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92 lines
3.2 KiB
Markdown
92 lines
3.2 KiB
Markdown
<!--[metadata]>
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+++
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aliases = ["/engine/reference/logging/journald/"]
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title = "journald logging driver"
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description = "Describes how to use the fluentd logging driver."
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keywords = ["Fluentd, docker, logging, driver"]
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[menu.main]
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parent = "smn_logging"
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weight = 2
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+++
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<![end-metadata]-->
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# Journald logging driver
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The `journald` logging driver sends container logs to the [systemd
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journal](http://www.freedesktop.org/software/systemd/man/systemd-journald.service.html). Log entries can be retrieved using the `journalctl`
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command, through use of the journal API, or using the `docker logs` command.
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In addition to the text of the log message itself, the `journald` log
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driver stores the following metadata in the journal with each message:
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| Field | Description |
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----------------------|-------------|
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| `CONTAINER_ID` | The container ID truncated to 12 characters. |
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| `CONTAINER_ID_FULL` | The full 64-character container ID. |
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| `CONTAINER_NAME` | The container name at the time it was started. If you use `docker rename` to rename a container, the new name is not reflected in the journal entries. |
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| `CONTAINER_TAG` | The container tag ([log tag option documentation](log_tags.md)). |
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## Usage
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You can configure the default logging driver by passing the
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`--log-driver` option to the Docker daemon:
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docker daemon --log-driver=journald
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You can set the logging driver for a specific container by using the
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`--log-driver` option to `docker run`:
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docker run --log-driver=journald ...
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## Options
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Users can use the `--log-opt NAME=VALUE` flag to specify additional
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journald logging driver options.
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### tag
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Specify template to set `CONTAINER_TAG` value in journald logs. Refer to
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[log tag option documentation](log_tags.md) for customizing the log tag format.
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### labels and env
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The `labels` and `env` options each take a comma-separated list of keys. If there is collision between `label` and `env` keys, the value of the `env` takes precedence. Both options add additional metadata in the journal with each message.
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## Note regarding container names
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The value logged in the `CONTAINER_NAME` field is the container name
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that was set at startup. If you use `docker rename` to rename a
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container, the new name will not be reflected in the journal entries.
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Journal entries will continue to use the original name.
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## Retrieving log messages with journalctl
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You can use the `journalctl` command to retrieve log messages. You
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can apply filter expressions to limit the retrieved messages to a
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specific container. For example, to retrieve all log messages from a
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container referenced by name:
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# journalctl CONTAINER_NAME=webserver
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You can make use of additional filters to further limit the messages
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retrieved. For example, to see just those messages generated since
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the system last booted:
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# journalctl -b CONTAINER_NAME=webserver
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Or to retrieve log messages in JSON format with complete metadata:
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# journalctl -o json CONTAINER_NAME=webserver
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## Retrieving log messages with the journal API
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This example uses the `systemd` Python module to retrieve container
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logs:
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import systemd.journal
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reader = systemd.journal.Reader()
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reader.add_match('CONTAINER_NAME=web')
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for msg in reader:
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print '{CONTAINER_ID_FULL}: {MESSAGE}'.format(**msg)
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