A special shell will be launched by this option with a fixit floppy
(or 2nd CDROM) mounted as /mnt2.  This provides access to extra
commands under /mnt2 as well as a more complete set of device files in
/mnt2/dev.  Some device operations, like fsck and disklabel, may
therefore require you to go to /mnt2/dev and use the entries there
rather than assuming that they will be present in the default /dev
(which came from the boot floppy and is very minimal).