Mysql Modify Tmpdir parameter _mysql

Today suddenly received an alarm message saying yes/disk space used over the threshold. After viewing, found that there are a lot of abnormal SQL, can not be executed, resulting in processing, resulting in a temporary consumption of/TMP disk space.

Due to the limited/TMP space of the operating system, parameter modification is required to modify the Tmpdir value path.

Mysql> Show variables like ' tmpdir ';
+---------------+-------+
| variable_name | Value |
+---------------+-------+
| tmpdir |/    tmp
| +---------------+-------+
1 row in Set (0.00 sec)

mysql> set global tmpdir = '/data/app/mysql5.6.25/mysqltmp ' ;
ERROR 1238 (HY000): Variable ' Tmpdir ' is a-read only Variable

can only be modified through a configuration file.

Restart MySQL

Mysql> Show variables like ' tmpdir ';
+---------------+--------------------------------+
| variable_name | Value             |
+---------------+--------------------------------+
| tmpdir |    /mysql5.6/var/tmp
| +---------------+--------------------------------+
1 row in Set (0.00 sec)

Ask: But the production environment can not restart the service, this How to do?