When sulogin asks you for the root password and you've entered the password, a shell needs to be started. Usually this is the bash shell. Since there are no libraries installed yet, we need to link bash statically, just like we did with Sysvinit.
Unpack the Bash archive
Install Bash by running:
./configure --enable-static-link
make; make -e prefix=$LFS/usr install
mv $LFS/usr/bin/bash $LFS/bin
cd $LFS/bin; ln -s bash sh