This might be useful to connect e.g. Windows XP to ZeroTier network or other machines which you can't or don't want to install ZeroTier client to.

1. Create ZeroTier network in control panel and join it on your host

2. Allow Ethernet bridging for your host in control panel

   

3. In VM …

By default Akonadi uses MySQL and lots of agents, so total memory usage could be ~300-400 MB right from the start. If you don't need all of its capabilities, there is a way to make it use less memory.

1. Replace MySQL with SQLite:

   sudo apt install akonadi-backend-sqlite
   sed -i 's …

All at once:

sudo wget -O /usr/share/keyrings/element-io-archive-keyring.gpg \
          https://packages.element.io/debian/element-io-archive-keyring.gpg

echo "deb [signed-by=/usr/share/keyrings/element-io-archive-keyring.gpg] https://packages.element.io/debian/ default main" \
| sudo tee /etc/apt/sources.list.d/element-io.list

sudo apt update
sudo apt install element-desktop

Step-by-step …

UPD: Just use ZeroTier — open source, cross-platform, secure and easy to use virtual LAN. Add your remote computers to a virtual network and connect to them as if they are in the same LAN. Connections are end-to-end encrypted and P2P, so you always get the best speed and latency possible …

This one is similar to persistent local SSH server forwarding setup (although much more simple). Preparation part is exactly the same, so if you've already done that, you may skip it and go straight to persistent SSH proxy configuration.

After each file and command there will be a location label …

SSH keys come in pairs: a public and a private key. It might be easier to think of them as a lock (public part) and key (private part). You add public key (lock) to the computer you want to connect to, and then you can connect from elswhere and unlock …

(
  username=support
  icon_path=/var/lib/AccountsService/icons/$username

  sudo adduser --gecos '' $username
  sudo adduser $username sudo

  sudo wget -qO "$icon_path" https://shevchuk.co/cog.png
  echo "[User]" | sudo tee /var/lib/AccountsService/users/$username
  echo "Icon=$icon_path" | sudo tee -a /var/lib/AccountsService/users/$username
)

Hide user from login manager …