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Sospeter Mong'are
Sospeter Mong'are

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Fixing “502 Bad Gateway” with Gunicorn and Nginx on Ubuntu

#python #django

Gunicon Error

When deploying a Django (or any Python) app using Gunicorn behind Nginx, you might encounter a 502 Bad Gateway error. This article walks you through resolving it, especially if the root cause is:

PermissionError: [Errno 13] Permission denied: '/path/to/app.sock'
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🔍 Root Cause

This error occurs when Gunicorn lacks permission to create or connect to the Unix socket file specified in your systemd service file.

This results in:

  • Gunicorn crashing
  • Nginx failing to connect to the backend
  • A 502 Bad Gateway error in the browser

✅ Solution Steps

1. Fix Socket File Permissions

Ensure the user running Gunicorn (e.g., www-data, ubuntu, or a custom deployment user like resquser) has the right permissions to access and create the socket file.

Run the following:

sudo chown -R www-data:www-data /var/www/your_project_directory
sudo chmod -R 755 /var/www/your_project_directory
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Replace www-data with the actual user specified in your systemd service file under the [Service] section:

User=www-data
Group=www-data
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2. Remove Any Existing Socket File

If a .sock file was previously created by another user or process, delete it:

sudo rm /var/www/your_project_directory/your_app.sock
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3. Restart Gunicorn 

sudo systemctl daemon-reexec
sudo systemctl restart your_app.service
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Verify it’s running without errors:

sudo systemctl status your_app.service
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4. (Optional) Add Nginx to Correct Group

If Nginx needs access to the socket file (and the group owner differs from nginx), you can add Nginx to that group:

sudo usermod -aG www-data nginx
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Then restart Nginx:

sudo systemctl restart nginx
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5. Verify Gunicorn Socket Works

Test Gunicorn’s socket manually:

curl --unix-socket /var/www/your_project_directory/your_app.sock http://localhost
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If you get an HTTP response, Gunicorn is now functioning correctly.

🧼 Pro Tips

  • Avoid placing .sock files in /tmp/ or root-owned directories without adjusting permissions.
  • Always define a clean User and Group in your systemd service file for predictable file access.
  • Use journalctl -u your_app.service -n 50 to debug failures.

📌 Summary

Step Action
🧾 1 Ensure directory and socket file permissions are correct
🗑 2 Delete leftover .sock file
🔁 3 Restart Gunicorn service
🔐 4 Add Nginx to appropriate group if needed
✅ 5 Test socket with curl

With these steps, your Gunicorn and Nginx setup should serve your Django app without throwing 502 Bad Gateway errors.

Let me know if you will get stuck

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