cp lib/Makefile.in lib/Makefile.in.backup : We run this command in order to keep a backup of the file we are about to change. cp lib/Makefile.in lib/Makefile.in.backup && sed -e 's/\(.*\)\(fopen-safer\.c \)\\/\1\2atexit.c \\/' \    -e 's/\(.*\)\(idcache\$U\.\$.*\)\\/\1\2atexit$U.$(OBJEXT) \\/' \    lib/Makefile.in > lib/Makefile.in~ && mv lib/Makefile.in~ lib/Makefile.in: This is used to fix a problem with building fileutils statically on glibc 2.2.3 systems. If this isn't done, then there is the possibility of all of the fileutils programs causing segmentation faults once chroot is entered in chapter 6. --libexecdir=$LFS/bin: This configure option will set the program executable directory to $LFS/bin. This is normally set to /usr/libexec, but nothing is placed in it. Changing it just prevents that directory from being created.