Read the daemon logs

The daemon logs may help you diagnose problems. The logs may be saved in one of a few locations, depending on the operating system configuration and the logging subsystem used:

To view the dockerd logs on macOS, open a terminal Window, and use the tail command with the -f flag to "follow" the logs. Logs will be printed until you terminate the command using CTRL+c:

$ tail -f ~/Library/Containers/com.docker.docker/Data/log/vm/dockerd.log
2021-07-28T10:21:21Z dockerd time="2021-07-28T10:21:21.497642089Z" level=debug msg="attach: stdout: begin"
2021-07-28T10:21:21Z dockerd time="2021-07-28T10:21:21.497714291Z" level=debug msg="attach: stderr: begin"
2021-07-28T10:21:21Z dockerd time="2021-07-28T10:21:21.499798390Z" level=debug msg="Calling POST /v1.41/containers/35fc5ec0ffe1ad492d0a4fbf51fd6286a087b89d4dd66367fa3b7aec70b46a40/wait?condition=removed"
2021-07-28T10:21:21Z dockerd time="2021-07-28T10:21:21.518403686Z" level=debug msg="Calling GET /v1.41/containers/35fc5ec0ffe1ad492d0a4fbf51fd6286a087b89d4dd66367fa3b7aec70b46a40/json"
2021-07-28T10:21:21Z dockerd time="2021-07-28T10:21:21.527074928Z" level=debug msg="Calling POST /v1.41/containers/35fc5ec0ffe1ad492d0a4fbf51fd6286a087b89d4dd66367fa3b7aec70b46a40/start"
2021-07-28T10:21:21Z dockerd time="2021-07-28T10:21:21.528203579Z" level=debug msg="container mounted via layerStore: &{/var/lib/docker/overlay2/6e76ffecede030507fcaa576404e141e5f87fc4d7e1760e9ce5b52acb24
...
^C

Enable debugging

There are two ways to enable debugging. The recommended approach is to set the debug key to true in the daemon.json file. This method works for every Docker platform.

1. Edit the daemon.json file, which is usually located in /etc/docker/. You may need to create this file, if it doesn't yet exist. On macOS or Windows, don't edit the file directly. Instead, edit the file through the Docker Desktop settings.

2. If the file is empty, add the following:

   {
     "debug": true
   }

   If the file already contains JSON, just add the key "debug": true, being careful to add a comma to the end of the line if it's not the last line before the closing bracket. Also verify that if the log-level key is set, it's set to either info or debug. info is the default, and possible values are debug, info, warn, error, fatal.

3. Send a HUP signal to the daemon to cause it to reload its configuration. On Linux hosts, use the following command.

   $ sudo kill -SIGHUP $(pidof dockerd)
   

   On Windows hosts, restart Docker.

Instead of following this procedure, you can also stop the Docker daemon and restart it manually with the debug flag -D. However, this may result in Docker restarting with a different environment than the one the hosts' startup scripts create, and this may make debugging more difficult.

Force a stack trace to be logged

If the daemon is unresponsive, you can force a full stack trace to be logged by sending a SIGUSR1 signal to the daemon.

• Linux:

  $ sudo kill -SIGUSR1 $(pidof dockerd)
  

• Windows Server:

  Download docker-signal.

  Get the process ID of dockerd Get-Process dockerd.

  Run the executable with the flag --pid=<PID of daemon>.

This forces a stack trace to be logged but doesn't stop the daemon. Daemon logs show the stack trace or the path to a file containing the stack trace if it was logged to a file.

The daemon continues operating after handling the SIGUSR1 signal and dumping the stack traces to the log. The stack traces can be used to determine the state of all goroutines and threads within the daemon.

View stack traces

The Docker daemon log can be viewed by using one of the following methods:

• By running journalctl -u docker.service on Linux systems using systemctl
• /var/log/messages, /var/log/daemon.log, or /var/log/docker.log on older Linux systems

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It isn't possible to manually generate a stack trace on Docker Desktop for Mac or Docker Desktop for Windows. However, you can click the Docker taskbar icon and choose Troubleshoot to send information to Docker if you run into issues.

Look in the Docker logs for a message like the following:

...goroutine stacks written to /var/run/docker/goroutine-stacks-2017-06-02T193336z.log

The locations where Docker saves these stack traces and dumps depends on your operating system and configuration. You can sometimes get useful diagnostic information straight from the stack traces and dumps. Otherwise, you can provide this information to Docker for help diagnosing the problem.