elasticsearch启动常见错误；max file descriptors [4096] for elasticsearch process is too low

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，注意带* 号

*               soft    nofile          65536
*               hard    nofile          65536

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（和问题1是一个文件），增加配置

*               soft    nproc           4096
*               hard    nproc           4096

　　可通过命令查看

ulimit -Hu
ulimit -Su

修改后的文件：

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

 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/