关于MySQL主从设置

主服务器，运行如下命令怎么 Binlog_Do_DB  显示为空呢？
我在my.cnf中设置过要同步数据库啊?
mysql> SHOW MASTER STATUS;
+-------------------+----------+--------------+------------------+
| File              | positiion | Binlog_Do_DB | Binlog_Ignore_DB |
+-------------------+----------+--------------+------------------+
| mysqld-bin.000001 |       98 |              |                  |
+-------------------+----------+--------------+------------------+
1 row in set (0.00 sec)
my.cnf设置如下所示
[mysqld]
datadir=/var/lib/mysql
socket=/var/lib/mysql/mysql.sock
user=mysql
# Default to using old password format for compatibility with mysql 3.x
# clients (those using the mysqlclient10 compatibility package).
old_passwords=1[mysqld_safe]
log-error=/var/log/mysqld.log
pid-file=/var/run/mysqld/mysqld.pidlog-bin=mysql-bin.log
binlog-do-db=school               
server-id=1