diff --git a/content/fundamentals/ssh.md b/content/fundamentals/ssh.md
index 1e8b6ad..3831814 100644
--- a/content/fundamentals/ssh.md
+++ b/content/fundamentals/ssh.md
@@ -26,6 +26,9 @@ approaches for day to day use and troubleshooting.
 
 ## Prerequisites
 
+A basic understanding of [the command-line] is required.
+
+[the command-line]: http://write.flossmanuals.net/command-line/introduction/
 
 The SSH ecosystem is very established. It is available on all modern GNU/Linux
 distributions, MacOS and Windows. You can use your home server or if you don't have one yet you can use your own personal laptop to experiment (in this case, your laptop will