Shut down, disconnect the monitor and peripherals and power on, then test that everything is working

Notes:

• This gives you a Windows remote support like experience, where you log in to the "physical" session via VNC. If you tested the VNC connection with the monitor attached, you can see the mouse moving on the local screen and everything is "real time"
• No multiple logins at a time this way
• It's probably a good idea to experiment with the different flags x11vnc offers. For my use case these very basic ones have been ok so far.
• There are better ways to handle the automatic starting, like systemd units, but this way the process runs as non-root and works quite consistently.
• If you want to use the display managers login screen, see the Arch wiki, there are lots of tips there.
• DON'T log out. Disconnect the VNC client instead. If you log out, the VNC server is stopped and you'll have to reboot to get back to a graphical session. Maybe restarting your display manager via SSH might be enough, but I haven't tested it
• Share if you find this useful! There might be mistakes, please let me know and I'll fix them