この場合ログファイルは、/var/run/mysqld/mysqld.log

mysql> show global variables like 'general_log_file';
+------------------+----------------------------+
| Variable_name    | Value                      |
+------------------+----------------------------+
| general_log_file | /var/run/mysqld/mysqld.log |
+------------------+----------------------------+
1 row in set (0.00 sec)
mysql> set global general_log='OFF';

mysql> set global general_log='ON';

mysql> set global general_log='OFF';