github.com/portworx/docker@v1.12.1/docs/admin/logging/log_tags.md (about) 1 <!--[metadata]> 2 +++ 3 aliases = ["/engine/reference/logging/log_tags/"] 4 title = "Log tags for logging driver" 5 description = "Describes how to format tags for." 6 keywords = ["docker, logging, driver, syslog, Fluentd, gelf, journald"] 7 [menu.main] 8 parent = "smn_logging" 9 weight = -1 10 +++ 11 <![end-metadata]--> 12 13 # Log Tags 14 15 The `tag` log option specifies how to format a tag that identifies the 16 container's log messages. By default, the system uses the first 12 characters of 17 the container id. To override this behavior, specify a `tag` option: 18 19 ``` 20 docker run --log-driver=fluentd --log-opt fluentd-address=myhost.local:24224 --log-opt tag="mailer" 21 ``` 22 23 Docker supports some special template markup you can use when specifying a tag's value: 24 25 | Markup | Description | 26 |--------------------|------------------------------------------------------| 27 | `{{.ID}}` | The first 12 characters of the container id. | 28 | `{{.FullID}}` | The full container id. | 29 | `{{.Name}}` | The container name. | 30 | `{{.ImageID}}` | The first 12 characters of the container's image id. | 31 | `{{.ImageFullID}}` | The container's full image identifier. | 32 | `{{.ImageName}}` | The name of the image used by the container. | 33 | `{{.DaemonName}}` | The name of the docker program (`docker`). | 34 35 For example, specifying a `--log-opt tag="{{.ImageName}}/{{.Name}}/{{.ID}}"` value yields `syslog` log lines like: 36 37 ``` 38 Aug 7 18:33:19 HOSTNAME docker/hello-world/foobar/5790672ab6a0[9103]: Hello from Docker. 39 ``` 40 41 At startup time, the system sets the `container_name` field and `{{.Name}}` in 42 the tags. If you use `docker rename` to rename a container, the new name is not 43 reflected in the log messages. Instead, these messages continue to use the 44 original container name. 45 46 For advanced usage, the generated tag's use [go 47 templates](http://golang.org/pkg/text/template/) and the container's [logging 48 context](https://github.com/docker/docker/blob/master/daemon/logger/context.go). 49 50 As an example of what is possible with the syslog logger: 51 52 ``` 53 $ docker run -it --rm \ 54 --log-driver syslog \ 55 --log-opt tag="{{ (.ExtraAttributes nil).SOME_ENV_VAR }}" \ 56 --log-opt env=SOME_ENV_VAR \ 57 -e SOME_ENV_VAR=logtester.1234 \ 58 flyinprogrammer/logtester 59 ``` 60 61 Results in logs like this: 62 63 ``` 64 Apr 1 15:22:17 ip-10-27-39-73 docker/logtester.1234[45499]: + exec app 65 Apr 1 15:22:17 ip-10-27-39-73 docker/logtester.1234[45499]: 2016-04-01 15:22:17.075416751 +0000 UTC stderr msg: 1 66 ``` 67