Thank you. I made a stupid mistake. When I added “REQUIRES_LIBS = libpthread” into Makefile, I modified three Makefiles. There are hello/Makefile, hello/server/Makefile, and hello/server/src/Makefile. I tested one by one. But I found I made a mistake. At last try, I wrote REQUIRES = libpthread instead of REQUIRES_LIBS = libpthread on hello/server/src/Makefile. After correcting my mistake, I can test pthread application. Thank you! Marcus Hyunchul Seok.