Today I had a problem booting my Ubuntu desktop – with booting stuck on the purple screen. An Alt-1 showed me that there were problems with the disk and a manual fsck should be run.
So at the Grub screen I pressed ‘e’ to edit the current entry and on the linux (kernel) line I typed init=/bin/bash and then pressed F10 to boot.
Arriving at a bash prompt I was able to run the fsck on the device i.e. fsck /dev/sda1
Previously I might have used a LiveCD/LiveUSB to perform this but the init=/bin/bash is much quicker and easier – thanks LPIC exams!