CONFIGURE JCONSOLE FOR JVM (TOMCAT) on CENTOS:
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1) #vi /etc/profile

insert -->
CATALINA_OPTS="-Dcom.sun.management.jmxremote -Dcom.sun.management.jmxremote.port=8999 -Dcom.sun.management.jmxremote.ssl=false -Dcom.sun.management.jmxremote.authenticate=false -Djava.rmi.server.hostname=127.0.0.1"
export CATALINA_OPTS

2) #jconsole

go to remote process,type:
localhost:8999 --> connect

Please refer to:

http://download.oracle.com/javase/1.5.0/docs/guide/management/faq.html
http://www.markomedia.com.au/blog/monitor-railo-on-tomcat-using-jconsole.html (best to refer)
https://wiki.internet2.edu/confluence/display/CPD/Monitoring+Tomcat+with+JMX

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How to check port 8999 listening:
#netstat -anp | grep 8999

Enable 8999 to listen:
#iptables --list
#/usr/sbin/iptables -I INPUT -s 127.0.0.1/192.168.10.220 -p tcp --destination-port 8999 -j ACCEPT

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HOW TO ENABLE GC LOG IN CATALINA.OUT

In /etc/profile:
-->
CATALINA_OPTS="-verbose:gc -Xms256m -Xmx512m -XX:+PrintGCTimeStamps -XX:+PrintGCDetails"
export CATALINA_OPTS