不要紧记 L 和 K ， E 。
那有什么用呢？可以正常运行的Elasticsearch安装需要什么？
=============安装硬件：
Raspberry Pi 3+
Raspbian GNU/Linux 9 (stretch)
=============通过apt安装：
sudo apt-get install elasticsearch
Setting up libelasticsearch1.7-java (1.7.5-1) ...
Setting up elasticsearch (1.7.5-1) ...
按照安装说明的说明，我去更改/etc/elasticsearch/elasticsearch.yml。
所有行均已注释，因此我取消注释3行，并按照说明添加了配置信息：
network.host: 0.0.0.0
http.port: 9200
path.logs: /var/log/elasticsearch
path.data: /var/lib/elasticsearch
=============根据安装，Elasticsearch正在作为服务运行：
$ sudo service elasticsearch status
● elasticsearch.service - LSB: Starts elasticsearch
Loaded: loaded (/etc/init.d/elasticsearch; generated; vendor preset: enabled)
Active: active (exited) since Tue 2019-05-21 02:53:17 PDT; 2min 52s ago
Docs: man:systemd-sysv-generator(8)
Process: 21421 ExecStop=/etc/init.d/elasticsearch stop (code=exited, status=0/SUCCESS)
Process: 21455 ExecStart=/etc/init.d/elasticsearch start (code=exited, status=0/SUCCESS)
May 21 02:53:17 xxxx systemd[1]: Starting LSB: Starts elasticsearch...
May 21 02:53:17 xxxx systemd[1]: Started LSB: Starts elasticsearch.
=============但未在活动连接中列出： $ sudo netstat -natp
[PRIVATE DATA]
=============测试安装：
$ curl http://localhost:9200
curl: (7) Failed to connect to localhost port 9200: Connection refused
没有日志文件：
$ sudo ls -l /var/{log,lib}/elasticsearch
/var/lib/elasticsearch:
total 0
/var/log/elasticsearch:
total 0
没有任何日志，就无法追踪任何内容。并设置log.path不会创建任何日志文件。