Each replication slave must have a unique server ID. If this has not already been done, this part of slave setup requires a server restart.

If the slave server ID is not already set, or the current value conflicts with the value that you have chosen for the master server, shut down the slave server and edit the [mysqld] section of the configuration file to specify a unique server ID. For example:

[mysqld]
server-id=2

After making the changes, restart the server.

If you are setting up multiple slaves, each one must have a unique server-id value that differs from that of the master and from any of the other slaves.

You do not have to enable binary logging on the slave for replication to be set up. However, if you enable binary logging on the slave, you can use the slave's binary log for data backups and crash recovery, and also use the slave as part of a more complex replication topology. For example, where this slave then acts as a master to other slaves.

To set up the slave to communicate with the master for replication, configure the slave with the necessary connection information. To do this, execute the following statement on the slave, replacing the option values with the actual values relevant to your system:

mysql> CHANGE MASTER TO
    ->     MASTER_HOST='master_host_name',
    ->     MASTER_USER='replication_user_name',
    ->     MASTER_PASSWORD='replication_password',
    ->     MASTER_LOG_FILE='recorded_log_file_name',
    ->     MASTER_LOG_POS=recorded_log_position;

The CHANGE MASTER TO statement has other options as well. For example, it is possible to set up secure replication using SSL. For a full list of options, and information about the maximum permissible length for the string-valued options, see Section 13.4.2.1, “CHANGE MASTER TO Syntax”.

The next steps depend on whether you have existing data to import to the slave or not. See Section 16.1.2.4, “Choosing a Method for Data Snapshots” for more information. Choose one of the following:

When there is no snapshot of a previous database to import, configure the slave to start the replication from the new master.

To set up replication between a master and a new slave:

Perform these slave setup steps on each slave.

This method can also be used if you are setting up new servers but have an existing dump of the databases from a different server that you want to load into your replication configuration. By loading the data into a new master, the data is automatically replicated to the slaves.

If you are setting up a new replication environment using the data from a different existing database server to create a new master, run the dump file generated from that server on the new master. The database updates are automatically propagated to the slaves:

shell> mysql -h master < fulldb.dump

When setting up replication with existing data, transfer the snapshot from the master to the slave before starting replication. The process for importing data to the slave depends on how you created the snapshot of data on the master.

Choose one of the following:

If you used mysqldump:

If you created a snapshot using the raw data files:

After you have performed this procedure, the slave connects to the master and replicates any updates that have occurred on the master since the snapshot was taken.

If the server-id option for the master is not correctly set, slaves cannot connect to it. Similarly, if you have not set the server-id option correctly for the slave, you get the following error in the slave's error log:

Warning: You should set server-id to a non-0 value if master_host
is set; we will force server id to 2, but this MySQL server will
not act as a slave.

You also find error messages in the slave's error log if it is not able to replicate for any other reason.

The slave stores information about the master you have configured in its master info repository. The master info repository can be in the form of files or a table, as determined by the value set for --master-info-repository. When a slave uses --master-info-repository=FILE, two files are stored in the data directory, named master.info and relay-log.info. If --master-info-repository=TABLE instead, this information is saved in the master_slave_info table in the mysql database. In either case, do not remove or edit the files or table. Always use the CHANGE MASTER TO statement to change replication parameters. The slave can use the values specified in the statement to update the status files automatically. See Section 16.2.4, “Replication Relay and Status Logs”, for more information.

A single snapshot of the master suffices for multiple slaves. To set up additional slaves, use the same master snapshot and follow the slave portion of the procedure just described.