Jenkins comes as a WAR file (there are also a wide variety of Linux packages available and a Windows installer) that you can drop into your favourite JEE container (Tomcat, Jetty, Glassfish etc.) or you can start the WAR file directly with java -jar jenkins.war. That’s it! Now that it is up and running, you can start configuring jobs and installing plugins. It will use a folder in your $HOME to persist the configuration and store the actual jobs. No database, no special installation, no special registration. Clean and easy.