What is the missing configuration step in VSCode rdbg Ruby Debugger "Can not find attachable Ruby process."?

3 min read 04-10-2024

What is the missing configuration step in VSCode rdbg Ruby Debugger "Can not find attachable Ruby process."?

Debugging Ruby in VSCode: "Can't Find Attachable Ruby Process" and How to Fix It

Debugging Ruby code is essential for developers, and Visual Studio Code (VSCode) offers a powerful debugger for Ruby. However, you might encounter the frustrating error message: "Can not find attachable Ruby process." This usually means there's a missing configuration step preventing the debugger from connecting to your running Ruby process. Let's break down the common causes and provide solutions.

The Scenario: Debugging Ruby in VSCode

Imagine you're working on a Ruby project in VSCode, eager to debug your code. You've set up breakpoints, launched the debugger, but all you see is the error: "Can not find attachable Ruby process." You're puzzled because your Ruby code is definitely running, but the debugger can't seem to find it.

Here's a typical example of the code you might be working with:

# app.rb
puts "Hello, world!"

And this is how you might launch the debugger in VSCode:

# Using the "Run and Debug" view
1.  Click "Run and Debug" in the left sidebar.
2.  Select "Ruby" from the drop-down menu.
3.  Click "Start Debugging" (or "F5").

Understanding the Problem

This error occurs because the debugger needs to connect to your running Ruby process. However, the debugger doesn't magically know how to find it. It requires a specific configuration telling it where and how to attach.

Common Causes and Solutions

Let's explore the most common reasons why this error arises and how to resolve them:

Missing ruby-debug-ide gem:
- Explanation: The ruby-debug-ide gem provides the necessary functionality for the VSCode debugger to interact with your Ruby code.
- Solution: Install the gem in your project:
```
gem install ruby-debug-ide
```
Incorrect Debug Configuration:
- Explanation: VSCode uses a configuration file (.vscode/launch.json) to define how the debugger should be launched. If this file is missing or incorrectly configured, the debugger won't be able to find your process.
- Solution: Open the "Run and Debug" view, create a new configuration (usually "Ruby"), and update the program field to point to the location of your Ruby script. For example:
```
{
    "version": "0.2.0",
    "configurations": [
        {
            "name": "Ruby",
            "type": "Ruby",
            "request": "launch",
            "program": "${workspaceFolder}/app.rb"
        }
    ]
}
```
Running the Script in a Different Terminal:
- Explanation: The debugger only connects to processes started within the terminal from which it was launched. If your Ruby script is running in a separate terminal, the debugger won't find it.
- Solution: Run your script in the same terminal window from which you launched the debugger in VSCode.
Ruby Version Mismatch:
- Explanation: If the debugger uses a different Ruby version than the one running your script, the connection may fail.
- Solution: Ensure you're using the same Ruby version for both the debugger and your project. You can check and manage your Ruby versions using rvm or rbenv.

Additional Tips

Restart VSCode: Sometimes, restarting VSCode can help resolve debugger issues.
Check the Output: Look for any error messages in the "Debug Console" output panel for additional hints about the cause of the problem.
Verify the ruby-debug-ide Gem: Make sure the ruby-debug-ide gem is loaded within your running Ruby process. You can use require 'ruby-debug-ide' to explicitly load it.

Conclusion

Debugging Ruby code with VSCode offers a streamlined workflow, but you might encounter the "Can not find attachable Ruby process" error. By understanding the common causes, such as missing gem dependencies, incorrect configuration, and version mismatches, you can swiftly resolve these issues and take full advantage of the power of debugging in VSCode. Remember to check your terminal, your configurations, and your Ruby version for a smoother debugging experience!