Fix Elasticsearch max file descriptors warning

You might encounter the following warning when you run Elasticsearch:

[2016-08-08 13:48:17,065][WARN ][env                      ] [Michael Nowman] max file descriptors [4096] for elasticsearch process likely too low, consider increasing to at least [65536]

Check your max file descriptors as follows:

$ ulimit -n
1024
$ ulimit -Hn
4096
$

Change the value as follows:

$ sudo vi /etc/security/limits.conf

izeye     soft    nofile  65536
izeye     hard    nofile  65536

Check again as follows:

$ ulimit -n
65536
$ ulimit -Hn
65536
$

The warning should disappear now.

Reference:
http://stackoverflow.com/questions/21515463/how-to-increase-maximum-file-open-limit-ulimit-in-ubuntu