问题：

curl: (7) Failed to connect to walker001 port 9200: 拒绝连接

异常原因可查看logs目录下es_cluster.log进行查看

[2021-04-01T16:13:47,645][ERROR][o.e.b.Bootstrap          ] Exception
java.lang.RuntimeException: can not run elasticsearch as root
	at org.elasticsearch.bootstrap.Bootstrap.initializeNatives(Bootstrap.java:106) ~[elasticsearch-5.6.2.jar:5.6.2]
	at org.elasticsearch.bootstrap.Bootstrap.setup(Bootstrap.java:195) ~[elasticsearch-5.6.2.jar:5.6.2]
	at org.elasticsearch.bootstrap.Bootstrap.init(Bootstrap.java:342) [elasticsearch-5.6.2.jar:5.6.2]
	at org.elasticsearch.bootstrap.Elasticsearch.init(Elasticsearch.java:132) [elasticsearch-5.6.2.jar:5.6.2]
	at org.elasticsearch.bootstrap.Elasticsearch.execute(Elasticsearch.java:123) [elasticsearch-5.6.2.jar:5.6.2]
	at org.elasticsearch.cli.EnvironmentAwareCommand.execute(EnvironmentAwareCommand.java:67) [elasticsearch-5.6.2.jar:5.6.2]
	at org.elasticsearch.cli.Command.mainWithoutErrorHandling(Command.java:134) [elasticsearch-5.6.2.jar:5.6.2]
	at org.elasticsearch.cli.Command.main(Command.java:90) [elasticsearch-5.6.2.jar:5.6.2]
	at org.elasticsearch.bootstrap.Elasticsearch.main(Elasticsearch.java:91) [elasticsearch-5.6.2.jar:5.6.2]
	at org.elasticsearch.bootstrap.Elasticsearch.main(Elasticsearch.java:84) [elasticsearch-5.6.2.jar:5.6.2]
[2021-04-01T16:13:47,651][WARN ][o.e.b.ElasticsearchUncaughtExceptionHandler] [es-node] 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:136) ~[elasticsearch-5.6.2.jar:5.6.2]
	at org.elasticsearch.bootstrap.Elasticsearch.execute(Elasticsearch.java:123) ~[elasticsearch-5.6.2.jar:5.6.2]
	at org.elasticsearch.cli.EnvironmentAwareCommand.execute(EnvironmentAwareCommand.java:67) ~[elasticsearch-5.6.2.jar:5.6.2]
	at org.elasticsearch.cli.Command.mainWithoutErrorHandling(Command.java:134) ~[elasticsearch-5.6.2.jar:5.6.2]
	at org.elasticsearch.cli.Command.main(Command.java:90) ~[elasticsearch-5.6.2.jar:5.6.2]
	at org.elasticsearch.bootstrap.Elasticsearch.main(Elasticsearch.java:91) ~[elasticsearch-5.6.2.jar:5.6.2]
	at org.elasticsearch.bootstrap.Elasticsearch.main(Elasticsearch.java:84) ~[elasticsearch-5.6.2.jar:5.6.2]
Caused by: java.lang.RuntimeException: can not run elasticsearch as root
	at org.elasticsearch.bootstrap.Bootstrap.initializeNatives(Bootstrap.java:106) ~[elasticsearch-5.6.2.jar:5.6.2]
	at org.elasticsearch.bootstrap.Bootstrap.setup(Bootstrap.java:195) ~[elasticsearch-5.6.2.jar:5.6.2]
	at org.elasticsearch.bootstrap.Bootstrap.init(Bootstrap.java:342) ~[elasticsearch-5.6.2.jar:5.6.2]
	at org.elasticsearch.bootstrap.Elasticsearch.init(Elasticsearch.java:132) ~[elasticsearch-5.6.2.jar:5.6.2]
	... 6 more
[2021-04-01T16:14:06,387][ERROR][o.e.b.Bootstrap          ] Exception
java.lang.RuntimeException: can not run elasticsearch as root
	at org.elasticsearch.bootstrap.Bootstrap.initializeNatives(Bootstrap.java:106) ~[elasticsearch-5.6.2.jar:5.6.2]
	at org.elasticsearch.bootstrap.Bootstrap.setup(Bootstrap.java:195) ~[elasticsearch-5.6.2.jar:5.6.2]
	at org.elasticsearch.bootstrap.Bootstrap.init(Bootstrap.java:342) [elasticsearch-5.6.2.jar:5.6.2]
	at org.elasticsearch.bootstrap.Elasticsearch.init(Elasticsearch.java:132) [elasticsearch-5.6.2.jar:5.6.2]
	at org.elasticsearch.bootstrap.Elasticsearch.execute(Elasticsearch.java:123) [elasticsearch-5.6.2.jar:5.6.2]
	at org.elasticsearch.cli.EnvironmentAwareCommand.execute(EnvironmentAwareCommand.java:67) [elasticsearch-5.6.2.jar:5.6.2]
	at org.elasticsearch.cli.Command.mainWithoutErrorHandling(Command.java:134) [elasticsearch-5.6.2.jar:5.6.2]
	at org.elasticsearch.cli.Command.main(Command.java:90) [elasticsearch-5.6.2.jar:5.6.2]
	at org.elasticsearch.bootstrap.Elasticsearch.main(Elasticsearch.java:91) [elasticsearch-5.6.2.jar:5.6.2]
	at org.elasticsearch.bootstrap.Elasticsearch.main(Elasticsearch.java:84) [elasticsearch-5.6.2.jar:5.6.2]
[2021-04-01T16:14:06,393][WARN ][o.e.b.ElasticsearchUncaughtExceptionHandler] [es-node] 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:136) ~[elasticsearch-5.6.2.jar:5.6.2]
