github.com/jogo/docker@v1.7.0-rc1/docs/sources/reference/logging/journald.md (about)

     1  # Journald logging driver
     2  
     3  The `journald` logging driver sends container logs to the [systemd
     4  journal](http://www.freedesktop.org/software/systemd/man/systemd-journald.service.html).  Log entries can be retrieved using the `journalctl`
     5  command or through use of the journal API.
     6  
     7  In addition to the text of the log message itself, the `journald` log
     8  driver stores the following metadata in the journal with each message:
     9  
    10  | Field               | Description |
    11  ----------------------|-------------|
    12  | `CONTAINER_ID`      | The container ID truncated to 12 characters. |
    13  | `CONTAINER_ID_FULL` | The full 64-character container ID. |
    14  | `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. |
    15  
    16  ## Usage
    17  
    18  You can configure the default logging driver by passing the
    19  `--log-driver` option to the Docker daemon:
    20  
    21      docker --log-driver=journald
    22  
    23  You can set the logging driver for a specific container by using the
    24  `--log-driver` option to `docker run`:
    25  
    26      docker run --log-driver=journald ...
    27  
    28  ## Note regarding container names
    29  
    30  The value logged in the `CONTAINER_NAME` field is the container name
    31  that was set at startup.  If you use `docker rename` to rename a
    32  container, the new name will not be reflected in the journal entries.
    33  Journal entries will continue to use the original name.
    34  
    35  ## Retrieving log messages with journalctl
    36  
    37  You can use the `journalctl` command to retrieve log messages.  You
    38  can apply filter expressions to limit the retrieved messages to a
    39  specific container.  For example, to retrieve all log messages from a
    40  container referenced by name:
    41  
    42      # journalctl CONTAINER_NAME=webserver
    43  
    44  You can make use of additional filters to further limit the messages
    45  retrieved.  For example, to see just those messages generated since
    46  the system last booted:
    47  
    48      # journalctl -b CONTAINER_NAME=webserver
    49  
    50  Or to retrieve log messages in JSON format with complete metadata:
    51  
    52      # journalctl -o json CONTAINER_NAME=webserver
    53  
    54  ## Retrieving log messages with the journal API
    55  
    56  This example uses the `systemd` Python module to retrieve container
    57  logs:
    58  
    59      import systemd.journal
    60  
    61      reader = systemd.journal.Reader()
    62      reader.add_match('CONTAINER_NAME=web')
    63  
    64      for msg in reader:
    65        print '{CONTAINER_ID_FULL}: {MESSAGE}'.format(**msg)
    66