Before fuzzing an application it needs to be compiled, to ease detection of unwanted behaviour (e.g. out-of-bounds buffer accesses), compiling with all-asan is highly recommended. For example:

make -C fuzzing/<application> all-asan

Afterwards invoke afl using:

make -C fuzzing/<application> fuzz

Parallel Fuzzing

Parallel fuzzing is supported through AFL_FLAGS, e.g.:

# Start first AFL instance
AFL_FLAGS="-M fuzzer01" make -C fuzzing/gnrc_tcp/ fuzz

# Start second AFL instance in a different terminal
AFL_FLAGS="-M fuzzer02" make -C fuzzing/gnrc_tcp/ fuzz