how to take jave heap dump every 30 seconds using kill -3 command

Question

Please help in this, i want to run a shell script where it should take jave heap dump every 30 seconds using kill -3 command. Thanks in advance.

Have you looked into [cron](http://stackoverflow.com/questions/9619362/running-a-cron-every-30-seconds)? — Thomas, Jul 26 '12 at 12:39

Tomasz Nurkiewicz · Answer 1 · 2012-07-26T13:01:30.073

7

Have you tried such a simple shell script?

while true
do
  jmap -dump:file=/tmp/java-`date +%s`.hprof PID_OF_JVM
  sleep 30
done

This will create one file pear each snapshot. For thread dump you can use similar script:

while true
do
  jstack PID_OF_JVM > stack-`date +%s`.txt
  sleep 30
done

~~I guess you can use kill -3 instead of jstack.~~

edited Jul 26 '12 at 13:01

answered Jul 26 '12 at 12:39

Tomasz Nurkiewicz

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+1 but kill -3 won't dump the stack to the console that you run it from, unlike jstack – Brian Agnew Jul 26 '12 at 12:41
@BrianAgnew: thanks, I tried first with `kill -3` but I thought it's my fault that I can't see the stack dump. – Tomasz Nurkiewicz Jul 26 '12 at 12:43
kill -3 will dump it to the process' stdout (err?) but jstack appears to dump it to the jstack's console – Brian Agnew Jul 26 '12 at 12:49

score 4 · Answer 2 · answered Jul 26 '12 at 12:39

you can do thread dumping from java application using code like this

 public static String getDumpFor(Thread thread) {
    StringBuilder sb = new StringBuilder();
    if (thread.isAlive()) {
        StackTraceElement[] stackTrace = thread.getStackTrace();
        sb.append(thread.toString()).append("\n")
                .append(String.format(" State - %s,", thread.getState()))
                .append(String.format(" Is daemon = %s,", thread.isDaemon()));
        for (StackTraceElement s : stackTrace)
            sb.append("\tat ").append(s.getClassName()).append(".").append(s.getMethodName()).append("(").append(s.getFileName()).append(":").append(s.getLineNumber()).append(")")
                    .append("\n");
    }
    return sb.toString();
}


public static void dumpActiveThreads() {
    Map<Thread, StackTraceElement[]> stackTraces = Thread.getAllStackTraces();
    Set<Thread> keySet = stackTraces.keySet();
    System.out.println("\nThread dump begin:");
    for (Thread thread : keySet)
        dumpActiveThread(thread);
    System.out.println("\nThread dump end.");

}

and then schedule task like this

 final ScheduledFuture<?> scheduledFuture = scheduledExecutorService.scheduleWithFixedDelay(
            new Runnable() {dumpActiveThreads()},
            0,
            30, TimeUnit.SECONDS);

score 1 · Answer 3 · answered Jul 26 '12 at 12:43

1

I have not used kill -3 command but i have used jmap command provided by sun sdk

You can write a script and then in script run below command.

${JAVA_HOME}/bin/jmap -dump:file=/home/MyDump.hprof PID

answered Jul 26 '12 at 12:43

amicngh

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score 0 · Answer 4 · answered Mar 16 '16 at 19:08

3 will give only the thread dump but not the heap dump.Thread dump means you can only check the stack traces for each thread in the JVM.But you are lookin g for the heap dump on linux then need to use the below commands. jmap -dump:file=myheap.bin {pid of which you are looking to take heap dump}. The output "myheap.bin" is not human readable,to read the file you can use the MAT tool. MAT download link: http://www.eclipse.org/mat/

how to take jave heap dump every 30 seconds using kill -3 command

4 Answers4