一、错误信息如下（意思是不能用root用户来启动，我们新建一个用户来启动）
[2019-49-07T19:43:10,628][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:127) ~[elasticsearch-5.5.2.jar:5.5.2]
at org.elasticsearch.bootstrap.Elasticsearch.execute(Elasticsearch.java:114) ~[elasticsearch-5.5.2.jar:5.5.2]
at org.elasticsearch.cli.EnvironmentAwareCommand.execute(EnvironmentAwareCommand.java:67) ~[elasticsearch-5.5.2.jar:5.5.2]
at org.elasticsearch.cli.Command.mainWithoutErrorHandling(Command.java:122) ~[elasticsearch-5.5.2.jar:5.5.2]
at org.elasticsearch.cli.Command.main(Command.java:88) ~[elasticsearch-5.5.2.jar:5.5.2]
at org.elasticsearch.bootstrap.Elasticsearch.main(Elasticsearch.java:91) ~[elasticsearch-5.5.2.jar:5.5.2]
at org.elasticsearch.bootstrap.Elasticsearch.main(Elasticsearch.java:84) ~[elasticsearch-5.5.2.jar:5.5.2]
Caused by: java.lang.RuntimeException: can not run elasticsearch as root
at org.elasticsearch.bootstrap.Bootstrap.initializeNatives(Bootstrap.java:106) ~[elasticsearch-5.5.2.jar:5.5.2]
at org.elasticsearch.bootstrap.Bootstrap.setup(Bootstrap.java:194) ~[elasticsearch-5.5.2.jar:5.5.2]
at org.elasticsearch.bootstrap.Bootstrap.init(Bootstrap.java:351) ~[elasticsearch-5.5.2.jar:5.5.2]
at org.elasticsearch.bootstrap.Elasticsearch.init(Elasticsearch.java:123) ~[elasticsearch-5.5.2.jar:5.5.2]
... 6 more
二、、解决步骤如下：
1、新建一个elastic用户
[root@ ~]# useradd elastic
2、把目录权限赋予给elastic 用户
[root@ ~]# chown -R elastic:elastic /software/elastic/elasticsearch-5.5.2/
3、切换成elastic用户，然后执行elasticsearch
[root@~]# su elastic
[elastic@ root]$ sh /software/elastic/elasticsearch-5.5.2/bin/elasticsearch
