When fsck finds a really serious error, and you are given a choice of either pressing Ctrl-D for normal startup or typing in the root password doesn't bypass fsck when pressing Ctrl-D, pretty much leaving you in a loop every time you restart and Ctrl-D'ing, if you don't have a rescue/boot disk.
Should be fixed in the bash currently in rawhide.
*** Bug 16757 has been marked as a duplicate of this bug. ***