问题现象:
elasticsearch启动失败
启动成功变成running后立马变成failed

查看log

[root@db03 /data]$ systemctl status elasticsearch.service -l
● elasticsearch.service - Elasticsearch
   Loaded: loaded (/usr/lib/systemd/system/elasticsearch.service; enabled; vendor preset: disabled)
  Drop-In: /etc/systemd/system/elasticsearch.service.d
           └─override.conf
   Active: failed (Result: signal) since Sat 2020-04-18 17:20:49 CST; 6min ago
     Docs: http://www.elastic.co
  Process: 23456 ExecStart=/usr/share/elasticsearch/bin/elasticsearch -p ${PID_DIR}/elasticsearch.pid --quiet (code=killed, signal=KILL)
 Main PID: 23456 (code=killed, signal=KILL)

Apr 18 17:20:23 db03 systemd[1]: Started Elasticsearch.
Apr 18 17:20:24 db03 elasticsearch[23456]: OpenJDK 64-Bit Server VM warning: If the number of processors is expected to increase from one, then you should configure the number of parallel GC threads appropriately using -XX:ParallelGCThreads=N
Apr 18 17:20:49 db03 systemd[1]: elasticsearch.service: main process exited, code=killed, status=9/KILL
Apr 18 17:20:49 db03 systemd[1]: Unit elasticsearch.service entered failed state.
Apr 18 17:20:49 db03 systemd[1]: elasticsearch.service failed.
[root@db03 /data]$  

分析:
看到GC的错误,判断应该是内存问题
free看了服务器的内存本身只有1个G
查看了elasticsearch的内存设定
vim /etc/elasticsearch/jvm.options
当前设置的是需要占用1个g
-Xms1g
-Xmx1g

解决方案:
修改elasticsearch占用的的内存参数
vim /etc/elasticsearch/jvm.options
-Xms512m
-Xmx512m

修改完后重启服务
systemctl restart elasticsearch.service
systemctl status elasticsearch.service
测试成功!

[root@db03 /data]$ systemctl status elasticsearch.service
● elasticsearch.service - Elasticsearch
   Loaded: loaded (/usr/lib/systemd/system/elasticsearch.service; enabled; vendor preset: disabled)
  Drop-In: /etc/systemd/system/elasticsearch.service.d
           └─override.conf
   Active: active (running) since Sat 2020-04-18 17:44:13 CST; 9min ago
     Docs: http://www.elastic.co
 Main PID: 23590 (java)
   CGroup: /system.slice/elasticsearch.service
           ├─23590 /bin/java -Xms512m -Xmx512m -XX:+UseConcMarkSweepGC -XX:CMSInitiatingOccupancyFraction=75 -XX:+UseCMSInitiatingOccupancyOnly -Des.networkaddress.cache.ttl=60 -Des.networkaddres...
           └─23645 /usr/share/elasticsearch/modules/x-pack-ml/platform/linux-x86_64/bin/controller

Apr 18 17:44:13 db03 systemd[1]: Started Elasticsearch.
Apr 18 17:44:16 db03 elasticsearch[23590]: OpenJDK 64-Bit Server VM warning: If the number of processors is expected to increase from one, then you should configure the number of par...elGCThreads=N
Hint: Some lines were ellipsized, use -l to show in full.
[root@db03 /data]$ curl localhost:9200
{
  "name" : "node-3",
  "cluster_name" : "linux",
  "cluster_uuid" : "gG8lF9pMQxi8EtIyX0pB0A",
  "version" : {
    "number" : "6.6.0",
    "build_flavor" : "default",
    "build_type" : "rpm",
    "build_hash" : "a9861f4",
    "build_date" : "2019-01-24T11:27:09.439740Z",
    "build_snapshot" : false,
    "lucene_version" : "7.6.0",
    "minimum_wire_compatibility_version" : "5.6.0",
    "minimum_index_compatibility_version" : "5.0.0"
  },
  "tagline" : "You Know, for Search"
}