错误信息描述：
3405 -- main class information unavailable [root@master bin]# [2019-06-20T00:14:04,792][WARN ][o.e.b.ElasticsearchUncaughtExceptionHandler] [es1] 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:163) ~[elasticsearch-6.8.0.jar:6.8.0] at org.elasticsearch.bootstrap.Elasticsearch.execute(Elasticsearch.java:150) ~[elasticsearch-6.8.0.jar:6.8.0] at org.elasticsearch.cli.EnvironmentAwareCommand.execute(EnvironmentAwareCommand.java:86) ~[elasticsearch-6.8.0.jar:6.8.0] at org.elasticsearch.cli.Command.mainWithoutErrorHandling(Command.java:124) ~[elasticsearch-cli-6.8.0.jar:6.8.0] at org.elasticsearch.cli.Command.main(Command.java:90) ~[elasticsearch-cli-6.8.0.jar:6.8.0] at org.elasticsearch.bootstrap.Elasticsearch.main(Elasticsearch.java:116) ~[elasticsearch-6.8.0.jar:6.8.0] at org.elasticsearch.bootstrap.Elasticsearch.main(Elasticsearch.java:93) ~[elasticsearch-6.8.0.jar:6.8.0] Caused by: java.lang.RuntimeException: can not run elasticsearch as root at org.elasticsearch.bootstrap.Bootstrap.initializeNatives(Bootstrap.java:103) ~[elasticsearch-6.8.0.jar:6.8.0] at org.elasticsearch.bootstrap.Bootstrap.setup(Bootstrap.java:170) ~[elasticsearch-6.8.0.jar:6.8.0] at org.elasticsearch.bootstrap.Bootstrap.init(Bootstrap.java:333) ~[elasticsearch-6.8.0.jar:6.8.0] at org.elasticsearch.bootstrap.Elasticsearch.init(Elasticsearch.java:159) ~[elasticsearch-6.8.0.jar:6.8.0] ... 6 more
解决方法：
创建elsearch用户组及elsearch用户：
groupadd elsearch useradd elsearch -g elsearch passwd elsearch
更改elasticsearch文件夹及内部文件的所属用户及组为elsearch:elsearch
cd /opt chown -R elsearch:elsearch elasticsearch-6.8.0
切换到elsearch用户再启动
su elsearch cd /opt/elasticsearch-6.8.0/bin ./elasticsearch
