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Docker logs dump to file

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Docker logs dump to file

1. Overview

In this article, we will learn to dump Docker logs into a file. You can learn more about Docker by following these articles.

2. Docker logs

You could have used docker logs to get the logs of the container.

> docker logs CONTAINER_ID
logs statements
>

Most of the time, we would want to capture docker logs in a file and debug.

3. Docker logs dump to file

3.1. Default docker log file

Docker by default stores logs in a log file. You can use the docker inspect command to return low-level information on the container.

To get the log path of a container instance, you can use the below command:

docker inspect --format='{{.LogPath}}' $INSTANCE_ID

For example, it retrieves the log path similar to below:

> docker inspect --format='{{.LogPath}}' dazzling_cray
/var/lib/docker/containers/36ef4edbf9898d9cc1abe13d8dd0916eff3b44a9e92fdd6f078842a7157e2258/36ef4edbf9898d9cc1abe13d8dd0916eff3b44a9e92fdd6f078842a7157e2258-json.log

You can use cat command to open the log file in your machine.

log file in linux folder – Windows host machine

A drawback of this approach is that the log statements are in JSON formats and may be less readable.

{"log":"Hi\n","stream":"stdout","time":"2022-12-22T02:27:01.5556507Z"}
{"log":"hihoi\n","stream":"stdout","time":"2022-12-22T03:49:48.9149033Z"}

3.2. Docker logs to dump a file

You can use docker logs to get logs of the container in the detached mode.

> docker logs -f 6d12d35591f4 &> output.log &
  • -f (i.e.--follow): writes all existing logs and follows logging everything that comes next.
  • &> redirects both the standard output and standard error to the file.
  • You can run in the background using the & at the end.
  • You can separate stdout and stderr by: > output.log 2> error.log (instead of using &>).
> docker logs -f 6d12d35591f4 > output.log 2> error.log

4. Conclusion

To sum up, we have learned to dump docker logs.

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