Syntax:
CHANGE MASTER TO option [, option] ...

option:
    MASTER_HOST = 'host_name'
  | MASTER_USER = 'user_name'
  | MASTER_PASSWORD = 'password'
  | MASTER_PORT = port_num
  | MASTER_CONNECT_RETRY = interval
  | MASTER_LOG_FILE = 'master_log_name'
  | MASTER_LOG_POS = master_log_pos
  | RELAY_LOG_FILE = 'relay_log_name'
  | RELAY_LOG_POS = relay_log_pos
  | MASTER_SSL = {0|1}
  | MASTER_SSL_CA = 'ca_file_name'
  | MASTER_SSL_CAPATH = 'ca_directory_name'
  | MASTER_SSL_CERT = 'cert_file_name'
  | MASTER_SSL_KEY = 'key_file_name'
  | MASTER_SSL_CIPHER = 'cipher_list'

CHANGE MASTER TO changes the parameters that the slave server uses for
connecting to the master server, for reading the master binary log, and
reading the slave relay log. It also updates the contents of the
master.info and relay-log.info files. To use CHANGE MASTER TO, the
slave replication threads must be stopped (use STOP SLAVE if
necessary).

Options not specified retain their value, except as indicated in the
following discussion. Thus, in most cases, there is no need to specify
options that do not change. For example, if the password to connect to
your MySQL master has changed, you just need to issue these statements
to tell the slave about the new password:

STOP SLAVE; -- if replication was running
CHANGE MASTER TO MASTER_PASSWORD='new3cret';
START SLAVE; -- if you want to restart replication

MASTER_HOST, MASTER_USER, MASTER_PASSWORD, and MASTER_PORT provide
information to the slave about how to connect to its master:

o MASTER_HOST and MASTER_PORT are the host name (or IP address) of the
  master host and its TCP/IP port.

  *Note*: Replication cannot use Unix socket files. You must be able to
  connect to the master MySQL server using TCP/IP.

  If you specify the MASTER_HOST or MASTER_PORT option, the slave
  assumes that the master server is different from before (even if the
  option value is the same as its current value.) In this case, the old
  values for the master binary log file name and position are
  considered no longer applicable, so if you do not specify
  MASTER_LOG_FILE and MASTER_LOG_POS in the statement,
  MASTER_LOG_FILE='' and MASTER_LOG_POS=4 are silently appended to it.

  Setting MASTER_HOST=''---that is, setting its value explicitly to an
  empty string---is not the same as not setting it at all. Setting this
  option to an empty string causes START SLAVE subsequently to fail.
  (Bug #28796)

o MASTER_USER and MASTER_PASSWORD are the user name and password of the
  account to use for connecting to the master.

  The text of a running CHANGE MASTER TO statement, including values
  for MASTER_USER and MASTER_PASSWORD, can be seen in the output of a
  concurrent SHOW PROCESSLIST statement.

The MASTER_SSL_xxx options provide information about using SSL for the
connection. They correspond to the --ssl-xxx options described in
http://dev.mysql.com/doc/refman/5.0/en/ssl-options.html, and
http://dev.mysql.com/doc/refman/5.0/en/replication-solutions-ssl.html.
These options can be changed even on slaves that are compiled without
SSL support. They are saved to the master.info file, but are ignored if
the slave does not have SSL support enabled.

MASTER_CONNECT_RETRY specifies how many seconds to wait between connect
retries. The default is 60. The number of reconnection attempts is
limited by the --master-retry-count server option; for more
information, see
http://dev.mysql.com/doc/refman/5.0/en/replication-options.html.

MASTER_LOG_FILE and MASTER_LOG_POS are the coordinates at which the
slave I/O thread should begin reading from the master the next time the
thread starts. RELAY_LOG_FILE and RELAY_LOG_POS are the coordinates at
which the slave SQL thread should begin reading from the relay log the
next time the thread starts. If you specify either of MASTER_LOG_FILE
or MASTER_LOG_POS, you cannot specify RELAY_LOG_FILE or RELAY_LOG_POS.
If neither of MASTER_LOG_FILE or MASTER_LOG_POS is specified, the slave
uses the last coordinates of the slave SQL thread before CHANGE MASTER
TO was issued. This ensures that there is no discontinuity in
replication, even if the slave SQL thread was late compared to the
slave I/O thread, when you merely want to change, say, the password to
use.

CHANGE MASTER TO deletes all relay log files and starts a new one,
unless you specify RELAY_LOG_FILE or RELAY_LOG_POS. In that case, relay
log files are kept; the relay_log_purge global variable is set silently
to 0.

CHANGE MASTER TO is useful for setting up a slave when you have the
snapshot of the master and have recorded the master binary log
coordinates corresponding to the time of the snapshot. After loading
the snapshot into the slave to synchronize it to the slave, you can run
CHANGE MASTER TO MASTER_LOG_FILE='log_name', MASTER_LOG_POS=log_pos on
the slave to specify the coordinates at which the slave should begin
reading the master binary log.

The following example changes the master server the slave uses and
establishes the master binary log coordinates from which the slave
begins reading. This is used when you want to set up the slave to
replicate the master:

CHANGE MASTER TO
  MASTER_HOST='master2.mycompany.com',
  MASTER_USER='replication',
  MASTER_PASSWORD='bigs3cret',
  MASTER_PORT=3306,
  MASTER_LOG_FILE='master2-bin.001',
  MASTER_LOG_POS=4,
  MASTER_CONNECT_RETRY=10;

The next example shows an operation that is less frequently employed.
It is used when the slave has relay log files that you want it to
execute again for some reason. To do this, the master need not be
reachable. You need only use CHANGE MASTER TO and start the SQL thread
(START SLAVE SQL_THREAD):

CHANGE MASTER TO
  RELAY_LOG_FILE='slave-relay-bin.006',
  RELAY_LOG_POS=4025;

URL: http://dev.mysql.com/doc/refman/5.0/en/change-master-to.html