	at org.elasticsearch.bootstrap.Elasticsearch.execute(Elasticsearch.java:123) ~[elasticsearch-5.6.2.jar:5.6.2]
	at org.elasticsearch.cli.EnvironmentAwareCommand.execute(EnvironmentAwareCommand.java:67) ~[elasticsearch-5.6.2.jar:5.6.2]
	at org.elasticsearch.cli.Command.mainWithoutErrorHandling(Command.java:134) ~[elasticsearch-5.6.2.jar:5.6.2]
	at org.elasticsearch.cli.Command.main(Command.java:90) ~[elasticsearch-5.6.2.jar:5.6.2]
	at org.elasticsearch.bootstrap.Elasticsearch.main(Elasticsearch.java:91) ~[elasticsearch-5.6.2.jar:5.6.2]
	at org.elasticsearch.bootstrap.Elasticsearch.main(Elasticsearch.java:84) ~[elasticsearch-5.6.2.jar:5.6.2]
Caused by: java.lang.RuntimeException: can not run elasticsearch as root
	at org.elasticsearch.bootstrap.Bootstrap.initializeNatives(Bootstrap.java:106) ~[elasticsearch-5.6.2.jar:5.6.2]
	at org.elasticsearch.bootstrap.Bootstrap.setup(Bootstrap.java:195) ~[elasticsearch-5.6.2.jar:5.6.2]
	at org.elasticsearch.bootstrap.Bootstrap.init(Bootstrap.java:342) ~[elasticsearch-5.6.2.jar:5.6.2]
	at org.elasticsearch.bootstrap.Elasticsearch.init(Elasticsearch.java:132) ~[elasticsearch-5.6.2.jar:5.6.2]
	... 6 more
[2021-04-01T16:20:20,476][ERROR][o.e.b.Bootstrap          ] Exception
java.lang.RuntimeException: can not run elasticsearch as root
	at org.elasticsearch.bootstrap.Bootstrap.initializeNatives(Bootstrap.java:106) ~[elasticsearch-5.6.2.jar:5.6.2]
	at org.elasticsearch.bootstrap.Bootstrap.setup(Bootstrap.java:195) ~[elasticsearch-5.6.2.jar:5.6.2]
	at org.elasticsearch.bootstrap.Bootstrap.init(Bootstrap.java:342) [elasticsearch-5.6.2.jar:5.6.2]
	at org.elasticsearch.bootstrap.Elasticsearch.init(Elasticsearch.java:132) [elasticsearch-5.6.2.jar:5.6.2]
	at org.elasticsearch.bootstrap.Elasticsearch.execute(Elasticsearch.java:123) [elasticsearch-5.6.2.jar:5.6.2]
	at org.elasticsearch.cli.EnvironmentAwareCommand.execute(EnvironmentAwareCommand.java:67) [elasticsearch-5.6.2.jar:5.6.2]
	at org.elasticsearch.cli.Command.mainWithoutErrorHandling(Command.java:134) [elasticsearch-5.6.2.jar:5.6.2]
	at org.elasticsearch.cli.Command.main(Command.java:90) [elasticsearch-5.6.2.jar:5.6.2]
	at org.elasticsearch.bootstrap.Elasticsearch.main(Elasticsearch.java:91) [elasticsearch-5.6.2.jar:5.6.2]
	at org.elasticsearch.bootstrap.Elasticsearch.main(Elasticsearch.java:84) [elasticsearch-5.6.2.jar:5.6.2]
[2021-04-01T16:20:20,481][WARN ][o.e.b.ElasticsearchUncaughtExceptionHandler] [es-node] 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:136) ~[elasticsearch-5.6.2.jar:5.6.2]
	at org.elasticsearch.bootstrap.Elasticsearch.execute(Elasticsearch.java:123) ~[elasticsearch-5.6.2.jar:5.6.2]
	at org.elasticsearch.cli.EnvironmentAwareCommand.execute(EnvironmentAwareCommand.java:67) ~[elasticsearch-5.6.2.jar:5.6.2]
	at org.elasticsearch.cli.Command.mainWithoutErrorHandling(Command.java:134) ~[elasticsearch-5.6.2.jar:5.6.2]
	at org.elasticsearch.cli.Command.main(Command.java:90) ~[elasticsearch-5.6.2.jar:5.6.2]
	at org.elasticsearch.bootstrap.Elasticsearch.main(Elasticsearch.java:91) ~[elasticsearch-5.6.2.jar:5.6.2]
	at org.elasticsearch.bootstrap.Elasticsearch.main(Elasticsearch.java:84) ~[elasticsearch-5.6.2.jar:5.6.2]
Caused by: java.lang.RuntimeException: can not run elasticsearch as root
	at org.elasticsearch.bootstrap.Bootstrap.initializeNatives(Bootstrap.java:106) ~[elasticsearch-5.6.2.jar:5.6.2]
	at org.elasticsearch.bootstrap.Bootstrap.setup(Bootstrap.java:195) ~[elasticsearch-5.6.2.jar:5.6.2]
	at org.elasticsearch.bootstrap.Bootstrap.init(Bootstrap.java:342) ~[elasticsearch-5.6.2.jar:5.6.2]
	at org.elasticsearch.bootstrap.Elasticsearch.init(Elasticsearch.java:132) ~[elasticsearch-5.6.2.jar:5.6.2]
	... 6 more

主要问题：

[ERROR][o.e.b.Bootstrap          ] Exception
java.lang.RuntimeException: can not run elasticsearch as root

无法以根用户身份运行elasticsearch
说明安装的时候把程序安装在了root目录下，可以卸载使用普通用户重新安装，问题解决。

安装软件能用普通用户安装的尽量不要用root用户，如果普通用户进行了误操作，root用户可以救你一命。