Add an environment variable flag for -g

Fixes: #100

src/tini.c

@@ -98,6 +98,7 @@ static int32_t expect_status[(STATUS_MAX - STATUS_MIN + 1) / 32];
 #endif
 
 #define VERBOSITY_ENV_VAR "TINI_VERBOSITY"
+#define KILL_PROCESS_GROUP_GROUP_ENV_VAR "TINI_KILL_PROCESS_GROUP"
 
 #define TINI_VERSION_STRING "tini version " TINI_VERSION TINI_GIT
 
@@ -254,9 +255,10 @@ void print_usage(char* const name, FILE* const file) {
 
 	fprintf(file, "Environment variables:\n\n");
 #if HAS_SUBREAPER
-	fprintf(file, "  %s: Register as a process subreaper (requires Linux >= 3.4)\n", SUBREAPER_ENV_VAR);
+	fprintf(file, "  %s: Register as a process subreaper (requires Linux >= 3.4).\n", SUBREAPER_ENV_VAR);
 #endif
-	fprintf(file, "  %s: Set the verbosity level (default: %d)\n", VERBOSITY_ENV_VAR, DEFAULT_VERBOSITY);
+	fprintf(file, "  %s: Set the verbosity level (default: %d).\n", VERBOSITY_ENV_VAR, DEFAULT_VERBOSITY);
+	fprintf(file, "  %s: Send signals to the child's process group.\n", KILL_PROCESS_GROUP_GROUP_ENV_VAR);
 
 	fprintf(file, "\n");
 }
@@ -397,6 +399,10 @@ int parse_env() {
 	}
 #endif
 
+	if (getenv(KILL_PROCESS_GROUP_GROUP_ENV_VAR) != NULL) {
+		kill_process_group++;
+	}
+
 	char* env_verbosity = getenv(VERBOSITY_ENV_VAR);
 	if (env_verbosity != NULL) {
 		verbosity = atoi(env_verbosity);

test/run_inner_tests.py

@@ -113,13 +113,24 @@ def main():
     # This test has Tini spawn a process that ignores SIGUSR1 and spawns a child that doesn't (and waits on the child)
     # We send SIGUSR1 to Tini, and expect the grand-child to terminate, then the child, and then Tini.
     if not args_disabled:
-        print "Running process group test"
+        print "Running process group test (arguments)"
         p = subprocess.Popen([tini, '-g', os.path.join(src, "test", "pgroup", "stage_1.py")], stdout=subprocess.PIPE, stderr=subprocess.PIPE)
 
         busy_wait(lambda: len(psutil.Process(p.pid).children(recursive=True)) == 2, 10)
         p.send_signal(signal.SIGUSR1)
         busy_wait(lambda: p.poll() is not None, 10)
 
+    print "Running process group test (environment variable)"
+    p = subprocess.Popen(
+        [tini, os.path.join(src, "test", "pgroup", "stage_1.py")],
+        stdout=subprocess.PIPE, stderr=subprocess.PIPE,
+        env=dict(os.environ, TINI_KILL_PROCESS_GROUP="1")
+    )
+
+    busy_wait(lambda: len(psutil.Process(p.pid).children(recursive=True)) == 2, 10)
+    p.send_signal(signal.SIGUSR1)
+    busy_wait(lambda: p.poll() is not None, 10)
+
     # Run failing test. Force verbosity to 1 so we see the subreaper warning
     # regardless of whether MINIMAL is set.
     print "Running zombie reaping failure test (Tini should warn)"