so you want to learn to make an ssh app pt. 1

basics

It’s cool and fun! I promise! This guide is by no means a comprehensive one, but I hope it helps nonetheless.

how

First of all, pick a language which has an SSH server library. This is how you make your app accessible over SSH. Here are some examples.

 

• Go: github.com/gliderlabs/ssh (simplest)
• Python: github.com/paramiko/paramiko
• JavaScript (Node.js): github.com/mscdex/ssh2
• Rust: github.com/Eugeny/russh

 

For more cool links, check here (and specifically here for libraries). In my experience, gliderlab’s SSH package is a higher-level wrapper around another package which makes it super simple to use.

 

You don’t have to go super low-level - for instance Wish is a framework made specifically for creating SSH apps! - but if you choose not to, don’t just make an app which just prints stuff. A more complex and feature-rich SSH app is expected.

interfaces

TUI libraries can make your programs look great, particularly if you want to handle user interactions.

 

• Go: github.com/charmbracelet/bubbletea
• Python: github.com/Textualize/textual
• JavaScript (Node.js): github.com/chjj/blessed
• Rust: github.com/ratatui/ratatui

 

what to make?

Literally anything! Don’t restrict yourself to basic CLI apps. You can get a lot of information about the user simply from them SSH’ing (a good example of this is ssh whoami.filippo.io). You can make:

 

• Games (ssh -p 8080 -l magnetic magneticscrolls.net, ssh sshtron.zachlatta.com)
• Chatrooms (ssh devzat.hackclub.com, ssh ssh.chat)
• CTF-style challenges (ssh bandit0@bandit.labs.overthewire.org -p 2220)
• Other things (ssh guestbook.phthallo.com -p 2222, Sylviettee/ssh-llm)

 

Remember that your final app will be something that’s online all (ish) of the time, so think about how this can be used to create cool interactive, multiplayer/multi-user experiences for others.

Also, consider how you’ll be handling user inputs and interactions (in a typical app you’ll want to redirect stdin and stdout from the server and to the client) and other functionality like window resizing, which may be covered by the library you’re using.

notes

• If you intend on using colours to theme your app, note that some terminals can’t render them correctly at all. Try printing \u001b[32mfoobar\u001b[39m to your console to see if your terminal does. If it’s green, it does support colours. When SSHing, you may also need to run export TERM=xterm-256color/otherwise set the environment variable TERM to force colours in your session.
• If you are Dockerising your app, you’ll probably need to set tty: true in your docker-compose.yml file for the app to work as intended.
• You may come across REMOTE HOST IDENTIFICATION errors after you SSH for the first time, when testing locally. This is because your SSH server does not have a set host key of its own and will keep regenerating it every time it restarts, confusing SSH clients. To alleviate this, you can generate a SSH key in the directory of your SSH server (make sure that these are included in your .gitignore) and instruct your SSH server to use that, or use an existing SSH key.

other resources

• a guide on making an ssh server with python