org.elasticsearch.bootstrap.StartupException: java.lang.RuntimeException: can not run elasticsearch as root
        at org.elasticsearch.bootstrap.Elasticsearch.init(Elasticsearch.java:163) ~[elasticsearch-6.8.9.jar:6.8.9]
        at org.elasticsearch.bootstrap.Elasticsearch.execute(Elasticsearch.java:150) ~[elasticsearch-6.8.9.jar:6.8.9]
        at org.elasticsearch.cli.EnvironmentAwareCommand.execute(EnvironmentAwareCommand.java:86) ~[elasticsearch-6.8.9.jar:6.8.9]
        at org.elasticsearch.cli.Command.mainWithoutErrorHandling(Command.java:124) ~[elasticsearch-cli-6.8.9.jar:6.8.9]
        at org.elasticsearch.cli.Command.main(Command.java:90) ~[elasticsearch-cli-6.8.9.jar:6.8.9]
        at org.elasticsearch.bootstrap.Elasticsearch.main(Elasticsearch.java:116) ~[elasticsearch-6.8.9.jar:6.8.9]
        at org.elasticsearch.bootstrap.Elasticsearch.main(Elasticsearch.java:93) ~[elasticsearch-6.8.9.jar:6.8.9]
Caused by: java.lang.RuntimeException: can not run elasticsearch as root
        at org.elasticsearch.bootstrap.Bootstrap.initializeNatives(Bootstrap.java:103) ~[elasticsearch-6.8.9.jar:6.8.9]
        at org.elasticsearch.bootstrap.Bootstrap.setup(Bootstrap.java:170) ~[elasticsearch-6.8.9.jar:6.8.9]
        at org.elasticsearch.bootstrap.Bootstrap.init(Bootstrap.java:333) ~[elasticsearch-6.8.9.jar:6.8.9]
        at org.elasticsearch.bootstrap.Elasticsearch.init(Elasticsearch.java:159) ~[elasticsearch-6.8.9.jar:6.8.9]
        ... 6 more

在执行elasticSearch时加上参数-Des.insecure.allow.root=true，完整命令如下

./elasticsearch -Des.insecure.allow.root=true

#或者 用vi打开elasicsearch执行文件，在变量ES_JAVA_OPTS使用前添加以下命令

ES_JAVA_OPTS="-Des.insecure.allow.root=true"

adduser es
passwd es
chown -R es:es elasticsearch-6.8.9/
chmod 770 elasticsearch-6.8.9/
su es