START SLAVE [thread_type [, thread_type] ... ]
START SLAVE [SQL_THREAD] UNTIL
    MASTER_LOG_FILE = 'log_name', MASTER_LOG_POS = log_pos
START SLAVE [SQL_THREAD] UNTIL
    RELAY_LOG_FILE = 'log_name', RELAY_LOG_POS = log_pos

thread_type: IO_THREAD | SQL_THREAD

START SLAVE with no options starts both of the slave threads.
The I/O thread reads queries from the master server and stores them in the
relay log.  The SQL thread reads the relay log and executes the
queries.
START SLAVE requires the SUPER privilege.

If START SLAVE succeeds in starting the slave threads, it
returns without any error. However, even in that case, it might be that the slave
threads start and then later stop (for example, because they don't manage to
connect to the master or read its binary logs, or some other
problem). START SLAVE will not warn you about this. You must
check your slave's error log for error messages generated by
the slave threads, or check that they are running fine with SHOW
SLAVE STATUS.
