Valid values are 'ON' and 'OFF'
select @@global.innodb_read_only;
@@global.innodb_read_only
0
select @@session.innodb_read_only;
ERROR HY000: Variable 'innodb_read_only' is a GLOBAL variable
show global variables like 'innodb_read_only';
Variable_name	Value
innodb_read_only	OFF
show session variables like 'innodb_read_only';
Variable_name	Value
innodb_read_only	OFF
select * from information_schema.global_variables where variable_name='innodb_read_only';
VARIABLE_NAME	VARIABLE_VALUE
INNODB_READ_ONLY	OFF
select * from information_schema.session_variables where variable_name='innodb_read_only';
VARIABLE_NAME	VARIABLE_VALUE
INNODB_READ_ONLY	OFF
set global innodb_read_only=1;
ERROR HY000: Variable 'innodb_read_only' is a read only variable
set session innodb_read_only=1;
ERROR HY000: Variable 'innodb_read_only' is a read only variable
