Figure 3.10. Upgrading Jenkins from the web interface
Once Jenkins has downloaded the upgrade, you can also tell it to restart when no jobs are running. This
is probably the most convenient way to upgrade Jenkins, although it will not work in all environments.
In particular, you need to be running Jenkins as a stand-alone application, and the user running Jenkins
needs to have read-write access to the jenkins.war file.
If you are running Jenkins on an application server such as Tomcat or JBoss, you might need to do a
bit more tidying up when you upgrade your Jenkins instance. Tomcat, for example, places compiled
JSP pages in the CATALINA_BASE/work directory. When you upgrade your Jenkins version, these files
need to be removed to prevent the possibility of any stale pages being served.
Any plugins you have installed will be unaffected by your Jenkins upgrades. However, plugins can also
be upgraded, independently of the main Jenkins executable. You upgrade your plugins directly in the
Jenkins web application, using the Jenkins Plugin Manager. We discuss plugins in more detail further
on in this book.
3.16. Conclusion
In this chapter, we have seen how to install and run Jenkins in different environments, and learned a few
basic tips on how to maintain your Jenkins installation once running. Jenkins is easy to install, both as a
stand-alone application and as a WAR file deployed to an existing application server. The main things
you need to consider when choosing a build server to host Jenkins are CPU, memory, and disk space.