Setup Reverse ssh

1. Make sure SSH is installed on both machines

sudo apt-get update
sudo apt-get install openssh-server

2. On your hidden machine run

ssh -f -N -R 2222:localhost:22 someuser@example.com  -i ~/.ssh/id_rsa_rev

This command opens an SSH connection to greggallardo.com (the machine exposed to the internet) sets up aa tunnel back to localhost (the home machine) on port 22 (the standard SSH port).

• -f and -N : Tells SSH to go into the background and not execute any remote commands, respectively.
• -R : Specifies that the given port on the remote (server) host is to be forwarded to the given host and port on the local side.

3. make it persist with cron

crontab -e

tell it to use

@reboot sleep 60;ssh -f -N -R 2222:localhost:22 someuser@example.com  -i /home/locakuser/.ssh/id_rsa_rev

Connect from the outer machine

1. SSH into your remote machine

 ssh froderick@example.com

2. Onec inside, you can reverse ssh to the hidden machine with

ssh -p 2222 localuser@localhost