diff --git a/devlib/connection.py b/devlib/connection.py
index aacb48a0f..a857a57bc 100644
--- a/devlib/connection.py
+++ b/devlib/connection.py
@@ -35,7 +35,7 @@
 
 
 def _kill_pgid_cmd(pgid, sig, busybox):
-    return '{} kill -{} -- -{}'.format(busybox, sig.value, pgid)
+    return '{} kill -{} -{}'.format(busybox, sig.value, pgid)
 
 def _popen_communicate(bg, popen, input, timeout):
     try:
@@ -170,7 +170,7 @@ def send_signal(self, sig):
         :type signal: signal.Signals
         """
         try:
-            self._send_signal(signal.SIGKILL)
+            return self._send_signal(sig)
         finally:
             # Deregister if the command has finished
             self.poll()
@@ -188,7 +188,7 @@ def cancel(self, kill_timeout=_KILL_TIMEOUT):
         """
         try:
             if self.poll() is None:
-                self._cancel(kill_timeout=kill_timeout)
+                return self._cancel(kill_timeout=kill_timeout)
         finally:
             self._deregister()
 
@@ -208,7 +208,7 @@ def wait(self):
         Block until the background command completes, and return its exit code.
         """
         try:
-            self._wait()
+            return self._wait()
         finally:
             self._deregister()