troubleshooting boot hang

[Chris Murphy]

GRUB 2.00-25 (Fedora 20) booting a 2011 MacbookPro in EFI mode.

About 1 in 4 times, I get a boot hang with a particular kernel entry. I choose 
the entry in grub, press return, the grub menu goes away and is replaced with a 
black screen with a white _ and that's it. Nothing.

If I add 'set debug=all' right before the linuxefi line, I get at least 10 
minutes of text scroll of very verbose information for every boot attempt; even 
the good kernel entries it's way too verbose and so I give up. What less 
verbose options are available that will help isolate the problem?

I just now thought to try 'set debug=all' after the initrdefi line?

Thanks,

Chris Murphy