Stuck at fsck "/dev/sda1: clean xxx/xxx files [...] " after upgrade to Ubuntu 16 from 14

You'll also run into this exact error if you run out of disk space as well. I was stuck at boot

Ctrl + Alt + F1 or F2 into tty2 login

df -h says /dev/sda1 is 100% used

I find the stuff I need to delete with this command

du -d1 -h /home/username | sort -h

For example, I deleted some folders like so

sudo rm -rf /home/username/Desktop/folder/*
sudo rm -rf /home/username/.cache/*
sudo rm -rf /home/username/.mozilla/*

reboot and now it boots up no problem now