td agent execution log

$ /var/log/td-agent/td-agent.log
~ omission  ~
013-11-16 14:21:22 +0900 [info]: adding source type="forward"
2013-11-16 14:21:22 +0900 [info]: adding source type="http"
2013-11-16 14:21:22 +0900 [info]: adding source type="debug_agent"
2013-11-16 14:21:22 +0900 [info]: adding source type="tail"
2013-11-16 14:21:22 +0900 [warn]: 'pos_file PATH' parameter is not set to a 'tail' source.
2013-11-16 14:21:22 +0900 [warn]: this parameter is highly recommended to save the position to resume tailing.
2013-11-16 14:21:22 +0900 [info]: adding match pattern="td.*.*" type="tdlog"
2013-11-16 14:21:22 +0900 [info]: adding match pattern="debug.**" type="stdout"
2013-11-16 14:21:22 +0900 [info]: adding match pattern="mongo.**" type="mongo"
2013-11-16 14:21:22 +0900 [info]: adding match pattern="apache.access" type="file"
2013-11-16 14:21:22 +0900 [error]: unexpected error error_class=Mongo::ConnectionFailure error=#
  2013-11-16 14:21:22 +0900 [error]: /usr/lib64/fluent/ruby/lib/ruby/gems/1.9.1/gems/mongo-1.8.6/lib/mongo/networking.rb:167:in `receive_header'
~ omission  ~