The fix I had him make was also not pretty, but the best I could do over the phone.

thelenm: OK, get to a shell prompt.
customer: All right, I'm there.
thelenm: Type "R M space dash F space" and the name of the file.
customer: Uhm...
thelenm: No, no, just listen. Now type "C A T greater-than space" and the name of the file.
thelenm: Now, listen very carefully....

Sorry, couldn't resist. ;-)

The closest I came to this was when I worked for a scientific computer manufacturer, and we delivered a computer to a client. I realized when it booted that the interface driver that had been shipped with the machine was way old. I had written most of it, so I pulled up the file in vi, called back to the shop, and asked them to read me the text of particular subroutines. It was not a pretty sight.

And yes, there were choice words when I got back.