ELK: start logstash fails, illegalstateexception - elasticsearch

Question

Since my server could not access internet. I downloaded filebeat, logstash, elasticsearch and kibana's rpm format files.
I use command rpm -Uvh xxx.rpm to install filebeat logstash elasticsearch and kibana. Then I modified configuration. For logstash, I updated pipelines.yml and copy it to /etc/logstash/conf.d directory.
The piplelines.yml is as follows:
input {
beats {
port => "5044"
}
}
filter {
grok {
match => {
"message" => [
"%{TIMESTAMP_ISO8601:timestamp} \[%{DATA:threadname}\] - %{LOGLEVEL:loglevel} - app-info-exception-info - params:%{SPACE}\{\"%{DATA:jsondata}\"\} %{DATA:excentionname}: %{DATA:exceptiondetail}\n(?m)%{GREEDYDATA:extralines}",
"(?<timestamp>[\d\-\s\:]+)\s\[(?<threadname>[\d\.\w\s\(\)\-]+)\]\s-\s(?<loglevel>[\w]+)\s+-\s(?<appinfo>app-info)\s-\s(?<systemmsg>[\w\d\:\{\}\,\-\(\)\s\"]+)",
"(?<timestamp>[\d\-\s\:]+)\s\[(?<threadname>[\d\.\w\s\(\)\-]+)\]\s-\s(?<loglevel>[\w]+)\s+-\s+(?<systemmsg>[\s\.\w\-\'\:\d\[\]\/]+)"
]
}
}
}
output {
#stdout { codec => rubydebug }
elasticsearch {
hosts => [ "localhost:9200" ]
index => "ykt"
}
}
From /var/log/, I could see filebeat, elasticsearch are fine. But in logstash's logstash-plain.log, there are error messages:
[2018-06-20T20:21:54,138][ERROR][org.logstash.Logstash ] java.lang.IllegalStateException: Logstash stopped processing because of an error: (SystemExit) exit
[2018-06-20T20:22:07,642][ERROR][org.logstash.Logstash ] java.lang.IllegalStateException: Logstash stopped processing because of an error: (SystemExit) exit
[2018-06-20T20:22:21,299][ERROR][org.logstash.Logstash ] java.lang.IllegalStateException: Logstash stopped processing because of an error: (SystemExit) exit
[2018-06-20T20:22:34,572][ERROR][org.logstash.Logstash ] java.lang.IllegalStateException: Logstash stopped processing because of an error: (SystemExit) exit
[2018-06-20T20:22:48,019][ERROR][org.logstash.Logstash ] java.lang.IllegalStateException: Logstash stopped processing because of an error: (SystemExit) exit
After updation yml/configuration, I do
systemctl daemon-reload
systemctl restart logstash
I do not why there is illegalStateException. Any help?