In order for certain programs to be able to determine where certain partitions are supposed to be mounted by default, the /etc/fstab file is used. Create a new file /etc/fstab containing the following:
# Begin /etc/fstab
/dev/<LFS-partition designation> / ext2 defaults 0 1
/dev/<swap-partition designation> none swap sw 0 0
proc /proc proc defaults 0 0
# End /etc/fstab
Replace <LFS-partition designation> and <swap-partition designation> with the appropriate devices (/dev/hda5 and /dev/hda6 in my case).