ElasticSearch max file descriptors too low error

ElasticSearch 5.x requires a minimum of Max file descriptors 65536 and Max virtual memory areas 262144.
It throws an error on start-up if these are set to very low value.

ERROR: bootstrap checks failed
max file descriptors [16384] for elasticsearch process is too low, increase to at least [65536]
max virtual memory areas vm.max_map_count [65530] is too low, increase to at least [262144]

Check current values using:

$ cat /proc/sys/fs/file-max 
16384
$ cat /proc/sys/vm/max_map_count
65530
$ ulimit -Hn
16384
$ ulimit -Sn
4096

To fix this, following files need to change/add below settings:

• Recommended: Add a new file 99-elastic.conf under /etc/security/limits.d with following settings:
  

  elasticsearch          - nofile  800000
  elasticsearch          - nproc   16384
  defaultusername        - nofile  800000
  defaultusername        - nproc   16384
  

• Alternatively, edit /etc/sysctl.conf with following settings:
  

  fs.file-max = 800000
  vm.max_map_count=300000