kill -3 to get java thread dump

Question

I am using kill -3 command to see the JVM's thread dump in unix. But where can I find the output of this kill command? I am lost!!

Answer 1

1. Find the process id [PS ID]
2. Execute jcmd [PS ID] Thread.print

Answer 2

With Java 8 in picture, jcmd is the preferred approach.

jcmd <PID> Thread.print

Following is the snippet from Oracle documentation :

The release of JDK 8 introduced Java Mission Control, Java Flight Recorder, and jcmd utility for diagnosing problems with JVM and Java applications. It is suggested to use the latest utility, jcmd instead of the previous jstack utility for enhanced diagnostics and reduced performance overhead.

However, shipping this with the application may be licensing implications which I am not sure.

Answer 3

There is a way to redirect JVM thread dump output on break signal to separate file with LogVMOutput diagnostic option:

-XX:+UnlockDiagnosticVMOptions -XX:+LogVMOutput -XX:LogFile=jvm.log

Answer 4

In the same location where the JVM's stdout is placed. If you have a Tomcat server, this will be the catalina_(date).out file.

Answer 5

When using kill -3 one should see the thread dump in the standard output. Most of the application servers write the standard output to a separate file. You should find it there when using kill -3. There are multiple ways of getting thread dumps:

• Kill -3 : 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 std output.
• For hotspot VM we can also use jstack command to generate thread dump. It’s a part of the JDK. Syntax is as follows: Usage: jstack [-l] (to connect to running process) jstack -F [-m] [-l] (to connect to a hung process)
• For JRockit JVM we can use JRCMD command which comes with JDK Syntax: jrcmd [ []] [-l] [-f file] [-p] -h]

Answer 6

In Jboss you can perform the following

nohup $JBOSS_HOME/bin/run.sh -c  yourinstancename $JBOSS_OPTS >> console-$(date +%Y%m%d).out  2>&1 < /dev/null &
kill -3 <java_pid>

This will redirect your output/threadump to the file console specified in the above command.