elasticsearch之JAVA環境變量報錯：could not find java; set JAVA_HOME or ensure java is in PATH

在以RPM包安裝elasticsearch過程中出現報錯JAVA環境的問題：

● elasticsearch.service - Elasticsearch
   Loaded: loaded (/usr/lib/systemd/system/elasticsearch.service; enabled; vendor preset: disabled)
   Active: failed (Result: exit-code) since Mon 2019-01-14 11:27:16 CST; 5s ago
     Docs: http://www.elastic.co
  Process: 2035 ExecStart=/usr/share/elasticsearch/bin/elasticsearch -p ${PID_DIR}/elasticsearch.pid --quiet (code=exited, status=1/FAILURE)
 Main PID: 2035 (code=exited, status=1/FAILURE)

Jan 14 11:27:16 ip-172-31-30-62.ec2.internal systemd[1]: Started Elasticsearch.
Jan 14 11:27:16 ip-172-31-30-62.ec2.internal systemd[1]: Starting Elasticsearch...
Jan 14 11:27:16 ip-172-31-30-62.ec2.internal elasticsearch[2035]: which: no java in (/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin)
Jan 14 11:27:16 ip-172-31-30-62.ec2.internal elasticsearch[2035]: could not find java; set JAVA_HOME or ensure java is in PATH
Jan 14 11:27:16 ip-172-31-30-62.ec2.internal systemd[1]: elasticsearch.service: main process exited, code=exited, status=1/FAILURE
Jan 14 11:27:16 ip-172-31-30-62.ec2.internal systemd[1]: Unit elasticsearch.service entered failed state.
Jan 14 11:27:16 ip-172-31-30-62.ec2.internal systemd[1]: elasticsearch.service failed.

也就是說就算是你設置好JAVA全局環境變量后，elasticsearch啟動的時候依然是在上面紅色字體的PATH變量里面找java變量。這個不清楚究竟是什么原因。我們暫時把它當做是丟環境變量的原因吧。不過我們倒是有其他的解決方法：

在/etc/sysconfig/elasticsearch的這個文件里面設置JAVA_HOME環境變量：

################################
# Elasticsearch
################################

# Elasticsearch home directory
#ES_HOME=/usr/share/elasticsearch

# Elasticsearch Java path
JAVA_HOME=/usr/local/jdk

# Elasticsearch configuration directory
ES_PATH_CONF=/etc/elasticsearch

# Elasticsearch PID directory
#PID_DIR=/var/run/elasticsearch

就是上面背景為青色的字體，設置一下環境變量后就可以正常啟動了。

有時候也是編譯環境的問題，比如上面這個問題就是，JAVA的jdk是源碼安裝的，而elasticsearch是yum一鍵安裝的，因此很容易出現問題，所以我建議兩者的安裝盡量一致，jdk也使用yum安裝比較好，這個問題就不會出現了。