patch -Np1 -i ../glibc-2.1.3.patch: This applies a patch that fixes a minor bug in Glibc. Glibc defines a few variables names with illegal characters in the name. Bash-2.03 and older don't complain about that but Bash-2.04 does and won't compile Glibc properly. --enable-add-ons: This enabled the add-ons that we install with Glibc: linuxthreads and crypt. --with-headers=$LFS/usr/include: This makes Glibc use the kernel header files on our LFS system and not the kernel header files from your starting distribution which may be out-of-date or modified. make install_root=$LFS: This is the Glibc way to specify the equivalent of --prefix=.