Logstash Embedded ElasticSearch Logging config

Elastic Stack Elasticsearch
1

I am using logstash1.4.1 and config the output to embedded elasticsearch like this :
output {
elasticsearch {
embedded => true
index => "logstash-%{type}"
}
}
I also add -Des.path.conf=<diretory path of elasticsearch.yml/logging.yml files> as one of the parameters to start logstash.
In the elasticsearch.yml , I have configure the path.data, path.conf ,path.logs . And the index data can be created in the <path.data> , but the logs can not be created in the <path.logs>.
How can I make the embedded elasticsearch output its logs to my indicated file ?

Thanks !
Pete