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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: 
docker system info
Look for the Debug Mode line in the output: 
Debug Mode: false

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2. Create a Test Container & Inspect Default Logs

Launch a simple HTTPD container: 
docker run -d --name test httpd:latest
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: 
tail -n 20 /var/log/messages

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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: 
    {
  "debug": true
}
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:
sudo systemctl reload docker

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4. Confirm Debug Mode Is Active

Run the inspect command again: 
docker system info
Now you should see Debug Mode: true along with extra metrics: 
Debug Mode: true
File Descriptors: 23
Goroutines: 36
System Time: 2020-05-21T11:38:33.79317432Z
EventsListeners: 0

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5. Generate and View Verbose Logs

Create a new container called test_debug: 
docker run -d --name test_debug httpd:latest
Then tail your logs to see debug-level details: 
tail -n 20 /var/log/messages
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: 
    {
  "debug": false
}
  2. Identify the Docker daemon PID and send SIGHUP: 
    pid=$(pgrep dockerd)
sudo kill -SIGHUP $pid
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:
docker system info | grep "Debug Mode"

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Command Reference

ActionCommand
Check debug statusdocker system info
Launch a containerdocker run -d --name <name> httpd:latest
View system logstail -n 20 /var/log/messages
Enable debug in daemon.jsonAdd "debug": true to /etc/docker/daemon.json
Reload Docker via systemdsudo systemctl reload docker
Reload Docker via SIGHUPsudo kill -SIGHUP $(pgrep dockerd)
Disable debug in daemon.jsonChange "debug": false in /etc/docker/daemon.json
Verify debug flag only`docker system infogrep “Debug Mode”`

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