Introduction

&project; Robert Slifka Introduction

For administrators and web developers alike, there are some important bits of information you should familiarize yourself with before starting out. This document serves as a brief introduction to some of the concepts and terminology behind the Tomcat container. As well, where to go when you need help.

In the course of reading these documents, you will run across a number of terms; some specific to Tomcat, and others defined by the Servlet and JSP specifications.

Context - In a nutshell, a Context is a web application.

That is it. If you find any more terms we need to add to this section, please do let us know.

These are some of the key tomcat directories:

/bin - Startup, shutdown, and other scripts. The *.sh files (for Unix systems) are functional duplicates of the *.bat files (for Windows systems). Since the Win32 command-line lacks certain functionality, there are some additional files in here.
/conf - Configuration files and related DTDs. The most important file in here is server.xml. It is the main configuration file for the container.
/logs - Log files are here by default.
/webapps - This is where your webapps go.

Throughout the documentation, there are references to the two following properties:

CATALINA_HOME: Represents the root of your Tomcat installation, for example /home/tomcat/apache-tomcat-9.0.10 or C:\Program Files\apache-tomcat-9.0.10.
CATALINA_BASE: Represents the root of a runtime configuration of a specific Tomcat instance. If you want to have multiple Tomcat instances on one machine, use the CATALINA_BASE property.

If you set the properties to different locations, the CATALINA_HOME location contains static sources, such as .jar files, or binary files. The CATALINA_BASE location contains configuration files, log files, deployed applications, and other runtime requirements.

By default, CATALINA_HOME and CATALINA_BASE point to the same directory. Set CATALINA_BASE manually when you require running multiple Tomcat instances on one machine. Doing so provides the following benefits:

Easier management of upgrading to a newer version of Tomcat. Because all instances with single CATALINA_HOME location share one set of .jar files and binary files, you can easily upgrade the files to newer version and have the change propagated to all Tomcat instances using the same CATALIA_HOME directory.
Avoiding duplication of the same static .jar files.
The possibility to share certain settings, for example the setenv shell or bat script file (depending on your operating system).

Before you start using CATALINA_BASE, first consider and create the directory tree used by CATALINA_BASE. Note that if you do not create all the recommended directories, Tomcat creates the directories automatically. If it fails to create the necessary directory, for example due to permission issues, Tomcat will either fail to start, or may not function correctly.

Consider the following list of directories:

The bin directory with the setenv.sh, setenv.bat, and tomcat-juli.jar files.

Recommended: No.

Order of lookup: CATALINA_BASE is checked first; fallback is provided to CATALINA_HOME.
The lib directory with further resources to be added on classpath.

Recommended: Yes, if your application depends on external libraries.

Order of lookup: CATALINA_BASE is checked first; CATALINA_HOME is loaded second.
The logs directory for instance-specific log files.

Recommended: Yes.
The webapps directory for automatically loaded web applications.

Recommended: Yes, if you want to deploy applications.

Order of lookup: CATALINA_BASE only.
The work directory that contains temporary working directories for the deployed web applications.

Recommended: Yes.
The temp directory used by the JVM for temporary files.

Recommended: Yes.

We recommend you not to change the tomcat-juli.jar file. However, in case you require your own logging implementation, you can replace the tomcat-juli.jar file in a CATALINA_BASE location for the specific Tomcat instance.

We also recommend you copy all configuration files from the CATALINA_HOME/conf directory into the CATALINA_BASE/conf/ directory. In case a configuration file is missing in CATALINA_BASE, there is no fallback to CATALINA_HOME. Consequently, this may cause failure.

At minimum, CATALINA_BASE must contain:

conf/server.xml
conf/web.xml

That includes the conf directory. Otherwise, Tomcat fails to start, or fails to function properly.

For advanced configuration information, see the RUNNING.txt file.

The CATALINA_BASE property is an environment variable. You can set it before you execute the Tomcat start script, for example:

On Unix: CATALINA_BASE=/tmp/tomcat_base1 bin/catalina.sh start
On Windows: CATALINA_BASE=C:\tomcat_base1 bin/catalina.bat start

This section will acquaint you with the basic information used during the configuration of the container.

All of the information in the configuration files is read at startup, meaning that any change to the files necessitates a restart of the container.

While we've done our best to ensure that these documents are clearly written and easy to understand, we may have missed something. Provided below are various web sites and mailing lists in case you get stuck.

Keep in mind that some of the issues and solutions vary between the major versions of Tomcat. As you search around the web, there will be some documentation that is not relevant to Tomcat , but only to earlier versions.

Current document - most documents will list potential hangups. Be sure to fully read the relevant documentation as it will save you much time and effort. There's nothing like scouring the web only to find out that the answer was right in front of you all along!
Tomcat FAQ
Tomcat WIKI
Tomcat FAQ at jGuru
Tomcat mailing list archives - numerous sites archive the Tomcat mailing lists. Since the links change over time, clicking here will search Google.
The TOMCAT-USER mailing list, which you can subscribe to here. If you don't get a reply, then there's a good chance that your question was probably answered in the list archives or one of the FAQs. Although questions about web application development in general are sometimes asked and answered, please focus your questions on Tomcat-specific issues.
The TOMCAT-DEV mailing list, which you can subscribe to here. This list is reserved for discussions about the development of Tomcat itself. Questions about Tomcat configuration, and the problems you run into while developing and running applications, will normally be more appropriate on the TOMCAT-USER list instead.

And, if you think something should be in the docs, by all means let us know on the TOMCAT-DEV list.