https://makandracards.com/makandra/1585-address-already-in-use-with-autossh

If you get an error "Adress already in use" with autossh check with lsof or netstat if something already listen on the Ports you want to use.

There are three Ports you have to look at. If your Command look like this:

/usr/local/bin/autossh -f -M 5100 -g -N -C -L 8080:127.0.0.1:80 example.com -i ~/.ssh/id_rsa -l user

The following three ports need to be available:

1. 8080: The Port you want the tunnel to listen
2. 5100: The Autossh Monitoring Port
3. 5101: Autossh also uses the Monitoring Port +1