Setting Up File Browser with Nginx Proxy Manager and Troubleshooting 502 Errors

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Recently, I set up File Browser behind Nginx Proxy Manager on a Docker host. While the setup was straightforward, I ran into several common issues and learned how to resolve them.

1. File Browser Container Issues

After starting the container, logs showed repeated errors like:

chown: changing ownership of '/srv': Read-only file system
s6-applyuidgid: fatal: unable to set supplementary group list: Operation not permitted

This happens when File Browser runs as a non-root user but the volume permissions are not set correctly. To fix it:

  • Ensure the host directory is owned by the UID/GID expected by File Browser (default 33:33 for linuxserver images).
  • Mount the volumes with proper permissions, for example:
sudo chown -R 33:33 /path/to/config /path/to/srv

After correcting permissions, the container started successfully and initialized the database.

2. Configuring Nginx Proxy Manager

When adding File Browser as a proxy host:

  • Use the container's internal Docker IP or service name (filebrowser) as the forward hostname.
  • Use port 80 since File Browser listens on 80 inside the container.

Example configuration:

Domain Names: files.example.com
Scheme: http
Forward Hostname / IP: filebrowser
Forward Port: 80
Location: /

3. Troubleshooting 502 Bad Gateway

If you see 502 Bad Gateway:

  • Check that the File Browser container is running and listening on port 80.
  • Verify connectivity from the Nginx Proxy Manager container using the internal Docker network.
  • Ensure the volumes are not read-only and the container can write to /srv and /config.

4. SSH Tunnel Considerations

While testing remotely, I used an SSH tunnel:

ssh -L 8081:127.0.0.1:81 bijakit@your-server -p 20022

After closing the tunnel, the page still loaded due to browser caching. To fully disconnect:

  • Clear the browser cache and cookies for 127.0.0.1:8081.
  • Use Force Reload (Ctrl+F5 / Cmd+Shift+R) or open an incognito window.

5. Lessons Learned

  • Always set correct UID/GID for Docker volumes when using non-root containers.
  • 502 errors usually indicate connectivity issues or permission problems between Nginx and the backend service.
  • Browser caching can mislead you during SSH tunneling tests.

With these steps, I successfully set up File Browser behind Nginx Proxy Manager and resolved all 502 errors.


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