How can I diagnose a startup failure on a live USB?

[David Seaward]

Hi all,

I am trying to run Guix SD from a live USB on two machines. On machine
A this works: I can select "linux-libre" from GRUB and the startup
process runs, ending with a prompt on TTY 1 and documentation on TTY 2.

On machine B, the startup process runs but towards the end (ssh-
keygen... ncsd...) the screen goes black and I can't switch between
TTYs.

How can I diagnose the cause of this problem? Even enough to report an
error message.

Regards,
David

P.S. Cross-posted on Stack Exchange if you like that kind of thing:

https://unix.stackexchange.com/questions/391156