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In this demo, you’ll learn how to turn on Docker daemon debug mode, verify that it’s active, and inspect verbose logs during container operations.

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1. Check Current Debug Status

Start by viewing your Docker daemon’s current settings:
Look for the Debug Mode line in the output:

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2. Create a Test Container & Inspect Default Logs

Launch a simple HTTPD container:
Then review your system log (e.g., /var/log/messages or journalctl -u docker.service). You should only see high-level entries about container creation:

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3. Enable Docker Debug Mode

To capture detailed debug output, edit the Docker daemon configuration:
  1. Open /etc/docker/daemon.json (create it if missing) and add:
If the file doesn’t exist, you can create it. Make sure the JSON remains valid—use a JSON linter if needed.
  1. Reload the Docker daemon:

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4. Confirm Debug Mode Is Active

Run the inspect command again:
Now you should see Debug Mode: true along with extra metrics:

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5. Generate and View Verbose Logs

Create a new container called test_debug:
Then tail your logs to see debug-level details:
You’ll notice granular messages describing each step of the container lifecycle.

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6. Reload Docker with SIGHUP & Disable Debug

If you prefer a manual reload instead of systemctl:
  1. Update /etc/docker/daemon.json to disable debug mode:
  2. Identify the Docker daemon PID and send SIGHUP:
Always verify you have the correct PID before sending signals. Killing the wrong process can disrupt your system.
  1. Check that debug is now off:

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Command Reference

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