How to use the command jhsdb (with examples)

Jhsdb is a command-line tool that is used to attach to a Java process or launch a postmortem debugger to analyze the core dump from a crashed Java Virtual Machine. It provides a set of commands to perform various debugging tasks.

Use case 1: Print stack and locks information of a Java process

Code:

jhsdb jstack --pid pid

Motivation: The jhsdb jstack command is used to print the stack trace and information about the locks held by a Java process. It is helpful in diagnosing performance issues, deadlocks, and identifying which threads are causing high CPU utilization.

Explanation:

• jhsdb jstack: The jhsdb command with the jstack option is used to print stack information.
• --pid pid: The –pid option is used to specify the process id of the Java process for which the stack trace is required.

Example output:

Attaching to process ID pid, please wait...
Debugger attached successfully.
Thread 1 (Thread ID: 1234):
  Stack trace information

Thread 2 (Thread ID: 5678):
  Stack trace information

...

Use case 2: Open a core dump in interactive debug mode

Code:

jhsdb clhsdb --core path/to/core_dump --exe path/to/jdk/bin/java

Motivation: The jhsdb clhsdb command is used to open a core dump file in interactive debug mode. This is useful for analyzing a crashed Java Virtual Machine and identifying the cause of the crash.

Explanation:

• jhsdb clhsdb: The jhsdb command with the clhsdb option is used to launch a postmortem debugger in interactive mode.
• --core path/to/core_dump: The –core option is used to specify the path to the core dump file.
• --exe path/to/jdk/bin/java: The –exe option is used to specify the path to the Java executable.

Example output:

Processing core dump file...
Attaching to core file...
Debugger attached successfully.
Enter command to execute:

Use case 3: Start a remote debug server

Code:

jhsdb debugd --pid pid --serverid optional_unique_id

Motivation: The jhsdb debugd command is used to start a remote debug server on a Java process. This allows remote debugging and analysis of the Java process using a debugger tool.

Explanation:

• jhsdb debugd: The jhsdb command with the debugd option is used to start a remote debug server.
• --pid pid: The –pid option is used to specify the process id of the Java process for which the debug server should be started.
• --serverid optional_unique_id: The –serverid option is used to specify an optional unique identifier for the debug server.

Example output:

Starting remote debug server for process ID pid and server ID optional_unique_id...
Remote debug server started successfully.

Use case 4: Connect to a process in interactive debug mode

Code:

jhsdb clhsdb --pid pid

Motivation: The jhsdb clhsdb command is used to attach to a running Java process in interactive debug mode. This allows interactive debugging and analysis of the Java process.

Explanation:

• jhsdb clhsdb: The jhsdb command with the clhsdb option is used to launch a postmortem debugger in interactive mode.
• --pid pid: The –pid option is used to specify the process id of the Java process to which to connect.

Example output:

Attaching to process ID pid, please wait...
Debugger attached successfully.
Enter command to execute:

Conclusion:

The jhsdb command provides a set of useful debugging capabilities for analyzing Java processes. Whether it is printing stack and locks information, opening core dumps for analysis, starting remote debug servers, or connecting to running processes, jhsdb is a powerful tool for diagnosing and debugging Java applications.