MySQL Master / Slave replication is amazingly easy to set up.

But what if you do everything by the book, log into the slave, and issue the climactic SLAVE START; command, followed by SHOW SLAVE STATUS\G, and see this error?

Last_IO_Errno: 1045
Last_IO_Error: error connecting to master 'slave_user@master.domain.int:3306' - retry-time: 60 retries: 86400

and your log file shows:

110201 22:53:26 [Note] 'CHANGE MASTER TO executed'. Previous state master_host='master.domain.int', master_port='3306', master_log_file='', master_log_pos='4'. New state master_host='10.0.0.10', master_port='3306', master_log_file='mysql-bin.000001', master_log_pos='106'.
110201 22:53:26 [Note] Slave SQL thread initialized, starting replication in log 'mysql-bin.000001' at position 106, relay log '/mnt/mysql/logs/relay-bin.000001' position: 4
110201 22:53:26 [ERROR] Slave I/O: error connecting to master 'slave-user@10.0.0.10:3306' - retry-time: 60  retries: 86400, Error_code: 1045

The master isn’t rejecting your password, and there isn’t useful feedback indicating why the slave cannot connect.

Note the error code 1045, which indicates a credentials problem.  Double-check the length of your password; MySQL has a MASTER_PASSWORD maximum length limit of 32 characters.  Shorten that puppy up and have another try.

From the command line, you can issue a command such as mysql --user=slave-user --host=master -p to verify that your credentials are valid.  However, be aware that you can connect this way with a password that is too long and that will not work for replication.  Also, double-check that neither firewalls nor SELinux are blocking the connection, you can telnet master 3306 to verify that MySQL is listening and accepting connections on that port.

More MySQL variable restrictions at: MySQL :: MySQL 5.1 Reference Manual :: 12.5.2.1 CHANGE MASTER TO Syntax.

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