JVMs and kill signals

Ever wondered how a JVM reacts to various kill signals? The (intended) behaviour might be documented somewhere already, but I found having a table of the actual behaviour available quite useful. In particular I wanted to know which kill signals trigger the JVM to run registered shutdown hooks, and which kill signals don't actually terminate the JVM. So I decided to compile a table of that information.

I wrote up a small Java application that just registers a shutdown hook that I can detect whether it has executed or not, and then sleeps until I get a chance to kill it:

class Death {
  public static void main(String... args) throws Exception {
    Runtime.getRuntime().addShutdownHook( new Thread(){
      @Override
      public void run()
      {
        System.out.println("Shutting down");
      }
    } );
    for (;;) Thread.sleep(100);
  }
}

Then I ran the program in one terminal window (java Death; echo $?) while iterating through all kill signals (0-31) in another:

kill -$SIGNAL $(jps | grep Death | cut -d\  -f1)

signal	shutdown	runs hook	exit code	comment
default (15)	yes	yes	143	SIGTERM is the default unix kill signal
0	no	-	-
1 (SIGHUP)	yes	yes	129
2 (SIGINT)	yes	yes	130	SIGINT is the signal sent on ^C
3 (SIGQUIT)	no	-	-	Makes the JVM dump threads / stack-traces
4 (SIGILL)	yes	no	134	Makes the JVM write a core dump and abort on trap 6
5	yes	no	133	Makes the JVM exit with "Trace/BPT trap: 5"
6 (SIGABRT)	yes	no	134	Makes the JVM exit with "Abort trap: 6"
7	yes	no	135	Makes the JVM exit with "EMT trap: 7"
8 (SIGFPE)	yes	no	134	Makes the JVM write a core dump and abort on trap 6
9 (SIGKILL)	yes	no	137	The JVM is forcibly killed (exits with "Killed: 9")
10 (SIGBUS)	yes	no	134	Emulates a "Bus Error"
11 (SIGSEGV)	yes	no	134	Emulates a "Segmentation fault"
12	yes	no	140	Makes the JVM exit with "Bad system call: 12"
13	no	-	-
14	yes	no	142	Makes the JVM exit with "Alarm clock: 14"
15 (SIGTERM)	yes	yes	143	This is the default unix kill signal
16	no	-	-
17	no	-	145	Stops the application (sends it to the background), same as ^Z
18	no	-	146	Stops the application (sends it to the background), same as ^Z
19	no	-	-
20	no	-	-
21	no	-	149	Stops the application (sends it to the background), same as ^Z
22	no	-	150	Stops the application (sends it to the background), same as ^Z
23	no	-	-
24	yes	no	152	Makes the JVM exit with "Cputime limit exceeded: 24"
25	no	-	-
26	yes	no	154	Makes the JVM exit with "Virtual timer expired: 26"
27	yes	no	155	Makes the JVM exit with "Profiling timer expired: 27"
28	no	-	-
29	no	-	-
30	yes	no	158	Makes the JVM exit with "User defined signal 1: 30"
31	yes	no	134	Makes the JVM exit on Segmentation fault

This list was compiled using (a quite old) Oracle Hotspot Java 8 EA on Mac OS X:

java version "1.8.0-ea"
Java(TM) SE Runtime Environment (build 1.8.0-ea-b65)
Java HotSpot(TM) 64-Bit Server VM (build 25.0-b09, mixed mode)

Hope this is useful to more people than myself.