Unable to change innodb_buffer_pool_size MySQL 5.6 in CentOS 6.7
About     Service mysqld start --defaults-file=..


AFAIK it isn't correct way to pass argument. It should not be accepting that argument.
Never done that; importantly it isn't even necessary for default location!!!


Confirm the which my.cnf is being used:


mysqld –verbose –help | grep -C1 my.cnf


Confirm we have correct entry in my.cnf


grep innodb_buffer_pool_size /etc/my.cnf


Verify your error log, you should see something like 


InnoDB: Initializing buffer pool size = ...