# SHOW OPEN FILES LIMIT FOR MYSQL
su - mysql -c 'ulimit -aHS' -s '/bin/bash'

# CHECK FILES IN /etc/security/limits.d/ THEY CAN REWRITE YOUR CONFS 
cat /etc/security/limits.conf
*          soft     nproc          65535
*          hard     nproc          65535
*          soft     nofile         65535
*          hard     nofile         65535