github.com/portworx/docker@v1.12.1/docs/admin/logging/journald.md (about) 1 <!--[metadata]> 2 +++ 3 aliases = ["/engine/reference/logging/journald/"] 4 title = "Journald logging driver" 5 description = "Describes how to use the fluentd logging driver." 6 keywords = ["Journald, docker, logging, driver"] 7 [menu.main] 8 parent = "smn_logging" 9 +++ 10 <![end-metadata]--> 11 12 # Journald logging driver 13 14 The `journald` logging driver sends container logs to the [systemd 15 journal](http://www.freedesktop.org/software/systemd/man/systemd-journald.service.html). Log entries can be retrieved using the `journalctl` 16 command, through use of the journal API, or using the `docker logs` command. 17 18 In addition to the text of the log message itself, the `journald` log 19 driver stores the following metadata in the journal with each message: 20 21 | Field | Description | 22 ----------------------|-------------| 23 | `CONTAINER_ID` | The container ID truncated to 12 characters. | 24 | `CONTAINER_ID_FULL` | The full 64-character container ID. | 25 | `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. | 26 | `CONTAINER_TAG` | The container tag ([log tag option documentation](log_tags.md)). | 27 28 ## Usage 29 30 You can configure the default logging driver by passing the 31 `--log-driver` option to the Docker daemon: 32 33 docker daemon --log-driver=journald 34 35 You can set the logging driver for a specific container by using the 36 `--log-driver` option to `docker run`: 37 38 docker run --log-driver=journald ... 39 40 ## Options 41 42 Users can use the `--log-opt NAME=VALUE` flag to specify additional 43 journald logging driver options. 44 45 ### tag 46 47 Specify template to set `CONTAINER_TAG` value in journald logs. Refer to 48 [log tag option documentation](log_tags.md) for customizing the log tag format. 49 50 ### labels and env 51 52 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. 53 54 ## Note regarding container names 55 56 The value logged in the `CONTAINER_NAME` field is the container name 57 that was set at startup. If you use `docker rename` to rename a 58 container, the new name will not be reflected in the journal entries. 59 Journal entries will continue to use the original name. 60 61 ## Retrieving log messages with journalctl 62 63 You can use the `journalctl` command to retrieve log messages. You 64 can apply filter expressions to limit the retrieved messages to a 65 specific container. For example, to retrieve all log messages from a 66 container referenced by name: 67 68 # journalctl CONTAINER_NAME=webserver 69 70 You can make use of additional filters to further limit the messages 71 retrieved. For example, to see just those messages generated since 72 the system last booted: 73 74 # journalctl -b CONTAINER_NAME=webserver 75 76 Or to retrieve log messages in JSON format with complete metadata: 77 78 # journalctl -o json CONTAINER_NAME=webserver 79 80 ## Retrieving log messages with the journal API 81 82 This example uses the `systemd` Python module to retrieve container 83 logs: 84 85 import systemd.journal 86 87 reader = systemd.journal.Reader() 88 reader.add_match('CONTAINER_NAME=web') 89 90 for msg in reader: 91 print '{CONTAINER_ID_FULL}: {MESSAGE}'.format(**msg)