Forward Local Unix Socket Over SSH to Ubuntu

This guide explains how to securely forward a local Unix domain socket to a remote Ubuntu Linux server using SSH. By leveraging SSH stream local forwarding, you can bridge local and remote socket-based applications without exposing them to the public internet. This article covers the exact SSH commands, configuration requirements, and troubleshooting steps needed to establish this connection.

Prerequisites

OpenSSH version 6.7 or newer installed on both the local machine and the remote Ubuntu server (modern Ubuntu versions have this by default).
SSH access to the remote Ubuntu server with appropriate permissions to create socket files in the target directory.

Step 1: The SSH Forwarding Command

To forward a local Unix socket to a remote server, use the SSH remote port forwarding flag (-R). The syntax requires specifying the path to the remote socket followed by the path to the local socket.

Run the following command on your local machine:

ssh -R /var/run/remote.sock:/tmp/local.sock user@ubuntu-server

In this command: * /var/run/remote.sock is the path where the socket will be created on the remote Ubuntu server. * /tmp/local.sock is the path to your existing local Unix socket. * user@ubuntu-server represents your remote SSH login credentials.

Step 2: Configure Automatic Socket Cleanup

By default, if the remote socket file already exists from a previous session, OpenSSH will fail to recreate it, resulting in a “bind: Address already in use” error.

To configure the Ubuntu server to automatically delete the old socket file when a new connection is established:

Open the SSH daemon configuration file on your remote Ubuntu server:
```
sudo nano /etc/ssh/sshd_config
```
Add or uncomment the following line:
```
StreamLocalBindUnlink yes
```
Save the file and restart the SSH service to apply the changes:
```
sudo systemctl restart ssh
```

If you do not have administrative access to modify sshd_config, you must manually remove the remote socket file before running the SSH command:

ssh user@ubuntu-server "rm -f /var/run/remote.sock" && ssh -R /var/run/remote.sock:/tmp/local.sock user@ubuntu-server

Step 3: Verify the Connection

Once the SSH session is active, verify that the socket has been successfully created on the remote Ubuntu server by listing the file:

ls -la /var/run/remote.sock

You can test the communication flow through the forwarded socket using netcat on the remote server:

nc -U /var/run/remote.sock