GNet Solutions » GNU/Linux Administration

This is a guide on how I setup an automatic reverse SSH tunnel that connects back to a server using Arch Linux.

• Start by creating an SSH keypair; this guide uses the user bob (replace as necessary):
  

  ssh-keygen -t ed25519
  

• Copy the key over to the server and add it to the ~/.ssh/authorized_keys file.

• Create the systemd tunnel-home.service unit file:
  

  sudo vi /etc/systemd/system/tunnel-home.service
  

  • And add the following:
    

    [Unit]
    Description=Reverse SSH Tunnel Service
    ConditionPathExists=|/usr/bin
    After=network.target
    
    [Service]
    User=bob
    ExecStart=/usr/bin/ssh -NTC -o ServerAliveInterval=60 -o ExitOnForwardFailure=yes -o StrictHostKeyChecking=no -i %h/.ssh/id_ed25519 -p 10000 -R 12345:localhost:22 bob@server.example.com
    
    # Restart every >2 seconds to avoid StartLimitInterval failure
    RestartSec=3
    Restart=always
    
    [Install]
    WantedBy=multi-user.target
    

    
    NOTE: This connects to server.example.com as the user bob on port 10000, creating port 12345 on the remote server to connect back to.

• Start and enable it at boot:
  

  sudo systemctl daemon-reload
  sudo systemctl enable tunnel-home.service
  sudo systemctl start tunnel-home.service
  

Resources¶

• http://blog.kylemanna.com/linux/2014/02/20/ssh-reverse-tunnel-on-linux-with-systemd/
• http://blog.philippklaus.de/2013/03/start-autossh-on-system-startup-using-systemd-on-arch-linux/