AutoSSH: Automatically Reconnect SSH Tunnels

Introduction link

If like me you need to maintain a permanent tunnel, and you want it to automatically reconnect in case of disconnection, you need to use a tool like AutoSSH. I’ll skip the details of its complete operation, but you should know that it can work in 2 ways:

1. By establishing a loop with the remote server and regularly checking that data is flowing through it
2. By querying a service on the remote machine at regular intervals

Installation link

To install it, it’s simple:

  aptitude install autossh
  

Configuration link

Personally, I don’t use the method that regularly listens to a port; the other one is quite sufficient for me. So I’ll cover the basic method. Let’s imagine that I usually use an SSH connection by creating a socks and a local forward:

  ssh -D12345 -N -f -L2222:10.0.0.1:22 deimos@server.deimos.fr
  

To use it with autossh, it’s simple, just use all the SSH options and paste them after the autossh command:

  autossh -M 0 -D12345 -N -f -L2222:10.0.0.1:22 deimos@server.deimos.fr
  

The -M 0 option allows you to not use the monitoring option (solution #1). And that’s it, autossh manages this connection for you.

At Boot link

If you want to enable it at boot, here’s an example to add to rc.local:

  # /etc.rc.local
autossh -M 0 -q -f -N -oServerAliveInterval=60 -oServerAliveCountMax=3 -L2222:10.0.0.1:22 deimos@server.deimos.fr
  

The SSH options ServerAliveInterval and ServerAliveCountMax allow the connection to be cut if there’s a problem to force autossh to restart it.

References link

https://www.harding.motd.ca/autossh/README