Syntax:
SHOW SLAVE HOSTS

Displays a list of replication slaves currently registered with the
master.

SHOW SLAVE HOSTS should be executed on a server that acts as a
replication master. The statement displays information about servers
that are or have been connected as replication slaves, with each row of
the result corresponding to one slave server, as shown here:

mysql> SHOW SLAVE HOSTS;
+------------+-----------+------+-----------+
| Server_id  | Host      | Port | Master_id |
+------------+-----------+------+-----------+
|  192168010 | iconnect2 | 3306 | 192168011 |
| 1921680101 | athena    | 3306 | 192168011 |
+------------+-----------+------+-----------+

o Server_id: The unique server ID of the slave server, as configured in
  the slave server's option file, or on the command line with
  --server-id=value.

o Host: The host name of the slave server as specified on the slave
  with the --report-host option. This can differ from the machine name
  as configured in the operating system.

o User: The slave server user name as, specified on the slave with the
  --report-user option. Statement output includes this column only if
  the master server is started with the --show-slave-auth-info option.

o Password: The slave server password as, specified on the slave with
  the --report-password option. Statement output includes this column
  only if the master server is started with the --show-slave-auth-info
  option.

o Port: The port on the master to which the slave server is listening,
  as specified on the slave with the --report-port option.

  In MySQL 5.5.23 and later, a zero in this column means that the slave
  port (--report-port) was not set. Prior to MySQL 5.5.23, 3306 was
  used as the default in such cases (Bug #13333431).

o Master_id: The unique server ID of the master server that the slave
  server is replicating from. This is the server ID of the server on
  which SHOW SLAVE HOSTS is executed, so this same value is listed for
  each row in the result.

URL: http://dev.mysql.com/doc/refman/5.5/en/show-slave-hosts.html

