make -f Makefile-libbz2_so: This will cause bzip2 to be built using a different Makefile file, in this case the Makefile-libbz2_so file which creates a dynamic libbz2.so library and links the bzip2 utilities against it. The reason we don't use make install is that bzip2's make install doesn't install the shared libbz2.so, nor the bzip2 binary that's linked against that library. So we have no choice but to manually install the files.