((none)) > show variables like 'expire_logs_days';
+------------------+-------+
| Variable_name    | Value |
+------------------+-------+
| expire_logs_days | 7     |
+------------------+-------+
1 row in set (0.00 sec)

Mon Oct 14 10:04:16 2019((none)) >  set global expire_logs_days=30;
Query OK, 0 rows affected (0.00 sec)

Mon Oct 14 10:04:43 2019((none)) > show variables like 'expire_logs_days';
+------------------+-------+
| Variable_name    | Value |
+------------------+-------+
| expire_logs_days | 30    |
+------------------+-------+
1 row in set (0.00 sec)

Mon Oct 14 10:04:47 2019((none)) >