From Pi My Life Up:
In this Raspberry Pi terminal sharing tutorial, we are going to show you how to utilize a software package called tmate so that you can share your terminal with other computers, even when you are behind a firewall.
While the Raspberry Pi comes with VNC which allows you to share your desktop with other computers, it does not come with any methods to just share access to the terminal. That can be an issue when you are running a headless system as VNC will not be of any use.
Our solution to this is to utilize a program designed to share the terminal. In our tutorials case, this is tmate.
This tmate application allows you to share access to the current terminal session with anyone you share the special key with regardless of if you are behind a firewall. Tmate works by relaying it through tmates own secure servers.
Each Friday is PiDay here at Adafruit! Be sure to check out our posts, tutorials and new Raspberry Pi related products. Adafruit has the largest and best selection of Raspberry Pi accessories and all the code & tutorials to get you up and running in no time!