Read Java JVM startup parameters (eg -Xmx)

Question

I'm trying to figure out if there's a way to determine the JVM startup properties from within a running java process. Specifically I'm trying to find out where parameters such as -Xmx (max heap size) and -XX:MaxPermSize are stored. I'm running Sun's 1.6 jvm.

If you're wondering why I want to do this, I have a number of JVM webservers that may or may not be configured correctly and I want to add this to the startup code check. It's much easier for me to check in a piece of java code that gets deployed everywhere than to manually find and check all of the jvm startup files. Right now the jvm configuration files for better or worse are not part of our build process or checked into source control.

Community · Accepted Answer · 2020-06-20 09:12:55Z

56

Try:

import java.lang.management.ManagementFactory;
import java.lang.management.RuntimeMXBean;

import java.util.List;

public void runtimeParameters() {
  RuntimeMXBean bean = ManagementFactory.getRuntimeMXBean();
  List<String> aList = bean.getInputArguments();

  for (int i = 0; i < aList.size(); i++) {
    System.out.println( aList.get( i ) );
  }
}

That should show all JVM parameters.

Note: we do not have JVM parameter in VCS either, but in a database, read by our own launchers in productions. That way, we can change those values remotely, without having to redeploy JVM parameter file settings.

You will find a good sumary of various JVM tools to use in this article (from the "Dustin's Software Development Cogitations and Speculations"), including Java Application Launcher links to :

ManagementFactory.getRuntimeMXBean() call
getInputArguments() javadoc
Accessing JVM Arguments from Java (to determine, for instance, if JVM is running in debug mode, in order to alter the "grid initialization" logic of an application)
Annotation Type MXBean
MXBean Java Tutorial

This technique takes advantage of Platform MXBeans available since J2SE 5 (custom MXBeans support was added in Java SE 6).

Two useful sources of information on the JVM parameters available when using Sun's JVM are:

A Collection of JVM Options and

Charles Nutter's Favorite Hotspot JVM Flags.

Both of these resources list and describe some/all of the not-recommended-for-the-casual-developer double X arguments (-XX) that are available.

edited Jun 20, 2020 at 9:12

CommunityBot

11 silver badge

answered Oct 5, 2009 at 4:20

VonC

1.4m569 gold badges4.8k silver badges5.7k bronze badges

Sign up to request clarification or add additional context in comments.

1 Comment

Bob Albright Over a year ago

Works like a charm! I clearly don't know java.lang.management as well as I should.

Mike Duigou · Accepted Answer · 2015-06-09 18:30:42Z

12

With Java 7 or later it's as easy as

java -XshowSettings:all

edited Jun 9, 2015 at 18:30

answered Jan 17, 2013 at 17:54

Mike Duigou

90110 silver badges19 bronze badges

Comments

bric3 · Accepted Answer · 2025-07-02 08:34:13Z

0

Since Java 9 one can use `java.lang.ProcessHandle`.

var ph = ProcessHandle.current()

Optional<String>   = ph.info().commandLine()
Optional<String[]> = ph.info().arguments()

The arguments one is particularly interesting because it returns an array which avoids the issue of space in args as there's not need to split the args.

The ProcessHandle has other useful functions like .pid(), it can also look at the process hierarchy, either parent or process descendant.

On older one can peek into system property sun.java.command, but parsing can be problematic when args have spaces.

answered Jul 2 at 8:34

bric3

42.7k9 gold badges99 silver badges116 bronze badges

Collectives™ on Stack Overflow

Read Java JVM startup parameters (eg -Xmx)

3 Answers 3

1 Comment

Comments

Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

3 Answers 3

1 Comment

Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related