JMX setup, how *not* to do it

You may want to monitor your Java server with jconsole. It once happened to us while using a custom tomcat installation that it simply failed to finish the deploy scripts. The problem was that the JMX options were included in catalina.sh:

JAVA_OPTS="$JAVA_OPTS -Djava.net.preferIPv4Stack=true"
JAVA_OPTS="$JAVA_OPTS -Dcom.sun.management.jmxremote.port=$JMXPORT"
JAVA_OPTS="$JAVA_OPTS -Dcom.sun.management.jmxremote.authenticate=false"
JAVA_OPTS="$JAVA_OPTS -Dcom.sun.management.jmxremote.ssl=false"
JAVA_OPTS="$JAVA_OPTS -Djava.rmi.server.hostname=$SERVERIP"

When the shutdown script tried to run, it thrown a somewhat weird exception:

Error: Exception thrown by the agent : java.rmi.server.ExportException: Port already in use: <port> nested exception is:
     java.net.BindException: Address already in use

It turns out that shutdown.sh invokes catalina.sh directly, by passing "stop" and including all other parameters:

EXECUTABLE=catalina.sh
[...]
exec "$PRGDIR"/"$EXECUTABLE" stop "$@"

Moving the options to startup.sh wouldn't have been trivial, so we added a simple if to keep this code from running when the server is shutting down:

if [ "$1" = "start" ]; then
        JAVA_OPTS="$JAVA_OPTS -Djava.net.preferIPv4Stack=true"
        JAVA_OPTS="$JAVA_OPTS -Dcom.sun.management.jmxremote.port=$JMXPORT"
        JAVA_OPTS="$JAVA_OPTS -Dcom.sun.management.jmxremote.authenticate=false"
        JAVA_OPTS="$JAVA_OPTS -Dcom.sun.management.jmxremote.ssl=false"
        JAVA_OPTS="$JAVA_OPTS -Djava.rmi.server.hostname=$SERVERIP"
fi