After restarting my virtualbox and trying to start exactly from where I left off, I realized that I have several things that I had to "resetup." Here's the commands I went through to get back to where I could start compiling.

• export LFS=/mnt/lfs

  
  

• mkdir -pv $LFS

  
  

• sudo mount -v -t ext3 /dev/sdb $LFS

  ...