Are you trying to setup on replication on mysql5.5+ ? After upgrading, your mysql can’t start,and  the log show “unknown variabled ‘master-host=’

The following options are removed in MySQL 5.5. If you attempt to start mysqld with any of these options in MySQL 5.5, the server aborts with an unknown variable error.

–master-host
–master-user
–master-password
–master-port

Solution, comment the master- related variables.
Do following,
On Master:
mysql>GRANT REPLICATION SLAVE ON *.* TO ‘slave_user’@’%’ IDENTIFIED BY ‘‘; (Replace with a real password!)
mysql>FLUSH PRIVILEGES;
mysql>FLUSH TABLES WITH READ LOCK;
mysql>SHOW MASTER STATUS;
# get the DB dump.
mysql>UNLOCK TABLES;

On Slave:
# import the DB dump
mysql>stop slave;
mysql>CHANGE MASTER TO MASTER_HOST=’prod_master’, MASTER_USER=’slave_user’, MASTER_PASSWORD=’‘, MASTER_LOG_FILE=’mysql-bin.0xx‘, MASTER_LOG_POS=33421;
mysql>start slave;

Ref: http://dev.mysql.com/doc/refman/5.5/en/replication-options-slave.html