Percona-server-5.6.41 and sql_mode When setting 

sql_mode=""

in  /etc/mysql/my.cnf  server leaves this variable in it default value: 


mysql> show variables like 'sql_mode';

+-------------------+------------------------------------------------------------------------+ 
| Variable_name | Value                                                                                 |
+-------------------+------------------------------------------------------------------------+ 
| sql_mode         | STRICT_TRANS_TABLES,NO_ENGINE_SUBSTITUTION  |
+-------------------+------------------------------------------------------------------------+


However, if i set it manually in mysql shell: 

set global sql_mode=""; 

server sets it as desired - to empty value. Till next server restart, when server sets this variable to default value again.

Tried in single and double quotes - no matter.
No errors in error log. No other default configuration files of mysql loaded
What's wrong?

Why?
Found: another MySQL config is /usr/my.cnf and it contains:

sql_mode=NO_ENGINE_SUBSTITUTION,STRICT_TRANS_TABLES

so, setting sql_mode="" did the thing I need.

Debian stretch. Percona server was installed after removing installed MySQL-5.6 community. 

Intrecting thing: log doesn't mention this config for reading during server's startup...