logstash通过配置文件启动报错

刚刚开始学elk，请大家不要笑话。
按照ELK stack权威指南的书中写的通过elasticsearch官方仓库安装好elk后，通过配置文件启动时报错，请大家指导一下，谢谢，版本是5.6， 报错信息如下：
[root@localhost bin]# ./logstash -f logstash.conf
WARNING: Could not find logstash.yml which is typically located in $LS_HOME/config or /etc/logstash. You can specify the path using --path.settings. Continuing using the defaults
Could not find log4j2 configuration at path /usr/share/logstash/config/log4j2.properties. Using default config which logs errors to the console
[ERROR] 2018-01-02 21:37:02.846 [LogStash::Runner] elasticsearch - Unknown setting 'Rost' for elasticsearch
[ERROR] 2018-01-02 21:37:02.865 [LogStash::Runner] agent - Cannot create pipeline {:reason=>"Something is wrong with your configuration."}
 
配置文件如下：
input {
        stdin { }
}
output {
        stdout {
                codec => rubydebug{}
        }
        elasticsearch {
                Rost=>["127.0.0.1"]
        }
}