Why is innodb strict mode not enabling?
You can set this SESSION variable from the command line:

mysql&gt; show variables like '%strict%';
+--------------------+-------+
| Variable_name      | Value |
+--------------------+-------+
| innodb_strict_mode | OFF   |
+--------------------+-------+
1 row in set (0.01 sec)


Then, you do this:

mysql&gt; set innodb_strict_mode = ON;
Query OK, 0 rows affected (0.00 sec)


Then, to check:

mysql&gt; show variables like '%strict%';
+--------------------+-------+
| Variable_name      | Value |
+--------------------+-------+
| innodb_strict_mode | ON    |
+--------------------+-------+


Then, on exiting and reconnecting, and rechecking the variable, it is again OFF - the default. Use SET GLOBAL innodb_strict_mode = ON if you don't want it to reset after logging off. But, setting it in the client will not make the change stick after a reboot of the server.

Edit my.cnf - I've never seen or touched mysqld.cnf. 

Put the line(s) below in the [mysqld] section of my.cnf.

sql_mode    = "STRICT_TRANS_TABLES,NO_ENGINE_SUBSTITUTION,ONLY_FULL_GROUP_BY"
innodb_strict_mode = ON


(I recommend the sql_mode line also - otherwise, for example, certain GROUP BY queries will return (ahem...) anomalous results).

Bounce the server - and relog in.

mysql&gt; show variables like '%strict%';
+--------------------+-------+
| Variable_name      | Value |
+--------------------+-------+
| innodb_strict_mode | ON    |
+--------------------+-------+
1 row in set (0.01 sec)


It's all in the documentation here.


  You can turn innodb_strict_mode ON or OFF on the command line when you
  start mysqld, or in the configuration file my.cnf or my.ini. You can
  also enable or disable innodb_strict_mode at runtime with the
  statement SET [GLOBAL|SESSION] innodb_strict_mode=mode, where mode is
  either ON or OFF. Changing the GLOBAL setting requires the SUPER
  privilege and affects the operation of all clients that subsequently
  connect. Any client can change the SESSION setting for
  innodb_strict_mode, and the setting affects only that client.


Maybe you don't have the SUPER privilege? Log in and run SHOW GRANTS to find out.