Increase Linux Open File Limit

ulimit open tables [1]

## Add the following at the bottom of the file /etc/security/limits.conf
    * soft nofile 1024000
    * hard nofile 1024000
    * soft nproc 10240
    * hard nproc 10240

##Add the following to the file /etc/security/limits.d/90-nproc.conf

    * soft nofile 1024000
    * hard nofile 1024000
    * soft nproc 10240
    * hard nproc 10240
    root soft nproc unlimited

Add this line under [mysqld] & [mysqld_safe] in the cnf file /etc/mysql/my.cnf  as shown below, and restart the mysql server. Later verify that the changes took place

[mysqld]
open_files_limit = 1024000

[mysqld_safe]
open_files_limit = 1024000


## Restart mysqld
service mysqld restart
   
##Verify the changes took effect
mysql>show global variables like 'open%';

Next, you should reboot your server and repeat the mysql steps to make sure they are being loaded at bootup.

mysql -u root -p
mysql>show global variables like 'open%';
 

REFERENCES

[1]http://duntuk.com/how-raise-ulimit-open-files-and-mysql-openfileslimit
[2] https://www.percona.com/blog/2010/08/23/innodb-memory-allocation-ulimit-and-opensuse/
[3]http://duntuk.com/how-raise-ulimit-open-files-and-mysql-openfileslimit