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Customize log driver output

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Customize log driver output

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The tag log option specifies how to format a tag that identifies the container's log messages. By default, the system uses the first 12 characters of the container ID. To override this behavior, specify a tag option:

$ docker run --log-driver=fluentd --log-opt fluentd-address=myhost.local:24224 --log-opt tag="mailer"

Docker supports some special template markup you can use when specifying a tag's value:

Markup	Description
{{.ID}}	The first 12 characters of the container ID.
{{.FullID}}	The full container ID.
{{.Name}}	The container name.
{{.ImageID}}	The first 12 characters of the container's image ID.
{{.ImageFullID}}	The container's full image ID.
{{.ImageName}}	The name of the image used by the container.
{{.DaemonName}}	The name of the Docker program (docker).

For example, specifying a --log-opt tag="{{.ImageName}}/{{.Name}}/{{.ID}}" value yields syslog log lines like:

Aug  7 18:33:19 HOSTNAME hello-world/foobar/5790672ab6a0[9103]: Hello from Docker.

At startup time, the system sets the container_name field and {{.Name}} in the tags. If you use docker rename to rename a container, the new name isn't reflected in the log messages. Instead, these messages continue to use the original container name.