[2019-03-18T22:24:21,549][WARN ][o.e.b.ElasticsearchUncaughtExceptionHandler] [] uncaught exception in thread [main]
org.elasticsearch.bootstrap.StartupException: java.lang.RuntimeException: can not run elasticsearch as root
	at org.elasticsearch.bootstrap.Elasticsearch.init(Elasticsearch.java:125) ~[elasticsearch-6.2.4.jar:6.2.4]
	at org.elasticsearch.bootstrap.Elasticsearch.execute(Elasticsearch.java:112) ~[elasticsearch-6.2.4.jar:6.2.4]
	at org.elasticsearch.cli.EnvironmentAwareCommand.execute(EnvironmentAwareCommand.java:86) ~[elasticsearch-6.2.4.jar:6.2.4]
	at org.elasticsearch.cli.Command.mainWithoutErrorHandling(Command.java:124) ~[elasticsearch-cli-6.2.4.jar:6.2.4]
	at org.elasticsearch.cli.Command.main(Command.java:90) ~[elasticsearch-cli-6.2.4.jar:6.2.4]
	at org.elasticsearch.bootstrap.Elasticsearch.main(Elasticsearch.java:92) ~[elasticsearch-6.2.4.jar:6.2.4]
	at org.elasticsearch.bootstrap.Elasticsearch.main(Elasticsearch.java:85) ~[elasticsearch-6.2.4.jar:6.2.4]
Caused by: java.lang.RuntimeException: can not run elasticsearch as root
	at org.elasticsearch.bootstrap.Bootstrap.initializeNatives(Bootstrap.java:105) ~[elasticsearch-6.2.4.jar:6.2.4]
	at org.elasticsearch.bootstrap.Bootstrap.setup(Bootstrap.java:172) ~[elasticsearch-6.2.4.jar:6.2.4]
	at org.elasticsearch.bootstrap.Bootstrap.init(Bootstrap.java:323) ~[elasticsearch-6.2.4.jar:6.2.4]
	at org.elasticsearch.bootstrap.Elasticsearch.init(Elasticsearch.java:121) ~[elasticsearch-6.2.4.jar:6.2.4]
	... 6 more

解决方案：ElasticSearch为了安全起见，不允许以root用户登录，切换其他系统用户即可