elasticsearch启动常见错误

问题出现环境，OS版本：CentOS-7-x86_64-Minimal-1708；ES版本：elasticsearch-6.2.2。

1、max file descriptors [4096] for elasticsearch process is too low, increase to at least [65536]

每个进程最大同时打开文件数太小，可通过下面2个命令查看当前数量

ulimit -Hn
ulimit -Sn

修改/etc/security/limits.conf文件，增加配置，用户退出后重新登录生效

soft nofile 65536
hard nofile 65536

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2、max number of threads [3818] for user [es] is too low, increase to at least [4096]

问题同上，最大线程个数太低。修改配置文件/etc/security/limits.conf，增加配置

1* soft nproc 4096

2* hard nproc 4096

可通过命令查看

ulimit -Hu
ulimit -Su

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3、max virtual memory areas vm.max_map_count [65530] is too low, increase to at least [262144]

修改/etc/sysctl.conf文件，增加配置vm.max_map_count=262144

vi /etc/sysctl.conf
sysctl -p

执行命令sysctl -p生效

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4、Exception in thread "main" java.nio.file.AccessDeniedException: /usr/local/elasticsearch/elasticsearch-6.2.2-1/config/jvm.options

elasticsearch用户没有该文件夹的权限，执行命令

chown -R es:es /usr/local/elasticsearch/