How to use the command 'jps' (with examples)

The ‘jps’ command, standing for Java Virtual Machine Process Status, is a diagnostic tool used in Java environments to list the running Java processes on a machine for the current user. This command provides critical insights into JVM applications, helping developers and administrators monitor and manage Java applications efficiently. By leveraging this tool, users can gather information about ongoing Java processes, understand their resource utilization, and troubleshoot potential application issues.

List all JVM processes

Code:

jps

Motivation: When working in a Java development or production environment, it’s essential to have visibility into all running Java processes. This initial inquiry provides an immediate snapshot of the JVM landscape on your machine. By executing jps, you can quickly identify which Java applications or services are active, helping in both development and operational contexts where process management is key.

Explanation: Executing jps without any additional flags or options will list all Java processes currently running under the user’s account. This basic use of the command provides a convenient way to monitor your Java applications at a glance.

Example output:

12345 MyFirstJavaApp
67890 AnotherJavaProcess

In this output, 12345 and 67890 are the process IDs (PIDs) of the running Java applications, and MyFirstJavaApp and AnotherJavaProcess are their respective main classes.

List all JVM processes with only PID

Code:

jps -q

Motivation: There are scenarios where you may only want to know the process identifiers of Java applications, for instance, when managing processes through automated scripts that require minimal information for process handling tasks. Using this mode can make parsing output in scripts simpler, as the output is cleaner and more focused.

Explanation: The -q option stands for “quiet mode,” which suppresses the display of the class name, JAR file name, and arguments for each process, returning only the PIDs. This can be used to streamline process monitoring tasks that require only the identification number.

Example output:

12345
67890

Here, the output strictly contains the PIDs of the Java processes without any additional application names or arguments.

Display the arguments passed to the processes

Code:

jps -m

Motivation: Understanding what parameters or arguments were provided when launching Java applications can be crucial for debugging and optimization tasks. Whether it’s passing configuration files, memory parameters, or other important operational arguments, recognizing these can elucidate runtime behavior and help diagnose issues rapidly.

Explanation: The -m flag adds the ability to see the arguments passed to the Java applications or utilities at the command line when they were started. This detail can offer insight into the operational configuration of the JVM processes.

Example output:

12345 MyFirstJavaApp config.yaml
67890 AnotherJavaProcess --verbose --port 8080

In this result, config.yaml and --verbose --port 8080 are inputs fed to the applications upon execution, allowing users to verify input correctness and effectiveness.

Display the full package name of all processes

Code:

jps -l

Motivation: Viewing the full package name of Java processes can be particularly useful when dealing with multiple applications with similar or identical main class names, but that live in different packages. This specificity aids in distinguishing between processes, ensuring accurate process management and analysis.

Explanation: The -l option extends the output to include the long form of the class name or the complete path of the JAR file used when launching the Java processes. This option is valuable for identifying specific instances among several processes sharing the same simple class names.

Example output:

12345 com.example.myapp.MyFirstJavaApp
67890 org.mypackage.services.AnotherJavaProcess

Here, the fully-qualified package names facilitate precise identification and management of each process.

Display the arguments passed to the JVM

Code:

jps -v

Motivation: Detailed visibility into JVM arguments like heap size, garbage collection options, and Java system properties is crucial for performance tuning and troubleshooting. Knowing exactly what JVM configuration is in use allows developers and administrators to optimize resource usage and diagnose memory or performance-related issues efficiently.

Explanation: The -v option enables the display of the arguments provided specifically to the JVM at startup, not just those to the application. This might include options adjusting heap size, enabling or configuring garbage collection logs, and setting system properties, among others.

Example output:

12345 MyFirstJavaApp -Xms256m -Xmx512m -Dproperty=value
67890 AnotherJavaProcess -XX:+UseG1GC

The output displays JVM-specific parameters such as -Xms, which sets initial heap size, -Xmx for maximum heap size, and other specific configurations enhancing control and observability of Java applications.

Conclusion:

The jps command, with its various flags, provides vital oversight and understanding of Java applications running within a system. By employing these examples in appropriate contexts, users gain enriched insights and management capabilities, enhancing their troubleshooting, diagnostics, and overall Java process administration efforts. Whether you are scripting automated tasks, resolving issues, or performing checks, jps is an indispensable tool within the Java developer’s and administrator’s toolkit.