Disable MySQL Strict mode in Debian 8 permanently

All blogs say:

 for turning off strict mode you must add following line to /etc/mysql/my.cnf:

sql_mode=""

and restart the mysql server.

That was not working me.

I have found another setting file for mysql: /usr/my.cnf

and in this file exists sql_mode parameter too.

sql_mode=NO_ENGINE_SUBSTITUTION,STRICT_TRANS_TABLES

this line must be commented out too:

#sql_mode=NO_ENGINE_SUBSTITUTION,STRICT_TRANS_TABLES

Don't forget to restart the mysql server.