C.5.2.6. Host 'host_name' isblocked

If the following error occurs, it means that mysqld has received many connection requests from the given host that were interrupted in the middle:

Host 'host_name' is blocked because of many connection errors.Unblock with 'mysqladmin flush-hosts'

The value of the max_connect_errors system variable determines how many successive interrupted connection requests are permitted. (See Section 5.1.4, "Server System Variables".) After max_connect_errors failed requests without a successful connection, mysqld assumes that something is wrong (for example, that someone is trying to break in), and blocks the host from further connections until you issue a FLUSH HOSTS statement or execute a mysqladmin flush-hosts command.

By default, mysqld blocks a host after 100 connection errors (10 before MySQL 5.6.6). You can adjust the value by setting max_connect_errors at server startup:

shell> mysqld_safe --max_connect_errors=10000
        &

The value can also be set at runtime:

mysql> SET GLOBAL
        max_connect_errors=10000;

If you get the Host 'host_name' is blocked error message for a given host, you should first verify that there is nothing wrong with TCP/IP connections from that host. If you are having network problems, it does you no good to increase the value of the max_connect_errors variable.