JMap and JStack for Beginners

1. What is Jstack used for?
2. What is Jstack and JMap?
3. Does Jstack kill the process?
4. How do I read Jstack?
5. What is Kill 3?
6. When should I take a heap dump?
7. What is JMAP histo?
8. What is Jstack in Java?
9. What is JMAP?
10. What thread dump contains?
11. How do you get PID?
12. Where does kill thread dump go?

What is Jstack used for?

The jstack command-line utility attaches to the specified process or core file and prints the stack traces of all threads that are attached to the virtual machine, including Java threads and VM internal threads, and optionally native stack frames. The utility also performs deadlock detection.

What is Jstack and JMap?

JMap and JStack are probably the most valuable utilities in the toolbox of any Java developer. With the functionality of both these tools combined, you can debug issues and run diagnostics for the java program you're coding.

Does Jstack kill the process?

Get the thread dump

kill -3 $PID - From Unix Terminal only. It will NOT kill the process, but instead generate a thread dump. This NOT generate any output which is normal. The output of this command is sent to system err/out logs.

How do I read Jstack?

The simplest way to generate a thread dump is by using jStack. jStack ships with JVM and can be used from the command line. Here, we need the PID of the process for which we want to generate the thread dump. To get PID we can use jps command as shown below.

What is Kill 3?

kill -3 <PID> : Gives output to standard output. If one has access to the console window where server is running, one can use Ctrl + Break combination of keys to generate the stack trace on STDOUT. For hotspot VM's we can also use jstack command to generate a thread dump. It's a part of the JDK.

When should I take a heap dump?

Taking a Heap Dump

You can use Java VisualVM to take a heap dump of a local running application. When you use Java VisualVM to take a heap dump, the file is only temporary until you explicitly save it. If you do not save the file, the file will be deleted when the application terminates.

What is JMAP histo?

The jmap command with the -histo option can be used to obtain a class specific histogram of the heap. Depending on the parameter specified, the jmap -histo command can print out the heap histogram for a running process or a core file.

What is Jstack in Java?

DESCRIPTION. jstack prints Java stack traces of Java threads for a given Java process or core file or a remote debug server. For each Java frame, the full class name, method name, 'bci' (byte code index) and line number, if available, are printed.

What is JMAP?

jmap is Java standard command-line utility which comes with JDK (starting from JDK 1.6). jmap prints memory-related statistics for a running VM or core file.

What thread dump contains?

A thread dump is a snapshot of the state of all threads that are part of the process. The state of each thread is presented with a so called stack trace, which shows the contents of a thread's stack. Some of the threads belong to the Java application you are running, while others are JVM internal threads.

How do you get PID?

How do I get PID?

1. Have an STD and do not get treated;
2. Have more than one sex partner;
3. Have a sex partner who has sex partners other than you;
4. Have had PID before;
5. Are sexually active and are age 25 or younger;
6. Douche;
7. Use an intrauterine device (IUD) for birth control.

Where does kill thread dump go?

When 'kill -3' option is used thread dump is sent to the standard error stream. If you are running your application in tomcat, thread dump will be sent into <TOMCAT_HOME>/logs/catalina.