I wanted to pair with a friend of mine, exploring Magit mode in Emacs. There are a couple of projects to make it easy to use tmux(-like) to simplify this.

• pairing lets you share a screen and pair, on a common server where both the users have access to. But I wanted to use my machine, instead of the server.

• tmate gets around the restriction of having a common server where both users have access, but needs a custom install of tmux, and the use of a 3rd party service.

I worked around this, using an ssh reverse tunnels. Here are the steps, for anyone who’d like to reproduce.

1. Add your partner(-in-crime)’s ssh key to authorized keys on a server that has a public IP (example.com, let’s say).

2. Add your server’s key to authorized keys on your local machine.

3. Create a reverse tunnel from your machine to the server.

   ssh -fNR 19999:localhost:22 server_user@example.com
   

   -R 19999 essentially forwards port 19999 on example.com to localhost’s 22. -fN is to say no terminal, send connection to background.

4. Your partner first ssh’s to example.com and then ssh’s to your laptop.

   On your partner’s machine

   ssh server_user@example.com
   

   On the server, your partner does

   ssh your_username@localhost -p 19999
   

   Your partner is on your machine, and can run rm -rf! But, hopefully they’ll only run tmux attach. Obviously, do this only with people you trust!

5. Start a tmux session locally.

6. Profit!