src/Pure/System/isabelle_system.scala

         Exn.Interrupt.dispose()
       }
     (output, rc)
   }
 
-  def kill(signal: String, group_pid: String): (String, Int) =
+  def process_signal(group_pid: String, signal: String = "0"): Boolean =
   {
     val bash =
       if (Platform.is_windows) List(cygwin_root() + "\\bin\\bash.exe")
       else List("/usr/bin/env", "bash")
-    process_output(process(bash ::: List("-c", "kill -" + signal + " -" + group_pid)))
+    val (_, rc) = process_output(process(bash ::: List("-c", "kill -" + signal + " -" + group_pid)))
+    rc == 0
   }
 
 
   /* GNU bash */