centos 启动 elasticsearch 失败集

环境： elasticsearch 6.5.2, java

连接失败

启动后当你 使用 curl http://localhost:9200 测试时，得到如下结果

Curl: (7) Failed connect to localhost:9200; Connection refused

这个问题一般是其他问题导致的，请看你启动日志，如果用的管理服务工具来启动的，则看它的日志，我这里是 systemctl ，然后命令以及输出结果是

root@localhost ~]# systemctl status elasticsearch
● elasticsearch.service - Elasticsearch
   Loaded: loaded (/usr/lib/systemd/system/elasticsearch.service; enabled; vendor preset: disabled)
   Active: failed (Result: exit-code) since Mon 2018-12-10 15:26:08 EST; 11min ago
     Docs: http://www.elastic.co
  Process: 22651 ExecStart=/usr/share/elasticsearch/bin/elasticsearch -p ${PID_DIR}/elasticsearch.pid --quiet (code=exited, status=1/FAILURE)
 Main PID: 22651 (code=exited, status=1/FAILURE)

Dec 10 15:26:08 localhost.localdomain systemd[1]: Started Elasticsearch.
Dec 10 15:26:08 localhost.localdomain systemd[1]: Starting Elasticsearch...
Dec 10 15:26:08 localhost.localdomain elasticsearch[22651]: which: no java in (/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin)
Dec 10 15:26:08 localhost.localdomain elasticsearch[22651]: could not find java; set JAVA_HOME or ensure java is in PATH
Dec 10 15:26:08 localhost.localdomain systemd[1]: elasticsearch.service: main process exited, code=exited, status=1/FAILURE
Dec 10 15:26:08 localhost.localdomain systemd[1]: Unit elasticsearch.service entered failed state.
Dec 10 15:26:08 localhost.localdomain systemd[1]: elasticsearch.service failed.

没有发现 java 环境

如上图错误细节，告诉我们没有java 相关环境，首先确认下 是否能 运行 java，不过不能，请配置Java环境然后source,具体请百度。

解决了java 环境问题，还需要将 java 可执行命令 放到 /usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin 下的任意一个中， 这里放到 /usr/bin

命令： ln -s /usr/local/jdk1.8.0_XXX/bin/java /usr/bin/java