service logs reference documentation

Signed-off-by: Andrea Luzzardi <aluzzardi@gmail.com>

docs/reference/commandline/service_logs.md

@@ -0,0 +1,67 @@
+---
+title: "service logs (experimental)"
+description: "The service logs command description and usage"
+keywords: "service, logs"
+advisory: "experimental"
+---
+
+<!-- This file is maintained within the docker/docker Github
+     repository at https://github.com/docker/docker/. Make all
+     pull requests against that repo. If you see this file in
+     another repository, consider it read-only there, as it will
+     periodically be overwritten by the definitive file. Pull
+     requests which include edits to this file in other repositories
+     will be rejected.
+-->
+
+# service logs
+
+```Markdown
+Usage:  docker service logs [OPTIONS] SERVICE
+
+Fetch the logs of a service
+
+Options:
+      --details        Show extra details provided to logs
+  -f, --follow         Follow log output
+      --help           Print usage
+      --since string   Show logs since timestamp
+      --tail string    Number of lines to show from the end of the logs (default "all")
+  -t, --timestamps     Show timestamps
+```
+
+The `docker service logs` command batch-retrieves logs present at the time of execution.
+
+> **Note**: this command is only functional for services that are started with
+> the `json-file` or `journald` logging driver.
+
+For more information about selecting and configuring login-drivers, refer to
+[Configure logging drivers](https://docs.docker.com/engine/admin/logging/overview/).
+
+The `docker service logs --follow` command will continue streaming the new output from
+the service's `STDOUT` and `STDERR`.
+
+Passing a negative number or a non-integer to `--tail` is invalid and the
+value is set to `all` in that case.
+
+The `docker service logs --timestamps` command will add an [RFC3339Nano timestamp](https://golang.org/pkg/time/#pkg-constants)
+, for example `2014-09-16T06:17:46.000000000Z`, to each
+log entry. To ensure that the timestamps are aligned the
+nano-second part of the timestamp will be padded with zero when necessary.
+
+The `docker service logs --details` command will add on extra attributes, such as
+environment variables and labels, provided to `--log-opt` when creating the
+service.
+
+The `--since` option shows only the service logs generated after
+a given date. You can specify the date as an RFC 3339 date, a UNIX
+timestamp, or a Go duration string (e.g. `1m30s`, `3h`). Besides RFC3339 date
+format you may also use RFC3339Nano, `2006-01-02T15:04:05`,
+`2006-01-02T15:04:05.999999999`, `2006-01-02Z07:00`, and `2006-01-02`. The local
+timezone on the client will be used if you do not provide either a `Z` or a
+`+-00:00` timezone offset at the end of the timestamp. When providing Unix
+timestamps enter seconds[.nanoseconds], where seconds is the number of seconds
+that have elapsed since January 1, 1970 (midnight UTC/GMT), not counting leap
+seconds (aka Unix epoch or Unix time), and the optional .nanoseconds field is a
+fraction of a second no more than nine digits long. You can combine the
+`--since` option with either or both of the `--follow` or `--tail` options.