monline

First of all, where to find JConsole: it's part of Sun's JDK. Both the Windows and the Linux versions of Sun's JDK (not JRE!) contain JConsole, so it's quite trivial to get. Second: enable JMX remote connections in your Tomcat. If you're running Tomcat on a Debian or Ubuntu server, then you've to add the required startup parameters to the /etc/default/tomcat5.5 file to the CATALINA_OPTS variable. Eg.
(Note: the -Djava.awt.headless=true -Xmx128M -server parameters are there by default).

Now start JConsole (if you're using an Ubuntu desktop and installed the sun-java5-jdk package, then you'll find a "Sun Java 5.0 Console" item in your Applications / System Tools menu), select the Remote tab, enter hostname and port number (7091 in the above example) and connect. You might still get connection error though.

If you're using JDK6 on your desktop, then try running JConsole from the command line using the -debug option. It'll display the exceptions that JConsole throws. Eg. I got something like this:

As it turned out, the hosts file on the Tomcat server was "corrupt". It contained something like this:

There was no network interface set up with the IP 127.0.1.1 and JConsole tried to connect to this IP since Tomcat's JVM told it to. (Note: even if there was an interface with that IP, it'd have been no good since it's an internal/loopback IP address and my desktop PC could not have connected to it anyway.) Fixing the hosts file (by changing the 127.0.1.1 to the correct 192.168.0.108 IP) fixed the JConsole connection problem too.

However your problem might lie elsewhere. If you're using JDK5, then the -debug option is not available with that version of JConsole. You've to use Java logging as described here or here. It involves creation of a special logging.properties file and starting JConsole with the -J-Djava.util.logging.config.file=logging.properties option.

P.S.: unfortunately JConsole is unusably slow for me, but this might be a problem with LTSP (since my client is an LTSP "thin" client - it's actually a normal PC, but the X11 over SSH solution used in LTSP already caused me some headache with other programs, so it might be the culprit here as well).

P.S.2: setting up JMX in Tomcat with the -Dcom.sun.management.jmxremote.authenticate=false -Dcom.sun.management.jmxremote.ssl=false options is totally insecure! So if your Tomcat server is public and it's JMX port is unprotected, then don't use it like I did in my example.