Add AFL_FORK_SERVER_KILL_SIGNAL environment variable.

The AFL_FORK_SERVER_KILL_SIGNAL variable allows to configure the signal
used to kill the fork server on termination.

1 files changed, 9 insertions, 2 deletions

diff --git a/docs/env_variables.md b/docs/env_variables.md
index 1abe9438..6fd08910 100644
--- a/docs/env_variables.md
+++ b/docs/env_variables.md
@@ -409,11 +409,18 @@ checks or alter some of the more exotic semantics of the tool:
     the afl-fuzz -g/-G command line option to control the minimum/maximum
     of fuzzing input generated.
 
-  - `AFL_KILL_SIGNAL`: Set the signal ID to be delivered to child processes on
-    timeout. Unless you implement your own targets or instrumentation, you
+  - `AFL_KILL_SIGNAL`: Set the signal ID to be delivered to child processes
+    on timeout. Unless you implement your own targets or instrumentation, you
     likely don't have to set it. By default, on timeout and on exit, `SIGKILL`
     (`AFL_KILL_SIGNAL=9`) will be delivered to the child.
 
+  - `AFL_FORK_SERVER_KILL_SIGNAL`: Set the signal ID to be delivered to the
+    fork server when AFL++ is terminated. Unless you implement your
+    fork server, you likely do not have to set it. By default, `SIGTERM`
+    (`AFL_FORK_SERVER_KILL_SIGNAL=15`) will be delivered to the fork server.
+    NOTE: Uncatchable signals, such as `SIGKILL`, cause child processes of
+    the fork server to be orphaned and leaves them in a zombie state.
+
   - `AFL_MAP_SIZE` sets the size of the shared map that afl-analyze, afl-fuzz,
     afl-showmap, and afl-tmin create to gather instrumentation data from the
     target. This must be equal or larger than the size the target was compiled