Port 5678 Guide - Localhost Dev Server

5678.md

root@localhost:~# cat 5678.md

# Services and Software That Use Port 5678

## Development Tools

• debugpy

Microsoft's Python debugger that uses port 5678 by default for remote debugging sessions.

• VS Code Python Extension

Visual Studio Code Python extension that connects to debugpy on port 5678 for debugging.

• PyCharm Remote Debugger

JetBrains PyCharm IDE remote debugging capability that can use port 5678.

• Python Debug Adapter

Debug adapters that implement Debug Adapter Protocol for Python debugging on this port.

## Development Frameworks

• Django Debug Server

Django applications running in debug mode with debugpy attached on port 5678.

• Flask Debug Sessions

Flask applications with integrated debugging capabilities using port 5678.

• FastAPI Debugging

FastAPI applications configured for remote debugging through port 5678.

• Jupyter Notebook Debugging

Jupyter notebooks with debugging capabilities enabled on port 5678.

## Application Servers

• Python WSGI Debuggers

WSGI applications with attached debuggers listening on port 5678.

• Containerized Python Apps

Python applications running in Docker containers exposing debug port 5678.

• Remote Python Processes

Python processes running on remote servers with debug ports forwarded to localhost:5678.

## Other Tools

• Python Language Servers

Language server protocol implementations that may use port 5678 for debugging features.

• Testing Frameworks

Pytest and unittest frameworks running with debugger attached on port 5678.

• Data Science Tools

Data analysis tools and notebooks with debugging capabilities on port 5678.

# Frequently Asked Questions

Q: What is debugpy and why does it use port 5678?

debugpy is Microsoft's implementation of the Debug Adapter Protocol for Python. It uses port 5678 by default as it's uncommon for other services and easy to remember, providing a standard port for Python debugging across different IDEs.

Q: Is it safe to use port 5678 for remote debugging in production?

No, debug ports should never be exposed in production environments. They provide full access to your application's runtime. Only use debugging ports in development environments and ensure they're properly secured.

Q: Can I run multiple Python debug sessions simultaneously?

Yes, but each session needs a different port. You can specify alternative ports in debugpy.listen() calls (e.g., 5679, 5680) and configure your IDE accordingly for each debug session.

Q: How do I debug Python applications running in Docker containers?

Expose port 5678 in your Docker container, install debugpy in the container, and configure port forwarding. Use docker run -p 5678:5678 or add port mapping to docker-compose.yml.

Q: How do I set up VS Code for Python debugging with port 5678?

Install the Python extension, create a launch.json with 'Python: Remote Attach' configuration pointing to localhost:5678, and add debugpy code to your Python application.

Q: Does debugging significantly impact Python application performance?

Yes, debugging can slow down execution significantly, especially when stepping through code or inspecting variables. This is normal and expected during debugging sessions.

Q: Can I enable debugging conditionally in my Python application?

Yes, you can use environment variables or command-line arguments to conditionally start debugpy. This allows you to enable debugging only when needed without modifying code.

Q: How do I debug Django, Flask, or FastAPI applications?

Add debugpy.listen() calls to your application startup code, ensure debug mode is enabled in your web framework, and configure your IDE to attach to port 5678. Some frameworks may need special configuration for debugging.

# How to Use Port 5678

Install Python Debugger

Install debugpy package using pip. This is the recommended Python debugger that works with VS Code and other IDEs.

                        bash
                    
pip install debugpy

Configure Debug Server

Add debugpy import and listen call to your Python application. This will start the debug server on port 5678 waiting for client connections.

                        bash
                    
import debugpy
debugpy.listen(5678)
debugpy.wait_for_client()  # Optional: pause execution until debugger attaches

Start Your Python Application

Run your Python application with the debugpy configuration. The application will start and listen for debugger connections on port 5678.

                        bash
                    
python your_app.py

Attach Debugger from IDE

In VS Code, create a launch.json configuration for "Python: Remote Attach" and connect to localhost:5678. Set breakpoints and start debugging.

                        bash
                    
# launch.json configuration
{
  "name": "Python: Remote Attach",
  "type": "python",
  "request": "attach",
  "connect": {
    "host": "localhost",
    "port": 5678
  }
}

Debug and Inspect Code

Use the debugger to set breakpoints, step through code, inspect variables, and evaluate expressions. The debug session provides full interactive debugging capabilities.

