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documenting rateLimit wich leads to the confusion of #28641 (#670) 

* documenting rateLimit which leads to the confusion of #28641
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Nils Otto Johansen 2016-12-19 20:15:45 +01:00 committed by Misty Stanley-Jones
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engine/admin/logging/journald.md
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title: Journald logging driver title: Journald logging driver
--- ---
The `journald` logging driver sends container logs to the [systemd The `journald` logging driver sends container logs to the
journal](http://www.freedesktop.org/software/systemd/man/systemd-journald.service.html). [`systemd` journal](http://www.freedesktop.org/software/systemd/man/systemd-journald.service.html).
Log entries can be retrieved using the `journalctl` command, through use of the Log entries can be retrieved using the `journalctl` command, through use of the
journal API, or using the `docker logs` command. `journal` API, or using the `docker logs` command.
In addition to the text of the log message itself, the `journald` log driver In addition to the text of the log message itself, the `journald` log driver
stores the following metadata in the journal with each message: stores the following metadata in the journal with each message:
@ -24,69 +24,91 @@ stores the following metadata in the journal with each message:
## Usage ## Usage
You can configure the default logging driver by passing the `--log-driver` Configure the default logging driver by passing the `--log-driver` option to the
option to the Docker daemon: Docker daemon:
dockerd --log-driver=journald ```bash
$ dockerd --log-driver=journald
```
You can set the logging driver for a specific container by using the To configure the logging driver for a specific container, use the `--log-driver`
`--log-driver` option to `docker run`: flag on the `docker run` command.
docker run --log-driver=journald ... ```bash
$ docker run --log-driver=journald ...
```
## Options ## Options
Users can use the `--log-opt NAME=VALUE` flag to specify additional journald Use the `--log-opt NAME=VALUE` flag to specify additional `journald` logging
logging driver options. driver options.
### tag ### `tag`
Specify template to set `CONTAINER_TAG` value in journald logs. Refer to Specify template to set `CONTAINER_TAG` value in `journald` logs. Refer to
[log tag option documentation](log_tags.md) for customizing the log tag format. [log tag option documentation](log_tags.md) to customize the log tag format.
### labels and env ### `labels` and `env`
The `labels` and `env` options each take a comma-separated list of keys. If 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 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 precedence. Each option adds additional metadata to the journal with each
message. message.
## Note regarding container names ## Note regarding container names
The value logged in the `CONTAINER_NAME` field is the container name that was The value logged in the `CONTAINER_NAME` field is the name of the container that
set at startup. If you use `docker rename` to rename a container, the new name was set at startup. If you use `docker rename` to rename a container, the new
will not be reflected in the journal entries. Journal entries will continue to name **is not reflected** in the journal entries. Journal entries will continue
use the original name. to use the original name.
## Retrieving log messages with journalctl ## Retrieving log messages with `journalctl`
You can use the `journalctl` command to retrieve log messages. You Use the `journalctl` command to retrieve log messages. You can apply filter
can apply filter expressions to limit the retrieved messages to a expressions to limit the retrieved messages to those associated with a specific
specific container. For example, to retrieve all log messages from a container:
container referenced by name:
# journalctl CONTAINER_NAME=webserver ```bash
$ sudo journalctl CONTAINER_NAME=webserver
```
You can make use of additional filters to further limit the messages You can use additional filters to further limit the messages retrieved. The `-b`
retrieved. For example, to see just those messages generated since flag only retrieves messages generated since the last system boot:
the system last booted:
# journalctl -b CONTAINER_NAME=webserver ```bash
$ sudo journalctl -b CONTAINER_NAME=webserver
```
Or to retrieve log messages in JSON format with complete metadata: The `-o` flag specifies the format for the retried log messages. Use `-o json`
to return the log messages in JSON format.
# journalctl -o json CONTAINER_NAME=webserver ```bash
$ sudo journalctl -o json CONTAINER_NAME=webserver
```
## Retrieving log messages with the journal API ## Retrieving log messages with the `journal` API
This example uses the `systemd` Python module to retrieve container This example uses the `systemd` Python module to retrieve container
logs: logs:
import systemd.journal ```python
import systemd.journal
reader = systemd.journal.Reader() reader = systemd.journal.Reader()
reader.add_match('CONTAINER_NAME=web') reader.add_match('CONTAINER_NAME=web')
for msg in reader: for msg in reader:
print '{CONTAINER_ID_FULL}: {MESSAGE}'.format(**msg) print '{CONTAINER_ID_FULL}: {MESSAGE}'.format(**msg)
```
## `journald` configuration
Docker hosts with many containers may produce large amounts of logging data.
By default, `journald` limits the number of messages stored per service per
time-unit.
If your application needs large-scale logging, configure `RateLimitIntervalSec`
and `RateLimitBurst` in the `journald` configuration file. By default,
`systemd` drops messages in excess of 1000 messages per service per 30 seconds.
For more information about configuring `journald`, see the
[`journald` documentation](https://www.freedesktop.org/software/systemd/man/journald.conf.html).