A simple usecase of jconsole

1: What is jconsole?
The jconsole command launches a graphical console tool that enables you to monitor and manage Java applications and virtual machines on a local or remote machine.

2: What it can do?
The jconsole can:
1) Viewing summary information
2) Monitoring Memory Consumption
3) Monitoring Thread Use
4) Monitoring Class Loading
5) Monitoring and Managing MBeans
6) Viewing VM Information

3: How to use it?
refer to 4: demo

4: Jconsole config files location
You can set the ssl/remote port/access right in below jconsole config folder,
%JAVA_HOME%\jre\lib\management\
After you setup the config in the management.properties file you can specified the config file location in the java application start parameter,such as:
-Dcom.sun.management.config.file=%java_home%\jre\lib\management\management.properties -jar C:\oc4j_101330_seed\j2ee\home\oc4j.jar

5: Demo
Here use Java2DDemo again to demonstrate the usage:
a) start the Java2DDemo with -Dcom.sun.management.jmxremote options
C:\>java -Dcom.sun.management.jmxremote -jar "C:\Program Files\Java\jdk1.5.0_06\demo\jfc\Java2D\Java2Demo.jar

b) use jps to find the PID of the Java2DDemo java application, you can find the PID by window task manager.

C:\>jps
1440 Program
492 Jps

c) start jconsole

C:\>jconsole 1440

Now the jconsole UI displayed.


d) Test for monitor the local application server
Here choose the OC4J to do the test.
For WindowsXP platform, pls change your TMP path to another place, here i changed it to c:\TEMP
Start the oc4j with -Dcom.sun.management.jmxremote option. it's better to start it separately, will get error when start it in eclipse servers console.
the error messgae is:
Exception in thread "main" java.lang.Exception: Could not open
PerfMemory
find the PID of it.
C:\>jps
5332 oc4j.jar
2032 Jps

e) Start remote monitor
without authentications because just used for test env
com.sun.management.jmxremote.port=9999
com.sun.management.jmxremote.ssl=false
com.sun.management.jmxremote.authenticate=false
--> Start jconsole --> set the right hostname/port/username/password (if any) to connect.

6: Problems
a) When use jconsole meet: Exception in thread "main" java.lang.Exception: Could not open PerfMemory
the solution is:
set the tmp variable to c:\tmp for the process calling the application as well as the process calling the monitoring tool.
quote from http://forums.sun.com/thread.jspa?threadID=730397
This is usually due to a permissions problem. There's two known causes.
The first happens when the tools (jstat and jps) are run by a different
user id than the application. The second, which is probably more likely
here, is cause by a bug the JVM when it encounters inherited DACLS in
the default temporary directory. inherited DACLS are usually set up by
the IT organization on users home directories, though they can also
occur on other system directories. We do not yet have a fix for this bug
but there is a work around.

The workaround is to set the TMP environment variable (either globally
or for all processes started by a specific user or for just the target
process and the tools) to point to a directory that doesn't get
inherited DACLS. Usually something like c:\tmp will work. Trying setting
TMP=c:\tmp (after making the directory, of course) for both the
application(s) you want to monitor and the command window where you run
the jstat and jps tools and see if that fixes the problem. If it doesn't
fix the problem, I'll need to see the output of the following commands
(using the original TMP setting and then again with TMP=c:\tmp)

cacls %TMP%
cacls %TMP%\hsperfdata_*

Another workaround is to point TMP to a FAT32 file system and then set
-XX:+PerfBypassFileSystemCheck on the target applications' command lines
and -J-XX:+PerfBypassFileSystemCheck on the jstat and jps command lines.
This works because FAT32 doesn't support DACLS, so the JVM doesn't
attempt to create them; however, the the PerfBypassFileSystemCheck is
needed because the JVM won't enable the monitoring capaibilties when TMP
is set to device that doesn't support DACLs.

There's more information about setting TMP globally and on a per-user
basis in the jvmstat faq:

http://java.sun.com/performance/jvmstat/faq.html

See item #4.

Brian

b) meet below error when use jconsole:
Unable to attach to 4800: Could not map vmid to user name

the cause can be found in http://java.sun.com/performance/jvmstat/faq.html#15

but i could not understand and don't know how to use the workaround it provides. My solution here is to start the OC4J separately instead of start it in eclipse servers. It works.

7: Reference
[1]http://java.sun.com/j2se/1.5.0/docs/guide/management/jconsole.html
[2]http://java.sun.com/j2se/1.5.0/docs/guide/management/faq.html
[3]http://java.sun.com/j2se/1.5.0/docs/guide/management/agent.html
[4]