原因：
為了安全不允許使用root用戶啟動
解決：
es5之后的都不能使用添加啟動參數或者修改配置文件等方法啟動了，必須要創建用戶
問題：
es安裝好之后，使用root啟動會報錯：can not run elasticsearch as root
[root@iZbp1bb2egi7w0ueys548pZ bin]# ./elasticsearch
[2019-01-21T09:50:59,387][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:134) ~[elasticsearch-6.0.0.jar:6.0.0]
at org.elasticsearch.bootstrap.Elasticsearch.execute(Elasticsearch.java:121) ~[elasticsearch-6.0.0.jar:6.0.0]
at org.elasticsearch.cli.EnvironmentAwareCommand.execute(EnvironmentAwareCommand.java:69) ~[elasticsearch-6.0.0.jar:6.0.0]
at org.elasticsearch.cli.Command.mainWithoutErrorHandling(Command.java:134) ~[elasticsearch-6.0.0.jar:6.0.0]
at org.elasticsearch.cli.Command.main(Command.java:90) ~[elasticsearch-6.0.0.jar:6.0.0]
at org.elasticsearch.bootstrap.Elasticsearch.main(Elasticsearch.java:92) ~[elasticsearch-6.0.0.jar:6.0.0]
at org.elasticsearch.bootstrap.Elasticsearch.main(Elasticsearch.java:85) ~[elasticsearch-6.0.0.jar:6.0.0]
Caused by: java.lang.RuntimeException: can not run elasticsearch as root
at org.elasticsearch.bootstrap.Bootstrap.initializeNatives(Bootstrap.java:104) ~[elasticsearch-6.0.0.jar:6.0.0]
at org.elasticsearch.bootstrap.Bootstrap.setup(Bootstrap.java:171) ~[elasticsearch-6.0.0.jar:6.0.0]
at org.elasticsearch.bootstrap.Bootstrap.init(Bootstrap.java:322) ~[elasticsearch-6.0.0.jar:6.0.0]
at org.elasticsearch.bootstrap.Elasticsearch.init(Elasticsearch.java:130) ~[elasticsearch-6.0.0.jar:6.0.0]
... 6 more
1、創建用戶：elasticsearch
[root@iZbp1bb2egi7w0ueys548pZ bin]# adduser elasticsearch
2、創建用戶密碼，需要輸入兩次
[root@iZbp1bb2egi7w0ueys548pZ bin]# passwd elasticsearch
3、將對應的文件夾權限賦給該用戶
[root@iZbp1bb2egi7w0ueys548pZ local]# chown -R elasticsearch elasticsearch-6.0.0
4、切換至elasticsearch用戶
[root@iZbp1bb2egi7w0ueys548pZ etc]# su elasticsearch
5、進入啟動目錄啟動 /usr/local/elasticsearch-6.0.0/bin 使用后台啟動方式：./elasticsearch -d
[elasticsearch@vmt10003 bin]$ ./elasticsearch -d
6、啟動后測試
輸入curl ip:9200,如果返回一個json數據說明啟動成功