B.4.2.5 Host 'host_name' is blocked

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. 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 flush the host cache by executing a FLUSH HOSTS statement, a TRUNCATE TABLE statement that truncates the Performance Schema host_cache table, or a mysqladmin flush-hosts command.

To adjust the permitted number of successive connection errors, set max_connect_errors at server startup. For example, put these lines in the server my.cnf file:

[mysqld]
max_connect_errors=10000

The value can also be set at runtime:

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 no good to increase the value of max_connect_errors.

For more information about how the host cache works, see Section 8.12.4.2, “DNS Lookup Optimization and the Host Cache”.