mirror of https://github.com/docker/docs.git
103 lines
3.3 KiB
Markdown
103 lines
3.3 KiB
Markdown
---
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description: Describes how to use the fluentd logging driver.
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keywords: Journald, docker, logging, driver
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redirect_from:
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- /engine/reference/logging/journald/
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title: Journald logging driver
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---
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The `journald` logging driver sends container logs to the
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[`systemd` journal](http://www.freedesktop.org/software/systemd/man/systemd-journald.service.html).
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Log entries can be retrieved using the `journalctl` command, through use of the
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`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 driver
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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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| `CONTAINER_PARTIAL_MESSAGE` | A field that flags log integrity. Improve logging of long log lines. |
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## Usage
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Configure the default logging driver by passing the `--log-driver` option to the
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Docker daemon:
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```bash
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$ dockerd --log-driver=journald
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```
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To configure the logging driver for a specific container, use the `--log-driver`
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flag on the `docker run` command.
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```bash
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$ docker run --log-driver=journald ...
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```
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## Options
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Use the `--log-opt NAME=VALUE` flag to specify additional `journald` logging
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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) to customize 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
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there is collision between `label` and `env` keys, the value of the `env` takes
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precedence. Each option adds additional metadata to the journal with each
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message.
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## Note regarding container names
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The value logged in the `CONTAINER_NAME` field is the name of the container that
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was set at startup. If you use `docker rename` to rename a container, the new
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name **is not reflected** in the journal entries. Journal entries will continue
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to use the original name.
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## Retrieving log messages with `journalctl`
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Use the `journalctl` command to retrieve log messages. You can apply filter
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expressions to limit the retrieved messages to those associated with a specific
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container:
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```bash
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$ sudo journalctl CONTAINER_NAME=webserver
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```
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You can use additional filters to further limit the messages retrieved. The `-b`
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flag only retrieves messages generated since the last system boot:
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```bash
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$ sudo journalctl -b CONTAINER_NAME=webserver
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```
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The `-o` flag specifies the format for the retried log messages. Use `-o json`
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to return the log messages in JSON format.
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```bash
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$ sudo journalctl -o json CONTAINER_NAME=webserver
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```
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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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```python
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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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```
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