JDowser: Quick Start Guide

Contents

• JDowser Overview
• Build JDowser
• JDowser usage
• Sample JDowser run
• Remote JDowser usage with Ansible

JDowser Overview

JDowser is a command-line tool that can locate all the Java installations on local and network drives. JDowser recursively searches for Java installations starting from the root directory that is provided as a startup parameter. This section describes the JDowser usage and shows how to manage the application remotely with Ansible. The application is available for the Linux platform.

Build JDowser

You can build JDowser from the source code that is freely available on GitHub. The application is written in Golang, so you need to have a Golang package installed.

To build JDowser:

1. Clone the JDowser project from the GitHub repository.

2. In your terminal, cd to the JDowser project directory.

3. Run make:

   $ make

   This generates the jdowser executable file.

4. (Optional) If you observe dependency errors, run:

   $ make resolve; \
   make

JDowser usage

To use JDowser, run the jdowser executable with a command and one or more optional parameters as shown below:

  jdowser [-json|-csv] [-skipfs fstype[,fstype..]] [-nojvmrun] [-root=<scanroot>] [-wait] start
  jdowser [-json|-csv] [-wait] status
  jdowser [-json|-csv] [-wait] report
  jdowser [-json|-csv] stop

The supported commands are the following:

• start: Starts scanning of the file system for Java installations. After the scan is complete, the application stops automatically.
• status: Displays the current application state. The possible states are Running, Finished, Terminated, Error, and Unknown.
• report: Displays the list of detected Java installations. If you run this command while the scanning is still in progress, you might get an incomplete list of Java installations detected so far.
• stop: Stops scanning of the file system.

The supported parameters are listed below. All the parameters are optional:

• [-json|-csv]: Sets the output format to JSON or CSV. By default, JDowser outputs text in a human-readable format.

• [-skipfs fstype[,fstype..]]: Defines file system types to skip. If this parameter is not set, the default file systems to skip are nfs,tmp,proc. If you specify this parameter, the default values are ignored.

• [-nojvmrun]: Instructs JDowser not to use java -version under the hood.

  By default, JDowser executes java -version to retrieve information about detected JVMs. Since some Java vendors may require a special license to run Java for commercial use, you can use the -nojvmrun parameter. With this parameter, JDowser uses alternative methods to analyze detected Java instances. These methods include scanning of JVM files (.jar, .so, etc.) and may produce less accurate results.

• [-root=<scanroot>]: Sets a root directory for scanning. The default path is /.

• [-wait]: Runs JDowser in foreground so the terminal waits until the scanning is complete.

Sample JDowser run

$ ./jdowser -root=/opt start

$ ./jdowser status

host: host
state: Running
start_time: 2020-08-28 12:08:51 -0700 PDT
end_time: -1
args: -root=/opt

$ ./jdowser -json status

{
  "host": "host",
  "state": "Finished",
  "start_time": 1598641731,
  "end_time": 1598641733,
  "args": [
    "-root=/opt"
  ]
}

$ ./jdowser report

host: host
libjvm: /opt/jvm/zulu-11-amd64/lib/server/libjvm.so
libjvm_hash: 1e4f56ecacb3458513beb17537197c2b
java_home: /opt/jvm/zulu-11-amd64
is_jdk: true
java_version: 11.0.7
java_runtime_name: Zulu11.39+15-CA
java_runtime_version: 11.0.7+10-LTS
java_runtime_vendor: Azul Systems, Inc.
java_vm_name: OpenJDK 64-Bit Server VM
java_vm_version: 11.0.7+10-LTS
java_vm_vendor: Azul Systems, Inc.

Use JDowser with Ansible

The JDowser project directory contains the wrapper script ansible-jdowser that shows how to manage JDowser over the network using Ansible. In this case, all authorization/authentication is delegated to Ansible. For more information, see Ansible documentation.

NOTE: The ansible-jdowser script has been verified to work with Ansible 2.9 and later.

Install Ansible

To install Ansible, follow Ansible Installation Guide.

Run JDowser with Ansible

To run JDowser with Ansible, run the ansible-jdowser script as shown in the example below:

ansible-jdowser [ansible args] start|stop|status|report [-csv|-json] [-wait]

The script startup options are the same as with direct JDowser invocation. However, some parameters are pre-defined in the script: -nojvmrun, -root=/ Appending -wait to the end of the command-line adds -wait to the JDowser arguments list. You can also change the output format from the default JSON to CSV by passing the -csv parameter.

Sample ansible-jdowser run

$ ./ansible-jdowser -i "host1,host2," start

[
  {
    "host": "host1",
    "state": "Running",
    "start_time": 1598670527,
    "end_time": -1,
    "args": [
      "-root=/",
      "-nojvmrun",
      "-json"
    ]
  },
  {
    "host": "host2",
    "state": "Running",
    "start_time": 1598670527,
    "end_time": -1,
    "args": [
      "-root=/",
      "-nojvmrun",
      "-json"
    ]
  }
]