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afl-fuzz(8) System Manager's Manual afl-fuzz(8)




afl-fuzz [ options ] -- /path/to/fuzzed_app [ ... ]


Required parameters:

-i dir - input directory with test cases
-o dir - output directory for fuzzer findings Execution control settings:
-p schedule - power schedules compute a seed's performance score:
fast(default), explore, exploit, seek, rare, mmopt, coe, lin
quad -- see docs/ for more information
-f file - location read by the fuzzed program (default: stdin or @@)
-t msec - timeout for each run (auto-scaled, default 1000 ms). Add a '+'
to auto-calculate the timeout, the value being the maximum.
-m megs - memory limit for child process (0 MB, 0 = no limit [default])
-O - use binary-only instrumentation (FRIDA mode)
-Q - use binary-only instrumentation (QEMU mode)
-U - use unicorn-based instrumentation (Unicorn mode)
-W - use qemu-based instrumentation with Wine (Wine mode)
-X - use VM fuzzing (NYX mode - standalone mode)
-Y - use VM fuzzing (NYX mode - multiple instances mode) Mutator settings:
-g minlength - set min length of generated fuzz input (default: 1)
-G maxlength - set max length of generated fuzz input (default: 1048576)
-D - enable deterministic fuzzing (once per queue entry)
-L minutes - use MOpt(imize) mode and set the time limit for entering the
pacemaker mode (minutes of no new finds). 0 = immediately,
-1 = immediately and together with normal mutation.
See docs/
-c program - enable CmpLog by specifying a binary compiled for it.
if using QEMU/FRIDA or the fuzzing target is compiled
for CmpLog then just use -c 0.
-l cmplog_opts - CmpLog configuration values (e.g. "2AT"):
1=small files, 2=larger files (default), 3=all files,
A=arithmetic solving, T=transformational solving. Fuzzing behavior settings:
-Z - sequential queue selection instead of weighted random
-N - do not unlink the fuzzing input file (for devices etc.)
-n - fuzz without instrumentation (non-instrumented mode)
-x dict_file - fuzzer dictionary (see, specify up to 4 times) Test settings:
-s seed - use a fixed seed for the RNG
-V seconds - fuzz for a specified time then terminate
-E execs - fuzz for an approx. no. of total executions then terminate
Note: not precise and can have several more executions. Other stuff:
-M/-S id - distributed mode (-M sets -Z and disables trimming)
see docs/
for effective recommendations for parallel fuzzing.
-F path - sync to a foreign fuzzer queue directory (requires -M, can
be specified up to 32 times)
-T text - text banner to show on the screen
-I command - execute this command/script when a new crash is found
-C - crash exploration mode (the peruvian rabbit thing)
-b cpu_id - bind the fuzzing process to the specified CPU core (0-...)
-e ext - file extension for the fuzz test input file (if needed) Environment variables used: LD_BIND_LAZY: do not set LD_BIND_NOW env var for target ASAN_OPTIONS: custom settings for ASAN
(must contain abort_on_error=1 and symbolize=0) MSAN_OPTIONS: custom settings for MSAN
(must contain exitcode=86 and symbolize=0) AFL_AUTORESUME: resume fuzzing if directory specified by -o already exists AFL_BENCH_JUST_ONE: run the target just once AFL_BENCH_UNTIL_CRASH: exit soon when the first crashing input has been found AFL_CMPLOG_ONLY_NEW: do not run cmplog on initial testcases (good for resumes!) AFL_CRASH_EXITCODE: optional child exit code to be interpreted as crash AFL_CUSTOM_MUTATOR_LIBRARY: lib with afl_custom_fuzz() to mutate inputs AFL_CUSTOM_MUTATOR_ONLY: avoid AFL++'s internal mutators AFL_CYCLE_SCHEDULES: after completing a cycle, switch to a different -p schedule AFL_DEBUG: extra debugging output for Python mode trimming AFL_DEBUG_CHILD: do not suppress stdout/stderr from target AFL_DISABLE_TRIM: disable the trimming of test cases AFL_DUMB_FORKSRV: use fork server without feedback from target AFL_EXIT_WHEN_DONE: exit when all inputs are run and no new finds are found AFL_EXIT_ON_TIME: exit when no new coverage finds are made within the specified time period AFL_EXPAND_HAVOC_NOW: immediately enable expand havoc mode (default: after 60 minutes and a cycle without finds) AFL_FAST_CAL: limit the calibration stage to three cycles for speedup AFL_FORCE_UI: force showing the status screen (for virtual consoles) AFL_FORKSRV_INIT_TMOUT: time spent waiting for forkserver during startup (in milliseconds) AFL_HANG_TMOUT: override timeout value (in milliseconds) AFL_I_DONT_CARE_ABOUT_MISSING_CRASHES: don't warn about core dump handlers AFL_IGNORE_UNKNOWN_ENVS: don't warn on unknown env vars AFL_IGNORE_PROBLEMS: do not abort fuzzing if an incorrect setup is detected during a run AFL_IMPORT_FIRST: sync and import test cases from other fuzzer instances first AFL_INPUT_LEN_MIN/AFL_INPUT_LEN_MAX: like -g/-G set min/max fuzz length produced AFL_PIZZA_MODE: 1 - enforce pizza mode, 0 - disable for April 1st AFL_KILL_SIGNAL: Signal ID delivered to child processes on timeout, etc. (default: SIGKILL) AFL_MAP_SIZE: the shared memory size for that target. must be >= the size
the target was compiled for AFL_MAX_DET_EXTRAS: if more entries are in the dictionary list than this value
then they are randomly selected instead all of them being
used. Defaults to 200. AFL_NO_AFFINITY: do not check for an unused cpu core to use for fuzzing AFL_TRY_AFFINITY: try to bind to an unused core, but don't fail if unsuccessful AFL_NO_ARITH: skip arithmetic mutations in deterministic stage AFL_NO_AUTODICT: do not load an offered auto dictionary compiled into a target AFL_NO_CPU_RED: avoid red color for showing very high cpu usage AFL_NO_FORKSRV: run target via execve instead of using the forkserver AFL_NO_SNAPSHOT: do not use the snapshot feature (if the snapshot lkm is loaded) AFL_NO_STARTUP_CALIBRATION: no initial seed calibration, start fuzzing at once AFL_NO_UI: switch status screen off AFL_PATH: path to AFL support binaries AFL_PYTHON_MODULE: mutate and trim inputs with the specified Python module AFL_QUIET: suppress forkserver status messages AFL_PRELOAD: LD_PRELOAD / DYLD_INSERT_LIBRARIES settings for target AFL_TARGET_ENV: pass extra environment variables to target AFL_SHUFFLE_QUEUE: reorder the input queue randomly on startup AFL_SKIP_BIN_CHECK: skip afl compatibility checks, also disables auto map size AFL_SKIP_CPUFREQ: do not warn about variable cpu clocking AFL_STATSD: enables StatsD metrics collection AFL_STATSD_HOST: change default statsd host (default AFL_STATSD_PORT: change default statsd port (default: 8125) AFL_STATSD_TAGS_FLAVOR: set statsd tags format (default: disable tags)
Supported formats are: 'dogstatsd', 'librato',
'signalfx' and 'influxdb' AFL_SYNC_TIME: sync time between fuzzing instances (in minutes) AFL_NO_CRASH_README: do not create a README in the crashes directory AFL_TESTCACHE_SIZE: use a cache for testcases, improves performance (in MB) AFL_TMPDIR: directory to use for input file generation (ramdisk recommended) AFL_EARLY_FORKSERVER: force an early forkserver in an afl-clang-fast/
afl-clang-lto/afl-gcc-fast target AFL_PERSISTENT: enforce persistent mode (if __AFL_LOOP is in a shared lib AFL_DEFER_FORKSRV: enforced deferred forkserver (__AFL_INIT is in a .so Compiled with Python 3.11.2 module support, see docs/ Compiled without AFL_PERSISTENT_RECORD support. Compiled with shmat support. For additional help please consult docs/ :)


afl++ was written by Michal "lcamtuf" Zalewski and is maintained by Marc "van Hauser" Heuse <>, Heiko "hexcoder-" Eissfeldt <>, Andrea Fioraldi <> and Dominik Maier <> The homepage of afl++ is:


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2023-03-24 afl++