Exploring file types in Linux

My setupI don't actually run a Linux desktop, strictly speaking - I use MobaXTerm on my Windows laptop to ssh in. Moba runs an X server, so I can open windows from the Linux machine as if they were native

X doesn't exist

When Linux keeps reporting that a binary doesn't exist, when it clearly does? That's annoying. One possible reason is below - this is the one that bit me a few days ago. If you don't know what bits and bytes