I have built gcl-1.0 successfully on linux. FASYNC is defined in /usr/include/linux/fcntl.h, "/usr/include/linux" usally is a symbolic link to LINUX_KERNEL_SRC_DIR/include/linux, where LINUX_KERNEL_SRC_DIR is where the kernal source files live, did you install them? BTW, my linux is 1.1.50. Dong