Skip to content
reliable reverse-ssh tunnel for raspberry pi
Shell
Branch: master
Clone or download
Fetching latest commit…
Cannot retrieve the latest commit at this time.
Permalink
Type Name Latest commit message Commit time
Failed to load latest commit information.
LICENSE
README.md
install.sh
tunnel.service
tunnel.sh

README.md

Reverse SSH Tunnel

Suppose you have a machine (like a Raspberry Pi) that lives behind a home router or on another inaccessible network. Or, maybe this machine occasionally changes it's IP address. This repo will set up a tunnel from the machine (called the local machine) to another machine (called remote) that has a reliable internet-connectible address. You will be able to reliably connect to local by first connecting to remote and then jumping from remote to local via the configured remote_port.

Remote setup

Make sure the remote machine is reliably online. I use a server with a static IP address, but you can also use a dynamic DNS name.

Create a remote_user for the tunnel; here, I use pitunnel. Replace <ssh_key> with the SSH key you create in the Local setup section.

$ sudo useradd -m pitunnel
$ sudo su - pitunnel
$ mkdir ~/.ssh
$ echo <ssh_key> > authorized_keys
$ exit

You should also configure the SSH service to time out stale connections. Edit /etc/ssh/sshd_config and make add a section like so:

# disconnect idle clients after a minute
ClientAliveInterval 20s
ClientAliveCountMax 3

This will cause the SSH server to ping connected clients every 20 seconds, and disconnect if 3 pings fail. Make sure your sshd_config is still valid by running:

$ sshd -t && echo 'looks good' || echo 'sshd config is invalid'

If it outputs looks good then you can go ahead and restart sshd:

$ sudo systemctl reload sshd

Local setup

First, install autossh:

$ sudo apt-get install -y autossh

Next, create an SSH key for your tunnel. Don't specify a password.

$ ssh-keygen -t ed25519
$ cat ~/.ssh/id_ed25519.pub
<ssh_key>

Copy the output (<ssh_key>) and paste it into the /home/<remote_user>/.ssh/authorized_keys file on remote.

Next, clone this repo and edit tunnel.sh. You will need to customize these variables:

  • remote_host -- the hostname or IP of the remote server
  • remote_port -- the port on the remote server where local will be available
  • remote_user -- the user you created in the remote setup section

If you're not running on a Raspberry Pi, you should also edit tunnel.service and customize this line:

User=pi

Replace pi with the local username (output of whoami).

Once configured, you can run install.sh:

$ sudo ./install.sh

This will begin running the SSH tunnel.

Usage

To connect to the local machine, first connect to remote. Then, on remote, run:

$ ssh pi@localhost -p <remote_port>

Replace pi with your local username (whatever you put as User= in local setup.

Troubleshooting

So long as local can communicate with remote, the tunnel will be re-created if it does for any reason. It might take a minute or two for existing connections to time out, so keep trying if it doesn't work at first.

To check on the status of the tunnel, you can run:

$ systemctl status tunnel
You can’t perform that action at this time.