jhsdb

jhsdb is a Serviceability Agent (SA) tool. Serviceability Agent (SA) is a JDK component used to provide snapshot debugging, performance analysis and to get an in-depth understanding of the Hotspot JVM and the Java application executed by the Hotspot JVM.

Even though native debuggers like gdb are available for examining the JVM, unlike jhsdb, these native debuggers do not have an inbuilt understanding of the data structures in Hotspot and hence, are not able to throw insights on the Java application being executed. jhsdb knows about the locations and address ranges of crucial components of the JVM like the Java heap, heap generations, regions, code cache, etc.

Synopsis

jhsdb clhsdb [--pid pid | --exe executable --core coredump]

jhsdb debugd [options] (pid | executable coredump) [server-id]

jhsdb hsdb [--pid pid | --exe executable --core coredump]

jhsdb jstack [--pid pid | --exe executable --core coredump] [options]

jhsdb jmap [--pid pid | --exe executable --core coredump] [options]

jhsdb jinfo [--pid pid | --exe executable --core coredump] [options]

jhsdb jsnap [options] [--pid pid | --exe executable --core coredump]

pid: The process ID to which the jhsdb tool should attach. The process must be a Java process. To get a list of Java processes running on a machine, use the ps command or, if the JVM processes are not running in a separate docker instance, the jps command.

Note:
JDK 10 added support for using the Attach API when attaching to Java processes running in a separate docker process. However, the jps command will not list the JVM processes that are running in a separate docker instance. If you are trying to connect a Linux host with a Virtual Machine that is in a docker container, you must use tools such as ps to look up the PID of the JVM.
server-id: An optional unique ID to use when multiple debug servers are running on the same remote host.
executable: The Java executable file from which the core dump was produced.
coredump: The core file to which the jhsdb tool should attach.
options: The command-line options for a jhsdb mode. See Common Options for jhsdb Modes, Options for the debugd Mode, Options for the jinfo Mode, Options for the jmap Mode, Options for the jmap Mode, Options for the jstack Mode, and Options for the jsnap Mode.

Note:

Either the pid or the pair of executable and coredump files must be provided.

Description

You can use the jhsdb tool to attach to a Java process or to launch a postmortem debugger to analyze the content of a core-dump from a crashed Java Virtual Machine (JVM). This command is experimental and unsupported.

Note:

Attaching the jhsdb tool to a live process will cause the process to hang and the process will probably crash when the debugger detaches.

The jhsdb tool can be launched in any one of the following modes:

jhsdb clhsdb: Starts the interactive command-line debugger.
jhsdb debugd: Starts the remote debug server.
jhsdb hsdb: Starts the interactive GUI debugger.
jhsdb jstack: Prints stack and locks information.
jhsdb jmap: Prints heap information.
jhsdb jinfo: Prints basic JVM information.
jhsdb jsnap: Prints performance counter information.

Common Options for jhsdb Modes

In addition to any required jstack, jmap, jinfo or jsnap mode specific options, the pid, exe, or core options must be provided for all modes. The following options are available for all modes.

--pid: The process ID of the hanging process.
--exe: The executable file name.
--core: The core dump file name.
--help: Displays the options available for the command.

Options for the debugd Mode

server-id: An optional unique ID for this debug server. This is required if multiple debug servers are run on the same machine.

Options for the jinfo Mode

Without specified options, the jhsdb jinfo command prints both flags and properties.

--flags: Prints the VM flags.
--sysprops: Prints the Java system properties.
no option: Prints the VM flags and the Java system properties.

Options for the jmap Mode

In addition to the following mode specific options, the pid, exe, or core options described in Common Options for jhsdb Modes must be provided.

no option: Prints the same information as Solaris pmap.
--heap: Prints the java heap summary.
--binaryheap: Dumps the java heap in hprof binary format.
--dumpfile: The name of the file to which the information needs to be written.
--histo: Prints the histogram of java object heap.
--clstats: Prints the class loader statistics.
--finalizerinfo: Prints the information on objects awaiting finalization.

Options for the jstack Mode

In addition to the following mode specific options, the pid, exe, or core options described in Common Options for jhsdb Modes must be provided.

--locks: Prints the java.util.concurrent locks information.
--mixed: Attempts to print both java and native frames if the platform allows it.

Options for the jsnap Mode

In addition to the following mode specific option, the pid, exe, or core options described in Common Options for jhsdb Modes must be provided.

--all: Prints all performance counters.