I have a High Sierra system which I access via ssh and for which I program old-style from the command line in Objective-C and build via Makefiles. I have a very small program that employs the CoreAudio API and calls the AudioFileOpenURL and AudioFileClose functions. The program compiles ok but the linker is reporting that the symbols AudioFileOpenURL and AudioFileClose are undefined. I cannot find any dylib file among the libraries on my system that has those symbols. Can someone suggest where I might obtain the appropriate library? Here is the linker output that I am getting: gcc -o example1 example1.o -lobjc -lextension Undefined symbols for architecture x86_64: "_AudioFileClose", referenced from: _main in example1.o "_AudioFileGetProperty", referenced from: _main in example1.o "_AudioFileGetPropertyInfo", referenced from: _main in example1.o "_AudioFileOpenURL", referenced from: _main in example1.o ld: symbol(s) not found for architecture x86_64 clang: error: linker command failed with exit code 1 (use -v to see invocation) make: *** [example1] Error 1