Apache Tomcat, often referred to as Tomcat, is an open-source web server and servlet container developed by the Apache Software Foundation. It implements several Java EE specifications such as Java Servlet, JavaServer Pages (JSP), WebSocket, and others, providing a platform for deploying and managing Java web applications. Let us delve into understanding Tomcat CATALINA_OPTS vs JAVA_OPTS.

1. Importance of CATALINA_OPTS and JAVA_OPTS

Tomcat offers various configuration options to customize its behavior and performance according to specific requirements. Two essential environment variables used for configuring Tomcat are CATALINA_OPTS and JAVA_OPTS. Let us understand the important differences between CATALINA_OPTS and JAVA_OPTS –

PurposePrimarily used for configuring options that affect the Java Virtual Machine (JVM).Specifically used to configure Tomcat’s runtime options, directly influencing Tomcat’s behavior.
ScopeInfluences JVM behavior, affecting how Java applications run within Tomcat.Directly influences Tomcat’s behavior and configuration.
Configuration ParametersIncludes JVM-specific options such as heap size, garbage collection settings, and system properties.Includes Tomcat-specific configuration options such as port numbers, security settings, and logging configurations.
UsageConfigures options affecting the JVM, such as memory allocation and system properties.Configures options specific to the Tomcat server, such as HTTP/HTTPS ports and SSL settings.
PrecedenceOptions specified in JAVA_OPTS take precedence over similar options specified elsewhere.Options specified in CATALINA_OPTS override conflicting settings in other configuration files.
FlexibilityOffers flexibility in configuring JVM-related settings and system properties.Provides flexibility in configuring Tomcat-specific settings to suit application requirements.

2. Use of JAVA_OPTS

JAVA_OPTS is an environment variable used to specify options that are passed to the Java Virtual Machine (JVM) when Tomcat is started. These options primarily affect the JVM’s behavior, such as memory allocation, garbage collection settings, and enabling debugging.

2.1 Settings

Commonly used settings in JAVA_OPTS include:

  • -Xmx: Sets the maximum heap size available to the JVM.
  • -Xms: Sets the initial heap size.
  • -XX:+UseG1GC: Enables the Garbage First (G1) Garbage Collector.
  • -D: Sets system properties, such as database connection parameters or logging configuration.

For example, setting JAVA_OPTS="-Xmx1024m -Xms512m -Djava.awt.headless=true" would allocate a maximum heap size of 1024 MB, and an initial heap size of 512 MB, and enable headless mode for Java AWT.


CATALINA_OPTS is another environment variable used specifically for configuring Tomcat’s runtime options. Unlike JAVA_OPTS, which primarily affects the JVM, CATALINA_OPTS is used to configure Tomcat’s behavior.

3.1 Settings

Some examples of settings you might use in CATALINA_OPTS include:

  • -Xms: Sets the initial memory pool for Tomcat’s JVM.
  • -Xmx: Sets the maximum memory pool for Tomcat’s JVM.
  • Sets the source of entropy for secure random number generation.
  • -XX:+PrintGCDetails: Prints garbage collection details for diagnostic purposes.

An example usage of CATALINA_OPTS could be: CATALINA_OPTS="-Xms512m -Xmx1024m". This would set the initial heap size to 512 MB and, the maximum heap size to 1024 MB, and configure the source of entropy for secure random number generation.

4. Conclusion

Understanding and appropriately configuring CATALINA_OPTS and JAVA_OPTS is crucial for optimizing the performance and behavior of Apache Tomcat. These environment variables allow administrators to fine-tune various aspects of Tomcat’s runtime environment and JVM settings, ensuring that it operates efficiently and securely according to the specific needs of the deployed applications.


An experience full-stack engineer well versed with Core Java, Spring/Springboot, MVC, Security, AOP, Frontend (Angular & React), and cloud technologies (such as AWS, GCP, Jenkins, Docker, K8).
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