Changing hostname on Ubuntu Server 10.04LTS

I found out the hard way that it's changing the name of an Ubuntu Server 10.04LTS was not as straight forward as I initially thought. To save you and me the trouble and for future reference, I document how I did it here.

hostname NEW_NAME
echo NEW_NAME > /etc/hostname
cat /etc/hosts | sed s/OLD_NAME/NEW_NAME/g > /etc/hosts.new
mv /etc/hosts /etc/hosts.old
mv /etc/hosts.new /etc/hosts

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Monitoring Tomcat6 with VisualVM on Ubuntu

One of our applications running on Tomcat6 was encountering an issue which was drastically affecting the delivery of services to our clients. To diagnose this, we needed to monitor the state of the virtual machine running Tomcat6. This is what I had to do:

Assumptions:
- tomcat6 installed on an ubuntu server instance
- firewall on the server instance is enabled
- server has non public ip address: 10.0.0.1
- client machine installed with java6 which includes visualvm

1) download catalina-jmx-remote.jar and copy it into the tomcat6 lib folder. At the time of this writing, I found it here: http://apache.opensourceresources.org/tomcat/tomcat-6/v6.0.33/bin/extras/

2) modify /etc/defaults/tomcat6, add the following line to JAVA_OPTS

-Dcom.sun.management.jmxremote.ssl=false -Dcom.sun.management.jmxremote.authenticate=false -Djava.rmi.server.hostname=10.0.0.1

3) modify /etc/tomcat6/server.xml, add the following line inside the server block near the other listeners:

<Listener className="org.apache.catalina.mbeans.JmxRemoteLifecycleListener"
rmiRegistryPortPlatform="8086" rmiServerPortPlatform="8086" />

4) enable access to port 8086

ufw allow 8086

5) restart tomcat6

service tomcat6 restart

6) start visualvm on the client machine and add a jmx connection: 10.0.0.1:8086

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