                        bash
                    
# You can now:
# - Set breakpoints in your IDE
# - Step over/into/out of functions
# - Inspect variable values
# - Evaluate expressions in debug console

# Common Problems

## HIGH Severity Issues

⚠ Debugger connection refused

IDE cannot connect to the Python application on port 5678, often due to firewall issues, application not started with debugpy, or port conflicts.

## MEDIUM Severity Issues

⚠ Application hangs on wait_for_client()

Python application freezes when debugpy.wait_for_client() is called but no debugger attaches within reasonable time.

⚠ Breakpoints not being hit

Debugger connects successfully but breakpoints set in the IDE are ignored or not triggered during code execution.

⚠ Port 5678 already in use

Another debugging session or application is using port 5678, preventing the new debug session from starting.

## LOW Severity Issues

⚠ Debug session performance issues

Debugging significantly slows down application execution, especially with complex applications or when inspecting large data structures.

# Troubleshooting Solutions

## All Platform

Resolve Debug Connection Problems

For: connection_issues

Steps:

Verify that debugpy is properly installed and imported in your Python application
Check if the application is actually listening on port 5678 using netstat or similar tools
Ensure no firewall is blocking connections to port 5678
Verify the debugger configuration in your IDE matches the port and host
Try connecting from a simple test client to isolate the problem

                            all
                        
pip show debugpy

Fix Breakpoint and Debugging Issues

For: breakpoint_issues

Steps:

Ensure breakpoints are set in the correct file path that matches the running application
Verify that the Python source code matches what the debugger is seeing
Check if there are multiple Python interpreters and ensure you're debugging the right one
Try setting a simple breakpoint at the start of main execution to test basic functionality
Clear all breakpoints and set them again, or restart both the application and debugger

                            all
                        
import sys; print(sys.executable)

Fix Breakpoint and Debugging Issues

For: breakpoint_issues

Steps:

Ensure breakpoints are set in the correct file path that matches the running application
Verify that the Python source code matches what the debugger is seeing
Check if there are multiple Python interpreters and ensure you're debugging the right one
Try setting a simple breakpoint at the start of main execution to test basic functionality
Clear all breakpoints and set them again, or restart both the application and debugger

                            all
                        
debugpy.listen(('0.0.0.0', 5678))

## Windows Platform

Resolve Debug Connection Problems

For: connection_issues

Steps:

Verify that debugpy is properly installed and imported in your Python application
Check if the application is actually listening on port 5678 using netstat or similar tools
Ensure no firewall is blocking connections to port 5678
Verify the debugger configuration in your IDE matches the port and host
Try connecting from a simple test client to isolate the problem

                            windows
                        
netstat -an | findstr :5678

## macOS Platform

Resolve Debug Connection Problems

For: connection_issues

Steps:

Verify that debugpy is properly installed and imported in your Python application
Check if the application is actually listening on port 5678 using netstat or similar tools
Ensure no firewall is blocking connections to port 5678
Verify the debugger configuration in your IDE matches the port and host
Try connecting from a simple test client to isolate the problem

                            macos
                        
lsof -i :5678

## Linux Platform

Resolve Debug Connection Problems

For: connection_issues

Steps:

Verify that debugpy is properly installed and imported in your Python application
Check if the application is actually listening on port 5678 using netstat or similar tools
Ensure no firewall is blocking connections to port 5678
Verify the debugger configuration in your IDE matches the port and host
Try connecting from a simple test client to isolate the problem

                            linux
                        
ss -tlnp | grep :5678

# Summary

root@localhost:~# echo "Port 5678 Documentation Complete"

What it is: localhost:5678 is Localhost:5678 is commonly used for Python debugging tools, particularly debugpy (Python debugger) and VS Code remote debugging sessions. This port enables developers to attach external debuggers to Python applications, set breakpoints, and inspect variables during development, providing essential debugging capabilities for Python development workflows.

Who uses it: debugpy, VS Code Python Extension, PyCharm Remote Debugger, Python Debug Adapter, Django Debug Server, Flask Debug Sessions, FastAPI Debugging, Jupyter Notebook Debugging, Python WSGI Debuggers, Containerized Python Apps, Remote Python Processes, Python Language Servers, Testing Frameworks, Data Science Tools

Access URL: http://localhost:5678