Since the title isn't very descriptive, let us look at what we are trying to achieve. Click the image below to view the animation I recorded. The two terminals are made to mirror each other, i.e. anything I type on one terminal will appear on the second one, and vice versa.

This won't make much sense, or seem of any use, until you realize that the two terminals need not be on the same computer. That is, me and my friend from across the country could do this and it'd still work.

This has amazing applications. I have found it useful in teaching basic stuff to others, like programming, or how to use a terminal. There are a lot of high-end softwares like TeamViewer that do this for graphical environments. But it's good to know that something like this can be achieved tremendously easily on terminal.

So, how do I do it?

First of all, both machines need to SSH to a common server. If you don't have access to a common server, then you need to set up OpenSSH on one of the two computers and have the other person SSH into your computer.

Since I am at IIT Kanpur, I will use one of the computers in our Lab as the common server.

ssh username@ccpc121.cc.iitk.ac.in

Now on one of the PC, run TMUX (tmux). For this to work, you must have tmux installed. Install it using the usual package manager if you have root access or use Linuxbrew to install it if you don't. Now from the other computer, run tmux attach.

This should attach the second terminal to the same TMUX session.

ENJOY!

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